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[w2/K3] High SWR

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Don KA1KU

[w2/K3] High SWR

I built a new W2 today and added the coupler in-line with my G5RV, which recently replaced a 40M dipole.
Both my K2 and K3 have internal tuners, and I understand that the internal tuners match inside the K's and cannot change the antenna so therefore can not effect the SWR seen by the W2.
My MFJ 259 analyzer shows 1.1 to 1 at some point in most bands from 80 to 6 meters.
For example, on 40m the SWR reads 1.0-1 at 7.17MHz. Similar points on other bands.

Also, since the W2 is newly built, I checked the W2 out with a dummy load attached. On 40m, the internal tuner shows a match of 1.0-1, and the W2 reads SWR of 1.1. With K3 power set at 1.0 and 5.0, the W2 reads 1.1 and 5.0. On 20m, SWR (internal, W2) reads 1.0 , 1.1 and power at (1.0 and 5.0) reads 1.2 and 4. I think this rules out problems with the W2. My K2 readings match the W2 almost exactly. The K3 seems off a little but I have not tried to calibrate it.

With G5RV connected, I get a much different picture. On every band from 160 to 80 I get a SWR reading full scale, 5. On 6m the reading is 3. The internal tuner matched each band to 1.0 or 1.1 hto 1. Again, I understand this means nothing in regard to W2 reading. What I don't understand is why I have such a high SWR, especially since the antenna analyzer indicates a close match, 1.0-1 at 7.17MHz, which I used as my test frequency on 40m. I also get SWR of 5 when ATU is in bypass. This is repeated on every band, using the frequency of lowest SWR indicated by the antenna analyzer.

I also see odd power readings. For example, on 40m, with K3 power set at 1.0 the W2 shows 4 Watts. At 5, the W2 shows 14. This too is similar across all bands.

The G5RV has only been up a few months and seems to work great on receive. I've mostly been on 80, 40 and 20.
I thought I had a basic understanding of this but just don't understand what I'm seeing.

73,
Don KA1KU

Jim Wiley

Re: [w2/K3] High SWR

It is my understanding that the original G5RV design is a 20-meter only
antenna. If built according to the designer's specification, meaning
antenna length, feed line length, height above ground, etc. it should
show a reasonably low SWR on 20 meters. Many hams use it on other bands
with a greater or lesser degree of success (depending on band) by
feeding it via some sort of antenna matching unit, either internal or
external to the rig. But, and again, if built according to the original
design, it will naturally show high SWR a on any band except 20 meters.
If it shows a high SWR on 20 meters too, it may have been assembled
incorrectly or there may be some sort of fault. A common misconception
is that a G5RV antenna will automatically match with a low SWR on all HF
bands. This is incorrect. All this being said, keep in mind that there
is no rule anywhere that says an antenna has to be resonant to be an
efficient radiator. That's where the antenna matching unit comes into
play. And, you are correct in stating that there is nothing the antenna
matching (tuning) unit can do to change the SWR on the line between the
antenna and the shack. All the antenna matching unit does is make the
transmitter happy (low SWR) and enable the efficient transfer of power
between the antenna and the transceiver.

- Jim, KL7CC

On 11/8/2012 5:29 PM, Don KA1KU wrote:

> I built a new W2 today and added the coupler in-line with my G5RV, which
> recently replaced a 40M dipole.
> Both my K2 and K3 have internal tuners, and I understand that the internal
> tuners match inside the K's and cannot change the antenna so therefore can
> not effect the SWR seen by the W2.
> My MFJ 259 analyzer shows 1.1 to 1 at some point in most bands from 80 to 6
> meters.
> For example, on 40m the SWR reads 1.0-1 at 7.17MHz. Similar points on other
> bands.
>
> Also, since the W2 is newly built, I checked the W2 out with a dummy load
> attached. On 40m, the internal tuner shows a match of 1.0-1, and the W2
> reads SWR of 1.1. With K3 power set at 1.0 and 5.0, the W2 reads 1.1 and
> 5.0. On 20m, SWR (internal, W2) reads 1.0 , 1.1 and power at (1.0 and 5.0)
> reads 1.2 and 4. I think this rules out problems with the W2. My K2
> readings match the W2 almost exactly. The K3 seems off a little but I have
> not tried to calibrate it.
>
> With G5RV connected, I get a much different picture. On every band from 160
> to 80 I get a SWR reading full scale, 5. On 6m the reading is 3. The
> internal tuner matched each band to 1.0 or 1.1 hto 1. Again, I understand
> this means nothing in regard to W2 reading. What I don't understand is why
> I have such a high SWR, especially since the antenna analyzer indicates a
> close match, 1.0-1 at 7.17MHz, which I used as my test frequency on 40m. I
> also get SWR of 5 when ATU is in bypass. This is repeated on every band,
> using the frequency of lowest SWR indicated by the antenna analyzer.
>
> I also see odd power readings. For example, on 40m, with K3 power set at
> 1.0 the W2 shows 4 Watts. At 5, the W2 shows 14. This too is similar
> across all bands.
>
> The G5RV has only been up a few months and seems to work great on receive.
> I've mostly been on 80, 40 and 20.
> I thought I had a basic understanding of this but just don't understand what
> I'm seeing.
>
>
>
>
>
>
> -----
> 73,
> Don KA1KU
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/w2-K3-High-SWR-tp7565299.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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>
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>

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Mike Markowski-2

Re: [w2/K3] High SWR

Here is nice summary of g5rv antenna properties:

http://www.midtel.net/~pmam/g5rv.htm

73,
Mike ab3ap

On 11/08/2012 10:35 PM, Jim Wiley wrote:
> It is my understanding that the original G5RV design is a 20-meter only
> antenna. If built according to the designer's specification, meaning
> antenna length, feed line length, height above ground, etc. it should
> show a reasonably low SWR on 20 meters. [...]
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Don KA1KU

Re: [w2/K3] High SWR

In reply to this post by Don KA1KU

Thanks for your insight on this. I had no idea the SWR would be so high on the G5RV although I was aware of these characteristics in general.
I just did some checks across 20 meters and I get a SWR of 4 on the W2. The chart you sent indicates 2+ but not sure if I should expect that. This is a Full size G5RV at 45 feet feed with 31 feet of 450 ohm ladder line and about 90 feet of 50 ohm coax to shack.
With the new W2, first I wondered if it was working correctly. I think it is. Second, is something wrong somewhere in my antenna system? Looks like the high SWR is to be expected except perhaps on 20M. Does the SWR of 4 indicate a problem somewhere?
Lastly, about the power reading of the W2. With power set at 5.0 on K2/K3 the W2 reads 8 and 10 respectively. With power at 10.0 the W2 reads 15 and 17. This seems like a lot of difference. Could it be the K's are that much out of calibration? Is the W2 reading wrong? What else? Maybe the K's are just creating a lot of energy!

Thanks for all your help on this.

73,
Don KA1KU

Geoffrey Mackenzie-Kennedy-3

Re: [w2/K3] High SWR

In reply to this post by Don KA1KU

Hello Don,

Three questions:

Are both of your W2 and Antenna Analyzer powered from a PSU or a battery?

Do you have any form of common mode choke installed at the junction of the
coax and open wire feeders, or elsewhere along the coax?

Does the SWR reported by your W2 change at all (on any or all bands) if you
hold and slide your hand along that part of the coax feeder which you can
reach?

73,

Geoff
LX2AO

On November 09, 2012 at 3:29 AM, Don KA1KU wrote:

<snip>

> My MFJ 259 analyzer shows 1.1 to 1 at some point in most bands from 80 to
> 6
> With G5RV connected, I get a much different picture. On every band from
> 160
> to 80 I get a SWR reading full scale, 5. On 6m the reading is 3. The
> internal tuner matched each band to 1.0 or 1.1 hto 1. Again, I understand
> this means nothing in regard to W2 reading. What I don't understand is
> why
> I have such a high SWR, especially since the antenna analyzer indicates a
> close match, 1.0-1 at 7.17MHz, which I used as my test frequency on 40m.
> I
> also get SWR of 5 when ATU is in bypass. This is repeated on every band,
> using the frequency of lowest SWR indicated by the antenna analyzer.
>
> I also see odd power readings. For example, on 40m, with K3 power set at
> 1.0 the W2 shows 4 Watts. At 5, the W2 shows 14. This too is similar
> across all bands.

<snip>

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Donald Thompson-2

Re: [w2/K3] High SWR

Hi Geoff,
The W2 is powered from shack supply, Astron RS-20. The MJF-259 from fresh AA batteries. K3 also on shack supply. K2 on internal battery.
The coax is connected to the balun at end of ladder line as supplied by W8AMZ, nothing else.
The coax is passed thru a polyphaser at the lightning control panel outside shack, just outside the wall.
The w2 coupler is inside shack at coax entrance. The radio is grounded with 1/2 in copper strap to lightning panel.
There are no chokes.
The SWR does not vary with hand on line anywhere inside shack on any band.
Thanks
Sent from my iPhone
Don

On Nov 9, 2012, at 7:55 AM, "Geoffrey Mackenzie-Kennedy" <[hidden email]> wrote:

> Hello Don,
>
> Three questions:
>
> Are both of your W2 and Antenna Analyzer powered from a PSU or a battery?
>
> Do you have any form of common mode choke installed at the junction of the coax and open wire feeders, or elsewhere along the coax?
>
> Does the SWR reported by your W2 change at all (on any or all bands) if you hold and slide your hand along that part of the coax feeder which you can reach?
>
> 73,
>
> Geoff
>

John Oppenheimer

Re: [w2/K3] High SWR

In reply to this post by Don KA1KU

On 11/09/2012 06:46 AM, Don KA1KU wrote:

> Lastly, about the power reading of the W2. With power set at 5.0 on K2/K3
> the W2 reads 8 and 10 respectively. With power at 10.0 the W2 reads 15 and
> 17. This seems like a lot of difference. Could it be the K's are that much
> out of calibration? Is the W2 reading wrong? What else? Maybe the K's are
> just creating a lot of energy!

Hi Don,

I recently purchased W1 and found the default DC alignment to be rather
far off with respect to an Elecraft DL1 and new XK3-F. The DL1 and KX3-F
matched within 5% at the KX3's 7W factory alignment setting.

The DL1, when used with a 10 M-ohm accurate DVM, directly connected to
rig, and suggested algorithm, should be much more accurate then
advertised at lower frequencies, 7 MHz. My suggestion is to use a DL1 as
your standard and calibrate to it.

John KN5L
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Jim Wiley

Re: [w2/K3] High SWR

In reply to this post by Don KA1KU

Don -

A 50-ohm directional wattmeter can only read correctly when it is
connected to a 50-ohm source and a 50-ohm load. Anything else will
change the readings. For example: Suppose you have a 10-watt
transmitter that feeds an antenna that has a SWR of 3:1. That means
about 2 watts will be reflected. Assuming the source provides what is
termed a conjugate match, a directional wattmeter in that system will
now show 12 watts forward and 2 watts reflected. You still have a net
power to the antenna of 10 watts ( 12 - 2 = 10).

A conjugate match usually means that the source (the transmitter) has a
tuned output network. This can be either a tunable final amplifier, as
is found with most vacuum tube amplifiers, or it could be a broadband
untuned amplifier (most solid state rigs) followed by an antenna
matching unit, such as the KAT2 or KAT3 in an Elecraft rig.

In simplified terms, without having to get wound up in all sots of
mathematical talk, the conjugate match may be thought of as a perfect
one-way mirror for RF energy. It passes all power in the forward
direction without loss, but is 100% reflective for energy coming back
down the feed line. Any RF energy reflected from the load (the antenna)
comes back down the feed line, encounters the conjugate match, and
starts back up the lint toward the antenna. It eventually all gets
radiated, even if it has to make a few trips back and forth. This
disregards feed line losses, which burn up a bit of the power (by
converting it to heat) each time it goes up or down the line. This is
why SWR can be a problem at VHF or UHF, where line losses tend to be
higher.

But at HF, line loss is seldom a big issue. So, for practical purposes,
even if the power bounces up and down the line a few times, it (mostly)
all gets radiated eventually. For more on the conjugate match and why
SWR in and of itself really doesn't matter, as long as the antenna plus
feed line combination can be matched to the transmitter, see the book
"Reflections", by Maxwell, W2DU.

It also explains why antennas fed with open wire line, which has
vanishingly low loss at HF, can operate effectively with very high SWR,
often 10:1 or more. As long as the antenna + feed line can be matched
to 50-ohms nonreactive at the point where the antenna interfaces with
the final amplifier, all will be well.

- Jim, KL7CC

On 11/9/2012 3:46 AM, Don KA1KU wrote:

> Thanks for your insight on this. I had no idea the SWR would be so high on
> the G5RV although I was aware of these characteristics in general.
> I just did some checks across 20 meters and I get a SWR of 4 on the W2. The
> chart you sent indicates 2+ but not sure if I should expect that. This is a
> Full size G5RV at 45 feet feed with 31 feet of 450 ohm ladder line and about
> 90 feet of 50 ohm coax to shack.
> With the new W2, first I wondered if it was working correctly. I think it
> is. Second, is something wrong somewhere in my antenna system? Looks like
> the high SWR is to be expected except perhaps on 20M. Does the SWR of 4
> indicate a problem somewhere?
> Lastly, about the power reading of the W2. With power set at 5.0 on K2/K3
> the W2 reads 8 and 10 respectively. With power at 10.0 the W2 reads 15 and
> 17. This seems like a lot of difference. Could it be the K's are that much
> out of calibration? Is the W2 reading wrong? What else? Maybe the K's are
> just creating a lot of energy!
>
> Thanks for all your help on this.
>
>
>
> -----
> 73,
> Don KA1KU
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/w2-K3-High-SWR-tp7565299p7565324.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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
>

Geoffrey Mackenzie-Kennedy-3

Re: [w2/K3] High SWR

In reply to this post by Donald Thompson-2

Hi Don,

Thanks for your reply. According to the EZNEC and TLW programs, on 20m you
should be seeing the following SWR values at the shack end of the coax. I
have also shown the total loss of the 450 ohm ladder line and the coax, but
not the insertion loss of the 1:1 balun. For this exercise I have assumed
that your coax is RG-213, and is 90 ft in length.

14.00 MHz SWR = 4.22 : 1 Feeder loss = 1.99 db
14.31 MHz SWR = 1.87 : 1 Feeder loss = 0.94 db

The balun (which I have not included) will have some effect on the SWR and
the total loss of the feed system, because the load presented to it by the
ladder line and antenna is reactive - more so at 14.0 MHz than at 14.31 MHz.

I see that your W2 shows a SWR of 4:1 on 20m, was the measurement frequency
close to 14.0 MHz or right across the band?

Please let me know if you do not have EZNEC nor TLW, and would like to see
similar data for the other bands.

73,

Geoff
LX2AO

On November 09, 2012 2:29 PM, Donald Thompson wrote:

Hi Geoff,
The W2 is powered from shack supply, Astron RS-20. The MJF-259 from fresh
AA batteries. K3 also on shack supply. K2 on internal battery.
The coax is connected to the balun at end of ladder line as supplied by
W8AMZ, nothing else.
The coax is passed thru a polyphaser at the lightning control panel outside
shack, just outside the wall.
The w2 coupler is inside shack at coax entrance. The radio is grounded with
1/2 in copper strap to lightning panel.
There are no chokes.
The SWR does not vary with hand on line anywhere inside shack on any band.
Thanks
Sent from my iPhone
Don

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