[amsat-bb] Re: doppler tuning problem

[Erich Eichmann]

Hi Tim,
you wrote:
>I tune around the passband until I can
> hear a station clearly. When there's a break, I transmit my call. The
> other
> station will hear me, but by the time the reply comes, I can no longer
> hear
> them clearly.

When the other station answers and you don't hear his signal clearly don't
tune the radio with the VFO but use the "Downl.-Corr." controls in menu
"CAT" to correct your RX frequency until you hear the signal clearly again.
That will leave your uplink frequency unchanged.  You also may use the keys
2/8 and 3/9 of the numerical block of the keyboard to correct your downlink
frequency in steps of  +/- 10 or +/- 100 Hz.  I added these controls to menu
CAT particularly for the use with semi duplex radios (to fix the problem
that you can't correct your uplink frequency because you can't hear your own
signal).

The reason of your problem will be the following:
When you first answer the other station you will probably not transmit on
the exact uplink frequency - that means on the frequency on which the other
station is listening (and on which - with a satellite radio - he will hear
his own downlink signal). So, he will tune his radio until he hears your
signal with the right audio.  If he works with full Doppler  correction
changing  the downlink will also change his uplink frequency. So, you will
no longer hear his signal clearly.

The frequency values in Doppler.SQF that come with SatPC32 can't be exactly
precise for all radios, due to - i.e.- hardware depending deviations between
the radios up to a few KHz. Therefore these values should first be
calibrated (typically only once) for the particular radio. That can easily
be done if you can receive your own signal. With semi duplex radios it can
be done with the help of another station. For detailed hints regarding this
issue with semi duplex radios read the "Hints[CAT]" for "Yaesu users" sect.
IV. 3. f and g. You can open the file from the SatPC32 menu "?".

73s, Erich, DK1TB


----- Original Message ----- 
From: "Tim Goodrich" <tim at timgoodrich.net>
To: <amsat-bb at amsat.org>
Sent: Wednesday, January 07, 2009 7:21 AM
Subject: [amsat-bb] doppler tuning problem


> Hi all,
>
> Now that I finally have SatPC32 working with my 817, I'm having a new
> issue
> with Doppler tuning on the SSB birds. I tune around the passband until I
> can
> hear a station clearly. When there's a break, I transmit my call. The
> other
> station will hear me, but by the time the reply comes, I can no longer
> hear
> them clearly. It's almost as if the automatic Doppler tuning either can't
> keep up with or goes too fast to stay locked onto the correct frequency. I
> know its not the other station's frequency adjustment because this happens
> when there's a QSL already happening and they seem to be Doppler shifting
> at
> the same rate.
>
>
>
> Any suggestions?
>
>
>
> Thank you,
>
>
>
> Tim
>
> KC2DDS/AG
>
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