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KPA500 presents high SWR to radio driving it

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ARRL - N6MQL

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
> [hidden email]
> Follow me on APRS at: http://tinyurl.com/k5rhd-2
> Homepage: http://blog.randydiddel.com
>

ke9uw

Re: KPA500 presents high SWR to radio driving it

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: [hidden email] [[hidden email]] on behalf of ARRL - N6MQL [[hidden email]]
Sent: Sunday, December 09, 2012 4:19 PM
To: [hidden email]; [hidden email]
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

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Chuck, KE9UW