Re:Evaluation of SDR boards and toolchains [pdf]
by jhallenworld on Wednesday April 01, 2020 @11:29AM
(#22749666)
On SDRs that transmit, I'd like to see the how much harmonic suppression there is. For example, if you transmit at 144 MHz, what's going on at 432 MHz?
If they use switching mixers I would expect a lot of power in the harmonics. If they use analog multipliers, less. There has been work to make the front end mixer more multiplier-like using "harmonic rejection mixers". Apple bought one such company, I forgot which. The advantage is that you can reduce the analog filtering needed.
I think it should be the same for receivers: I assume they pick up a lot of noise from the harmonics.
Re:Evaluation of SDR boards and toolchains [pdf]
by madengr on Wednesday April 01, 2020 @12:22PM
(#22750427)
Yep. The killer for the AD9364 is the 5th harmonic of the 2m amateur band falling on this nation-wide (USA) LTE signal. That damn LTE seems to be everywhere, and it’s strong.
If they use switching mixers I would expect a lot of power in the harmonics. If they use analog multipliers, less. There has been work to make the front end mixer more multiplier-like using "harmonic rejection mixers". Apple bought one such company, I forgot which. The advantage is that you can reduce the analog filtering needed.
I think it should be the same for receivers: I assume they pick up a lot of noise from the harmonics.