[amsat-bb] ISS Packet Frequency?

Scott scott23192 at gmail.com
Mon Apr 24 22:20:02 UTC 2017

Hi everybody.

This is essentially a request for what I believe the scientific folks call
"peer review"...

I continue to try to understand why none of my equipment has been receiving
the ISS digipeater very well since the switch back to 2 meters, despite the
fact that the same hardware does well on terrestrial packet and in the case
of 145.825 in particular, I have even received packets from PSAT since
re-configuring for VHF reception on my Raspberry Pi / RTL-SDR iGate.  So,
my point is that it isn't that NOTHING is working on 2-meter packet or
145.825 here.  And as I've mentioned in the past, I hear from others with
similar stories so we're not sharing hardware or location.

This evening there was a favorable pass here and I see on ariss.net that
several stations were digipeated while the ISS was over the U.S.  Great

I monitored that pass in receive-only mode with the same type of TXCO
version-3 RTL-SDR that I use for my iGate.  The results were very strange
and I hope incorrect.  I certainly would appreciate it if someone might
repeat my test when time permits.

Here is an image showing my SDR tuned to the local NOAA Weather Radio on
162.475.  By all appearances, my frequency display is accurate in the VHF


... without changing any settings other than frequency, the following image
shows a Spectra-Vue plot of my reception of the packet transmissions from
the ISS on this evening's pass:


... I took a ballpark stab at the center point of closest approach and
unless I did something awfully wrong, it's roughly 5 KHz above the expected
145.825 frequency.  If by any chance this is accurate, it explains why I've
been seeing poor reception here.

(On the other hand, if my observations are completely wrong and flawed,
this makes just over 1000 times that I've looked foolish!)

Anyway, if anyone is setup to make similar observations, I would imagine
that we would all like to know if there is a frequency issue up there.  If
not, then of course I'm sorry to tie up the mailing list!


-Scott,  K4KDR
Montpelier, VA  USA

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