[sarex] FM Deviation

["Alderman, James" <aldermaja@xxxxxxxxxxxxxxxxxxx>]

Greetings Fellow Amateurs and Space Enthusiasts,  

>From my office here in Dallas, I was able to easily copy the ISS contact
with the school in Houston this past Tuesday.  It was about 3/4 scale signal
strength for most of the contact, then abruptly dropped to nothing as the
station dropped below the horizon.  I have copied the signal from the
station several times on my talkie.  

However, there is one thing I've noticed every time.  It seems like the
deviation of the FM voice signal is rather low.  So far I have not set up to
measure it on my communications service monitor during a contact, so I can't
tell you exactly how low it really is.  I do want to measure this sometime.


My observation is that I must always turn the radio volume all the way up in
order to hear the ISS well, while I can normally hear local stations clearly
with the radio volume turned about half way up.  

Perhaps the deviation is intentionally set low to keep the signal
narrow-banded, thereby concentrating a maximum amount of RF power on the
operating frequency.  This would perhaps allow the ISS station to
communicate during weak signal conditions when it otherwise might not be
able to.  

However, since the ISS must be overhead if you are to hear it, and since
it's not really that high up (230-240 miles), it would seem that under those
conditions we either have AOS or we don't.  I doubt if 2kc vs. 5kc of
deviation would make any difference.  

I'd be interested to hear whether others have noticed this apparent low FM
deviation situation.  Does anybody know why this radio was set to such a low
deviation?  I know that the MPA radio's deviation is adjusted with software.

73, James Alderman, KF5WT
Dallas, TX

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