Need help to determine most effective K3 vs KPA500 output

[Frederick Atchley]

I have a K3-100 with KAT3 and a KPA500 w/o a tuner. I use an all-band
"Mystery" (similar to a G5RV?) wire antenna. Because of the KAT3, the K3
"sees" a 1:1 antenna match which is good. However, I would like to operate
up to 200 watts out (low power) for the California QSO party.  The KPA500
tolerates a 3:1 SWR at 200 watts across the 20 meter band and in the CW
portion of the 80 meter band on the mystery antenna.

My question is which option is the most effective, 100 watts with 1:1 or 200
watts with 3:1? Keep in mind that both options use the identical antenna and
feedline.

Thanks in advance.

73, Fred, AE6IC

 

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[Don Wilhelm-4]

Fred,

That is a 'trick' question - right?  If not, read on - your loss in dB
does not change.

There will be no difference in your feedline loss - the KAT3 does not
change the loss on your feedline, it just makes the K3 happier.

Now if you were tuning that antenna at its feedpoint rather than at the
transmitter, it would make the difference between a matched feedline and
one with SWR - that is the advantage of a remote tuner.

If you are still interested in loss due to SWR (even if not applicable
in this case), consult the chart in the Transmission Line chapter of the
ARRL Handbook (most any edition).
You will find that with an SWR of 3 and a matched line loss of 1 dB the
additional loss is less than 0.5 dB - if the matched line loss is 4 dB,
the added loss due to SWR is only 1 dB.  Even at a 10 dB matched line
loss, the additional loss due to SWR is only about 1.3 dB.  The loss
does not increase drastically due to SWR, it is the matched line loss
that is the greater factor - that is why open wire feedlines work so
well even with very high SWR.

You realize a 3 dB gain by doubling your power,  so the transmitted gain
will be 3 dB - there is no change in the feedline loss (when expressed
in dB).

73,
Don W3FPR

On 9/14/2011 3:58 PM, Fred Atchley wrote:

> I have a K3-100 with KAT3 and a KPA500 w/o a tuner. I use an all-band
> "Mystery" (similar to a G5RV?) wire antenna. Because of the KAT3, the K3
> "sees" a 1:1 antenna match which is good. However, I would like to operate
> up to 200 watts out (low power) for the California QSO party.  The KPA500
> tolerates a 3:1 SWR at 200 watts across the 20 meter band and in the CW
> portion of the 80 meter band on the mystery antenna.
>
> My question is which option is the most effective, 100 watts with 1:1 or 200
> watts with 3:1? Keep in mind that both options use the identical antenna and
> feedline.
>
>

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[Frederick Atchley]

 

Thanks Don.

No, it's not a trick question, just tricky for me!  And yes, the feedline is
ladderline. So the bottom line is that the 200 watts w/o a tuner is slightly
better than 100 watts w/tuner using the same feedline and antenna. Every
little bit helps. I live in an area where CC&R antenna limitations force the
use of a stealth wire.

<snip>Now if you were tuning that antenna at its feedpoint rather than at
the transmitter, it would make the difference between a matched feedline and
one with SWR - that is the advantage of a remote tuner. <endsnip>

I can't wait to see the Elecraft KAT500, especially the remote tuner. That
will be a whole new ballgame for me. By not having to use a tuned antenna
design, I can then string a longer random wire to increase the RX capture
area. Life is good.

73, Fred, AE6IC.

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[Frederick Atchley]

<Snip>Fred, How does KPA 500 feed ladder line without tuner? <End snip>

Hi Mike,

I run coax from inside to the eve of the roof where I attach a 4:1 balun.
>From there it's 300 ohm ladder line. Works FB.

73, Fred, AE6IC

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