[amsat-bb] ISS Packet Frequency?

Graham planophore at aei.ca
Tue Apr 25 00:33:00 UTC 2017


I had a look at the two noted images. The first thing that I noticed was 
that the mode was set in both cases to wide band FM not narrow band FM. 
If you are trying to copy ISS packet using WBFM that might be the source 
of your problem. It could be that the new radio on the ISS has a 
somewhat lower deviation than the old radio.  The second image 
(Spectravue) does indicate that your receive might be a bit high in 

If you are not using your SDR to try and copy the ISS then perhaps you 
should state what equipment you are in fact using; I may have missed it 
from an earlier post.
I have been having good luck copying the ISS using my FT-817. Sometimes 
I use a dual band VHF/UHF collinear vertical and sometimes a small yagi, 
the yagi works better but the vertical still works OK too. I don't 
adjust for doppler, I just set the FT-817 to 145.825. Doppler on 145.825 
for a typical pass is about +/- 3.5 kHz at least according to GPredict.

cheers, Graham ve3gtc

On 2017-04-24 22:20, Scott wrote:
> 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
> news!
> 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
> band.
> https://www.dropbox.com/s/w1dll06xwinteap/NOAA-Wx-Radio-on-freq.png?raw=1
> ... 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:
> https://www.dropbox.com/s/s46o3pi87yk9t2h/spec-view.png?raw=1
> ... 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!
> 73!
> -Scott,  K4KDR
> Montpelier, VA  USA

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