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KPA100 - Problems on 15m

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Ken Alexander-2

KPA100 - Problems on 15m

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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Don Wilhelm-4

Re: KPA100 - Problems on 15m

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
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>
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>
>

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Ken Alexander-2

Re: KPA100 - Problems on 15m

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 <[hidden email]> wrote:

> From: Don Wilhelm <[hidden email]>
> Subject: Re: [Elecraft] KPA100 - Problems on 15m
> To: "Ken Alexander" <[hidden email]>
> Cc: [hidden email]
> 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
> >
> >
> >
> ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> ------------------------------------------------------------------------
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com Version: 9.0.733 / Virus
> Database: 271.1.1/2685 - Release Date: 02/13/10 03:43:00
> >
> >

Ken Alexander-2

Re: KPA100 - Problems on 15m

In reply to this post by Don Wilhelm-4

Hi Don,

I tried the same tests with my dummy load connected and got the same lower output on 15m when transmitting versus pressing Tune.

I increased the output from the audio interface to the rig and the transmitter output can be adjusted to give normal output. So maybe it just needed a little extra drive on 15 for some reason. The problem is that the audio level that gives good output on 15 gives me one solid ALC bar on 20m, so I'll have to be careful when going from band to band.

I can't think of a reason why the drive required on one band wouldn't be the same as all bands.

Ken

--- On Sun, 2/14/10, Don Wilhelm <[hidden email]> wrote: