[ao16aprs] More AO16 lessons?

[Jim White <jim@coloradosatellite.com>]

>2) I went to 145.91 and got MUCH BETTER results... almost 100% compared to
>my previous 10% yuky success on 90.  THen at the end of the pass, I
>thought I would try 145.915 and by golly, it still worked and, get this, I
>was seeing DOUBLE digipeats.  This tells me that I was getting into both
>the "145.90" and "145.92" receivers at the same time.  (does anyone have
>any other explaination?)  If this is so, then the 145.90 is actually at
>145.91 and the 145.92 would have to be quite low...
You were undoubtedly getting into both at once.  The receivers have about a
10 KHz bandwidth to reduce or eliminate the need to tune the uplink for
Doppler.  If you sit between them you will often get into two at once,
especially if you are a bit wide on deviation.  We have software in the 2nd
stage loader to check for this and kill one of the packets, which prevents
some problems when loading software.  But we found it useful to not include
that in the operational house keeping task so we could perform just the
experiment you are doing.  Even when the birds were very new in orbit it
was possible to get into any two receivers by sitting on just the right
frequency.  You will still see this happen today with stations using the
Packsat Broadcast Protocol.  Watch the downlink for "OK W0XX" twice in a
row.  Take care in drawing conclusions from a single pass worth of data.
Remember the uncontrolled and un-characterizable (is that a word?) uplink
interference situation.  There could be a signal on the low side of the
passband you can't compete with.  You move a bit higher and all of a sudden
things improve dramatically.  That does not necessarily prove the receiver
center frequency is off.
On a commercial UoSat we found a continuos carrier from Canada right smack
on one of the uplink freqs.  To get around it we observe where it falls in
the receiver passband given Doppler from it to the bird, and we go to the
other side and get in.  The difference is like flipping a switch.

Getting into two at once is yet another reason to keep your deviation low.

jw
jim@coloradosatellite.com


>
>I invite others to confirm or debunk these crazy results.   THe good
>news is that I am finally getting in successfully and reliably... on
>145.91.  (Then again, my HP SIg Gen could be out of cal?)
>
>The bad news is that I have found LUSAT is best on 145.895, so if that is
>true, then the great advantage of these birds all being on "145.900" is
>slowly flying out the window...
>
>SOrry for all the drivel here, but there is a lot to learn (or relearn)
>
>bob, WB4APR
>
>
>
>

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