My interest is in the area of microwave radiometry. Most recently I constructed a 1.4 GHz radiometer but found I need to use a filter with no larger than a 27 MHz bandwidth to operate in the FCC protected region. So far I was able to only acquire a filter with a 100 MHz bandwidth centered at 1.4 GHz. This is however found to be insufficient to remove all interference. Does anyone know when I might be able to obtain a narrower bandwidth filter?

I was able to cascade two high gain amplifiers, one with a gain of 20 with a noise figure of 0.5 db and the 2nd stage with a gain of 55 and a noise figure of 5 db. Both amplifiers were obtained from EBay for less than $30. The problem I had regarding stability and oscillations were removed using a 3 dB attenuator between them. However, I found a problem after connecting a dual-Schottky diode envelope detector ( obtained also from EBay) to the 2nd stage amplifier. Unfortunately, output from the higher gain amplifier produced oscillations again. Fortunately, however, this problem was resolved after using a tunnel diode detector. I wish I knew why the use of the 3 dB attenuator and tunnel diode approach worked.

I was able to cascade two high gain amplifiers, one with a gain of 20 with a noise figure of 0.5 db and the 2nd stage with a gain of 55 and a noise figure of 5 db. Both amplifiers were obtained from EBay for less than $30. The problem I had regarding stability and oscillations were removed using a 3 dB attenuator between them. However, I found a problem after connecting a dual-Schottky diode envelope detector ( obtained also from EBay) to the 2nd stage amplifier. Unfortunately, output from the higher gain amplifier produced oscillations again. Fortunately, however, this problem was resolved after using a tunnel diode detector.

Thanks, I agree with you. I was just hoping to avoid the need for digital processing in the time domain.

I am interested in such high frequency components. The 50 to 60 GHz frequency range is used in constructing microwave radiometers to profile atmospheric temperature. These front end components can be used as a start in constructing such radiometers.