Low power on 20m using the KPA100 option

[Renardy, Martin]

Dear all,

last weekend I finished the KPA100 option, which is causing a little
problem. Everything
Is running well except power on 20m, where I just reach 50 Watts.

The QRP output is not affected, so I am quite shure that the RF path to
the antenna
through the LPF is ok. Just to be shure I have checked all inductivities
and capacities
of the 20m filter. They are ok including the used core types of the
inductivities.

Somehow I am getting the impression, that on 20m the PA doesn't get
sufficient driver
Power. My signal reports on 20m have been ok, except the "missing
50Watt". This issue
drives me realy crasy, because everything else is working ufb.

Any suggestions?

vy 73 de Martin, DL6KMR


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[Vic K2VCO]

Renardy, Martin wrote:

> last weekend I finished the KPA100 option, which is causing a little
> problem. Everything
> Is running well except power on 20m, where I just reach 50 Watts.
>
> The QRP output is not affected, so I am quite shure that the RF path to
> the antenna
> through the LPF is ok. Just to be shure I have checked all inductivities
> and capacities
> of the 20m filter. They are ok including the used core types of the
> inductivities.

If you are getting 10 watts output when you set the power control to 10
watts, check the current draw at this power level by tapping Display.
You should be drawing less than 3 amperes in this condition.  Check also
at 11 watts, with the KPA100 on.  It shouldn't be much higher.  If it
is, you may have problem (2) below.

I found two problems in my K2/100 which caused slightly (in my case)
reduced output on 20 meters:

1) the bandpass filter tuning trimmers were both at maximum capacity.
Adding a few pf in parallel with them allowed the QRP portion of the K2
to develop more drive for the KPA100 with less current draw.

2) There is a known issue with some new KPA100s that the amplifier
requires abnormally high drive on 20 and sometimes 30 meters.  This
causes high current draw in the low-power stage and inability to reach
full output.  Gary at Elecraft was helpful to me about this
<[hidden email]>.

--
73
Vic, K2VCO
Fresno, CA
http://www.qsl.net/k2vco
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[Vic K2VCO]

Vic Rosenthal wrote:

> If you are getting 10 watts output when you set the power control to 10
> watts, check the current draw at this power level by tapping Display.
> You should be drawing less than 3 amperes in this condition.  Check also
> at 11 watts, with the KPA100 on.  It shouldn't be much higher.

I should have said 'with the power control set to 100 watts', not 11 watts.

--
73
Vic, K2VCO
Fresno, CA
http://www.qsl.net/k2vco
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