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Asunto: Psk31 Digest V1 #366
Fecha: martes 18 de abril de 2000 4:18
Psk31 Digest Tuesday, April 18 2000 Volume 01 : Number 366
In this issue:
[psk31] Question
Re: [psk31] Bad Sig. on 10M?
Re: [psk31] Question
[psk31] PSK31 IMD readings.
See the end of the digest for information about psk31-digest
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Date: Mon, 17 Apr 2000 09:02:24 -0500
From: Martin <rutherford.ulea@mcleodusa.net>
Subject: [psk31] Question
Hi Peter. Maybe you or someone on the list can answer this for me.
I seem to seldom see a PSK signal with a good IMD reading, and have
never seen a string signal with a good reading. However, if i turn doen
the rf gain on a strong signal, the IMD reading improves. My question
is this happens. I am using an Icom 706MKII, and cannot turn off the
AGC. Setting the AGC fast or slow sdoes not seem to make much (if any)
difference. Are these mostly good signals that I am seeing, and I don't
see the true IMD reading until I turn down the rf gain? Or am I just
losing the extra sidebands, so the program thinks it is getting a good
signal? Or maybe a combination?
- --
Cul8r
Martin Campbell rutherford.ulea@mcleodusa.net KB0HAE
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Date: Mon, 17 Apr 2000 10:38:09 -0400 (EDT)
From: Dan Halbert <halbert@bbn.com>
Subject: Re: [psk31] Bad Sig. on 10M?
>From: "Bud Patten" <bud.patten@worldnet.att.net>
>I'm monitoring 10M PSK today (Fri) with a temporary rx only cable (xfmr
>coupled) while building a permanent tx/rx cable for PSK. I'm watching a K2
>in Florida that appears to be spread over better than 1 kHz. I am using
>Digipan and can move the cursor over to the 5th or 6th harmonic of his tone
>and and still copy him solidly. His IMD appears to be jumping between -22
>and -30 db. Is this for real, or is it my setup. I don't believe that I'm
>overdriving my soundcard but there are a couple of other stations on that
>appear to be generating distortion but NOTHING compared to this guy.
I saw a K4 with similar wide spreading one night. He was CQ'ing though
no one was answering - not surprising. I did answer and told him what
I saw, and suggested he back down the mic gain. He was not offended
and did so. But I was still seeing 4th harmonic weakly, and he had the
mic gain essentially all the way down. So I suggested his attenuator
between sound card and mic connector needed adjustment. Ah ha! Turns
out he wasn't using one. (I thought that might be it.) He QRT'd
quickly. I managed to squeeze in a reference to the May '99 QST
article.
Regards,
Dan, KB1RT
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------------------------------
Date: Mon, 17 Apr 2000 12:30:59 -0500
From: Robbie Robertson <mwrobertson@mediaone.net>
Subject: Re: [psk31] Question
Martin wrote:
>
> Hi Peter. Maybe you or someone on the list can answer this for me.
> I seem to seldom see a PSK signal with a good IMD reading, and have
> never seen a string signal with a good reading. However, if i turn doen
> the rf gain on a strong signal, the IMD reading improves. My question
> is this happens. I am using an Icom 706MKII, and cannot turn off the
> AGC. Setting the AGC fast or slow sdoes not seem to make much (if any)
> difference. Are these mostly good signals that I am seeing, and I don't
> see the true IMD reading until I turn down the rf gain? Or am I just
> losing the extra sidebands, so the program thinks it is getting a good
> signal? Or maybe a combination?
>
> --
> Cul8r
>
> Martin Campbell rutherford.ulea@mcleodusa.net KB0HAE
Hi Martin,
Another possible cause for that kind of distortion,
would be that you may have TOO much receive audio into
the sound card.. I usually set my audio in level to the
point where there is visable "noise" across the
waterfall but not to the point of obstruction of weak
signals... A faint trace of noise with NO signals
across the waterfall works nice for me... Even then, I
sometimes am relunctant to give out bad IMD reports
because I can turn off agc and lower RF gain and in so
many cases, there are no sidebands and good IMD.. Where
to next?
Robbie
- --
- ----------------------------
Are we having fun yet?
73 - Robbie - WA9INF
******* --... ...-- *******
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Date: Mon, 17 Apr 2000 19:13:22 +0000
From: Peter Martinez <Peter.Martinez@btinternet.com>
Subject: [psk31] PSK31 IMD readings.
From Peter Martinez G3PLX
To answer KB0HAE Martin's question about IMD readings, I would expect
that on a radio which cannot otherwise disable the AGC, you are
probably getting less AGC action as you turn the RF gain down, and so
if the IMD readings improve as you do so, then it might be that the
AGC was making the IMD look worse. But of course, turning the RF gain
down will also reduce the level of audio into the soundcard and this
itself might improve the IMD if it's being caused in the soundcard
itself. To decide one way or the other would need a detailed set of
experiments winding the RF gain down and the soundcard gain up to
compensate and see what happens. However, I wouldn't expect a
soundcard to give detectable IMD below it's clipping level unless it
was broken, and if you exceed the clipping level you get a red-out of
the waterfall display (or whatever the other PSK31 programs do), so
it should be very easy to avoid that.
I can't speak for the IMD display in other PSK31 implementations, but
in mine if you take the input level right down, the IMD display
eventually starts showing WORSE when the intermod products hit the
bottom of the 60dB dynamic range of the waterfall FFT routine. Other
PSK31 implementations will probably work the same way, so it's not
the IMD display itself that make it look better as you wind the level
down.
73
Peter
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End of Psk31 Digest V1 #366
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