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Re: FM Deviation

It IS low, in my opinion.


At 01:04 PM 9/6/01 , Alderman, James wrote:
>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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