Digitally-Controlled RF Input Preselector

Hi Folks!

Anyway, before I spend the time and money to build one, I thought I will ask:

Here's a scenario: I need the ability to notch out or allow only certain narrowband frequencies (or a range/windowable FFT of 25KHz per channel, 800MHz SMR/LMR band) to pass through before the input of an ADC direct conversion IC.

I was wondering if there's a commercially available digitally-controlled RF input preselector (or any combination of downconverters, filters, frequency translators, etc.) with 12.5KHz resolution or better out there to perform this task well via USB/Seria or Ethernet connection. Basically, I want to eliminate any Adjacent Channel Interference that can confuse the demodulator in the ADC.

Thanks all in advance!

NMD

You could try a tunable filter, maybe with MEMS of barium strontium titanate substrate.

You could have a downconvert, narrowband fixed filter, and then up convert, using a tunable LO.

Hi biff44,

Thank you for your recommendation. Basically, I think I have to build something similar to SCR Preselector but with better narrowband selectivity:

Theoretically, this should work:

(bad signal + interference) ---> ADC I/Q--> FFT in DSP/FPGA -> LPF/Window/Resampler -> I/Q DAC -> Upconvert+LO (Freq synth/xlator) ---> (good signal w/o interference)

Definitely going to look into the MEMS RF Tunable Filters solution also. We shall see --Dang, digital RF is very touchy! :)

Sincerely,

NMD