21 April 2017

HB100 10 GHz module frequency agility

Before I can get my hands on two Sat-TV LNB's and work on a 10 GHz WFM transceiver, I wanted to measure the frequency agility of a stock HB100 radar module.

The plan was to use one module as a fixed receiver on the factory preset (presumably 10.525 GHz) and tune a second module. Remember that HB100 is both a TX and a RX at the same time, and it emits a continous carrier. If the two TX frequencies differ, their difference will be visible at the ultra-broadband (unfiltered) I.F. output.

At first I connected the IF output of a receiver module to the frequency counter (100 MHz), and I could read up to 10 MHz delta.

Then I routed the IF output to the oscilloscope (100 MHz bandwidth, 10 MHz probe) and, as long as the signal was above 1 mVpk the sine wave period indicated a signal of about 20 MHz.

Time to turn on the spectrum analyzer, that starts at 45 MHz. Bingo! The maximum delta I could get between an untouched HB100 (let's assume 10.525 GHz) and a fully unscrewed tuning harness was 232 MHz, so it was operating roughly on 10.293 GHz.

Also, the closer the tuning screw is to the DRO, the higher the frequency. Screw in to go up in frequency, unscrew to decrease frequency.

Last but not least, I confirm that the receiving mixer works better if it is terminated on some medium impedance. I will try to visualize the signal on the oscilloscope in parallel to the S.A.