Re: KX3 Field Ant. for 80/40/30

[K7TV]

End-fed antennas have gotten popular lately. When I look closer I see two
different popular approaches.

The first uses a 9:1 impedance transformer in combination with a wire length
that is not resonant on any band. The idea is that (assuming there is no
significant feedline length) you have a medium impedance (450 ohms) on the
antenna side of the transformer, and because the wire is not resonant so you
might have an impedance into the wire that is also "medium". By adjusting
the wire length, you might get pretty close to 450 ohms on one or two bands,
and with a wide range tuner you can probably get below swr 2:1 for the radio
PA to see.

The second approach, used by MyAntennas and others seems to use a
transformer with much higher impedance ratio. One way to construct such a
transformer would be to cascade two 9:1 units for an effective ratio of
81:1. This would mean the wire should present an impedance of 4000 ohms or
so. Another way would be using a single tranformer with a higher ratio. The
impedance ratio is the square of the turns ratio. With a turns ratio of 9:1
you should again get to about 4000 ohms. Somewhere I saw somebody using an
8:1 turns ratio for an ideal antenna wire impedance of about 3200 ohms.
These impedance levels are achieved by using a resonant wire.

I don't know how you arrived at your parameters, but your wire length is too
close to resonance on 80 and 40. Your transformer ratio wants a non-resonant
wire, so you might see better results if you shorten the wire significantly
and keep using the KX3 ATU. Alternatively, you could replace the transformer
for a much higher impedance ratio, in which case you can probably operate
with the tuner bypassed at least on 80 and 40 with a well adjusted wire
length. With this approach you want the wire resonant on each band. It
should be easy to achieve resonance on 80, 40, 20 and 10. As you double the
frequency, you are changing the number of half wavelengths covered by the
wire; the end feedpoint is always at the end of one of these half
wavelengths, and thus you get the very high impedance that you seek. 30
meters does not fit as clearly into this scheme. The commercial versions use
a small coil in the wire located close to the transformer end, and seem to
be able to achieve a reasoable match for all the bands 80 and up without
using a tuner. Now if you had placed the feedpoint in the center you would
not have been able to get this consistency of feedpoint impedance from band
to band. As I see it, this is a major reason for the popularity of the
end-fed approach as contrasted to the conventional center-fed approach. Note
that the 30m coverage of the 80 meter and up design is not replicated if you
try the same approach with half the wire length. In this case you will need
a tuner to get reasonable swr on 30.

An important consideration is antenna height. We all know that antennas
usually work better when placed higher. Looking a bit closer, we can look
beyond the general installation height and consider the height(s) of the
antenna part(s) that carry the most current. Antenna modelling may calculate
the field as resulting from current levels in different individual pieces of
the wire, and then it makes sense to elevate those portions more than other
parts of the wire that carry less current. Another reason for this is the
effect of ground losses. Jim Brown, in his article that he just linked to,
shows that ground losses get worse the closer a vertical antenna is to
ground. This makes sense as currents in the lossy soil are caused by
induction from currents in the antenna. When we look at the current
distribution within the vertical antenna wire it again makes sense to place
the part(s) of the wire with high current higher rather than lower. One of
the simplest portable antennas is a short wire or whip of a quarter wave or
less. It will have a low feedpoint impedance that can probably be matched
reasonably without a tuner or with a limited-range tuner. However, with a
low impedance comes a current maximum at the feedpoint. This often means
close to the ground, so even with a good set of elevated radials,
considerable ground losses could be expected. (An actual connection to the
soil would generally be much worse, unless you bury a lot of wires.) With a
longer wire (1/2 wavelengh at the lowest band) we can have a very high
feedpoint impedance, very low feedpoint current, and more elevated
location(s) of high curent portion(s) of the antenna, for lower ground
losses.

Any antenna feed point needs to provide two terminals for the feed current
to flow through a complete circuit. A end-fed designed for medium to high
feed impedance has small feed current. In practice this means that whatever
is used as the counterpoise side can be small. The applies with a "medium
impedance" design as discussed earlier, but it applies even more for a
resonant end-fed with its tiny feed current. A short piece of wire may be
used, but often not even that is needed, as the feed return current may flow
on the transformer and feedline (if used), and even on the radio box. This
is fine for QRP and maybe even medium power, as the current is small
relative to the higher current higher up on the wire. However, at medium to
high power, if matching problems are encountered, or bothersome RF around
the rig, I would consider a small counterpoise wire to the high impedance
side of the transformer, or experimenting with the length of the feedline,
as the length of it matters when "counterpoise current" flows on the outside
of it. I would not count on the impedance transformer to function as a
common mode choke for blocking such RF current. You could place a separate
common mode choke somewhere on the feedline, and move its position as a way
to adjust the length of the effective counterpoise. Look up Jim's article on
how to build an effective common mode choke.

73,
Erik K7TV

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of JT Croteau
Sent: Saturday, November 18, 2017 2:34 PM
To: [hidden email]
Subject: [Elecraft] KX3 Field Ant. for 80/40/30

Friends, what would be a good end fed wire setup that will match well with
the internal KX3 ATU and cover, hopefully, 80, 40, and 30 meters?

I went out to my winter camp site, with two really tall pine trees, and
tried to experiment with a 9:1 UNUN, 135' radiator, and 35' of RG8X.  It was
a total disaster.  Best matches were on 20, 17, and 15 meters but only with
6.4:1 SWR.  No match at all on the lower bands.
With my two trees, the radiator made for a perfect inverted-L shape.

What should I try next?  I did try some pruning of the antenna but quickly
gave up due to the WX conditions.

Thanks
N1ESE
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[Igor Sokolov-2]

Very useful post Erik,

Thank you

73, Igor UA9CDC


19.11.2017 13:22, Erik Basilier пишет:

> End-fed antennas have gotten popular lately. When I look closer I see two
> different popular approaches.
>
> The first uses a 9:1 impedance transformer in combination with a wire length
> that is not resonant on any band. The idea is that (assuming there is no
> significant feedline length) you have a medium impedance (450 ohms) on the
> antenna side of the transformer, and because the wire is not resonant so you
> might have an impedance into the wire that is also "medium". By adjusting
> the wire length, you might get pretty close to 450 ohms on one or two bands,
> and with a wide range tuner you can probably get below swr 2:1 for the radio
> PA to see.
>
> The second approach, used by MyAntennas and others seems to use a
> transformer with much higher impedance ratio. One way to construct such a
> transformer would be to cascade two 9:1 units for an effective ratio of
> 81:1. This would mean the wire should present an impedance of 4000 ohms or
> so. Another way would be using a single tranformer with a higher ratio. The
> impedance ratio is the square of the turns ratio. With a turns ratio of 9:1
> you should again get to about 4000 ohms. Somewhere I saw somebody using an
> 8:1 turns ratio for an ideal antenna wire impedance of about 3200 ohms.
> These impedance levels are achieved by using a resonant wire.
>
> I don't know how you arrived at your parameters, but your wire length is too
> close to resonance on 80 and 40. Your transformer ratio wants a non-resonant
> wire, so you might see better results if you shorten the wire significantly
> and keep using the KX3 ATU. Alternatively, you could replace the transformer
> for a much higher impedance ratio, in which case you can probably operate
> with the tuner bypassed at least on 80 and 40 with a well adjusted wire
> length. With this approach you want the wire resonant on each band. It
> should be easy to achieve resonance on 80, 40, 20 and 10. As you double the
> frequency, you are changing the number of half wavelengths covered by the
> wire; the end feedpoint is always at the end of one of these half
> wavelengths, and thus you get the very high impedance that you seek. 30
> meters does not fit as clearly into this scheme. The commercial versions use
> a small coil in the wire located close to the transformer end, and seem to
> be able to achieve a reasoable match for all the bands 80 and up without
> using a tuner. Now if you had placed the feedpoint in the center you would
> not have been able to get this consistency of feedpoint impedance from band
> to band. As I see it, this is a major reason for the popularity of the
> end-fed approach as contrasted to the conventional center-fed approach. Note
> that the 30m coverage of the 80 meter and up design is not replicated if you
> try the same approach with half the wire length. In this case you will need
> a tuner to get reasonable swr on 30.
>
> An important consideration is antenna height. We all know that antennas
> usually work better when placed higher. Looking a bit closer, we can look
> beyond the general installation height and consider the height(s) of the
> antenna part(s) that carry the most current. Antenna modelling may calculate
> the field as resulting from current levels in different individual pieces of
> the wire, and then it makes sense to elevate those portions more than other
> parts of the wire that carry less current. Another reason for this is the
> effect of ground losses. Jim Brown, in his article that he just linked to,
> shows that ground losses get worse the closer a vertical antenna is to
> ground. This makes sense as currents in the lossy soil are caused by
> induction from currents in the antenna. When we look at the current
> distribution within the vertical antenna wire it again makes sense to place
> the part(s) of the wire with high current higher rather than lower. One of
> the simplest portable antennas is a short wire or whip of a quarter wave or
> less. It will have a low feedpoint impedance that can probably be matched
> reasonably without a tuner or with a limited-range tuner. However, with a
> low impedance comes a current maximum at the feedpoint. This often means
> close to the ground, so even with a good set of elevated radials,
> considerable ground losses could be expected. (An actual connection to the
> soil would generally be much worse, unless you bury a lot of wires.) With a
> longer wire (1/2 wavelengh at the lowest band) we can have a very high
> feedpoint impedance, very low feedpoint current, and more elevated
> location(s) of high curent portion(s) of the antenna, for lower ground
> losses.
>
> Any antenna feed point needs to provide two terminals for the feed current
> to flow through a complete circuit. A end-fed designed for medium to high
> feed impedance has small feed current. In practice this means that whatever
> is used as the counterpoise side can be small. The applies with a "medium
> impedance" design as discussed earlier, but it applies even more for a
> resonant end-fed with its tiny feed current. A short piece of wire may be
> used, but often not even that is needed, as the feed return current may flow
> on the transformer and feedline (if used), and even on the radio box. This
> is fine for QRP and maybe even medium power, as the current is small
> relative to the higher current higher up on the wire. However, at medium to
> high power, if matching problems are encountered, or bothersome RF around
> the rig, I would consider a small counterpoise wire to the high impedance
> side of the transformer, or experimenting with the length of the feedline,
> as the length of it matters when "counterpoise current" flows on the outside
> of it. I would not count on the impedance transformer to function as a
> common mode choke for blocking such RF current. You could place a separate
> common mode choke somewhere on the feedline, and move its position as a way
> to adjust the length of the effective counterpoise. Look up Jim's article on
> how to build an effective common mode choke.
>
> 73,
> Erik K7TV
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of JT Croteau
> Sent: Saturday, November 18, 2017 2:34 PM
> To: [hidden email]
> Subject: [Elecraft] KX3 Field Ant. for 80/40/30
>
> Friends, what would be a good end fed wire setup that will match well with
> the internal KX3 ATU and cover, hopefully, 80, 40, and 30 meters?
>
> I went out to my winter camp site, with two really tall pine trees, and
> tried to experiment with a 9:1 UNUN, 135' radiator, and 35' of RG8X.  It was
> a total disaster.  Best matches were on 20, 17, and 15 meters but only with
> 6.4:1 SWR.  No match at all on the lower bands.
> With my two trees, the radiator made for a perfect inverted-L shape.
>
> What should I try next?  I did try some pruning of the antenna but quickly
> gave up due to the WX conditions.
>
> Thanks
> N1ESE
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html Message
> delivered to [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[JT Croteau-3]

Thanks for all the comments and suggestions.  Some great info to mull over.

N1ESE

On Sun, Nov 19, 2017 at 6:36 AM, Igor Sokolov <[hidden email]> wrote:

> Very useful post Erik,
>
> Thank you
>
> 73, Igor UA9CDC
>
>
> 19.11.2017 13:22, Erik Basilier пишет:
>>
>> End-fed antennas have gotten popular lately. When I look closer I see two
>> different popular approaches.
>>
>> The first uses a 9:1 impedance transformer in combination with a wire
>> length
>> that is not resonant on any band. The idea is that (assuming there is no
>> significant feedline length) you have a medium impedance (450 ohms) on the
>> antenna side of the transformer, and because the wire is not resonant so
>> you
>> might have an impedance into the wire that is also "medium". By adjusting
>> the wire length, you might get pretty close to 450 ohms on one or two
>> bands,
>> and with a wide range tuner you can probably get below swr 2:1 for the
>> radio
>> PA to see.
>>
>> The second approach, used by MyAntennas and others seems to use a
>> transformer with much higher impedance ratio. One way to construct such a
>> transformer would be to cascade two 9:1 units for an effective ratio of
>> 81:1. This would mean the wire should present an impedance of 4000 ohms or
>> so. Another way would be using a single tranformer with a higher ratio.
>> The
>> impedance ratio is the square of the turns ratio. With a turns ratio of
>> 9:1
>> you should again get to about 4000 ohms. Somewhere I saw somebody using an
>> 8:1 turns ratio for an ideal antenna wire impedance of about 3200 ohms.
>> These impedance levels are achieved by using a resonant wire.
>>
>> I don't know how you arrived at your parameters, but your wire length is
>> too
>> close to resonance on 80 and 40. Your transformer ratio wants a
>> non-resonant
>> wire, so you might see better results if you shorten the wire
>> significantly
>> and keep using the KX3 ATU. Alternatively, you could replace the
>> transformer
>> for a much higher impedance ratio, in which case you can probably operate
>> with the tuner bypassed at least on 80 and 40 with a well adjusted wire
>> length. With this approach you want the wire resonant on each band. It
>> should be easy to achieve resonance on 80, 40, 20 and 10. As you double
>> the
>> frequency, you are changing the number of half wavelengths covered by the
>> wire; the end feedpoint is always at the end of one of these half
>> wavelengths, and thus you get the very high impedance that you seek. 30
>> meters does not fit as clearly into this scheme. The commercial versions
>> use
>> a small coil in the wire located close to the transformer end, and seem to
>> be able to achieve a reasoable match for all the bands 80 and up without
>> using a tuner. Now if you had placed the feedpoint in the center you would
>> not have been able to get this consistency of feedpoint impedance from
>> band
>> to band. As I see it, this is a major reason for the popularity of the
>> end-fed approach as contrasted to the conventional center-fed approach.
>> Note
>> that the 30m coverage of the 80 meter and up design is not replicated if
>> you
>> try the same approach with half the wire length. In this case you will
>> need
>> a tuner to get reasonable swr on 30.
>>
>> An important consideration is antenna height. We all know that antennas
>> usually work better when placed higher. Looking a bit closer, we can look
>> beyond the general installation height and consider the height(s) of the
>> antenna part(s) that carry the most current. Antenna modelling may
>> calculate
>> the field as resulting from current levels in different individual pieces
>> of
>> the wire, and then it makes sense to elevate those portions more than
>> other
>> parts of the wire that carry less current. Another reason for this is the
>> effect of ground losses. Jim Brown, in his article that he just linked to,
>> shows that ground losses get worse the closer a vertical antenna is to
>> ground. This makes sense as currents in the lossy soil are caused by
>> induction from currents in the antenna. When we look at the current
>> distribution within the vertical antenna wire it again makes sense to
>> place
>> the part(s) of the wire with high current higher rather than lower. One of
>> the simplest portable antennas is a short wire or whip of a quarter wave
>> or
>> less. It will have a low feedpoint impedance that can probably be matched
>> reasonably without a tuner or with a limited-range tuner. However, with a
>> low impedance comes a current maximum at the feedpoint. This often means
>> close to the ground, so even with a good set of elevated radials,
>> considerable ground losses could be expected. (An actual connection to the
>> soil would generally be much worse, unless you bury a lot of wires.) With
>> a
>> longer wire (1/2 wavelengh at the lowest band) we can have a very high
>> feedpoint impedance, very low feedpoint current, and more elevated
>> location(s) of high curent portion(s) of the antenna, for lower ground
>> losses.
>>
>> Any antenna feed point needs to provide two terminals for the feed current
>> to flow through a complete circuit. A end-fed designed for medium to high
>> feed impedance has small feed current. In practice this means that
>> whatever
>> is used as the counterpoise side can be small. The applies with a "medium
>> impedance" design as discussed earlier, but it applies even more for a
>> resonant end-fed with its tiny feed current. A short piece of wire may be
>> used, but often not even that is needed, as the feed return current may
>> flow
>> on the transformer and feedline (if used), and even on the radio box. This
>> is fine for QRP and maybe even medium power, as the current is small
>> relative to the higher current higher up on the wire. However, at medium
>> to
>> high power, if matching problems are encountered, or bothersome RF around
>> the rig, I would consider a small counterpoise wire to the high impedance
>> side of the transformer, or experimenting with the length of the feedline,
>> as the length of it matters when "counterpoise current" flows on the
>> outside
>> of it. I would not count on the impedance transformer to function as a
>> common mode choke for blocking such RF current. You could place a separate
>> common mode choke somewhere on the feedline, and move its position as a
>> way
>> to adjust the length of the effective counterpoise. Look up Jim's article
>> on
>> how to build an effective common mode choke.
>>
>> 73,
>> Erik K7TV
>>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of JT Croteau
>> Sent: Saturday, November 18, 2017 2:34 PM
>> To: [hidden email]
>> Subject: [Elecraft] KX3 Field Ant. for 80/40/30
>>
>> Friends, what would be a good end fed wire setup that will match well with
>> the internal KX3 ATU and cover, hopefully, 80, 40, and 30 meters?
>>
>> I went out to my winter camp site, with two really tall pine trees, and
>> tried to experiment with a 9:1 UNUN, 135' radiator, and 35' of RG8X.  It
>> was
>> a total disaster.  Best matches were on 20, 17, and 15 meters but only
>> with
>> 6.4:1 SWR.  No match at all on the lower bands.
>> With my two trees, the radiator made for a perfect inverted-L shape.
>>
>> What should I try next?  I did try some pruning of the antenna but quickly
>> gave up due to the WX conditions.
>>
>> Thanks
>> N1ESE
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message
>> delivered to [hidden email]
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
>
> ______________________________________________________________
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[Lynn W. Taylor, WB6UUT-2]

If the wire is near an even multiple of 1/4 wave (1/2 wave, one full
wave, 1 1/2 wave, etc.) then the impedance at the end of the wire is
going to be very high.

If the wire is near an odd multiple of 1/4 wave (1/4 wave, 3/4 wave, 1
1/4 wave) then the impedance will be low.

If you're expecting a high impedance and you have a 3/4 wave wire, you
may have trouble getting a match with a 9:1 balun.

That's oversimplified, of course.

The reason "pseudo-random" antennas around 53' are popular is that
length isn't resonant on any popular ham band, and you can start making
assumptions about how it'll work.

73 -- Lynn

On 11/19/2017 12:22 AM, Erik Basilier wrote:
> End-fed antennas have gotten popular lately. When I look closer I see two
> different popular approaches.
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[VE3GAM Allen McRorie]

there is an End Fed Half Wave Antenna group on Facebook
started up by N4LQ. it certainly promotes the EFHW fed with
a 49:1 transformer. Steve loves the EFHW, but really does not
have much love for 9:1 unun antenna. still, it is an interesting
group to monitor.

al ve3gam

--------------------------------------------------
From: "Erik Basilier" <[hidden email]>
Sent: Sunday, November 19, 2017 3:22 AM
To: "'JT Croteau'" <[hidden email]>; <[hidden email]>
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

> End-fed antennas have gotten popular lately. When I look closer I see two
> different popular approaches.
>
> The first uses a 9:1 impedance transformer in combination with a wire
> length
> that is not resonant on any band. The idea is that (assuming there is no
> significant feedline length) you have a medium impedance (450 ohms) on the
> antenna side of the transformer, and because the wire is not resonant so
> you
> might have an impedance into the wire that is also "medium". By adjusting
> the wire length, you might get pretty close to 450 ohms on one or two
> bands,
> and with a wide range tuner you can probably get below swr 2:1 for the
> radio
> PA to see.
>
> The second approach, used by MyAntennas and others seems to use a
> transformer with much higher impedance ratio. One way to construct such a
> transformer would be to cascade two 9:1 units for an effective ratio of
> 81:1. This would mean the wire should present an impedance of 4000 ohms or
> so. Another way would be using a single tranformer with a higher ratio.
> The
> impedance ratio is the square of the turns ratio. With a turns ratio of
> 9:1
> you should again get to about 4000 ohms. Somewhere I saw somebody using an
> 8:1 turns ratio for an ideal antenna wire impedance of about 3200 ohms.
> These impedance levels are achieved by using a resonant wire.
>
> I don't know how you arrived at your parameters, but your wire length is
> too
> close to resonance on 80 and 40. Your transformer ratio wants a
> non-resonant
> wire, so you might see better results if you shorten the wire
> significantly
> and keep using the KX3 ATU. Alternatively, you could replace the
> transformer
> for a much higher impedance ratio, in which case you can probably operate
> with the tuner bypassed at least on 80 and 40 with a well adjusted wire
> length. With this approach you want the wire resonant on each band. It
> should be easy to achieve resonance on 80, 40, 20 and 10. As you double
> the
> frequency, you are changing the number of half wavelengths covered by the
> wire; the end feedpoint is always at the end of one of these half
> wavelengths, and thus you get the very high impedance that you seek. 30
> meters does not fit as clearly into this scheme. The commercial versions
> use
> a small coil in the wire located close to the transformer end, and seem to
> be able to achieve a reasoable match for all the bands 80 and up without
> using a tuner. Now if you had placed the feedpoint in the center you would
> not have been able to get this consistency of feedpoint impedance from
> band
> to band. As I see it, this is a major reason for the popularity of the
> end-fed approach as contrasted to the conventional center-fed approach.
> Note
> that the 30m coverage of the 80 meter and up design is not replicated if
> you
> try the same approach with half the wire length. In this case you will
> need
> a tuner to get reasonable swr on 30.
>
> An important consideration is antenna height. We all know that antennas
> usually work better when placed higher. Looking a bit closer, we can look
> beyond the general installation height and consider the height(s) of the
> antenna part(s) that carry the most current. Antenna modelling may
> calculate
> the field as resulting from current levels in different individual pieces
> of
> the wire, and then it makes sense to elevate those portions more than
> other
> parts of the wire that carry less current. Another reason for this is the
> effect of ground losses. Jim Brown, in his article that he just linked to,
> shows that ground losses get worse the closer a vertical antenna is to
> ground. This makes sense as currents in the lossy soil are caused by
> induction from currents in the antenna. When we look at the current
> distribution within the vertical antenna wire it again makes sense to
> place
> the part(s) of the wire with high current higher rather than lower. One of
> the simplest portable antennas is a short wire or whip of a quarter wave
> or
> less. It will have a low feedpoint impedance that can probably be matched
> reasonably without a tuner or with a limited-range tuner. However, with a
> low impedance comes a current maximum at the feedpoint. This often means
> close to the ground, so even with a good set of elevated radials,
> considerable ground losses could be expected. (An actual connection to the
> soil would generally be much worse, unless you bury a lot of wires.) With
> a
> longer wire (1/2 wavelengh at the lowest band) we can have a very high
> feedpoint impedance, very low feedpoint current, and more elevated
> location(s) of high curent portion(s) of the antenna, for lower ground
> losses.
>
> Any antenna feed point needs to provide two terminals for the feed current
> to flow through a complete circuit. A end-fed designed for medium to high
> feed impedance has small feed current. In practice this means that
> whatever
> is used as the counterpoise side can be small. The applies with a "medium
> impedance" design as discussed earlier, but it applies even more for a
> resonant end-fed with its tiny feed current. A short piece of wire may be
> used, but often not even that is needed, as the feed return current may
> flow
> on the transformer and feedline (if used), and even on the radio box. This
> is fine for QRP and maybe even medium power, as the current is small
> relative to the higher current higher up on the wire. However, at medium
> to
> high power, if matching problems are encountered, or bothersome RF around
> the rig, I would consider a small counterpoise wire to the high impedance
> side of the transformer, or experimenting with the length of the feedline,
> as the length of it matters when "counterpoise current" flows on the
> outside
> of it. I would not count on the impedance transformer to function as a
> common mode choke for blocking such RF current. You could place a separate
> common mode choke somewhere on the feedline, and move its position as a
> way
> to adjust the length of the effective counterpoise. Look up Jim's article
> on
> how to build an effective common mode choke.
>
> 73,
> Erik K7TV
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of JT Croteau
> Sent: Saturday, November 18, 2017 2:34 PM
> To: [hidden email]
> Subject: [Elecraft] KX3 Field Ant. for 80/40/30
>
> Friends, what would be a good end fed wire setup that will match well with
> the internal KX3 ATU and cover, hopefully, 80, 40, and 30 meters?
>
> I went out to my winter camp site, with two really tall pine trees, and
> tried to experiment with a 9:1 UNUN, 135' radiator, and 35' of RG8X.  It
> was
> a total disaster.  Best matches were on 20, 17, and 15 meters but only
> with
> 6.4:1 SWR.  No match at all on the lower bands.
> With my two trees, the radiator made for a perfect inverted-L shape.
>
> What should I try next?  I did try some pruning of the antenna but quickly
> gave up due to the WX conditions.
>
> Thanks
> N1ESE
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[Bill Frantz]

A useful post Erik.

Also useful is the "pseudo end-fed" design that K9YC shows on
<http://k9yc.com/VerticalHeight.pdf> starting at page 70. This
design is really a center fed dipole using the outside of the
feed line coax as one half of the dipole and an extension of the
center conductor as the other. The RF-electrical length of the
feed line outside is controlled by a common-mode choke on the
feed line.

I built one of these for 30 meters and found that the best
tuning occured when the coax shield between the common-mode
choke and the "center" feed location was slightly shorter than
the other half of the dipole.

73 Bill AE6JV

On 11/19/17 at 12:22 AM, [hidden email] (Erik Basilier) wrote:

>End-fed antennas have gotten popular lately. When I look closer I see two
>different popular approaches.

---------------------------------------------------------------------------
Bill Frantz        | "I wish there was a knob on the TV to turn
up the
408-356-8506       | intelligence.  There's a knob called
"brightness", but
www.pwpconsult.com | it doesn't work. -- Gallagher

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[K7TV]

That group sounds interesting, thanks.
73,
Erik K7TV

-----Original Message-----
From: VE3GAM [mailto:[hidden email]]
Sent: Sunday, November 19, 2017 12:09 PM
To: Erik Basilier <[hidden email]>; 'JT Croteau' <[hidden email]>;
[hidden email]
Cc: Al VE3GAM <[hidden email]>
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

there is an End Fed Half Wave Antenna group on Facebook started up by N4LQ.
it certainly promotes the EFHW fed with a 49:1 transformer. Steve loves the
EFHW, but really does not have much love for 9:1 unun antenna. still, it is
an interesting group to monitor.

al ve3gam


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[K7TV]

Bill, I am aware of Jim's innovative way of achieving center feed while seemingly attaching the feeder to the end. It should be useful in some situations. However, the thread creator wanted coverage of 4 bands with one antenna, and my personal interest right now is also solutions that cover serveral bands without adjustments and compromises. With that as the goal, I see no theoretical reason to want center feed. Only by feeding at the end can you get approximately the same impedance for each band, without moving the feedpoint, for so many bands. (That said, if you compare reality side-by-side to a map, reality tends to win. It would be interesting to compare side-by-side to make sure that the high-ratio transformer isn't lossy enough to hurt performance.) If you are looking at a single band, with a 1/2 wave vertical wire. The current distribution should theoretically be the same whether we feed it at the bottom or if we move the feed point to the center at the cost of 1/4 wav
 elength of additional coax plus the cost of the common mode choke (but there may be another justification to have the choke anyway).  If one is willing to compromise the requirement of covering several bands with very good match, there is also the option of Off-Center-Feed, which can allow operation on several bands, but the match on most or all bands will be a compromise that likely forces the use of a tuner, similar to the situation with an end-fed with 9:1 impedance transformer. If you compare the OCF with the end-fed with 9:1 impedance transformer, it is not clear to me which one has the edge in practical use (assuming both have the antenna wire suspended and shaped similarly). For the OCF the results will depend on the selection of feedpoint, and for the end-fed there is room for a wide range of wire lengths that are non-resonant and should produce "medium impedance". One can easily find suggestions online for both designs. However, it seems to me that the 9:1 fans are
 more prone to use low elevations and shapes that reduce performance.

73,
Erik K7TV

-----Original Message-----
From: Bill Frantz [mailto:[hidden email]]
Sent: Sunday, November 19, 2017 1:03 PM
To: Erik Basilier <[hidden email]>
Cc: 'JT Croteau' <[hidden email]>; [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

A useful post Erik.

Also useful is the "pseudo end-fed" design that K9YC shows on <http://k9yc.com/VerticalHeight.pdf> starting at page 70. This design is really a center fed dipole using the outside of the feed line coax as one half of the dipole and an extension of the center conductor as the other. The RF-electrical length of the feed line outside is controlled by a common-mode choke on the feed line.

I built one of these for 30 meters and found that the best tuning occured when the coax shield between the common-mode choke and the "center" feed location was slightly shorter than the other half of the dipole.

73 Bill AE6JV


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[donovanf]

Its easy to measure transformer loss by measuring the loss through
a pair of identical transformers connected to back-to-back.


The loss in a single transformer will be half of the loss through the
back-to-back pair.


73
Frank
W3LPL

----- Original Message -----

From: "Erik Basilier" <[hidden email]>
To: "Bill Frantz" <[hidden email]>
Cc: [hidden email]
Sent: Sunday, November 19, 2017 10:14:41 PM
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

Bill, I am aware of Jim's innovative way of achieving center feed while seemingly attaching the feeder to the end. It should be useful in some situations. However, the thread creator wanted coverage of 4 bands with one antenna, and my personal interest right now is also solutions that cover serveral bands without adjustments and compromises. With that as the goal, I see no theoretical reason to want center feed. Only by feeding at the end can you get approximately the same impedance for each band, without moving the feedpoint, for so many bands. (That said, if you compare reality side-by-side to a map, reality tends to win. It would be interesting to compare side-by-side to make sure that the high-ratio transformer isn't lossy enough to hurt performance.) If you are looking at a single band, with a 1/2 wave vertical wire. The current distribution should theoretically be the same whether we feed it at the bottom or if we move the feed point to the center at the cost of 1/4 wav
 
elength of additional coax plus the cost of the common mode choke (but there may be another justification to have the choke anyway). If one is willing to compromise the requirement of covering several bands with very good match, there is also the option of Off-Center-Feed, which can allow operation on several bands, but the match on most or all bands will be a compromise that likely forces the use of a tuner, similar to the situation with an end-fed with 9:1 impedance transformer. If you compare the OCF with the end-fed with 9:1 impedance transformer, it is not clear to me which one has the edge in practical use (assuming both have the antenna wire suspended and shaped similarly). For the OCF the results will depend on the selection of feedpoint, and for the end-fed there is room for a wide range of wire lengths that are non-resonant and should produce "medium impedance". One can easily find suggestions online for both designs. However, it seems to me that the 9:1 fans are
more prone to use low elevations and shapes that reduce performance.

73,
Erik K7TV

-----Original Message-----
From: Bill Frantz [mailto:[hidden email]]
Sent: Sunday, November 19, 2017 1:03 PM
To: Erik Basilier <[hidden email]>
Cc: 'JT Croteau' <[hidden email]>; [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

A useful post Erik.

Also useful is the "pseudo end-fed" design that K9YC shows on <http://k9yc.com/VerticalHeight.pdf> starting at page 70. This design is really a center fed dipole using the outside of the feed line coax as one half of the dipole and an extension of the center conductor as the other. The RF-electrical length of the feed line outside is controlled by a common-mode choke on the feed line.

I built one of these for 30 meters and found that the best tuning occured when the coax shield between the common-mode choke and the "center" feed location was slightly shorter than the other half of the dipole.

73 Bill AE6JV


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[K7TV]

I am well aware of that, Frank, and in fact I have multiple cores sitting here waiting for such measurements. However, performance of an isolated component is less important than overall system performance, where the matching to antenna impedance as well as counterpoise current routing and losses all play in. After the component testing to qualify different transformers as having low loss, I am planning to test different versions of resonant and non-resonant end-fed antennas against each other in pairs. The resonant (very high impedance) versons will include different transformer ratios. I may even include versions where the impedance transformation is performed with a tapped, tuned parallel-resonant circuit, which is the classic approach from the Zeppelin days. I may also include a center-fed dipole (conventional, K9YC?, sleeve around coax?). To be able to compare antenna systems with potentially small differences, I am set up with a pair of WSPRLite transmitters that let me run both antennas simultaneously in synchronization. In this type of testing one obtains two overlaid graphs representing the two antennas under test, versus time. Each value shows a composite number based on s/n ratios at a number of different receiving stations. Over time, the two curves tend to cross back and forth against each other, but over a few hours one can see whether one tends to dominate over the other. Transmission frequencies will not be exactly the same, but the difference will be very small. When done in my back yard, both antennas in a test will be influenced by all kinds of metal structures around it, including my tower, power lines, metal in the house, and the other antenna under test. I will minimize the latter  by erecting the wires at 90 degrees angle, with the feed points close together, so that I can always reach both transmitters at the same time to push the start buttons at the same time. My main method of compensating for interactions with metal objects will be to swap the matching/feeding systems while keeping the radiators and transmitters in place. I like to deploy wire antennas in the field on 24 ft masts, so I will use two of those for the testing and arrange the two wires as inverted vee’s. For reasons of space, I will not include 80 m, so the two wires will be in the 60+ foot range, except for the non-resonant version where 50+ feet are commonly used. For possible tests using center feed, I would use different arrangements that all resonate as ½ wavelength on 40. By comparing two antenna systems at a time, each time taking the winner to compare with the next antenna, I hope to determine an idea of what works best for me in field use.

 

73,

Erik K7TV

 

From: [hidden email] [mailto:[hidden email]]
Sent: Sunday, November 19, 2017 3:33 PM
To: [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

 

Its easy to measure transformer loss by measuring the loss through

a pair of identical transformers connected to back-to-back.  

 

The loss in a single transformer will be half of the loss through the

back-to-back pair.

 

73

Frank

W3LPL

 

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[donovanf]

Hi Erik,


Radiation results from RF current flowing in an antenna. An RF
ammeter is a useful instrument for measuring the relative efficiency
different types of matching networks feeding similar antennas.


I'm well familiar with the simultaneous synchronized WSPRlite
antenna performance analysis techniques, I developed the techniques
that SOTAbeams implemented earlier this year! They work very,
very well but a few things must be done to avoid significant
measurement errors and biases:


1. The two antennas under test should be located within less than
one wavelength of each other, otherwise independent selective fading
becomes a significant source of measurement error.


2; Horizontally polarized antennas should be oriented end-to-end
to each other to avoid significant parasitic interaction that washes
out the other differences in antenna performance


3, Do not attempt to compare horizontally polarized antennas to
vertically polarized antennas, independent selective fading
becomes a significant source of measurement error that takes
an extraordinary amount of data collection to overcome.


Enjoy!


73
Frank
W3LPL






----- Original Message -----

From: "Erik Basilier" <[hidden email]>
To: [hidden email], [hidden email]
Sent: Monday, November 20, 2017 1:51:47 AM
Subject: RE: [Elecraft] KX3 Field Ant. for 80/40/30



I am well aware of that, Frank, and in fact I have multiple cores sitting here waiting for such measurements. However, performance of an isolated component is less important than overall system performance, where the matching to antenna impedance as well as counterpoise current routing and losses all play in. After the component testing to qualify different transformers as having low loss, I am planning to test different versions of resonant and non-resonant end-fed antennas against each other in pairs. The resonant (very high impedance) versons will include different transformer ratios. I may even include versions where the impedance transformation is performed with a tapped, tuned parallel-resonant circuit, which is the classic approach from the Zeppelin days. I may also include a center-fed dipole (conventional, K9YC?, sleeve around coax?). To be able to compare antenna systems with potentially small differences, I am set up with a pair of WSPRLite transmitters that let me run both antennas simultaneously in synchronization. In this type of testing one obtains two overlaid graphs representing the two antennas under test, versus time. Each value shows a composite number based on s/n ratios at a number of different receiving stations. Over time, the two curves tend to cross back and forth against each other, but over a few hours one can see whether one tends to dominate over the other. Transmission frequencies will not be exactly the same, but the difference will be very small. When done in my back yard, both antennas in a test will be influenced by all kinds of metal structures around it, including my tower, power lines, metal in the house, and the other antenna under test. I will minimize the latter by erecting the wires at 90 degrees angle, with the feed points close together, so that I can always reach both transmitters at the same time to push the start buttons at the same time. My main method of compensating for interactions with metal objects will be to swap the matching/feeding systems while keeping the radiators and transmitters in place. I like to deploy wire antennas in the field on 24 ft masts, so I will use two of those for the testing and arrange the two wires as inverted vee’s. For reasons of space, I will not include 80 m, so the two wires will be in the 60+ foot range, except for the non-resonant version where 50+ feet are commonly used. For possible tests using center feed, I would use different arrangements that all resonate as ½ wavelength on 40. By comparing two antenna systems at a time, each time taking the winner to compare with the next antenna, I hope to determine an idea of what works best for me in field use.

73,
Erik K7TV



From: [hidden email] [mailto:[hidden email]]
Sent: Sunday, November 19, 2017 3:33 PM
To: [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30


Its easy to measure transformer loss by measuring the loss through

a pair of identical transformers connected to back-to-back.



The loss in a single transformer will be half of the loss through the

back-to-back pair.



73

Frank

W3LPL


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[K9MA]

On 11/19/2017 02:22, Erik Basilier wrote:
> The second approach, used by MyAntennas and others seems to use a
> transformer with much higher impedance ratio. One way to construct such a
> transformer would be to cascade two 9:1 units for an effective ratio of
> 81:1.

While I haven't tried it, it would probably be very hard to build a pair
of 9:1 transformers or a single 81:1 transformer with low enough stray
capacitance to work on the higher bands.  It might work up to 40 meters,
I suppose.

The big advantage of a resonant end-fed half wave is that very little
current flows in the ground system or counterpoise, so most of the power
is going into the antenna.  While it is hard to match that high
impedance with a non-resonant transformer, it is very easy to match with
a simple L network.  The only reason the internal ATU in the KX3, etc.,
can't match it is that it doesn't have enough range.  (And for good
reason.)  An external L network consisting of a tapped coil and variable
capacitor will do it nicely.

73,

Scott K9MA

--
Scott  K9MA

[hidden email]

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[Brian Hunt]

For several years I've been using a 33 ft wire and a pair of small
tapped loading coils to get  an EFHW vertical resonant on 20m. 30m and
40m.  It's fed with a link coupled tuned tank circuit consisting of a
coil on a 1 inch powdered iron toroid and an air variable capacitor. 
The link consists of 1-6 switch selected turns which gives a wide range
of impedance transformation.  Antenna is supported with a 33 ft MFJ
fiberglass mast.  Easy to set up and tune.  I do have to haul the wire
down to change the taps and retune for a band change.  Used with a K1 or
KX2, the internal ATU is usually in bypass.

73,
Brian, K0DTJ
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[K7TV]

Hi Frank,

 

Thanks for your very useful comments. Below my answers:

 

>Radiation results from RF current flowing in an antenna.  An RF

>ammeter is a useful instrument for measuring the relative efficiency

>different types of matching networks feeding similar antennas.

Granted. I might want to add that to my plans. I know that the WSPRLite tolerates no more than 100 mW of reflected power, and to avoid accident risk I intend to set the transmit power to no more than 100 mW. I do not know how the units might fold back transmit power in a scenario where the SWR is good but less than perfect. For this reason I am planning to use a tuner whenever SWR is not very close to ideal. The location of the tuner would be wherever it would make sense to place it in field operation. If I add ammeters, they would be placed at the feedpoint, which should work well when I compare different impedance transformers using identical wires. If I compare to non-resonant wires or center feed, it would be hard to compare ammeter readings.

 

> 1.  The two antennas under test should be located within less than

>one wavelength of each other, otherwise independent selective fading

>becomes a significant source of measurement error.  

Interesting. You are saying that this applies even if the comparison is done over several hours?

In my limited back yard, and because I want the feedpoints close to each other, I will certainly meet the requirement of staying withing one wavelength.

 

>2;  Horizontally polarized antennas should be oriented end-to-end

>to each other to avoid significant parasitic interaction that washes

>out the other differences in antenna performance

My earlier comments about end-fed antennas focused on vertical wires since the thread originator had tall trees that suggest vertical orientation. My preferred 24” support poles used with 60+ ft wires lead me to the inverted vee configuration which will be horizontally polarized. I am surprised that you can avoid parasitic interaction if you place the wires end-to-end. I was under the impression that end-to-end vertical wires, as in an elevated vertical with a resonant length of vertical feedline under it, with a common mode choke preventing current going from the radiator to the coax shield, would still suffer from parasitic coupling unless an additional common mode choke is added somewhere along the feedline to break up the resonance. I am influenced here by a QST article about vhf/uhf verticals where it seemed that multiple common mode chokes were found necessary to prevent feedline radiation. Anyway, these situations should be easy to model, and I assume you have looked closely at it. I should have enough room to place my inverted vee’s end-to-end if you are sure that is the best way.

 

>3,  Do not attempt to compare horizontally polarized antennas to

>vertically polarized antennas, independent selective fading

>becomes a significant source of measurement error that takes

>an extraordinary amount of data collection to overcome.

Comparison between horizontal and vertical configuration is not part of my present plans, but I have to admit previously comparing my R5 vertical to my horizontal HF beam. I ran it several hours in several sessions at different times.There were times of day where sometimes the vertical seemed to work better than the beam, although overall the beam looked much better. Do I understand you to say that this comparison was flawed because of insufficient time spent?

 

73,

Erik K7TV

 

>Enjoy!

 

>73

>Frank

>W3LPL

 

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[Bob McGraw - K4TAX]

For that very reason, in our camper operation, I use a end fed antenna. 
The matching network is a tapped coil and variable C forming an L
network.  The circuit is in a small plastic box with a SO-239 on each
end, thus it is reversible.   This allows a wide range of impedance
selections, plus the L network, unlike a T network, will only resolve a
match at one value combination of L and C values.

I carry a 100 ft spool of #22 insulated hook up wire.  Unroll some
estimated length, drop a half hitch around the spool and toss the spool
over a convenient limb.   When ready to retrieve the antenna, turn the
feed end loose and let the spool drop to the ground.  I've never
experienced a length or condition where I could not satisfactorily match
the band/frequency I wanted to use.

73

Bob, K4TAX


On 11/19/2017 10:26 PM, K9MA wrote:

> On 11/19/2017 02:22, Erik Basilier wrote:
>> The second approach, used by MyAntennas and others seems to use a
>> transformer with much higher impedance ratio. One way to construct
>> such a
>> transformer would be to cascade two 9:1 units for an effective ratio of
>> 81:1.
>
> While I haven't tried it, it would probably be very hard to build a
> pair of 9:1 transformers or a single 81:1 transformer with low enough
> stray capacitance to work on the higher bands.  It might work up to 40
> meters, I suppose.
>
> The big advantage of a resonant end-fed half wave is that very little
> current flows in the ground system or counterpoise, so most of the
> power is going into the antenna.  While it is hard to match that high
> impedance with a non-resonant transformer, it is very easy to match
> with a simple L network.  The only reason the internal ATU in the KX3,
> etc., can't match it is that it doesn't have enough range.  (And for
> good reason.)  An external L network consisting of a tapped coil and
> variable capacitor will do it nicely.
>
> 73,
>
> Scott K9MA
>

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[Ignacy]

Antenna performance does not depend on how it is fed (if feeder losses are
low) but on height and ground type. For KX3 with AT, any special length
makes little sense, especially in portable conditions. KX3 matches most
random wires, and KX3 with 4:1 balun matches any wires. Lack of balance is
not too important with battery operation. I try to make random wire +
counterpoise at least 1/4 wave on the lowest frequency for reasonable
efficiency.

For 1.5 KW, an endfed with a 49:1 or so transformer makes lots of sense as
wideband tuners for QRO are rare, expensive and heavy. "Myantennas.com"
perfected a  transformer that has very small losses and does not
self-destroy at high power. But in inv V configuration, it is way down from
a flattop.

Ignacy, NO9E  



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[K7TV]

Ignacy,
For an end-fed wire, I would see the possibility of power losses not only in
the feed feeder, but also in the tuner, the transformer, and the effective
counterpoise path. For low counterpoise losses, small counterpoise current
is desirable, which means a high antenna impedance. When a long counterpoise
wire is needed, and when that wire is close to the ground, I would also
expect ground losses from the counterpoise current interacting with the
ground, in addition to the ground losses caused by the antenna wire
interacting with the ground. When the feeder (outside or shield)-tuner-radio
path carries all or part of the counterpoise current, I would not rule out
the possibility that the possibiility that the resistance there is
sufficient to cause losses significant enough to affect overall efficiency
of the system. That is why I would like to compare like antennas with
different feed systems. Of course antenna wire configuration is the most
important thing to determine overall performance, but when putting up a long
wire, I usually start with the support structure that already exists, or
that I can put up most easily.

73,
Erik K7TV

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ignacy
Sent: Tuesday, November 21, 2017 5:07 PM
To: [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

Antenna performance does not depend on how it is fed (if feeder losses are
low) but on height and ground type. For KX3 with AT, any special length
makes little sense, especially in portable conditions. KX3 matches most
random wires, and KX3 with 4:1 balun matches any wires. Lack of balance is
not too important with battery operation. I try to make random wire +
counterpoise at least 1/4 wave on the lowest frequency for reasonable
efficiency.

For 1.5 KW, an endfed with a 49:1 or so transformer makes lots of sense as
wideband tuners for QRO are rare, expensive and heavy. "Myantennas.com"
perfected a  transformer that has very small losses and does not
self-destroy at high power. But in inv V configuration, it is way down from
a flattop.

Ignacy, NO9E  



--
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[K7TV]

I hope my interest in WSPRLite antenna comparisons doesn't lead this thread too far off topic, but I have further thoughts on how to orient the two antennas being compared.

Frank, who is much more experienced with this comparison system, suggested that two horizontally polarized antennas should be oriented end-to end, due to parasitic interacton between the antennas. I questioned whether the end-to-end configuration would be free from interactions. Be that as it may, but while thinking about configuration choices, I came up with another reason why end-to-end would be the right thing to do.

Suppose we are comparing two omnidirectional antennas such as verticals. Even if the receiving stations are unevenly distributed in different directions, the comparison based on received reports should be fair. If instead we are comparing two horizontal dipoles, that are not pointing in the same direction, and receiving stations are not distributed evenly in all directions, the antenna with fewer receivers in the main lobes would likely be at a disadvantage. If the feed system is the part that is different between the two ontennas, one could compensate, as I suggested, by swapping antennas for each feed system, but the time taken allows the conditions to change, so one would probably have to go back and forth a number of times to gain confidence in any observed difference in performance. Close to the coast receiving stations would be largely missing in roughtly half of possible compass directions, and unidirectional antennas would be affected more than a dipole with its bidirectional pattern. Much seems to depend on the proprietary algorithm used to composite a single performance number for from the WSPR received s/n rations at multiple receiving stations. What is the balance between the number of good reception reports vs. the distance for each one? When we talk about difficulty in comparing one vertical and one horizontal antenna, I suspect that similar considerations may account for result being inconsistent or difficult to interpret.

73,
Erik K7TV

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Erik Basilier
Sent: Sunday, November 19, 2017 11:13 PM
To: [hidden email]; [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

Hi Frank,

 

Thanks for your very useful comments. Below my answers:

 

>Radiation results from RF current flowing in an antenna.  An RF

>ammeter is a useful instrument for measuring the relative efficiency

>different types of matching networks feeding similar antennas.

Granted. I might want to add that to my plans. I know that the WSPRLite tolerates no more than 100 mW of reflected power, and to avoid accident risk I intend to set the transmit power to no more than 100 mW. I do not know how the units might fold back transmit power in a scenario where the SWR is good but less than perfect. For this reason I am planning to use a tuner whenever SWR is not very close to ideal. The location of the tuner would be wherever it would make sense to place it in field operation. If I add ammeters, they would be placed at the feedpoint, which should work well when I compare different impedance transformers using identical wires. If I compare to non-resonant wires or center feed, it would be hard to compare ammeter readings.

 

> 1.  The two antennas under test should be located within less than

>one wavelength of each other, otherwise independent selective fading

>becomes a significant source of measurement error.  

Interesting. You are saying that this applies even if the comparison is done over several hours?

In my limited back yard, and because I want the feedpoints close to each other, I will certainly meet the requirement of staying withing one wavelength.

 

>2;  Horizontally polarized antennas should be oriented end-to-end

>to each other to avoid significant parasitic interaction that washes

>out the other differences in antenna performance

My earlier comments about end-fed antennas focused on vertical wires since the thread originator had tall trees that suggest vertical orientation. My preferred 24” support poles used with 60+ ft wires lead me to the inverted vee configuration which will be horizontally polarized. I am surprised that you can avoid parasitic interaction if you place the wires end-to-end. I was under the impression that end-to-end vertical wires, as in an elevated vertical with a resonant length of vertical feedline under it, with a common mode choke preventing current going from the radiator to the coax shield, would still suffer from parasitic coupling unless an additional common mode choke is added somewhere along the feedline to break up the resonance. I am influenced here by a QST article about vhf/uhf verticals where it seemed that multiple common mode chokes were found necessary to prevent feedline radiation. Anyway, these situations should be easy to model, and I assume you have looked closely at it. I should have enough room to place my inverted vee’s end-to-end if you are sure that is the best way.

 

>3,  Do not attempt to compare horizontally polarized antennas to

>vertically polarized antennas, independent selective fading

>becomes a significant source of measurement error that takes

>an extraordinary amount of data collection to overcome.

Comparison between horizontal and vertical configuration is not part of my present plans, but I have to admit previously comparing my R5 vertical to my horizontal HF beam. I ran it several hours in several sessions at different times.There were times of day where sometimes the vertical seemed to work better than the beam, although overall the beam looked much better. Do I understand you to say that this comparison was flawed because of insufficient time spent?

 

73,

Erik K7TV

 

>Enjoy!

 

>73

>Frank

>W3LPL

 

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[Don Wilhelm]

Erik,

About all you can conclude from the WSPR readings is the relative
difference between antennas.  If you want to compare two horizontal
antennas, place them end to end.  The radiation at the end is at a
minimum and the antenna will not interact.

As for comparing a vertical with a horizontal antenna, or two verticals,
the only thing one can say is at that particular time and distance for
propagation, one antenna is better than the other.  That may not be true
for other propagation conditions, so be careful when generalizing.

As far as two horizonal antennas oriented in different directions, you
would expect greater signal strength in directions broadside to the
antenna.  That directivity may be useful in actual use, but is not a
valid comparison between the two antennas.

73,
Don W3FPR

On 11/21/2017 8:40 PM, Erik Basilier wrote:
> I hope my interest in WSPRLite antenna comparisons doesn't lead this thread too far off topic, but I have further thoughts on how to orient the two antennas being compared.
>
> Frank, who is much more experienced with this comparison system, suggested that two horizontally polarized antennas should be oriented end-to end, due to parasitic interacton between the antennas. I questioned whether the end-to-end configuration would be free from interactions. Be that as it may, but while thinking about configuration choices, I came up with another reason why end-to-end would be the right thing to do.
>
> Suppose we are comparing two omnidirectional antennas such as verticals. Even if the receiving stations are unevenly distributed in different directions, the comparison based on received reports should be fair. If instead we are comparing two horizontal dipoles, that are not pointing in the same direction, and receiving stations are not distributed evenly in all directions, the antenna with fewer receivers in the main lobes would likely be at a disadvantage. If the feed system is the part that is different between the two ontennas, one could compensate, as I suggested, by swapping antennas for each feed system, but the time taken allows the conditions to change, so one would probably have to go back and forth a number of times to gain confidence in any observed difference in performance. Close to the coast receiving stations would be largely missing in roughtly half of possible compass directions, and unidirectional antennas would be affected more than a dipole with its bid
 irectional pattern. Much seems to depend on the proprietary algorithm used to composite a single performance number for from the WSPR received s/n rations at multiple receiving stations. What is the balance between the number of good reception reports vs. the distance for each one? When we talk about difficulty in comparing one vertical and one horizontal antenna, I suspect that similar considerations may account for result being inconsistent or difficult to interpret.
>
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[Ignacy]

I tested the endfed from myantennas at 1 kw. The transformer was only warm
so no significant losses there. The feeder was RF hot so a toroid choke was
added. Cable no longer hot and toroid cold. SWR low on many bands. So the
only significant losses could have been through the ground.

This is obvious after a bit of thought. A vertical or inv L ( or low inv V)
needs either good ground or lots of radials for small ground losses. With
endfed, there is one radial, the feeder. So excellent performance by the
beach, not bad in good ground, so so in poor ground.

Ignacy

On Nov 21, 2017 7:58 PM, "Erik Basilier" <[hidden email]> wrote:

Ignacy,
For an end-fed wire, I would see the possibility of power losses not only in
the feed feeder, but also in the tuner, the transformer, and the effective
counterpoise path. For low counterpoise losses, small counterpoise current
is desirable, which means a high antenna impedance. When a long counterpoise
wire is needed, and when that wire is close to the ground, I would also
expect ground losses from the counterpoise current interacting with the
ground, in addition to the ground losses caused by the antenna wire
interacting with the ground. When the feeder (outside or shield)-tuner-radio
path carries all or part of the counterpoise current, I would not rule out
the possibility that the possibiility that the resistance there is
sufficient to cause losses significant enough to affect overall efficiency
of the system. That is why I would like to compare like antennas with
different feed systems. Of course antenna wire configuration is the most
important thing to determine overall performance, but when putting up a long
wire, I usually start with the support structure that already exists, or
that I can put up most easily.

73,
Erik K7TV

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ignacy
Sent: Tuesday, November 21, 2017 5:07 PM
To: [hidden email]
Subject: Re: [Elecraft] KX3 Field Ant. for 80/40/30

Antenna performance does not depend on how it is fed (if feeder losses are
low) but on height and ground type. For KX3 with AT, any special length
makes little sense, especially in portable conditions. KX3 matches most
random wires, and KX3 with 4:1 balun matches any wires. Lack of balance is
not too important with battery operation. I try to make random wire +
counterpoise at least 1/4 wave on the lowest frequency for reasonable
efficiency.

For 1.5 KW, an endfed with a 49:1 or so transformer makes lots of sense as
wideband tuners for QRO are rare, expensive and heavy. "Myantennas.com"
perfected a  transformer that has very small losses and does not
self-destroy at high power. But in inv V configuration, it is way down from
a flattop.

Ignacy, NO9E



--
Sent from: http://elecraft.365791.n2.nabble.com/
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