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135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

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Zac Brown-2

135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Fellow Elecrafters,

I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
about 60 ft. of 450 ohm ladder line, connecting the feedline to the BL2,
and tuning it with the KAT2.

I was wondering if anyone on the list has tried this arrangement and
could comment on whether the KAT2 will have any problems tuning this
setup from 80 - 20m. I'm also curious about which bands work better
with the balun set to 1:1 vs. 4:1 with this setup.

Thanks,

Zac Brown
KD5IEF
K2# 4907
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Karl Larsen

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Zac Brown wrote:
> Fellow Elecrafters,
>
> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
> about 60 ft. of 450 ohm ladder line, connecting the feedline to the
> BL2, and tuning it with the KAT2.
With the balun and auto-tuner you have a great antenna system!
However it may be the wrong length. I use the 88 foot flat-top which
works just fine on 80 and 40 meters, and 30 and 20 meters as well. With
135 feet of wire your antenna will not load up well on 40 and 20 meters.
But it will work great on 80 meters.

The flat-top length is not real important and it should not be
resonant at the Ham bands. The 88 feet is nice because on 20 meters it
is a double bazzoka and has gain off each side of the dipole.

73 Karl K5DI

>
> I was wondering if anyone on the list has tried this arrangement and
> could comment on whether the KAT2 will have any problems tuning this
> setup from 80 - 20m. I'm also curious about which bands work better
> with the balun set to 1:1 vs. 4:1 with this setup.
>
> Thanks,
>
> Zac Brown
> KD5IEF
> K2# 4907
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com
>
>

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N8LP

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

I have a 135' OCF (Off Center Fed) dipole which is coax fed with a 6:1
balun at the feedpoint, and it works on all bands from 80-10 except 15
with my K2/KAT2. Performance seems very good an all bands except 30m,
where it's just OK.

Larry N8LP

Karl Larsen wrote:

> Zac Brown wrote:
>> Fellow Elecrafters,
>>
>> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
>> about 60 ft. of 450 ohm ladder line, connecting the feedline to the
>> BL2, and tuning it with the KAT2.
> With the balun and auto-tuner you have a great antenna system!
> However it may be the wrong length. I use the 88 foot flat-top which
> works just fine on 80 and 40 meters, and 30 and 20 meters as well.
> With 135 feet of wire your antenna will not load up well on 40 and 20
> meters. But it will work great on 80 meters.
>
> The flat-top length is not real important and it should not be
> resonant at the Ham bands. The 88 feet is nice because on 20 meters it
> is a double bazzoka and has gain off each side of the dipole.
>
> 73 Karl K5DI
>
>>
>> I was wondering if anyone on the list has tried this arrangement and
>> could comment on whether the KAT2 will have any problems tuning this
>> setup from 80 - 20m. I'm also curious about which bands work better
>> with the balun set to 1:1 vs. 4:1 with this setup.
>>
>> Thanks,
>>
>> Zac Brown
>> KD5IEF
>> K2# 4907
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft Help:
>> http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
>
> _______________________________________________
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> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>

Stephen W. Kercel

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Zac Brown-2

Zac:

I'm guessing that the configuration that you propose could run you
into all sorts of trouble on 80 M. The problem is that the 135 ft
flat top would have low impedance, about 50 Ohms. The transmission
line is disturbingly close to a quarter wavelength. A 450 Ohm line
with an exact electrical quarter wavelength and a 50 Ohm load would
have 4050 Ohms impedance at the transmitter end, and the KAT-2 would
see it as an SWR of about 80:1. Even if your line is not an exact
quarter wavelength, if it is within a few feet either way, the
impedance that your KAT2 will see is very high.

You need to do a bit of studying with EZNEC and a Smith Chart. You
need to find out the feedpoint impedances that the flat top will give
you on all the bands on which you want to operate, and then find a
length of 450 Ohm line that presents acceptable impedances to your
KAT2/BL2 setup. This same set of calculations would tell you whether
you are better off with a 1:1 or 4:1 balun (or it might show you that
you need one balun for some bands, and the other balun for other
bands). You may discover that no single length of feedline works for
all bands 80-20 M. In that case you need to get a very big DPDT knife
switch (Military surplus outlets carry them) so that you can switch
an alternate section in or out to change the length of your line for
different bands.

73,

Steve Kercel
AA4AK

At 12:18 PM 10/1/2006, Zac Brown wrote:

>Fellow Elecrafters,
>
>I am putting up a 135 ft flat-top at my QTH. I'll be feeding it
>with about 60 ft. of 450 ohm ladder line, connecting the feedline to
>the BL2, and tuning it with the KAT2.
>
>I was wondering if anyone on the list has tried this arrangement and
>could comment on whether the KAT2 will have any problems tuning this
>setup from 80 - 20m. I'm also curious about which bands work better
>with the balun set to 1:1 vs. 4:1 with this setup.
>
>Thanks,
>
>Zac Brown
>KD5IEF
>K2# 4907
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
>http://mailman.qth.net/mailman/listinfo/elecraft
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com

Zac Brown-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Steve,

The feedline is actually 65 ft long. It happened to be the perfect
length from the antenna to my radio, but I could add some more line in
the middle if needed. I'd just have to make the feedline take a less
direct path through the attic. What would you suggest as a good
feedline length? 100 ft?

I read Cebik's paper at http://www.cebik.com/gup/gup5.html and was not
sure if the 65 ft would be a problem on 80m. In one of the first tables
in that article, he calculates the feedpoint impedance at 80m for my
setup for a 57.7 ft feedline and then for a 72.1 ft feedline.

80 57.7 17.6 2450 + 770
100 72.1 22.0 680 - 1107

I figured that I'd be somewhere between those two, maybe around 1600
ohms, but I didn't do any calculations. I guess I was a bit anxious to
get the antenna built and installed.

Thanks,

Zac
KD5IEF
K2# 4907

Stephen W. Kercel wrote:

> Zac:
>
> I'm guessing that the configuration that you propose could run you into
> all sorts of trouble on 80 M. The problem is that the 135 ft flat top
> would have low impedance, about 50 Ohms. The transmission line is
> disturbingly close to a quarter wavelength. A 450 Ohm line with an exact
> electrical quarter wavelength and a 50 Ohm load would have 4050 Ohms
> impedance at the transmitter end, and the KAT-2 would see it as an SWR
> of about 80:1. Even if your line is not an exact quarter wavelength, if
> it is within a few feet either way, the impedance that your KAT2 will
> see is very high.
>
> You need to do a bit of studying with EZNEC and a Smith Chart. You need
> to find out the feedpoint impedances that the flat top will give you on
> all the bands on which you want to operate, and then find a length of
> 450 Ohm line that presents acceptable impedances to your KAT2/BL2 setup.
> This same set of calculations would tell you whether you are better off
> with a 1:1 or 4:1 balun (or it might show you that you need one balun
> for some bands, and the other balun for other bands). You may discover
> that no single length of feedline works for all bands 80-20 M. In that
> case you need to get a very big DPDT knife switch (Military surplus
> outlets carry them) so that you can switch an alternate section in or
> out to change the length of your line for different bands.
>
> 73,
>
> Steve Kercel
> AA4AK
>
>
> At 12:18 PM 10/1/2006, Zac Brown wrote:
>> Fellow Elecrafters,
>>
>> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
>> about 60 ft. of 450 ohm ladder line, connecting the feedline to the
>> BL2, and tuning it with the KAT2.
>>
>> I was wondering if anyone on the list has tried this arrangement and
>> could comment on whether the KAT2 will have any problems tuning this
>> setup from 80 - 20m. I'm also curious about which bands work better
>> with the balun set to 1:1 vs. 4:1 with this setup.
>>
>> Thanks,
>>
>> Zac Brown
>> KD5IEF
>> K2# 4907
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>
>
>

Geoffrey Mackenzie-Kennedy-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Stephen W. Kercel

Perhaps Elecraft might like to consider adding an 'old fashioned' type of
balanced antenna tuner to their product range, with a balun at the
transmitter connection, to make it easier to match some types of antenna
system to the transmitter? One that could be used outside and be remotely
controlled would be useful.

73,
Geoff
GM4ESD

Stephen W. Kercel AA4AK wrote:

> I'm guessing that the configuration that you propose could run you into
> all sorts of trouble on 80 M. The problem is that the 135 ft flat top
> would have low impedance, about 50 Ohms. The transmission line is
> disturbingly close to a quarter wavelength. A 450 Ohm line with an exact
> electrical quarter wavelength and a 50 Ohm load would have 4050 Ohms
> impedance at the transmitter end, and the KAT-2 would see it as an SWR of
> about 80:1. Even if your line is not an exact quarter wavelength, if it is
> within a few feet either way, the impedance that your KAT2 will see is
> very high.

<snip>

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Zac Brown-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Zac Brown-2

So what's the best way to add some more line to the middle of my
feedline? Is there a technique for joining two pieces of 450 ohm ladder
line that doesn't create an imbalance in the line? Can I just leave one
"leg" straight and then wrap the corresponding "leg" (on the other
piece) other around it, then solder them together? Or should I just
leave both legs straight and then solder them together? Or how about
using those twist locks that you use for wiring up lights?

This is probably a silly question, but I took great care to route the
line away from anything that would imbalance it, and would hate to mess
that up now. This is my first experience with balanced line :)

Thanks,

Zac
KD5IEF
K2# 4907

Zac Brown wrote:

> Steve,
>
> The feedline is actually 65 ft long. It happened to be the perfect
> length from the antenna to my radio, but I could add some more line in
> the middle if needed. I'd just have to make the feedline take a less
> direct path through the attic. What would you suggest as a good
> feedline length? 100 ft?
>
> I read Cebik's paper at http://www.cebik.com/gup/gup5.html and was not
> sure if the 65 ft would be a problem on 80m. In one of the first tables
> in that article, he calculates the feedpoint impedance at 80m for my
> setup for a 57.7 ft feedline and then for a 72.1 ft feedline.
>
> 80 57.7 17.6 2450 + 770
> 100 72.1 22.0 680 - 1107
>
> I figured that I'd be somewhere between those two, maybe around 1600
> ohms, but I didn't do any calculations. I guess I was a bit anxious to
> get the antenna built and installed.
>
> Thanks,
>
> Zac
> KD5IEF
> K2# 4907
>
> Stephen W. Kercel wrote:
>> Zac:
>>
>> I'm guessing that the configuration that you propose could run you
>> into all sorts of trouble on 80 M. The problem is that the 135 ft flat
>> top would have low impedance, about 50 Ohms. The transmission line is
>> disturbingly close to a quarter wavelength. A 450 Ohm line with an
>> exact electrical quarter wavelength and a 50 Ohm load would have 4050
>> Ohms impedance at the transmitter end, and the KAT-2 would see it as
>> an SWR of about 80:1. Even if your line is not an exact quarter
>> wavelength, if it is within a few feet either way, the impedance that
>> your KAT2 will see is very high.
>>
>> You need to do a bit of studying with EZNEC and a Smith Chart. You
>> need to find out the feedpoint impedances that the flat top will give
>> you on all the bands on which you want to operate, and then find a
>> length of 450 Ohm line that presents acceptable impedances to your
>> KAT2/BL2 setup. This same set of calculations would tell you whether
>> you are better off with a 1:1 or 4:1 balun (or it might show you that
>> you need one balun for some bands, and the other balun for other
>> bands). You may discover that no single length of feedline works for
>> all bands 80-20 M. In that case you need to get a very big DPDT knife
>> switch (Military surplus outlets carry them) so that you can switch an
>> alternate section in or out to change the length of your line for
>> different bands.
>>
>> 73,
>>
>> Steve Kercel
>> AA4AK
>>
>>
>> At 12:18 PM 10/1/2006, Zac Brown wrote:
>>> Fellow Elecrafters,
>>>
>>> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
>>> about 60 ft. of 450 ohm ladder line, connecting the feedline to the
>>> BL2, and tuning it with the KAT2.
>>>
>>> I was wondering if anyone on the list has tried this arrangement and
>>> could comment on whether the KAT2 will have any problems tuning this
>>> setup from 80 - 20m. I'm also curious about which bands work better
>>> with the balun set to 1:1 vs. 4:1 with this setup.
>>>
>>> Thanks,
>>>
>>> Zac Brown
>>> KD5IEF
>>> K2# 4907
>>> _______________________________________________
>>> Elecraft mailing list
>>> Post to: [hidden email]
>>> You must be a subscriber to post to the list.
>>> Subscriber Info (Addr. Change, sub, unsub etc.):
>>> http://mailman.qth.net/mailman/listinfo/elecraft
>>>
>>> Help: http://mailman.qth.net/subscribers.htm
>>> Elecraft web page: http://www.elecraft.com
>>
>>
>>
>

Karl Larsen

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

I'm sorry but I need to add this before Zac Brown does something
real stupid. When using 450 ohm feed line you must use this EXACT
length. The exact length is that which goes from the antenna to the
balun in your shack.

Any talk about matching the 450 ohms is not correct. The feed line
runs with a very high SWR and since it is low loss there is just a tiny
loss. It will correct to a 1:1 SWR between your tuner and the radio.

And about the balun. Seems if you have a 4:1 or 1:1 to choose from I
would choose the 1:1 because it does a better job of keeping the current
balanced in the balanced feed line.

This is pretty complex stuff but you Zac do not need to do the math.
Just put it up and use it. I have been using it for 8 years now. Had to
get feed line. A hail storm just beat up my feed line :-)

I have done the math. It takes several Smith Charts to plot the
current through the system.

73 Karl K5DI

Zac Brown wrote:

> So what's the best way to add some more line to the middle of my
> feedline? Is there a technique for joining two pieces of 450 ohm
> ladder line that doesn't create an imbalance in the line? Can I just
> leave one "leg" straight and then wrap the corresponding "leg" (on the
> other piece) other around it, then solder them together? Or should I
> just leave both legs straight and then solder them together? Or how
> about using those twist locks that you use for wiring up lights?
>
> This is probably a silly question, but I took great care to route the
> line away from anything that would imbalance it, and would hate to
> mess that up now. This is my first experience with balanced line :)
>
> Thanks,
>
> Zac
> KD5IEF
> K2# 4907
>
>
> Zac Brown wrote:
>> Steve,
>>
>> The feedline is actually 65 ft long. It happened to be the perfect
>> length from the antenna to my radio, but I could add some more line
>> in the middle if needed. I'd just have to make the feedline take a
>> less direct path through the attic. What would you suggest as a good
>> feedline length? 100 ft?
>>
>> I read Cebik's paper at http://www.cebik.com/gup/gup5.html and was
>> not sure if the 65 ft would be a problem on 80m. In one of the first
>> tables in that article, he calculates the feedpoint impedance at 80m
>> for my setup for a 57.7 ft feedline and then for a 72.1 ft feedline.
>>
>> 80 57.7 17.6 2450 + 770
>> 100 72.1 22.0 680 - 1107
>>
>> I figured that I'd be somewhere between those two, maybe around 1600
>> ohms, but I didn't do any calculations. I guess I was a bit anxious
>> to get the antenna built and installed.
>>
>> Thanks,
>>
>> Zac
>> KD5IEF
>> K2# 4907
>>
>> Stephen W. Kercel wrote:
>>> Zac:
>>>
>>> I'm guessing that the configuration that you propose could run you
>>> into all sorts of trouble on 80 M. The problem is that the 135 ft
>>> flat top would have low impedance, about 50 Ohms. The transmission
>>> line is disturbingly close to a quarter wavelength. A 450 Ohm line
>>> with an exact electrical quarter wavelength and a 50 Ohm load would
>>> have 4050 Ohms impedance at the transmitter end, and the KAT-2 would
>>> see it as an SWR of about 80:1. Even if your line is not an exact
>>> quarter wavelength, if it is within a few feet either way, the
>>> impedance that your KAT2 will see is very high.
>>>
>>> You need to do a bit of studying with EZNEC and a Smith Chart. You
>>> need to find out the feedpoint impedances that the flat top will
>>> give you on all the bands on which you want to operate, and then
>>> find a length of 450 Ohm line that presents acceptable impedances to
>>> your KAT2/BL2 setup. This same set of calculations would tell you
>>> whether you are better off with a 1:1 or 4:1 balun (or it might show
>>> you that you need one balun for some bands, and the other balun for
>>> other bands). You may discover that no single length of feedline
>>> works for all bands 80-20 M. In that case you need to get a very big
>>> DPDT knife switch (Military surplus outlets carry them) so that you
>>> can switch an alternate section in or out to change the length of
>>> your line for different bands.
>>>
>>> 73,
>>>
>>> Steve Kercel
>>> AA4AK
>>>
>>>
>>> At 12:18 PM 10/1/2006, Zac Brown wrote:
>>>> Fellow Elecrafters,
>>>>
>>>> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it
>>>> with about 60 ft. of 450 ohm ladder line, connecting the feedline
>>>> to the BL2, and tuning it with the KAT2.
>>>>
>>>> I was wondering if anyone on the list has tried this arrangement
>>>> and could comment on whether the KAT2 will have any problems tuning
>>>> this setup from 80 - 20m. I'm also curious about which bands work
>>>> better with the balun set to 1:1 vs. 4:1 with this setup.
>>>>
>>>> Thanks,
>>>>
>>>> Zac Brown
>>>> KD5IEF
>>>> K2# 4907
>>>> _______________________________________________
>>>> Elecraft mailing list
>>>> Post to: [hidden email]
>>>> You must be a subscriber to post to the list.
>>>> Subscriber Info (Addr. Change, sub, unsub etc.):
>>>> http://mailman.qth.net/mailman/listinfo/elecraft
>>>>
>>>> Help: http://mailman.qth.net/subscribers.htm
>>>> Elecraft web page: http://www.elecraft.com
>>>
>>>
>>>
>>

Stuart Rohre

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Zac Brown-2

If you want to splice balanced line, you can do a simple splice with two
wire nuts of both the same size.

That theoretically, would affect each side of the line the same and preserve
balance. Your tuner takes care of that and any other "bumps'' even the
mixing of 300 ohm and 450 ohm line to complete a run.

We do this all the time for Field Days, where we have scored very well in
our class. We never see any major difference in tune up on the tuner
whether the line run is spliced pieces or one continuous piece!

-Stuart
K5KVH

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Don Wilhelm-3

RE: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Karl Larsen

Zac,

Why guess?

You can find the antenna feedpoint impedance for various bands on L B
Cebik's website (at least it used to be there) www.cebik.com .
Armed with that information along with the known length of your feedline,
use TLW which you can download from the ARRL website
http://www.arrl.org/notes/9043/TLW3B.zip and feed the information into TLW
to find your shack end impedance for each band of interest. A bit of cut
'n' try with TLW can find you the best compromise feedline length to ues
with your antenna.

73,
Don W3FPR

> -----Original Message-----
>
> I'm sorry but I need to add this before Zac Brown does something
> real stupid. When using 450 ohm feed line you must use this EXACT
> length. The exact length is that which goes from the antenna to the
> balun in your shack.
>
> Any talk about matching the 450 ohms is not correct. The feed line
> runs with a very high SWR and since it is low loss there is just a tiny
> loss. It will correct to a 1:1 SWR between your tuner and the radio.
>
> And about the balun. Seems if you have a 4:1 or 1:1 to choose from I
> would choose the 1:1 because it does a better job of keeping the current
> balanced in the balanced feed line.
>
> This is pretty complex stuff but you Zac do not need to do the math.
> Just put it up and use it. I have been using it for 8 years now. Had to
> get feed line. A hail storm just beat up my feed line :-)
>
> I have done the math. It takes several Smith Charts to plot the
> current through the system.
>
> 73 Karl K5DI
>
>
>
>
> Zac Brown wrote:
> > So what's the best way to add some more line to the middle of my
> > feedline? Is there a technique for joining two pieces of 450 ohm
> > ladder line that doesn't create an imbalance in the line? Can I just
> > leave one "leg" straight and then wrap the corresponding "leg" (on the
> > other piece) other around it, then solder them together? Or should I
> > just leave both legs straight and then solder them together? Or how
> > about using those twist locks that you use for wiring up lights?
> >
> > This is probably a silly question, but I took great care to route the
> > line away from anything that would imbalance it, and would hate to
> > mess that up now. This is my first experience with balanced line :)
> >
> > Thanks,
> >
> > Zac
> > KD5IEF
> > K2# 4907
>

Geoffrey Mackenzie-Kennedy-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Zac Brown-2

Doc,

I was thinking of the link coupled parallel or series tuned type of coupler
which was at one time known as an Antenna Matching Unit before the name
Antenna Tuner became the norm. The Johnson Matchbox was an example, and such
'tuners' can convert a considerable range of impedances as presented by the
feeder down to or up to 50 ohms, if 50 ohms is what you want. A variable
capacitor in series with the link allows for tweaking. Using a current choke
such as a bead 'balun' between the link circuit and the Tx is a nice
finishing touch, but not absolutely essential in my experience.

73,
Geoff
GM4ESD

On Sunday, October 01, 2006 11:40 PM you wrote:

> Geoff:
>
> Just got home, so I may have missed lots of this thread. BUT let me say
> that indeed indeed Elecraft does (or DID*) have a 4:1 balun kit. I bought
> one fully assembled from Rod N0RC. Works fabulously, and of course has
> the
> traditional and expected Elecraft quality, great manual. SO, perhaps they
> have discontinued it, but at least at one time they did offer such a
> product.
>
> GL and 73,
> --Doc/K0EVZ

Jack Brindle

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Don Wilhelm-3

Don suggested this would be worth posting...

When dealing with antennas, things are never as "precise" as we might
want them to be. Folks talk about antenna tuners as if they work
magic, then wonder why things aren't as good as they should be. An
ATU at the shack in line with a coax-fed antenna has one big purpose.
It provides a nice load for the transceiver. It does absolutely
nothing to help out the feedline or antenna itself. The very precious
RF gets burnt up in the coax (with its unknown, but potentially very
high SWR) between the tuner and the antenna. There are strange RF
currents all over the place, especially on the coax, which not only
heats the coax, but tend to screw up the antenna radiation pattern as
well.

My belief is that there are three solutions to the problem.
1) Place the ATU _AT_ the antenna feed point. The problem is that it
is really a pain to do in most cases.

2) Use matched antennas on all bands. Cebik points this out in a
great paper on his website that discusses open-wire vs coax fed
antennas (see "To Trap or Not To Trap",
http://www.cebik.com/wire/trapqq.html). This is also the solution
used by the larger (more serious, lots of money to spend) contesters.

3) Use open-wire feed. There we don't care about the mismatch since
the feedline loss is microscopic. The RF currents balance themselves
out so that the feedline doesn't radiate. But we then need a decent
tuner to feed the antenna & open-wire. Here I drop back to the old
tank-circuit tuners which make things "sing!" I don't like to use a
balun here - it's just another device to burn up the precious RF when
you hit a severe mis-match node.

Now if you don't have a swinging-link balanced tuner, but do have an
L-network tuner and are running low power, go ahead with a 1:1 balun.
At low power there is little chance you will saturate the balun core
unless you get really unlucky and hit a severe node at the operating
frequency.

I do use coax to feed my antennas, but only for those that are
matched for the band/frequency. For all others, especially ones that
are used on multiple bands, I use open-wire feed. The length of the
feed really doesn't matter because of the super low loss. What
happens is the feedline transposes the antenna feed impedance to a
value dependent on the feedline length and operating frequency. The
balanced antenna tuner then matches whatever impedance it is
presented with, making the transceiver very happy. And with the low-
loss characteristics of open-wire feed, just about everything the
K2/100 puts out gets radiated by the antenna!

On Oct 1, 2006, at 6:20 PM, Don Wilhelm wrote:

> Zac,
>
> Why guess?
>
> You can find the antenna feedpoint impedance for various bands on L B
> Cebik's website (at least it used to be there) www.cebik.com .
> Armed with that information along with the known length of your
> feedline,
> use TLW which you can download from the ARRL website
> http://www.arrl.org/notes/9043/TLW3B.zip and feed the information
> into TLW
> to find your shack end impedance for each band of interest. A bit
> of cut
> 'n' try with TLW can find you the best compromise feedline length
> to ues
> with your antenna.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> I'm sorry but I need to add this before Zac Brown does something
>> real stupid. When using 450 ohm feed line you must use this EXACT
>> length. The exact length is that which goes from the antenna to the
>> balun in your shack.
>>
>> Any talk about matching the 450 ohms is not correct. The feed
>> line
>> runs with a very high SWR and since it is low loss there is just a
>> tiny
>> loss. It will correct to a 1:1 SWR between your tuner and the radio.
>>
>> And about the balun. Seems if you have a 4:1 or 1:1 to choose
>> from I
>> would choose the 1:1 because it does a better job of keeping the
>> current
>> balanced in the balanced feed line.
>>
>> This is pretty complex stuff but you Zac do not need to do the
>> math.
>> Just put it up and use it. I have been using it for 8 years now.
>> Had to
>> get feed line. A hail storm just beat up my feed line :-)
>>
>> I have done the math. It takes several Smith Charts to plot the
>> current through the system.
>>
>> 73 Karl K5DI
>>
>>
>>
>>
>> Zac Brown wrote:
>>> So what's the best way to add some more line to the middle of my
>>> feedline? Is there a technique for joining two pieces of 450 ohm
>>> ladder line that doesn't create an imbalance in the line? Can I
>>> just
>>> leave one "leg" straight and then wrap the corresponding
>>> "leg" (on the
>>> other piece) other around it, then solder them together? Or
>>> should I
>>> just leave both legs straight and then solder them together? Or how
>>> about using those twist locks that you use for wiring up lights?
>>>
>>> This is probably a silly question, but I took great care to route
>>> the
>>> line away from anything that would imbalance it, and would hate to
>>> mess that up now. This is my first experience with balanced line :)
>>>
>>> Thanks,
>>>
>>> Zac
>>> KD5IEF
>>> K2# 4907
>>
>
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- Jack Brindle, W6FB
------------------------------------------------------------------------
---------------------

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Ron D'Eau Claire-2

RE: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Jack makes excellent points. I would like to elaborate on one comment he
made:

"...open-wire feed. There we don't care about the mismatch since
the feedline loss is microscopic. The RF currents balance themselves
out so that the feedline doesn't radiate. But we then need a decent
tuner to feed the antenna & open-wire. Here I drop back to the old
tank-circuit tuners which make things "sing!" I don't like to use a
balun here - it's just another device to burn up the precious RF when
you hit a severe mis-match node."

I have used open wire feed far more than coaxial lines for HF antennas over
the past half century.

The losses in open wire lines are not insignificant under many conditions.
Open wire line is still subject to ohmic losses. It is far less lossy than
coax because all common coaxial lines in use today are fairly low impedance
- typically 50 or 75 ohms. Good open wire line will have an impedance of 500
or 600 ohms. Even the common "ladder line" has an impedance of 450 ohms.
That higher impedance provides lower SWRs in most multiband antennas. For
example, a doublet may show an impedance of 3000 ohms at the feed point,
which is common for a center fed full wave doublet. That translates into an
SWR of about 60:1 if coaxial line is used and an SWR of less than 7:1 if 600
ohm open wire line is used. That difference results in a substantial
decrease in line losses.

Even among open wire lines, losses are not always insignificant. It depends
upon the feed point impedance (that's at the antenna or load end of the
feeder). For example, a short doublet or some transmitting loop antennas can
have an impedance of 10 ohms or less. With 600 ohm line that's an SWR or
60:1. The losses in the open wire line may be as great as those in coax
under those conditions.

One way to reduce those losses is to reduce the ohmic losses. That's where
virtually all the loss in any kind of transmission line occur: RF converted
to heat at the high-current points. Ladder line and "twinlead" that use
small conductors is very susceptible to such losses. RF flows in the skin of
the conductors; resistance is directly proportional to surface area. My open
wire lines are seldom built using smaller than #12 wires.

Jack is quite right about the need for a true wide-band tuner designed for
such lines. My tuner can be seen sitting above my K2/100 in the my picture
on QRZ.COM (AC7AC). It can handle impedances from a small fraction of an ohm
to many thousands of ohms The design is similar to those suggested by Cebik
in his on-line articles about ATUs. The downside are those clips for taps
and knobs. Such a tuner is often called upon to handle many thousands of
volts of RF even at moderate power. It needs to be big, relative to modern
rigs, to avoid flashover and excessive ohmic losses. Although such a setup
might be automated, it would require mechanically complex and large
switching systems to tune up automatically. So, when I jump from one band to
another, I have to spend 30 seconds or so readjusting the tuner: something
many operators find unacceptable. They prefer a less efficient, but much
faster and much, much smaller tuner.

Good Ham shack design calls for compromises. Many Hams today try of find an
antenna design that may not provide a low enough SWR on all the desired
bands to provide a good load to the rig, but which is low enough that a less
versatile but fully automatic tuner can handle. Designers like Elecraft work
to provide tuners with the greatest versatility that can still be packaged
into a small, efficient package. It's left up to the operator to contrive an
antenna system that can work efficiently with such a tuner if he/she wants
the small size and speed the automatic tuners provide.

Just remember that the antenna system starts at the input to the tuner.
Every element, the coils and relays in the tuners, a balun if you feel you
need one, the feed line itself all consume various amounts of the RF. Every
watt of RF consumed in those parts is never radiated.

Ron AC7AC

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Geoffrey Mackenzie-Kennedy-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Ron, AC7AC wrote:

But we then need a decent
tuner to feed the antenna & open-wire. Here I drop back to the old
tank-circuit tuners which make things "sing!" I don't like to use a
balun here - it's just another device to burn up the precious RF when
you hit a severe mis-match node.".

<snip>

Even among open wire lines, losses are not always insignificant. It depends
upon the feed point impedance (that's at the antenna or load end of the
feeder). For example, a short doublet or some transmitting loop antennas can
have an impedance of 10 ohms or less. With 600 ohm line that's an SWR or
60:1. The losses in the open wire line may be as great as those in coax
under those conditions.

One way to reduce those losses is to reduce the ohmic losses. That's where
virtually all the loss in any kind of transmission line occur: RF converted
to heat at the high-current points. Ladder line and "twinlead" that use
small conductors is very susceptible to such losses. RF flows in the skin of
the conductors; resistance is directly proportional to surface area. My open
wire lines are seldom built using smaller than #12 wires.

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

To put a balun at the shack end of a balanced feeder is, I agree, one way of
burning up the precious RF unless the feeder presents a suitable
non-reactive load compatible with the balun's characteristics. On the other
hand a current choke at the 50 ohm input of the old type of tuner, the TX
connection, could be seen as being necessay but in my experience not
essential - assuming that the tuner presents a load close to 50 ohms and
that the amount of common mode current is insignificant i.e. the outside of
the coax to the TX is 'cold'.

Another way to reduce ohmic and radiation loss in open wire lines is to use
the 4 wire cross-connected type. The characteristic impedance of such a line
is very approximately half that of a two wire line using the same size
conductors and spacing, which makes a 4 wire line useful when feeding a low
impedance load such as a short doublet. The downside is that 4 wire lines
are more difficult to build than two wire lines and need to be kept under a
small amount of tension, unless a fair number of spacers are used which can
increase loss. They also need to be 'cleaned' occasionally, especially in
the Fall after the trees have shed their leaves. The upside is that in
addition to reduced ohmic loss, a 4 wire line loses less power due to
radiation than a two wire line, and nearby objects such as masts have less
effect on the line. It could be argued that the effort to build 4 wire lines
for HF use is not worthwhile, however for use at 50 MHz it is very
worthwhile where the radiation loss in a long run of 2 wire line using a
practical spacing between wires can be significant.

73,
Geoff
GM4ESD

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Ron D'Eau Claire-2

RE: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

Geoff, GM4ESD, makes some excellent observations about using other types of
multi-wire line to maintain low resistive losses and to provide a
lower-impedance line when needed.

Jack Bindle took me to task, quite appropriately, about one statement in my
first comments in this thread in a private message. My example using typical
SWRs that may be encountered causing coax and open wire line to have similar
losses is too simplistic.

A look at any of the charts comparing loss in various types of transmission
line will bear this out. The plot for open wire line is always far, far
below the best coaxial line.

Ron AC7AC

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Zac Brown-2

Re: 135ft flat-top with K2, KAT2, BL2, and 450 ohm feedline

In reply to this post by Zac Brown-2

After spending some time modeling my antenna in EZNEC and then running
some calculations in TWL, I added 30 ft to the feedline. That brings
the total feedline length up to 90 ft. So far, the KAT2 seems to be
able to tune all bands very quickly with the BL2 set to the 1:1
position. Thanks for everyone's feedback.

73,

Zac
KD5IEF

Zac Brown wrote: