[Elecraft] KPA100 - Problems on 15m

[Ken Alexander]

Thanks for your input Don.  The contest just finished a few hours ago.  The PKA100 got a good workout.  I'll go inside and tighten the mounting screws on the power transistors (as they recommend) tomorrow.

The SGC autotuner is installed at the feedpoint of a 20m vertical in the back yard, about 80 ft from the house, not in the shack.  The K2 and my power meter indicate a perfect match (as one would hope) on 20m, and 1.2:1 on 15m.  That of course doesn't necessarily mean there's no RF in the shack, just laying out the setup a bit.

I'll run some tests with my dummy load in place and report back.

73 and thanks again,

Ken


--- On Sun, 2/14/10, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> From: Don Wilhelm <w3fpr at embarqmail.com>
> Subject: Re: [Elecraft] KPA100 - Problems on 15m
> To: "Ken Alexander" <k.alexander at rogers.com>
> Cc: elecraft at mailman.qth.net
> Date: Sunday, February 14, 2010, 3:08 AM
> Ken,
> 
> That does not make sense.  The Power output for RTTY
> is no different than CW (or TUNE) except that the audio
> input to the K2 is different from CW.  There is no band
> to band difference for the K2 - AFSK modulation is AFSK
> modulation no matter which band it is on.
> 
> I would be looking for RF Feedback problems on 15
> meters.  Try it into a dummy load and see if things are
> normal - if so, look at your antenna system or the
> solution.
> 
> OTOH, if all bands behave the same way when operated into a
> dummy load, then look to your RTTY driving software and
> whatever interface you are using.
> 
> Actually, RTTY AFSK is more related to SSB transmission
> than CW, so try SSB as well.  If SSB transmission os
> OK, then your RTTY driving system is suspect (but would be
> the same on all bands).  If your problems are confined
> to only 15 meters, then look at the possibility of RF
> Feedback on 15 meters.
> 
> 73,
> Don W3FPR
> 
> Ken Alexander wrote:
> > I completed building my KPA100 a few weeks ago. 
> It passed all tests and checks all the way through. 
> However, today I noticed something strange.
> > 
> > I'm operating in the CQ WPX RTTY contest this weekend
> and spent most of the day on 20m with the Power set to
> 50W.  I went to 15m to try it out.  With the Power
> control still set to 50W I hit the Tune button to get my
> remote autotuner to tune to 15m.  The K2 and my
> external power meter indicated the normal 20W, as it should
> in Tune mode when the power is set higher than 20W.
> > 
> > When I went to transmit RTTY (without touching the
> Power control), my external power meter barely indicated 10
> watts.  This only happens on 15m.
> > 
> > As an experiment, I went to the CW portion of the
> band.  Tune gives you 20W.  Keying the transmitter
> with my paddles give me 50W.
> > 
> > Any ideas would be appreciated.
> > 
> > 73,
> > 
> > Ken Alexander
> > VE3HLS
> > 
> > 
> >
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