[amsat-bb] ISS APRS Signal Quality? (tone skew?)

[Robert Bruninga]

Im gonna take a stab with zero current knowledge.

Butover the years, one DIGI on ISS uses a radio and an external TNC with
audio connections.  The other digi on ISS used a Kenwood with internal TNC
directly connected to the discriminator and modulator.  One has a flat
response and the other has the normal preemphasis and deemphasis.

So if one transmits tones that are inbalanced, then one system does better
than the other.  And in fact, with just a few dB of inbalance in the wrong
direction, no amount of RF power will correct that.  It simply will not
decode.

You can hear this on terrestrial packet frequencies.  Probably 80% of all
the signals on the air "work" but have terribly misconfigured tones.
People just hook'em'up and "it works" to the local digi, but they are not
aware that it might not work at all in weak signal realm where tone
settings must be ideal.

On my mobile, I see some signals that are dead full quieting with all
signal bars that do not decode, and then I see another kenwood with only 3
bars and noisy that does just fine.  Tone balance is exteremely critical.

Everyone should look at their tones on an oscope or at least listen to
their tones compared to a good known signal. (Factory TNC in a k enwood).
Though, when you listen to or look at "your " tones, the characteristics
of the audio in that receiver can also have a skew.

And, do NOT look at them one at a time.  That tells you nothing.  Since
the speech circuits will adjust them to the same level usually...  Look at
the relative amplitudes of the two.  You can fix them with the right
capacitor either in series to improve the high tone, or in parallel to
diminish the high tone.

But the right cap must perfectly match the impedance of your particular
set up.

Bob, WB4aPR

-----Original Message-----
From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Fernando Ramirez
Sent: Tuesday, February 12, 2019 9:43 PM
To: walterh at k5wh.net
Cc: AMSAT -BB <amsat-bb at amsat.org>
Subject: Re: [amsat-bb] ISS APRS Signal Quality?

I have tried two different radios, an Icom IC-2820h and a Kenwood TM-V71A.
No luck with the Icom at full power on a high elevation pass. Better luck
with the Kenwood but only on higher passes and transmitting with 50w.

Other operators have been able to get their packets digipeated with
Kenwood APRS-Ready HTs, so it's kind of puzzling.

I'm using a Mobilinkd TNC3. I have no problem hitting distant terrestrial
digipeaters with both setups.

73
Fernando, NP4JV

On Tue, Feb 12, 2019, 7:37 PM <walterh at k5wh.net> wrote:

> I definitely have to agree with you.
>
> The signal does seem to be less than half of what it used to be, and I
> have yet to hit it myself. When it used to be so easy.
>
> Not sure what has changed, but it's certainly not the same as it was
> before the shut down several weeks ago.
>
> Walter/K5WH
>
> -----Original Message-----
> From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Frank
> Karnauskas
> Sent: Tuesday, February 12, 2019 5:19 PM
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] ISS APRS Signal Quality?
>
> Is it me or does the APRS signal not sound as strong as it was before
> and is it not hearing quite as well?
>
> I am having a heck of a time pinging the digipeater and the signal
> seems to be down a bit.
>
> Could entirely be something on my end, but I would appreciate others'
> opinion.
>
> 73,
> Frank
>
> FRANK W. KARNAUSKAS, N1UW
> N1UW at GOKARNS.com
>
>
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_______________________________________________
Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available to
all interested persons worldwide without requiring membership. Opinions
expressed are solely those of the author, and do not reflect the official
views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb