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Re: working ISS, Noise and Doppler



Noise floor:

On FM satellites your signal needs to be approximately
10 db stronger than the noise floor.
If the noise at ISS or other FM sats, is S4, then your
signal needs to be S6+
If there are NO other stations calling ISS, then the
noise floor will be LOW.  When 20 stations are calling
ISS, then the noise floor is High.  The same is true
for other FM satellites.

Try working packet first to learn how to get access
during times 
when there are Fewer users.

When ISS is on Voice and calls QRZ on a Saturday
Afternoon Local time, you can expect a VERY high Noise
floor.  Week day and Off hour contacts with ISS will
have lower noise floors.

I talked to the crew on 1.75 watts ERP with a HT once.
But I did it when the channel was 100% clear, during
an off hour. And when ISS was only 400 kilometers
away.  It was a 1 in a million chance.
I do not recomend HT contacts, because they will only
work in very
very very very very very very rare occasions.  Normlay
i use a very big antenna.


Doppler:
Adjusting for doppler for 2-meter FM satellites will
help.
But.. if the FM down link on 2-meters is S4 or better,
then
there is not much need to compensate, because the FM
circuit
will already be capturing the reciever.  Doppler
adjustments
help the best when the FM signal is lower than S4.
So the weaker the FM signel, the more Doppler
corrections help.
Normlaly on FM you only need to get within 1 or 2K.

I tested FM Slow Scan TV from the Mir Space Station.
We found that an S3 signal, with 2.5k doppler decoded
great
without compensateing for FM doppler.



--- Francesco Messineo <iz5dwf@AMSAT.ORG> wrote:

> Hello,
> 
> On Tue, Jan 10, 2006 at 06:16:29AM -0800, MM wrote:
> > 
> > Hi Francesco:
> > 
> > If ISS is on 2meter mono band, then doppler is
> only
> > 3.3k max.
> > Doppler adjustment on 2meter FM is optional.
> 
> well, I have monitored several times the downlink
> and I feel that some
> adjustment is necessary on the frequency, at least
> on my radio. 
> I've never been able to get heard, I don't know if
> it's a QRM problem 
> (too many stations uplinking and/or too much power
> used) or a frequency
> problem on my side. I know that if I were the only
> station uplinking
> probably I could forget to adjust my TX frequency.
> 
> > 
> > If ISS is on the 440 band, then will need to
> adjust
> > for doppler.
> 
> sure, but in that case it's a U/V transponder, so I
> could hear
> myself on the downlink, as any other LEO, right?
> 
> Thanks for hints & links 
> 
> 73 de IS0FKQ
Just $16.99/mo. or less. 
dsl.yahoo.com 
----
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