[amsat-bb] FoxTelemetry on AO-91 and AO-92

Stephen E. Belter seb at wintek.com
Tue Oct 2 14:46:38 UTC 2018


Hasan,

The answer to your question about the difficulty is yes, and no.  

There are lots of things that can block the decoding of the DUV.  Get any *one* of them wrong, and it doesn't work.  Get them *all* right, it works great.

I am not an expert, but here are a few suggestions.

You need a solid, full-quieting signal to decode the packets.  Mark is right; this is much more difficult with an omnidirectional antenna like an eggbeater.  With 80-feet of coax, you probably need a low-noise preamp at the antenna (not in the shack).  When you make a voice QSO, is the signal really full-quieting?

The DUV information is very, very low frequency.  You need to be receiving everything from DC to 300 hertz, and passing it to FoxTelem.  Typical FM receivers (conventional analog and software defined) filter out the low frequencies so as to not include CTCSS tones which add an annoying rumble or hum to the audio.  So carefully check and adjust or remove any low-frequency filtering.  

Using a patch cord to connect the speaker output to a sound card input is unlikely to work.  You need to be using a virtual audio cable (software utility that simulates two sound cards connected by a patch cord).  Paul is correct, check the sample rates on the SDRC output, the input and output of your VAC, and the input to FoxTelem.  They should all be identical.

Check the levels to make sure nothing is clipping or overloaded:  Windows levels between the HF+ and SDRC, SDRC output, and VAC input and output.  I'm using a FUNcube Pro+ dongle and have the Windows level on the FCD set to 9 instead of the default 100.  The best level for your HF+ may be different.

I'm sorry you're having trouble.  Maybe these hints and the suggestions of others will help.

73, Steve N9IP
--
Steve Belter, seb at wintek.com



On 10/2/18, 7:56 AM, "AMSAT-BB on behalf of Hasan al-Basri" <amsat-bb-bounces at amsat.org on behalf of hbasri.schiers6 at gmail.com> wrote:

    Several of us are having a heck of a time getting any telemetry from the
    above birds. DUV just isn't producing anything.
    
    We hear both well enough to make QSOs on the FM transponders, but we can't
    seem to get any data thru the decoder.
    
    Is it really that much more difficult to get the TLM via DUV  than to
    listen to a voice on the 2m downlink?
    
    Setup:
    2m Eggbeater at 7', fed with 80' of 9913
    AirSpy HF+ SDR
    SDRC V3 Software
    FMN 12 kHz (Highpass Filter not checked) and FMW both tried, neither
    produce any decoded data.
    
    I am getting telemetry just fine from AO-73, and am also getting perfect Wx
    pix on 137.100 with SNR's of > 30 dB.
    
    Am I doing something wrong, or is it just that hard to get FoxTelem to work
    with DUV?
    
    Thanks for any help. 73,
    N0AN
    Hasan
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