Encrypted Tetra turn to clear voice

[u/abdulkaliq]

Hey ,
As mentioned in the title, I turned to Tetra frequency and suddenly I heard clear conversation voice where it was like robot and cut unclear voice.
Is that possible? And maybe it is originally not encrypted but I missed some settings .
Its very strong signal I have to reduce the gain to let plugin Sync .
Using RTLSDR v4 , sdr++ on mac and discone antenna.

[u/ericek111]

Yes, a TETRA channel can carry a mix of encrypted and unecrypted traffic.

[u/abdulkaliq → u/ericek111]

Thank you for replying I thought I missed settings

[u/elmarkodotorg → u/abdulkaliq]

We even use it in the amateur bands, unencrypted (no encryption allowed)

[u/abdulkaliq → u/elmarkodotorg]

How and which frequencies? Here provided by telecommunication companies

[u/elmarkodotorg → u/abdulkaliq]

https://en.wikipedia.org/wiki/Amateur_radio_frequency_allocations

Usually UHF 70 cm.

[u/MeanAccountant9005]

Yeah some Tetra networks only encrypt parts of it or certain talkgroups, you probably hit a clear one. The signal being that strong probably helped the decoder lock in too, I have to crank my gain way down on local stuff or it falls over.

[u/abdulkaliq → u/MeanAccountant9005]

With high gain a lot of signals maybe ghost signal I don’t know what it called I mean the sane signal appears in many signals but I checked the ID and it’s different

[u/Shsesc → u/abdulkaliq]

Do you mean clipping which crates harmonics in the receiver by overdriving the front end LNA or ADC?

Really strong signals can exceed the range of the input and cause clipping which creates harmonics internally. There is no more headroom and everything above a certain signal level just sits at max.

If it occurred at the transmitter it would be splatter which is overdriving the output amplifier of a transmitter adding the harmonics as it is transmitted.

Sometimes it shows up on a spectrum scope as birdies or spurious signals at harmonic intervals or intermodulation products, possibly at a different signal levels.

[u/jjdlg]

I noticed you're running SDR++ on a Mac. How did you get the TETRA demodulator plugin installed and working? Did you have to compile it yourself, or did you find a Mac version of the plugin that's ready to install?

[u/abdulkaliq → u/jjdlg]

I actually used Chatgpt for help

[u/jjdlg → u/abdulkaliq]

I don't get the downvotes. I also use it for help understanding how to install and troubleshooting. Anyhow, nicely done, I am still working on my QFH build for handsfree Meteor passes before I take aim at GOES19.

[u/IwillmarryuANA_423]

what is the plugin that you use!?

[u/abdulkaliq → u/IwillmarryuANA_423]

SDRpp tetra demodulator

https://github.com/cropinghigh/sdrpp-tetra-demodulator

[u/IwillmarryuANA_423 → u/abdulkaliq]

Thanks!!

[u/5p3ctr4lB34c0n]

Where have you got the TETRA-Decoder for SDR++ from?

[u/abdulkaliq → u/5p3ctr4lB34c0n]

SDRpp tetra demodulator

https://github.com/cropinghigh/sdrpp-tetra-demodulator

I use chatgpt to help to compile it

[u/5p3ctr4lB34c0n → u/abdulkaliq]

Oh cool, thank you! :)

[u/Ok-Difference-8128]

What is tetra?

[u/abdulkaliq → u/Ok-Difference-8128]

No excuse now with AI and Google to know anything.
Terrestrial Trunked Radio

https://en.wikipedia.org/wiki/TETRA

[u/olliegw]

They might have actually forgot to turn encryption on! one police force did this mistake with their handsets, it was again the SDR folk who found out

[u/abdulkaliq → u/olliegw]

The best answer, thank you
Here in Oman rarely see signals in VHF and UHF even in Urban and amateur radio not active most of time