Observation 155385: FOX-1B (43017)

Regarding Observation 155385
There’s a bit of somewhat noisy audio (QSOs) here that are worth listening to. I was not able to recover any telemetry data though.

1 Like

Saw this already on my station and started to discuss this sound (formerly known as “didupp” :D) with @fredy.

See observation in the link below:

1 Like

Also I have found to listen to Fox voice audio a filter to remove the DUV nosie works nicely from audacity

I’ve encountered something similar to DUV about 25 years ago…

I worked in the Trunking Radio industry before cellphones existed. The product I worked on was EF Johnson LTR compatible. The (wide-band FM) trunked radio repeaters would send its trunking information in sub-audible format and the radios would filter-out the sub-audible tones for the user and listen to the sub-audible trunking channel for trunking information. When the mobile (elliptical) high-pass filter was not adjusted right, there would be a “bo-bo” noise. When the low-pass data filter was not adjusted right, the result were trunking failures.

With these Fox-series satellites, the sub-audible information is the telemetry, but the issues remain the same.

The low-pass filter for the telemetry needs to be set correctly for the telemetry to decode properly. While running the FoxTelem decoder, I was noticing that the “eye” was not opening up correctly due to dropouts or an incorrect filter. The SNR was good enough, FoxTelem should be decoding on an SNR of ~4 or better. I’m going to run the .wav files through Audacity or Sonic Visualizer later this evening and take a look at what I find. Something is not right.

I’ve definitely seen this before in another life.
–Konrad, WA4OSH

Yes, you only need to add a high-pass filter with f_gmin of 400 Hz :wink:

1 Like

The decoder indeed needs some improvements, but there is no filter in front of the decoder. The Audio file also contains all information - this is done by intention (to run things like FoxTelem etc). If you would filter the data (that is located below 400 Hz), you won’t be able to decode it from the audio file. You can clearly hear that “machine-like” sound if you wear headphones - best heard with the telemetry beacon only. Frame type “2” starts when the beacon voice starts to tell you which satellite it is :slight_smile:

1 Like

Sorry, sure there is one, but: it’s wide enough and is a low-pass filter :slight_smile:

1 Like

I know that the ogg Vorbis encoding is not lossless. So are we perhaps losing fidelity on the low end? Eg. what happens when you have a long string of zeroes or ones on your sub-carrier, does the algorithm adequately reproduce sub-audible? … Just a thought.


Is there a reference that tells you what happens on the channel? This is actually quite interesting.


There are rather precise informations about DUV in the “FoxTelem Manual” from AMSAT at
the page 18 (section Data under voice). If this is what you are looking at.


1 Like

For the FOX guys it is interesting to d/l the ogg audio, sox convert to wav and load it into the FoxTelem java app - populates tabs for the various ones with data.

@cswiger … just like we documented in the Wiki? :smiley:



YES! Exactly like that - was wondering what to do with the data blocks then got excited to independently discover FoxTelem at amsat :blush:

This is a really cool system you guys have here - where you can schedule and check on your space observations on a phone while standing in line at the grocery store.


Thanks for your suggestion, but I was literally a week ahead of you in asking the same questions. I researched it and with the help of the community created that whole Decode Telemetry and Packets section.

If you find other cute ways to demodulate and decode telemetry and packets, (or anything else) let me know, I’ll be happy to document them in the Wiki. I love editing for simplicity and understanding.

Feel free to explore from the main page and drill-down into the various details of the documentation. If you find something that’s interesting or needs attention, let me know I will seek to improve the docs for everyone – beginners to experts.