Conversation
James Morris
jmorris
Testing a Ka band LNB, specified for 20.2-21.2 GHz. I could not see any signals beyond 22.8 GHz (well short of the 24 GHz amateur band), but that could be due to issues at the IF level. Worth investigating further. I was able to see a good signals at 22.2, an important radio astronomy frequency. #amateurradio #microwave #radioastronomy
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Test setup: 11.1 GHz output from a Kuhne freq synthesizer, into a small Log Periodic Dipole Array antenna. This signal will include a small amount of harmonics, and in this case, I'm utilizing the 22.2 GHz first harmonic (which I independently verified with the spectrum analyzer), which mixes with the LNB internal LO of 19.2 GHz, to produce a 3 GHz IF (22.2 - 19.2), which is displayed on the spectrum analyzer. I also verified operation by putting my finger over the waveguide input. This a pretty weak signal, given the additional losses from the PCB antenna, and all of the circuitry in the LNB and the Bias-T, which are out of range. It's working but at what cost?
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There's internal filtering in the LNB, both at the RF and IF levels, which will be limiting factors in how out of spec this can be operated at. It may be possible to adjust the internal LO upwards, and some of the filtering, but likely at some performance cost.
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