The 0 to 40 GHz SDR: Micro-Tel 1295+R820T USB RTL SDR

Having repaired two Micro-Tel 1295 microwave receivers recently, I noticed a IF (intermediate frequency) test port – this as a sample of the 30 MHz IF signal, from fundamental mixing of the input with the LO, for 0-18 GHz. Using 2nd and 3rd harmonics, and external mixers, the full range up to 40 GHz can be covered.

micro-tel 1295 if port

The 1295, despite its sensitivity, is actually not build for reception of real-world signal – it is an IF subsititution attentuation measurement receiver. However, this doesn’t mean it can’t be use to receive GHz signals… Recently I have been working on a 2-20 GHz digitally controlled preselector, and adding this to the 1295 will already help to get pretty much excellent selectivity.

0-40 GHz rtl-sdr using a Micro-Tel 1295

Now, a quick test: the IF test port, which is normally terminated in 50 Ohms, needs to be connected to the RTL USB SDR. To avoid overload of the RTL SDR by mirror signals, a little Micro-Circuit PBP-30+ filter was added, the silvery can, on the ESD foam, on top of the receiver.

pbp-30+ elliptical bandpass filter

This filter has a 6 MHz passband, 10 MHz 3 dB bandwidth – plenty for the USB SDR. Using a test signal at 11.02 GHz, with neither the receiver nor the source phase-locked, this is the result:

sdr at 11.02 GHz

Divisions are 100 kHz, so there is a bit of drift. But keep in mind: 0.1 MHz for 10000 MHz, that’s just about 10 ppm! – and a PLL will be added to the 1295 anyway.

After all, maybe a good idea to build a little 2-20 GHz downconverter, using a YIG pre-selector (currenty being developed anyway), a mixer and a LO (possibly using harmonic mixing). Stay tuned!

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