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Using your tower as a vertical - 160 or 80

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K7TV

Using your tower as a vertical - 160 or 80

Years ago, after putting up a heavy-duty crank-up tower with several
antennas on a tall mast at the top, I was interested in loading up the whole
metal tree for 160 and/or 80. However, I didn't like the prospect of
transmitted power getting back into the shack via the existing feedlines,
causing all kinds of problems including losses. From a surplus vendor I
obtained four square slabs of ferrite (no spec's) and taped them together to
form a box-shaped common mode choke around the existing feedlines (and rotor
control cable etc). I didn't have radials at the tower base, but a couple of
long and wide copper strips buried and connected to ground rods to which the
tower was grounded. I opened up the tower ground connection and I had a feed
point. Finding resonance was not as easy as using my antenna analyzer. The
signal from the analyzer was overwhelmed by picked-up broadcast signals,
rendering the analyzer unuseable. I got by using a custom measurement setup.
It turned out that the entire metal tree resonated in the broadcast band and
was inductive at 160. I tuned it with a serial variable capacitor, and found
the antenna worked very well on 160. However, I didn't continue using it, as
I didn't feel safe not to have the tower grounded. I pondered schemes to add
some kind of gamma-like matching device, but never got around to it. Also I
never tried it on 80, but I suspect it would not been ideal for low angle
radiation.

Later I added more antennas to the mast, and with the added cables, the
whole bundle would no longer fit in the makeshift ferrite choke. Out of
curiosity I once again tried ungrounding the tower to check on its
characteristics as a vertical antenna. I could no longer find the resonance
I had seen and used before. Apparently, the ferrite choke had been a crucial
part of the scheme.

At this point I still don't have an antenna for 160 or 80. (I did try an
inverted vee off the tower for 80, but it caused terrible de-tuning of the
40m part of my beam on the tower, so I gave up on that. Maybe I should try a
sloper.) I am thinking of putting up a dedicated vertical, but on my small
lot it would couple to the tower. Perhaps it would be better to give the
tower another look as my low-band vertical? My source of ferrite slabs dried
up years ago. I wonder if anyone else on the list has used a similar
approach and found a good way to choke off RF on a bundle of feedlines?
Individual chokes don't seem very attractive to me as I have many cables,
but if one has to go that route then it would make sense to look very
carefully at the choice of chokes. I would also be interested in knowing
about others' experiences with feed systems that leave the tower grounded.

Thanks in advance for any useful ideas!

73,

Erik K7TV

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Alan Bloom

Re: Using your tower as a vertical - 160 or 80

I use two of the top guy wires as an inverted vee. There are insulators
near the top of the guys and about 50 feet or so down. The vee is
brought to resonance on 80 meters with a center-tapped loading coil,
which also acts as a balun. The best match was with the coax tapped
right about at the end of one side of the coil (and of course the coax
shield to the grounded center tap).

Works great on 80 meters without a tuner and on 40 meters with a tuner.

Alan N1AL

On 02/28/2017 09:42 PM, Erik Basilier wrote:

> Years ago, after putting up a heavy-duty crank-up tower with several
> antennas on a tall mast at the top, I was interested in loading up the whole
> metal tree for 160 and/or 80. However, I didn't like the prospect of
> transmitted power getting back into the shack via the existing feedlines,
> causing all kinds of problems including losses. From a surplus vendor I
> obtained four square slabs of ferrite (no spec's) and taped them together to
> form a box-shaped common mode choke around the existing feedlines (and rotor
> control cable etc). I didn't have radials at the tower base, but a couple of
> long and wide copper strips buried and connected to ground rods to which the
> tower was grounded. I opened up the tower ground connection and I had a feed
> point. Finding resonance was not as easy as using my antenna analyzer. The
> signal from the analyzer was overwhelmed by picked-up broadcast signals,
> rendering the analyzer unuseable. I got by using a custom measurement setup.
> It turned out that the entire metal tree resonated in the broadcast band and
> was inductive at 160. I tuned it with a serial variable capacitor, and found
> the antenna worked very well on 160. However, I didn't continue using it, as
> I didn't feel safe not to have the tower grounded. I pondered schemes to add
> some kind of gamma-like matching device, but never got around to it. Also I
> never tried it on 80, but I suspect it would not been ideal for low angle
> radiation.
>
>
>
> Later I added more antennas to the mast, and with the added cables, the
> whole bundle would no longer fit in the makeshift ferrite choke. Out of
> curiosity I once again tried ungrounding the tower to check on its
> characteristics as a vertical antenna. I could no longer find the resonance
> I had seen and used before. Apparently, the ferrite choke had been a crucial
> part of the scheme.
>
>
>
> At this point I still don't have an antenna for 160 or 80. (I did try an
> inverted vee off the tower for 80, but it caused terrible de-tuning of the
> 40m part of my beam on the tower, so I gave up on that. Maybe I should try a
> sloper.) I am thinking of putting up a dedicated vertical, but on my small
> lot it would couple to the tower. Perhaps it would be better to give the
> tower another look as my low-band vertical? My source of ferrite slabs dried
> up years ago. I wonder if anyone else on the list has used a similar
> approach and found a good way to choke off RF on a bundle of feedlines?
> Individual chokes don't seem very attractive to me as I have many cables,
> but if one has to go that route then it would make sense to look very
> carefully at the choice of chokes. I would also be interested in knowing
> about others' experiences with feed systems that leave the tower grounded.
>
>
>
> Thanks in advance for any useful ideas!
>
>
>
> 73,
>
> Erik K7TV
>
> ______________________________________________________________
> 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]
>

K7TV

Re: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Alan,

Thanks for your reply. Your approach would provide 40m capability to replace
the 40m capability that my (Sommer) beam loses through detuning.
However, I wonder how hard your tuner must work on 40? Enough to create
substantial feedline losses when the tuner is in the shack?
Anyway, I have another reason not to choose your approach:
I am rebuilding my station to support SO2R, and it is tough to avoid
interference between the two radios operating on different bands, especially
40 - 20 and with the antennas close together.
I found to my surprise, before the QST review came out, that the Low Band
Systems multiplexer and band pass filters (my setup includes 40m) eliminates
the interference problem. However, this scheme requires that the antennas be
on a shared feedline. With your approach the 40m antenna would no longer be
on the same feedline as the higher bands.

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
Bloom
Sent: Tuesday, February 28, 2017 11:09 PM
To: [hidden email]
Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80

I use two of the top guy wires as an inverted vee. There are insulators
near the top of the guys and about 50 feet or so down. The vee is brought
to resonance on 80 meters with a center-tapped loading coil, which also acts
as a balun. The best match was with the coax tapped right about at the end
of one side of the coil (and of course the coax shield to the grounded
center tap).

Works great on 80 meters without a tuner and on 40 meters with a tuner.

Alan N1AL

On 02/28/2017 09:42 PM, Erik Basilier wrote:

> Years ago, after putting up a heavy-duty crank-up tower with several
> antennas on a tall mast at the top, I was interested in loading up the
> whole metal tree for 160 and/or 80. However, I didn't like the
> prospect of transmitted power getting back into the shack via the
> existing feedlines, causing all kinds of problems including losses.
> From a surplus vendor I obtained four square slabs of ferrite (no
> spec's) and taped them together to form a box-shaped common mode choke
> around the existing feedlines (and rotor control cable etc). I didn't
> have radials at the tower base, but a couple of long and wide copper
> strips buried and connected to ground rods to which the tower was
> grounded. I opened up the tower ground connection and I had a feed
> point. Finding resonance was not as easy as using my antenna analyzer.
> The signal from the analyzer was overwhelmed by picked-up broadcast

signals, rendering the analyzer unuseable. I got by using a custom
measurement setup.

> It turned out that the entire metal tree resonated in the broadcast
> band and was inductive at 160. I tuned it with a serial variable
> capacitor, and found the antenna worked very well on 160. However, I
> didn't continue using it, as I didn't feel safe not to have the tower
> grounded. I pondered schemes to add some kind of gamma-like matching
> device, but never got around to it. Also I never tried it on 80, but I
> suspect it would not been ideal for low angle radiation.
>
>
>
> Later I added more antennas to the mast, and with the added cables,
> the whole bundle would no longer fit in the makeshift ferrite choke.
> Out of curiosity I once again tried ungrounding the tower to check on
> its characteristics as a vertical antenna. I could no longer find the
> resonance I had seen and used before. Apparently, the ferrite choke
> had been a crucial part of the scheme.
>
>
>
> At this point I still don't have an antenna for 160 or 80. (I did try
> an inverted vee off the tower for 80, but it caused terrible de-tuning
> of the 40m part of my beam on the tower, so I gave up on that. Maybe I
> should try a
> sloper.) I am thinking of putting up a dedicated vertical, but on my
> small lot it would couple to the tower. Perhaps it would be better to
> give the tower another look as my low-band vertical? My source of
> ferrite slabs dried up years ago. I wonder if anyone else on the list
> has used a similar approach and found a good way to choke off RF on a

bundle of feedlines?
> Individual chokes don't seem very attractive to me as I have many
> cables, but if one has to go that route then it would make sense to
> look very carefully at the choice of chokes. I would also be
> interested in knowing about others' experiences with feed systems that
leave the tower grounded.

>
>
>
> Thanks in advance for any useful ideas!
>
>
>
> 73,
>
> Erik K7TV
>
> ______________________________________________________________
> 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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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html Message
delivered to [hidden email]

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Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Alan Bloom

Re: Using your tower as a vertical - 160 or 80

Hi Erik,

It is certainly possible to use a separate filter in the feedline to
each antenna. For example, here's an article I wrote many years ago on
how to homebrew your own:

http://p1k.arrl.org/pubs_archive/89595

Those filters are only good for 100W or so, but there is no fundamental
reason they couldn't be scaled up to 1500W. I haven't researched it,
but I'm thinking there must be commercial equivalents as well.

Alan N1AL

On 02/28/2017 10:41 PM, Erik Basilier wrote:

> Alan,
>
> Thanks for your reply. Your approach would provide 40m capability to replace
> the 40m capability that my (Sommer) beam loses through detuning.
> However, I wonder how hard your tuner must work on 40? Enough to create
> substantial feedline losses when the tuner is in the shack?
> Anyway, I have another reason not to choose your approach:
> I am rebuilding my station to support SO2R, and it is tough to avoid
> interference between the two radios operating on different bands, especially
> 40 - 20 and with the antennas close together.
> I found to my surprise, before the QST review came out, that the Low Band
> Systems multiplexer and band pass filters (my setup includes 40m) eliminates
> the interference problem. However, this scheme requires that the antennas be
> on a shared feedline. With your approach the 40m antenna would no longer be
> on the same feedline as the higher bands.
>
>
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
> Bloom
> Sent: Tuesday, February 28, 2017 11:09 PM
> To: [hidden email]
> Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80
>
> I use two of the top guy wires as an inverted vee. There are insulators
> near the top of the guys and about 50 feet or so down. The vee is brought
> to resonance on 80 meters with a center-tapped loading coil, which also acts
> as a balun. The best match was with the coax tapped right about at the end
> of one side of the coil (and of course the coax shield to the grounded
> center tap).
>
> Works great on 80 meters without a tuner and on 40 meters with a tuner.
>
> Alan N1AL
>
>
> On 02/28/2017 09:42 PM, Erik Basilier wrote:
>> Years ago, after putting up a heavy-duty crank-up tower with several
>> antennas on a tall mast at the top, I was interested in loading up the
>> whole metal tree for 160 and/or 80. However, I didn't like the
>> prospect of transmitted power getting back into the shack via the
>> existing feedlines, causing all kinds of problems including losses.
>> From a surplus vendor I obtained four square slabs of ferrite (no
>> spec's) and taped them together to form a box-shaped common mode choke
>> around the existing feedlines (and rotor control cable etc). I didn't
>> have radials at the tower base, but a couple of long and wide copper
>> strips buried and connected to ground rods to which the tower was
>> grounded. I opened up the tower ground connection and I had a feed
>> point. Finding resonance was not as easy as using my antenna analyzer.
>> The signal from the analyzer was overwhelmed by picked-up broadcast
> signals, rendering the analyzer unuseable. I got by using a custom
> measurement setup.
>> It turned out that the entire metal tree resonated in the broadcast
>> band and was inductive at 160. I tuned it with a serial variable
>> capacitor, and found the antenna worked very well on 160. However, I
>> didn't continue using it, as I didn't feel safe not to have the tower
>> grounded. I pondered schemes to add some kind of gamma-like matching
>> device, but never got around to it. Also I never tried it on 80, but I
>> suspect it would not been ideal for low angle radiation.
>>
>>
>>
>> Later I added more antennas to the mast, and with the added cables,
>> the whole bundle would no longer fit in the makeshift ferrite choke.
>> Out of curiosity I once again tried ungrounding the tower to check on
>> its characteristics as a vertical antenna. I could no longer find the
>> resonance I had seen and used before. Apparently, the ferrite choke
>> had been a crucial part of the scheme.
>>
>>
>>
>> At this point I still don't have an antenna for 160 or 80. (I did try
>> an inverted vee off the tower for 80, but it caused terrible de-tuning
>> of the 40m part of my beam on the tower, so I gave up on that. Maybe I
>> should try a
>> sloper.) I am thinking of putting up a dedicated vertical, but on my
>> small lot it would couple to the tower. Perhaps it would be better to
>> give the tower another look as my low-band vertical? My source of
>> ferrite slabs dried up years ago. I wonder if anyone else on the list
>> has used a similar approach and found a good way to choke off RF on a
> bundle of feedlines?
>> Individual chokes don't seem very attractive to me as I have many
>> cables, but if one has to go that route then it would make sense to
>> look very carefully at the choice of chokes. I would also be
>> interested in knowing about others' experiences with feed systems that
> leave the tower grounded.
>>
>>
>>
>> Thanks in advance for any useful ideas!
>>
>>
>>
>> 73,
>>
>> Erik K7TV
>>
>> ______________________________________________________________
>> 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]
>
> ______________________________________________________________
> 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]
>

K7TV

FW: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Hi Alan,

Your link didn't work for me, but I assume your article describes how to
make a good bandpass filter. I do in fact recall seeing such an article in
QST years ago. Assuming that you were just pointing out that I can put a
bandpass filter on each feedline, as is common practice in SO2R operations,
I need to state my case in more detail:

Since I have second antenna covering 20-15-10 (a vertical), I started out
doing just that: putting a bandpass filter on each. I was in a hurry and
bought the LBS commercial filters rather than building based on the old
article. The antennas are close together, and even after I upgraded so as to
have two K3 radios, I was unhappy with the isolation with one K3
transmitting on 40 on the beam and the other K3 receiving on 20 on the
vertical. Just out of curiosity I plan to dig deeper into this situation, as
I think somewhat better results could be achieved. However, seeing the big
difference in performance on a given band between the vertical and the beam,
I really wanted both radios to have a beam. That is where I decided to get
the multiplexer (a model that includes 40m). Performance wise, this was
going to be like having one multiband beam, including 40m, for each radio.
Much better than using the vertical for one radio, assuming of course that
the physical sharing of one beam would aggravate the interference situation
I had when using separate antennas and bandpass filters. With the
multiplexer, per manufacturer's recommendation, each band still uses its
separate bandpass filter, so that total attenuation between bands is much
greater than what can be expected with bandpass filters alone. Still, I was
apprehensive of a possible increase in interference. The outcome was nothing
short of stunning: No interference at all. I see a possiblity that I could
have somehow reduced the interference experienced with separate antennas and
using bandpass filters, but I can't see that approach competing with the
superior results using a single antenna + multiplexer + bandpass filters.
The QST review backs up my assumption that the great results with that
configuration was no fluke. Of course, I cannot include 80m in the same
approach as long as I don't have a single antenna that includes that band
(and I can't quickly get a multiplexer that includes all 5 bands). So, for
80 I will have a separate feedline and just a bandpass filter. BTW I am very
happy to not have yielded to the temptation to upgrade my beam to a Steppir,
as the multiplexer approach requires the antenna to be tuned simultaneously
to multiple bands, not to tune to one band at a time.

If I had been able to achieve really good isolation with just a bandpass
filter for each band, your approach with an 80m antenna that also covers 40
would make good sense to my situation. As it is, keeping 40m within the
beam, even with no gain over running 40m on the second antenna, makes sense
as it allows me to route 40m not just through the bandpass filter, but also
through the multiplexer. Since I already tried an 80m inverted vee on the
tower, and it ruined the 40m performance of the beam, I am looking for other
approaches for 80m. It might be possible to change the beam to bring it back
to resonance on 40, but this particular beam is a complicated design
already. A sloper is one possiblity, but it is not likely to be my first
attempt, as it would be close to the beam and it would be somewhat similar
to the vee. At this point I am leaning toward either a separate shortened
vertical such as a Butternut model for 80 and 40 (not likely to use the 40
part) or using the tower itself as a vertical. For the latter approach I
would need to prevent the tower's feedline bundle (the part going into the
house) from forming part of the radiating element. I remember an old Antenna
Book discussing methods of feeding the tower as a vertical, but the author
seemed to ignore the issue of the cables coming off the tower. Maybe it was
assumed that the cables would be disconnected at the bulkhead whenever the
tower would be used as a vertical. Nobody has replied to me about
experiences dealing with that issue. Also as the tower with its antennas is
resonant in the BC band, I would model it to find out if it has a resonable
vertical radiation pattern if fed as a whole on 80.

73,
Erik K7TV

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
Bloom
Sent: Wednesday, March 01, 2017 12:29 PM
To: [hidden email]
Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80

Hi Erik,

It is certainly possible to use a separate filter in the feedline to each
antenna. For example, here's an article I wrote many years ago on how to
homebrew your own:

http://p1k.arrl.org/pubs_archive/89595

Those filters are only good for 100W or so, but there is no fundamental
reason they couldn't be scaled up to 1500W. I haven't researched it, but
I'm thinking there must be commercial equivalents as well.

Alan N1AL

On 02/28/2017 10:41 PM, Erik Basilier wrote:

> Alan,
>
> Thanks for your reply. Your approach would provide 40m capability to
> replace the 40m capability that my (Sommer) beam loses through detuning.
> However, I wonder how hard your tuner must work on 40? Enough to
> create substantial feedline losses when the tuner is in the shack?
> Anyway, I have another reason not to choose your approach:
> I am rebuilding my station to support SO2R, and it is tough to avoid
> interference between the two radios operating on different bands,
> especially
> 40 - 20 and with the antennas close together.
> I found to my surprise, before the QST review came out, that the Low
> Band Systems multiplexer and band pass filters (my setup includes 40m)
> eliminates the interference problem. However, this scheme requires
> that the antennas be on a shared feedline. With your approach the 40m
> antenna would no longer be on the same feedline as the higher bands.
>
>
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of
> Alan Bloom
> Sent: Tuesday, February 28, 2017 11:09 PM
> To: [hidden email]
> Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80
>
> I use two of the top guy wires as an inverted vee. There are
> insulators near the top of the guys and about 50 feet or so down. The
> vee is brought to resonance on 80 meters with a center-tapped loading
> coil, which also acts as a balun. The best match was with the coax
> tapped right about at the end of one side of the coil (and of course
> the coax shield to the grounded center tap).
>
> Works great on 80 meters without a tuner and on 40 meters with a tuner.
>
> Alan N1AL
>
>
> On 02/28/2017 09:42 PM, Erik Basilier wrote:
>> Years ago, after putting up a heavy-duty crank-up tower with several
>> antennas on a tall mast at the top, I was interested in loading up
>> the whole metal tree for 160 and/or 80. However, I didn't like the
>> prospect of transmitted power getting back into the shack via the
>> existing feedlines, causing all kinds of problems including losses.
>> From a surplus vendor I obtained four square slabs of ferrite (no
>> spec's) and taped them together to form a box-shaped common mode
>> choke around the existing feedlines (and rotor control cable etc). I
>> didn't have radials at the tower base, but a couple of long and wide
>> copper strips buried and connected to ground rods to which the tower
>> was grounded. I opened up the tower ground connection and I had a
>> feed point. Finding resonance was not as easy as using my antenna

analyzer.

>> The signal from the analyzer was overwhelmed by picked-up broadcast
> signals, rendering the analyzer unuseable. I got by using a custom
> measurement setup.
>> It turned out that the entire metal tree resonated in the broadcast
>> band and was inductive at 160. I tuned it with a serial variable
>> capacitor, and found the antenna worked very well on 160. However, I
>> didn't continue using it, as I didn't feel safe not to have the tower
>> grounded. I pondered schemes to add some kind of gamma-like matching
>> device, but never got around to it. Also I never tried it on 80, but
>> I suspect it would not been ideal for low angle radiation.
>>
>>
>>
>> Later I added more antennas to the mast, and with the added cables,
>> the whole bundle would no longer fit in the makeshift ferrite choke.
>> Out of curiosity I once again tried ungrounding the tower to check on
>> its characteristics as a vertical antenna. I could no longer find the
>> resonance I had seen and used before. Apparently, the ferrite choke
>> had been a crucial part of the scheme.
>>
>>
>>
>> At this point I still don't have an antenna for 160 or 80. (I did try
>> an inverted vee off the tower for 80, but it caused terrible
>> de-tuning of the 40m part of my beam on the tower, so I gave up on
>> that. Maybe I should try a
>> sloper.) I am thinking of putting up a dedicated vertical, but on my
>> small lot it would couple to the tower. Perhaps it would be better to
>> give the tower another look as my low-band vertical? My source of
>> ferrite slabs dried up years ago. I wonder if anyone else on the list
>> has used a similar approach and found a good way to choke off RF on a
> bundle of feedlines?
>> Individual chokes don't seem very attractive to me as I have many
>> cables, but if one has to go that route then it would make sense to
>> look very carefully at the choice of chokes. I would also be
>> interested in knowing about others' experiences with feed systems
>> that
> leave the tower grounded.
>>
>>
>>
>> Thanks in advance for any useful ideas!
>>
>>
>>
>> 73,
>>
>> Erik K7TV
>>
>> ______________________________________________________________
>> 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]
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k1htv

Re: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Erik,
I've been feeding K3 RF to my house bracketed, 75 ft Rohn 25 tower for years with great success on 160 Meters. The tower is topped with HF and VHF yagis which act as a capacitive top hat. The 50 Ohm coax feedline is connected to a tap on the coil of a parallel tuned circuit. The top of the LC circuit is connected to a #16 THHN wire which runs parallel to the tower, about 18" outside one of the legs and connects to a bolt around 10 ft down from the top of the tower. At the base of the tower I simply tune the capacitor and find the best spot on the coil to tap to obtain the lowest SWR. There are 16 quarter wave radials around the tower, most of them on the tower side of the house from south to north and a few wrapping around and under the back deck toward the northeast. There are around a dozen 8 ft ground rods connected to the tower with #6 wire and the tower also is connected to a perimeter ground system surrounding the house.

The shields of most, but not all, of the coax cables leaving the tower are grounded at the tower base. Before all coax and control cables enter the shack they all are grounded at the steel entry box around 30 feet from the tower base.

So how does a shunt fed 75 ft tower work with a barefoot K3 feeding it? With 100 Watts I've confirmed 229 countries on the Topband and have worked 89 countries on all continents with QRP 5 Watts. You can check out the 160M QRP WAC cards at:
http://www.qrz.com/db/K1HTV

If you haven't tried shunt feeding your grounded tower, give it a try. You may be surprised at how well it can work on 160 Meters.

73,
Rich - K1HTV

= = =

Erik, K7TV wrote:

Years ago, after putting up a heavy-duty crank-up tower with several
antennas on a tall mast at the top, I was interested in loading up the whole
metal tree for 160 and/or 80. However, I didn't like the prospect of
transmitted power getting back into the shack via the existing feedlines,
causing all kinds of problems including losses. From a surplus vendor I
obtained four square slabs of ferrite (no spec's) and taped them together to
form a box-shaped common mode choke around the existing feedlines (and rotor
control cable etc). I didn't have radials at the tower base, but a couple of
long and wide copper strips buried and connected to ground rods to which the
tower was grounded. I opened up the tower ground connection and I had a feed
point. Finding resonance was not as easy as using my antenna analyzer. The
signal from the analyzer was overwhelmed by picked-up broadcast signals,
rendering the analyzer unuseable. I got by using a custom measurement setup.
It turned out that the entire metal tree resonated in the broadcast band and
was inductive at 160. I tuned it with a serial variable capacitor, and found
the antenna worked very well on 160. However, I didn't continue using it, as
I didn't feel safe not to have the tower grounded. I pondered schemes to add
some kind of gamma-like matching device, but never got around to it. Also I
never tried it on 80, but I suspect it would not been ideal for low angle
radiation.

Later I added more antennas to the mast, and with the added cables, the
whole bundle would no longer fit in the makeshift ferrite choke. Out of
curiosity I once again tried ungrounding the tower to check on its
characteristics as a vertical antenna. I could no longer find the resonance
I had seen and used before. Apparently, the ferrite choke had been a crucial
part of the scheme.

At this point I still don't have an antenna for 160 or 80. (I did try an
inverted vee off the tower for 80, but it caused terrible de-tuning of the
40m part of my beam on the tower, so I gave up on that. Maybe I should try a
sloper.) I am thinking of putting up a dedicated vertical, but on my small
lot it would couple to the tower. Perhaps it would be better to give the
tower another look as my low-band vertical? My source of ferrite slabs dried
up years ago. I wonder if anyone else on the list has used a similar
approach and found a good way to choke off RF on a bundle of feedlines?
Individual chokes don't seem very attractive to me as I have many cables,
but if one has to go that route then it would make sense to look very
carefully at the choice of chokes. I would also be interested in knowing
about others' experiences with feed systems that leave the tower grounded.

Thanks in advance for any useful ideas!

73,

Erik K7TV

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K7TV

Re: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Rich,

Thanks for your reply; very helpful!

Something similar to your shunt feeding method is what I have had in mind.
Since my tower is a crankup (55 ft topped by about 22 ft of mast+antennas),
I do have some misgivings about managing the wire running parallel to the
tower, in the scenario where the tower sections are telescoping and
releasing the tension on the wire. Maybe I should first try attaching the
feed to the top of the bottom section rather than the top of the tower.

The most interesting part of your installation is your grounding of most of
the coax cables at the tower base, and also at the entry box. When I
installed my tower in 1993 I had read a recommendation to let the cables
form a gentle curve almost touching ground, which is what I did. The idea of
grounding them at the tower base did not occur to me, and doesn't seem
compatible with the gentle curve concept. At the house I did think about
feedthrough panel that could be grounded, but I was in a hurry and didn't do
the work. Some of my vhf/uhf cables are of the thick variety (much thicker
than RG-213, and extra connectors cost significant money. Since then, it has
been on my to-do list to go back, cut the cables, install connectors, and
install a grounded plate or box. At the time when I wanted to try the tower
as a 160 vertical, I didn't feel confident that doing that work would be as
effective as choking off common mode currents with ferrites, and that did
seem to work well as long as the cables fit in the device. After reading
your post I get the impression that instead of obtaining choke(s) for the
cable bundle as it is today, I should do the work of grounding the cables at
the house entry and also at the tower base. For non-coax control cables I
could apply my choke. You state that not all of your cables were grounded.
For such a situation my first thought is that the result would depend on
cable length and frequency, and if there is no problem in your situation
then luck might have played a role. You did not mention trying your setup
for 80. In my case, I have more need for 80m than 160, and I am still unsure
if the whole metal tree might be on the big side for 80. That should be easy
to determine with a model. Thanks for the details of your ground system. If
I were to erect a separate vertical for 80, I would have to install a lot of
radials, so doing the same around the tower is not a big deal. Like in your
case, most of the radials would be on one side of the tower (directed away
from the house). When I did feed the tower on 160 as an experiment years
ago, I had (and still have) just two ground rods at the base, plus copper
ribbon, which was meant to encircle the house, a project that was never
finished, but has been on my to-do list ever since. I see a lot of
similarity with your situation, but I need to put in some work to catch up!
Now, supposing I get it all done, and it all works as expected, the next
step is seeing the resulting 80m capability in the context of a 2-radio
system. Obviously, only one radio can be on 80 at a given time, and it will
use a bandpass filter but not a multiplexer. The 80m antenna (=tower) will
be closer to the beam than my high-band vertical.The 80m rf will flow in
very close proximity to the beam, the use of which by another radio is
protected by both the multiplexer and the applicable bandpass filter. Will
that be enough protection, given that the proximity situation is worse than
with the high-band vertical? I am not totally sure, but it seems a
reasonably good bet to me.

73,

Erik K7TV

----------------------------------------------------------------------------
----------------------------------------------------------------------------
-------------------------------------------

Erik,

I've been feeding K3 RF to my house bracketed, 75 ft Rohn 25 tower for years
with great success on 160 Meters. The tower is topped with HF and VHF yagis
which act as a capacitive top hat. The 50 Ohm coax feedline is connected to
a tap on the coil of a parallel tuned circuit. The top of the LC circuit is
connected to a #16 THHN wire which runs parallel to the tower, about 18"
outside one of the legs and connects to a bolt around 10 ft down from the
top of the tower. At the base of the tower I simply tune the capacitor and
find the best spot on the coil to tap to obtain the lowest SWR. There are 16
quarter wave radials around the tower, most of them on the tower side of the
house from south to north and a few wrapping around and under the back deck
toward the northeast. There are around a dozen 8 ft ground rods connected to
the tower with #6 wire and the tower also is connected to a perimeter ground
system surrounding the house.

The shields of most, but not all, of the coax cables leaving the tower are
grounded at the tower base. Before all coax and control cables enter the
shack they all are grounded at the steel entry box around 30 feet from the
tower base.

So how does a shunt fed 75 ft tower work with a barefoot K3 feeding it? With
100 Watts I've confirmed 229 countries on the Topband and have worked 89
countries on all continents with QRP 5 Watts. You can check out the 160M QRP
WAC cards at:

http://www.qrz.com/db/K1HTV

If you haven't tried shunt feeding your grounded tower, give it a try. You
may be surprised at how well it can work on 160 Meters.

73,

Rich - K1HTV

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Vic Rosenthal

Re: FW: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Regarding using a tower as a vertical:

Some years ago I had a 50-foot mast with a tribander on it next to my
house. I ran two wires out my window, one down to the base of the mast
and one to a point on it that produced a reasonable SWR on 80 meters.
The rotor cable and feedline for the beam ran down to the ground, and
then back up to the shack. No ferrites or anything on the feedline. I
wrapped the rotor cable around a ferrite rod at the rotor controller. I
had a system of 16 radials, each about 20' long, and in a half-circle.

I ran about 600 watts to this arrangement and didn't notice RF issues in
the shack. It worked surprisingly well, producing contacts from here
into the US as far west as Illinois.

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 2 Mar 2017 05:21, Erik Basilier wrote:

> Hi Alan,
>
> Your link didn't work for me, but I assume your article describes how to
> make a good bandpass filter. I do in fact recall seeing such an article in
> QST years ago. Assuming that you were just pointing out that I can put a
> bandpass filter on each feedline, as is common practice in SO2R operations,
> I need to state my case in more detail:
>
> Since I have second antenna covering 20-15-10 (a vertical), I started out
> doing just that: putting a bandpass filter on each. I was in a hurry and
> bought the LBS commercial filters rather than building based on the old
> article. The antennas are close together, and even after I upgraded so as to
> have two K3 radios, I was unhappy with the isolation with one K3
> transmitting on 40 on the beam and the other K3 receiving on 20 on the
> vertical. Just out of curiosity I plan to dig deeper into this situation, as
> I think somewhat better results could be achieved. However, seeing the big
> difference in performance on a given band between the vertical and the beam,
> I really wanted both radios to have a beam. That is where I decided to get
> the multiplexer (a model that includes 40m). Performance wise, this was
> going to be like having one multiband beam, including 40m, for each radio.
> Much better than using the vertical for one radio, assuming of course that
> the physical sharing of one beam would aggravate the interference situation
> I had when using separate antennas and bandpass filters. With the
> multiplexer, per manufacturer's recommendation, each band still uses its
> separate bandpass filter, so that total attenuation between bands is much
> greater than what can be expected with bandpass filters alone. Still, I was
> apprehensive of a possible increase in interference. The outcome was nothing
> short of stunning: No interference at all. I see a possiblity that I could
> have somehow reduced the interference experienced with separate antennas and
> using bandpass filters, but I can't see that approach competing with the
> superior results using a single antenna + multiplexer + bandpass filters.
> The QST review backs up my assumption that the great results with that
> configuration was no fluke. Of course, I cannot include 80m in the same
> approach as long as I don't have a single antenna that includes that band
> (and I can't quickly get a multiplexer that includes all 5 bands). So, for
> 80 I will have a separate feedline and just a bandpass filter. BTW I am very
> happy to not have yielded to the temptation to upgrade my beam to a Steppir,
> as the multiplexer approach requires the antenna to be tuned simultaneously
> to multiple bands, not to tune to one band at a time.
>
> If I had been able to achieve really good isolation with just a bandpass
> filter for each band, your approach with an 80m antenna that also covers 40
> would make good sense to my situation. As it is, keeping 40m within the
> beam, even with no gain over running 40m on the second antenna, makes sense
> as it allows me to route 40m not just through the bandpass filter, but also
> through the multiplexer. Since I already tried an 80m inverted vee on the
> tower, and it ruined the 40m performance of the beam, I am looking for other
> approaches for 80m. It might be possible to change the beam to bring it back
> to resonance on 40, but this particular beam is a complicated design
> already. A sloper is one possiblity, but it is not likely to be my first
> attempt, as it would be close to the beam and it would be somewhat similar
> to the vee. At this point I am leaning toward either a separate shortened
> vertical such as a Butternut model for 80 and 40 (not likely to use the 40
> part) or using the tower itself as a vertical. For the latter approach I
> would need to prevent the tower's feedline bundle (the part going into the
> house) from forming part of the radiating element. I remember an old Antenna
> Book discussing methods of feeding the tower as a vertical, but the author
> seemed to ignore the issue of the cables coming off the tower. Maybe it was
> assumed that the cables would be disconnected at the bulkhead whenever the
> tower would be used as a vertical. Nobody has replied to me about
> experiences dealing with that issue. Also as the tower with its antennas is
> resonant in the BC band, I would model it to find out if it has a resonable
> vertical radiation pattern if fed as a whole on 80.
>
> 73,
> Erik K7TV

K7TV

Re: FW: Using your tower as a vertical - 160 or 80

In reply to this post by K7TV

Vic, thanks for your comments!
Erik K7TV

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Vic
Rosenthal 4X6GP
Sent: Thursday, March 02, 2017 12:21 AM
To: [hidden email]
Subject: Re: [Elecraft] FW: Using your tower as a vertical - 160 or 80

Regarding using a tower as a vertical:

Some years ago I had a 50-foot mast with a tribander on it next to my house.
I ran two wires out my window, one down to the base of the mast and one to a
point on it that produced a reasonable SWR on 80 meters.
The rotor cable and feedline for the beam ran down to the ground, and then
back up to the shack. No ferrites or anything on the feedline. I wrapped the
rotor cable around a ferrite rod at the rotor controller. I had a system of
16 radials, each about 20' long, and in a half-circle.

I ran about 600 watts to this arrangement and didn't notice RF issues in the
shack. It worked surprisingly well, producing contacts from here into the US
as far west as Illinois.

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

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Post: mailto:[hidden email]

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