DME client visualisation

ADS-B, ACARS, VOR, ILS, Airband AM
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keukenrol
Posts: 5
Joined: Sat Apr 08, 2023 7:50 pm

DME client visualisation

Post by keukenrol »

Hi

I was wondering if it would be possible to visualise DME pulse trains from air to ground stations? Based on the following website this would mean a single interrogation pulse (bit) takes only 3.5 microseconds. https://www.studyaircrafts.com/dme

With a sample rate of 2.4MSPs this would give us approximately 8.4 samples for a single pulse.
I am currently doing some research on this topic and would like to know if someone with basic programming experience in c and python would be able to develop their own plugin for sdrangel? This is a reception only topic!

Long story short, DME frequencies can be found online and the ground and air stations are 63MHz apart. To allow multiple aircraft to send to the same station, every aircraft has its own pulse train on which the ground station replies by repeating it. I would then map the amount of "connected clients" on a given beacon, possible also trying to determine their pulse train.

Thanks!
srcejon
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Re: DME client visualisation

Post by srcejon »

To visualise the pulses, you can use the scope within the channel analyzer plugin (set scope to show magnitude).
keukenrol
Posts: 5
Joined: Sat Apr 08, 2023 7:50 pm

Re: DME client visualisation

Post by keukenrol »

The pulses are of such short durations that it seems no pulses are there. I am relatively close to a ground station but I am unable to see pulses from both aircraft and ground station on their frequencies respectively.
srcejon
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Location: London
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Re: DME client visualisation

Post by srcejon »

Post a screenshot or IQ file, maybe?
keukenrol
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Joined: Sat Apr 08, 2023 7:50 pm

Re: DME client visualisation

Post by keukenrol »

I have been trying a few different settings, in the end I went for a wideband scanner antenna and the max gain of the SDR (49.6dB) in order to be able to see them. The the pulses seem to be shifted in frequency too, which might be due to reflections.
The next step would be to identify unique sets of pulse trains and map them.
Each green blob is in fact a pulse train, but it is happening so fast that it seems like a single pulse.
Attachments
dme.PNG
dme.PNG (265.18 KiB) Viewed 88 times
srcejon
Posts: 177
Joined: Thu Jan 19, 2023 2:30 pm
Location: London
Contact:

Re: DME client visualisation

Post by srcejon »

Use the Channel Analyzer to view the signal power vs time in the scope.
keukenrol
Posts: 5
Joined: Sat Apr 08, 2023 7:50 pm

Re: DME client visualisation

Post by keukenrol »

Allright, starting to get there. I will look for the documentation to get one shot triggers working and zoom in on a specific pulse.
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dmechan.png
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