I put my K3 on 20M and put out 20 watts into the KPA500 in operate connected to
a Bird dummy load and the K3 shows 1:1 SWR.
Chuck, KE9UW
Lionel Trains, TCA, LCCA, LRRC
aka Jack, BMW Motorcycles BMWMOA #224
From: elecraft-boun...@mailman.qth.net [elecraft-boun...@mailman.qth.net] on
behalf of ARRL - N6MQL [n6...@arrl.net]
Sent: Sunday, December 09, 2012 4:19 PM
To: elecraft@mailman.qth.net; k5rhd...@gmail.com
Subject: [Elecraft] KPA500 presents high SWR to radio driving it
Randy,
I'm not sure if it's normal or not, but I do find that if you use an
analyzer on the input of the KPA500 and a 50ohm dummy load on the
output, you will see a good 50 ohm 1.0:1 SWR on the analyzer in the
Stand by mode. However, when you put the amp into the Operate mode you
get somewhere in the neighborhood of a 2.8:1 SWR (on the 20 meter band).
When you put in around 10W to the input of that KPA500 while in operate
(or at least mine) than I find that I see an increase of about .5 in the
SWR.
IE. If I have a 50 Ohm Dummy load on the output and I put the amp on
operate and transmit the 10w into the input, I see a 1.5:1 SWR on the
rig connected to the input. I would see that the input level determines
the SWR on the input when the amp is in the operate mode. It doesn't
seem to have a fixed 50 Ohm load on the input as I would have expected
it to.
Now, if someone else who knows better than I would like to explain why
that is, or if this is NOT normal I would love to know as well. I think
that Randy's question is a very fair and reasonable one. An answer from
an authority would be helpful. If you DON'T know the answer but would
like to guess... I prefer you NOT, just let someone who does know do the
answering. Thank you,
Michael
N6MQL
> Hello,
>
> I just spent a most enjoyable afternoon assembling SN 1213 KPA 500. Took my
> time and double checked every connection, wire, etc. Everything is in the
> right place and there are no faults, errors etc. when I power it up. However
> both my radios (a KX3 with ATU in bypass, and a Flex 5000 without an ATU)
> report high SWR with KEY DOWN. I put my SWR meter on the input side and sure
> enough, most bands present a 1.9:1 or higher. I have discharged the unit and
> removed the rear panel just in case the RF input wires were disconnected some
> how in assembly-both input and output are secure. I am at a loss. Anyone
> have any ideas? Also, I should mention on receive all bands seem VERY quiet.
>
> Also, my KX3 with ATU enabled works really hard but does make it tune-still
> no auto band switching and no RF out that I can see.
>
> I was really hoping to work the 10M contest this weekend with my new amp
>
>
> RANDY DIDDEL
> k5rhd...@gmail.com
> Follow me on APRS at: http://tinyurl.com/k5rhd-2
> Homepage: http://blog.randydiddel.com
>
--
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