RF DOWNCONVERTER TO RTL-SDR

[vselic]

Hello,

some base stations, like tetra, dmr etc. base stations work on microlink between one radio repeater to another - point to point links. If you get the exact point between those microlinks, you could probably catch the traffic going on.

those microwaves Works between 17-18GHz (i know the exact frequency and wideness of the spectrum).

Is there any (low budget) possibilities to buy or made downconverter to rtl-sdr from those frequencies and than somehow process the data, captured "on air".

Best regards

 

[Ubbe]

Those signals are multiplexed, a subcarrier for each signal, and all links have an option to use encryption. It's a rumour that you can use SSB in a receiver to filter out one of the subcarriers, but that was probably for analog voice.

If you look at standard LNB for a satellite dish you have one type for the Ka band 18GHz-22GHz that might be possible to use directly or to modify it to lower it's frequency. LNB's have downconverters down to 750MHz-2GHz.

/Ubbe

 

[boatbod]

I'm going to call BS on being able to use SSB to decode the links. These are digital data links, not simple voice.

 

[Ubbe]

Yes, those digital links usually use E1 protocol 2MB speed with 32 channels at 64Kb each. There are standard multplexers to split them up into seperate 64Kb audio streams, even as expansion cards for a PC, but could be expensive.

The signal that you catch from the radiolink must be feed into a multiplexer of the same type that are used in the link, and then use the output E1's to a E1 card in a PC and extract the proper channels. I've seen software for this.

One interesting thing, like for instance with Tetra and many other systems that use encryption, are that the encryption and decryption are done in the basestation and if the link have not been enabled with encryption then it will send unencrypted traffic.

There seems to be a good deal of E1 equipment at Ebay. You probably need to have full insight in microwave link technology and experiance with E1 and multiplexed signal to even begin to think about evesdropping on links.

/Ubbe