14 March 2019

Finally measuring the frequency of my HB-100's

Yesterday I wired up the LNB to a TV-spectrum analyzer to check that the preliminary setup would work. Besides an occasional short into the coax that trips the power-over-line circuitry, the LNB noise is visible. Then I fired up my HB-100 transmitter, that has been sitting in a box for months: its modulated signal peaked at 621.45 MHz on the screen.

So, if the LNB L.O. is at 9750 MHz, my TX is at 10371.45 MHz. That's well within HAM allocation.

Then I measured the HB-100 I had used as a receiver, which sat at 694.70 MHz = 10444.70 MHz. This confirms the delta of 73 MHz I observed in May 2017 when doing my first experiments.

Last I measured an apparently untouched HB-100, my third and last sample, and it could be received at 676.35 MHz, meaning 10.42635 GHz. Knowing me, I think I had left this spare radar module untouched, as a reference.

So, if the assumption of 9750 MHz LO is correct, all my HB-100 modules fall within the 3 cm HAM band (10.0-10.5 GHz), even if I was expecting a "brand new" one to be at 10.525 GHz. Hypothesis: I bought off eBay HB-100 modules that were rejected because they did not meet the spec on the operating frequency, and luckily were too low. Unfortunately I haven't found someone that published a measurement of their frequency.

I need a beacon of known frequency to confirm these relative measurements. Fortunately there is a beacon in L.O.S. from home and QO-100 satellite few degrees away. It will not give me accurate frequency values, but enough "ballpark precision" to allow a fellow HAM to quickly tune on my TX frequency and complete a QSO.