270 foot (ish) Doublet & K3 ATU

[Iain G4SGX]

Hello,

Does anyone use a 270 foot doublet with the K3 ATU?

Is there a combination of feeder type/length and Balun type & coax
length that tunes OK on 160-10?

I am currently thinking a 1:1 balun and 33 foot of 300 ohm feeder.

Obviously the coax length should be short but too short may cause rfi
probs, but then I only run 100W.

Iain G4SGX


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[Matt Zilmer-3]

As long as the balanced line isn't resonant, you should be OK.  I use
61 feet here (18.6m) and it works fine from 2.8 MHz up.  The doublet
is 150 feet, total length.  So far I haven't found a freq that the
K3's ATU cannot tune, and that includes many MARS channels outside and
between the U.S. Amateur bands.

73,
matt W6NIA

On Thu, 15 May 2014 20:22:39 +0100, you wrote:

>Hello,
>
>Does anyone use a 270 foot doublet with the K3 ATU?
>
>Is there a combination of feeder type/length and Balun type & coax
>length that tunes OK on 160-10?
>
>I am currently thinking a 1:1 balun and 33 foot of 300 ohm feeder.
>
>Obviously the coax length should be short but too short may cause rfi
>probs, but then I only run 100W.
>
>Iain G4SGX
>
>
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>http://www.avast.com
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Matt Zilmer, W6NIA
--
"Give me six hours to chop down a tree and I will
spend the first four sharpening the axe." -A. Lincoln
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[Bob KD7YZ]

On 5/15/2014 15:22, Iain G4SGX wrote:
> Hello,
>
> Does anyone use a 270 foot doublet with the K3 ATU?

I am using circa 270 feet, as OCF. The 450-ladder-line is roughly 130
feet. The height above variable terrain is 80 feet. The ladder line
drops into a 4:1 balun then 4 feet of coax.

K3 KAT500 tunes all bands 160m to 10m, nicely.

--

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AMSAT LM 0901
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[Rick WA6NHC]

I use a 104 meter (340') dipole (double extended Zepp for 75/80 meters); fed in the middle with 100' of 450 ohm window line on all bands.  In it's original configuration, I fed that with a 1:1 common mode choke (a DX Engineering balun, converting the feed to coax) into the K3.  The K3 tuner was happy almost anywhere except 160M (6:1 was the best it could do there, at the higher end).  It loaded on 6M but I don't recommend it (expensive lesson).

I found that the length of the window line was not critical; adding 30' had zero effect (started with 70').

The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.

The wires are strung over/through oak trees that vary in height from 30-40' (oaks just don't grow taller here).  Tuning changes with the seasons (fuel moisture content).  Although cut for the lower portion of 75 meters, because of the low height, it doesn't like the low end of the band so I'm going to add another 12 meters of wire to bring the resonant point down on the bottom of 80 (should help with 160 too) since DX is more available on CW than phone.

Since I added the KAT500 (to use the KPA500 et al remotely), I found that a 4:1 CMC gives me all bands, including 160 (3:1 so I don't run a lot of power).  That one change alone has given me 5 new band mode countries, on 160.  I currently stand at 229 countries worked (all bands/modes) so it all seems to work pretty well.  Since I live in an HOA/CC&R infested neighborhood (a mistake of the most grievous nature), this stealth antenna is the best I can manage.  It's hidden in plain sight in a common area that no one uses (and no one looks UP anyway, human nature).

Expect to play with the dimensions and feed systems to find your sweet spot(s).

73,
Rick, WA6NHC

iPad = small keypad = typos = sorry ;-)

> On May 15, 2014, at 12:22 PM, Iain G4SGX <[hidden email]> wrote:
>
> Hello,
>
> Does anyone use a 270 foot doublet with the K3 ATU?
>
> Is there a combination of feeder type/length and Balun type & coax length that tunes OK on 160-10?
>
> I am currently thinking a 1:1 balun and 33 foot of 300 ohm feeder.
>
> Obviously the coax length should be short but too short may cause rfi probs, but then I only run 100W.
>
> Iain G4SGX

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[Wes (N7WS)]

This makes no logical sense, unless you have a big common-mode problem.

Wes  N7WS



On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
> Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.

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[Wes (N7WS)]

Why the caveat about line resonance? Should make no difference.  Besides when
the system is tuned, it's resonant.

Wes  N7WS


On 5/15/2014 12:46 PM, Matt Zilmer wrote:

> As long as the balanced line isn't resonant, you should be OK.  I use
> 61 feet here (18.6m) and it works fine from 2.8 MHz up.  The doublet
> is 150 feet, total length.  So far I haven't found a freq that the
> K3's ATU cannot tune, and that includes many MARS channels outside and
> between the U.S. Amateur bands.
>
> 73,
> matt W6NIA
>
>

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[k6dgw]

On 5/15/2014 12:22 PM, Iain G4SGX wrote:
> Hello,
>
> Does anyone use a 270 foot doublet with the K3 ATU?

Yes
>
> Is there a combination of feeder type/length and Balun type & coax
> length that tunes OK on 160-10?

My primary 40/60/80/160 antenna is a center-fed dipole in an inverted-V
configuration.  The apex is at 70 feet [~21 m] and the ends are elevated
enough that no one runs into them.  The legs are 135 ft [~41 m] long.
It is fed with 450 ohm ladder-line down the tower to a DXE 4:1 balun at
the base of the tower and RG-213 to the shack.

The ATU's in my KX1, K2, K3, and the KAT500 all match it fine, even on
30, 17, and 12 m.  Admittedly, the radiation angle is higher than
optimum on 160 [I put up an inverted-L in the winter for that], and on
17 and 12 m, it squirts RF in all sorts of directions, not all
desirable, but the ATU's all work fine with it.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org



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[Bill-3]

I use a 260 foot doublet fed with 600 ohm tuned feeder (4" spacing #14
wire). It is run as an NVIS antenna - up 26 feet and flat. The K3
auto-tuner and the KAT500 both tune it very well for 160/80/40/30
meters. I do not use it on the upper bands. The feedline is about 25
feet long and is terminated with a BalunDesigns 4:1 balun. 10 feet of
RG213 runs from the balun into the house to the switch/lightning panel.
If you have the optional RX board and AM filter, the antenna works great
for the broadcast band too.

Bill K-Line

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[Rick WA6NHC]

Sure it does, you're changing the line losses, tweaking C and L and therefore the SWR (always measured at the tuner, but moving peaks and valleys closer/further away from that point) any time you alter the system.

There are specific resonant points in an antenna system (typically each half wavelength).  The goal is to make one of them at the radio.  In a multiband antenna, this is um, challenging if not impossible.

The common mode choke stops any into the shack, but what is varying is the coax from rig to choke.  Those losses change and resonant portions of the feed system change so I'd expect to see the tuning change.

The odd part is no major difference from 70' of window line to 100'.   My presumption is that the antenna is simply too close to dirt, so changes are more subtle or masked.

The coax portion (if used) should be as short as feasible to keep line losses low.  If you can't, you'll have to accept the losses; sometimes I use 35' instead of 10' so I can be more effective (get a better tune) on the bottom of 80M and run the amp.  Signal loss is not as significant there and receiver gain is far more than ample.   I won't do that on 10M where the loss is major (2-3 S units).

It's a system, not just a bunch of pieces.  They all add up.

FWIW, 170' per leg of the dipole is 5/8 wave mid 75 meters; not a resonant antenna.  It requires a tuner.

If the OP has time and the space, an intriguing option is the 160 full wave loop.  It resonates in every ham band or close enough.  Only the 160 M loop does this, an 80 M loop does not.  I don't have the real estate, or tall trees.

So for field day, a meadow with enough tall trees on the edge... Hmmm...

73,
Rick wa6nhc

Tiny iPhone 5 keypad, typos are inevitable

> On May 15, 2014, at 1:33 PM, "Wes (N7WS)" <[hidden email]> wrote:
>
> This makes no logical sense, unless you have a big common-mode problem.
>
> Wes  N7WS
>
>
>
>> On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
>> Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.
>
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[Wes (N7WS)]

My apologies for confusing two different posters to this thread.  Partly a
consequence of threading and me using two different computers and two different
email clients.

I want to specifically address this:

Rick claims that when using a series connection of two different transmission
lines, one coaxial, one window line, changing the length of one (coax) affects
something or the other, while changing the length of the other portion (window
line) has no effect whatsoever.

This is clearly impossible.  I suggested earlier that one possibility is
common-mode current on the coax that is confusing the instrumentation.  Just
because a choke is applied doesn't mean that it is actually effective.

Rick should not be faulted for assuming that the window line is "low loss" while
the coax is not. I have been trying to debunk this myth since 1993 when, "The
Lure of the Ladder Line" was published in QST.  At that time, I had lots of
(snail mail!) correspondence with then Antenna Book editor, Dean Straw, about
this.  I pointed out that the chart of line loss vs. frequency that had appeared
in every ARRL Handbook and Antenna Book since antiquity was wrong (easily noted
by inspection).  We collaborated on a revision of this chart and I was invited
to write something about balanced line use.  See:
http://k6mhe.com/n7ws/Ladder_Line.pdf  published in the ARRL Antenna Compendium
Vol 6.

I should mention that during this correspondence I pointed out that tuner and
balun losses should not be ignored because they could be as detrimental as line
loss. I had access to Touchstone, an early professional circuit analysis
program, and gave examples of (IMHO) excessively high tuner losses that resulted
from low Q components and the misadjustment of Tee type tuners. (Regrettably, I
don't have copies of these letters any more.) After doing so, a QST favorite
author, Frank Witt had a two-part article about tuner losses published in the
April and May 1995, QST.  (I wasn't invited to write this one)  This month's
"Hands-On Radio" column in QST brings up these losses again.

Straw wrote the program TLW, bundled with the ARRL Antenna Book, which (again)
underestimated window line loss.  ARRL has just admitted this and offered a new
version that allegedly fixes the problem.  (I don't know, I don't have a new
enough version to qualify for the update, and I wouldn't use it anyway.  AC6LA's
programs (ac6la.com) are superior and highly recommended.)

Sorry to ramble on this somewhat off-topic thread but I think this is worth
mentioning.

Wes  N7WS

  On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
> [snip]
>
> The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.

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[Rick WA6NHC]

For clarity:  every line has loss.  Every single line.

What should have been better implied is that coax exhibits a significantly higher loss per foot than window line; while both have losses.  This is well proven over decades of use.

High SWR affects the losses in a negative way (the losses increase).  Since coax already has a higher loss, it can be substantially higher with the same high SWR than window line.

So, when a mixed feed system is used, it makes sense to minimize the losses through the coax to reduce the overall losses; keep the coax short.

Side notes:  since coax is often more subject to bending than window/ladder line, the internal spacing between elements will vary, potentially increasing the risk of failure while handling high RF voltages.  On the flip side, precip or nearby objects (rain gutter) affect window/ladder line, sometimes dramatically.  Result: Use "the good stuff" and keep everything as isolated from unrelated objects as possible.

As I've said many times; every station is a collection of compromises.  In making any choice, one reduces the potential options.  In my case, operational ability and efficiency were brought to an acceptable (to me) level through these choices and limitations.

I started with 340' feet of wire, center fed (opposing 5/8 wave at 75 meters) and 70' of window line.  Changing to 100' of window line had no significant effect (it changed the tuner values but not where I could operate with an acceptable SWR).

Changing from 10' of coax from rig to the CMC (common mode choke, typically incorrectly called a current balun, used at the shack window) to ~35' has a significant change in tuning and band use ability.  It allows me to operate above 300W on the bottom end of 80 meters when 10' makes it dicey (tuner matches, but can't handle/maintain the match above 300 watts).

So it isn't impossible, it's empirically determined.

Changing the 1:1 CMC to a 4:1 CMC (same everything otherwise) added low power (<200 watts) 160 meter ability (2:1 or worse, tuned) and substantially lowered the unmatched (bypassed) SWR on all bands.  If what I read is accurate, the 4:1 also has a slightly higher loss in efficiency than the 1:1.  It conveniently converts window line to coax (my preference in a shack) in this model.  

[I'm still planning on adding 12 meters more wire (17.5' each leg) to the antenna to lower the resonant frequency on 80 meters.  It should also help match on 160, but may cost me elsewhere.]

Ideally the KAT500 would be balanced feed capable with a CMC built in.  I have a couple capable balanced feed tuners, but they're manual only, not useful for remote ops (about a quarter of my radio time).

But then also ideally, I'd be wealthy, not live in an HOA and CCR infested development, not near an airport runway, in a ham tower friendly county with tall trees and salt water nearby. ;-)  choices:options

I do really need to get a good antenna analyzer, but for now my signal is heard and I hear with minimal noise, thanks in part to the CMC (the DX Eng. 10 KW model, which should be bullet proof for the KPA500 and high SWR).  The rest is all Elecraft, it really is "the good stuff".  ;-)

73,
Rick wa6nhc

Tiny iPhone 5 keypad, typos are inevitable

> On May 17, 2014, at 2:29 PM, "Wes (N7WS)" <[hidden email]> wrote:
>
> Rick claims that when using a series connection of two different transmission lines, one coaxial, one window line, changing the length of one (coax) affects something or the other, while changing the length of the other portion (window line) has no effect whatsoever.
>
> This is clearly impossible.  I suggested earlier that one possibility is common-mode current on the coax that is confusing the instrumentation.  Just because a choke is applied doesn't mean that it is actually effective.
>
> Rick should not be faulted for assuming that the window line is "low loss" while the coax is not. I have been trying to debunk this myth since 1993 when, "The Lure of the Ladder Line" was published in QST.  At that time, I had lots of (snail mail!) correspondence with then Antenna Book editor, Dean Straw, about this.  I pointed out that the chart of line loss vs. frequency that had appeared in every ARRL Handbook and Antenna Book since antiquity was wrong (easily noted by inspection).  We collaborated on a revision of this chart and I was invited to write something about balanced line use.  See: http://k6mhe.com/n7ws/Ladder_Line.pdf  published in the ARRL Antenna Compendium Vol 6.
>
> I should mention that during this correspondence I pointed out that tuner and balun losses should not be ignored because they could be as detrimental as line loss. I had access to Touchstone, an early professional circuit analysis program, and gave examples of (IMHO) excessively high tuner losses that resulted from low Q components and the misadjustment of Tee type tuners. (Regrettably, I don't have copies of these letters any more.) After doing so, a QST favorite author, Frank Witt had a two-part article about tuner losses published in the April and May 1995, QST.  (I wasn't invited to write this one)  This month's "Hands-On Radio" column in QST brings up these losses again.
>
> Straw wrote the program TLW, bundled with the ARRL Antenna Book, which (again) underestimated window line loss.  ARRL has just admitted this and offered a new version that allegedly fixes the problem.  (I don't know, I don't have a new enough version to qualify for the update, and I wouldn't use it anyway.  AC6LA's programs (ac6la.com) are superior and highly recommended.)
>
> Sorry to ramble on this somewhat off-topic thread but I think this is worth mentioning.
>
> Wes  N7WS
>
>> On 5/15/2014 12:54 PM, Rick Bates, WA6NHC wrote:
>> [snip]
>>
>> The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none.
>
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[k6dgw]

On 5/17/2014 2:29 PM, Wes (N7WS) wrote:
> My apologies for confusing two different posters to this thread.  Partly
> a consequence of threading and me using two different computers and two
> different email clients.
>
I thought that's what having an email client thread emails was supposed
to prevent.  Then again, I tried it in T-bird and quickly quit --
couldn't find anything again. :-))

> Rick claims that when using a series connection of two different
> transmission lines, one coaxial, one window line, changing the length of
> one (coax) affects something or the other, while changing the length of
> the other portion (window line) has no effect whatsoever.

I could certainly be wrong on this but I believe the post(s) were simply
pointing out that increasing the length of the "balanced" line affects
the losses much less than making it shorter with a correspondingly
longer coax line.

400 or 600 ohm "ladder line" [open wire line with a minimum number of
spreaders] *is* very low loss at HF even at high SWR, so long as the
separation is a very small fraction of a wavelength.  That's what the
coastal marine and HF point-to-point stations used in mid-20th century
and KPH/KSM still do.  Plastic insulated "window line" is significantly
more lossy than ladder line, but still less than coax at higher SWR's.
Window line is also sensitive to weather conditions.  I have window line
down the tower to a DXE 4:1 balun and coax to the shack.  KAT500 needs
to retune between a rainy and dry day.

There was a day when we brought open wire line into the shack.  With
today's equipment, I really don't recommend that. :-))

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

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[Wes (N7WS)]

I said earlier:

"Rick claims that when using a series connection of two different transmission lines, one coaxial, one window line, changing the length of one (coax) affects something or the other, while changing the length of the other portion (window line) has no effect whatsoever.

This is clearly impossible. "

I stand by those remarks.  Your empirical evidence to the contrary is wrong.

Rick also said:

"Changing from 10' of coax from rig to the CMC (common mode choke, typically incorrectly called a current balun, used at the shack window) to ~35' has a significant change in tuning and band use ability.  It allows me to operate above 300W on the bottom end of 80 meters when 10' makes it dicey (tuner matches, but can't handle/maintain the match above 300 watts)."

Yet earlier in the thread he said:

"The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none."

So which is it, 10' or 35'?

With that, I'm done.

Wes  N7WS


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[Rick WA6NHC]

I'll restate:  The length of coax should be as short as feasible because the losses from mismatch (SWR) are highest when compared to window or ladder line.

The shortest distance from my rig to the choke is about ten feet unless I bring the window line inside (too problematic) or put the rig in the window next to the choke (won't happen).  That is what I use, ten feet of coax; the shortest possible piece, for me.  Ideally it should be much shorter.

I most carefully explained (rather than presuming an understanding and trying to be more clear) in the last note that adding 30' of window line resulted in different tuner values, but no change in the band segments where I could operate at reasonably low SWR ergo no significant (cumulative) change at the rig (I was still band segment limited, same places).  On some (20M and up) bands, retuning was not required; it's simply two 'long wire' antennas in phase.

Empirical evidence is neither right or wrong.  It may bring more questions than answers, but it can't lie.  The tuner likely compensated for the slight change in the feed, the antenna elements were unchanged and the end result was no effective change.

Changing the coax portion length of the feed changes everything dramatically; the tuner values, the losses, lowering the SWR to give me ability anywhere 160-10.  But I don't want the line losses above 40 M; it gets worse quickly above that.  I only add that section in when home, I'm DXing and QRO.

In this case, my findings may go against standard beliefs, but stands as evidence nonetheless.

When I move the shack upstairs and replace the window line (the single strand solid copper elements make me nervous) I'll be sure to have an analyzer to make more careful measurements.  In the meantime, my 'wrong' system is working.  

Why wrong?  No part of the system (antenna or feed) is ham band resonant, which is why:

It's natively high in SWR;
A tuner is required;
It works on all bands (the KAT3 tuner loves it, the KAT500 under QRO, not so much on 160/80);
Any system change may give unexpected results.

It's at a point where it works on all bands about as well one can expect for a simple wire dipole; more so considering the lack of height.  Over 200 countries later, I have to say it's working.

However, I miss my tower and beams...  They're more effective and easier.  Next house I'll get them back.

I hope this answered your questions and concerns.

73,
Rick wa6nhc

Tiny iPhone 5 keypad, typos are inevitable

> On May 17, 2014, at 11:30 PM, "Wes (N7WS)" <[hidden email]> wrote:
>
>
> I said earlier:
>
> "Rick claims that when using a series connection of two different transmission lines, one coaxial, one window line, changing the length of one (coax) affects something or the other, while changing the length of the other portion (window line) has no effect whatsoever.
>
> This is clearly impossible. "
>
> I stand by those remarks.  Your empirical evidence to the contrary is wrong.
>
> Rick also said:
>
> "Changing from 10' of coax from rig to the CMC (common mode choke, typically incorrectly called a current balun, used at the shack window) to ~35' has a significant change in tuning and band use ability.  It allows me to operate above 300W on the bottom end of 80 meters when 10' makes it dicey (tuner matches, but can't handle/maintain the match above 300 watts)."
>
> Yet earlier in the thread he said:
>
> "The coax portion of the feed should be as SHORT as possible, in my case it is currently about 10' (2.8 meters).  The losses are highest there and the extreme SWR makes it MUCH worse, keep it short; use the best stuff, not the cheap stuff.  Changing the length of the coax portion has a HUGE impact on where (or if) the system tunes; the window line, none."
>
> So which is it, 10' or 35'?
>
> With that, I'm done.
>
> Wes  N7WS
>
>
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