regarding FM radiodesign

[audioguru]

Analog TV transmissions stop in a couple of months in the United States.
They stop in Canada in a couple of years.

Luckily the cable TV companies will convert the new digital transmissions to analog for old TVs. The few people with antennas can buy a digital to analog converter for their old TVs.

My son and my daughter have high definition TVs. They both have satellite receivers.

 

[Roff]

NTSC (No Two Similar Colours)

Similar colors are not a problem. The correct phrase is Never Twice the Same Color.

 

[audioguru]

Remember when North American TVs had a "flesh-colour" correction circuit?
Apples and bananas were orange like over-saturated flesh colour.
Grass was blue like the sky.

 

[Roff]

Remember when North American TVs had a "flesh-colour" correction circuit?
Apples and bananas were orange like over-saturated flesh colour.
Grass was blue like the sky.

**broken link removed**
No, grass was blue like the Boise State football "turf".

 

[theveekon]

Yes, that would be OK. Design a bandpass filter for 90 to 100MHz. Often, we integrate such filters into our amplifiers, by putting one at the input and another one as the output load of the transistor. This makes a Tuned RF Amplifier.

Don't make your filter too complicated. It would be fine if you could attenuate the signals outside your band by 30 dB or maybe 40 dB, and in this case, you might consider using a 4 pole configuration. Such a filter would typically include two inductors and two capacitors. This is as complicated as you want to get for your filter, anything bigger is just too much. Simpler is OK of course. One efficient approach would be to have a single LC (two pole) tank circuit at the input of your RF amp and another LC at the output. You can tune the center frequency of each of these parallel resonant circuits at slightly different frequencies so as to get a flat response from 90 to 100MHz. Try googling on Tuned RF Amplifier for some typical schematics.

well thank you RadioRon it cleared my doubts. i have attached two schematics one is active bandpass filter using opamp and the other one is second order butterworth BPF. I dont know how to choose the characteristic impedance for the filters and also not clear about the part played by the characteristic impedance. I know it takes care of the matching but i am interested in understanding little deeper. Can anybody help me in choosing appropriate circuit and clear my doubts.

 

[Mikebits]

At 90 to 100MHz you will have to forgo an active filter and go with a passive RC design, or tuned amp as Ron suggested. Unless opamps have changed lately(Which may have happened), I don't think they are the best for RF. Poor Bandwidth, Noise Figure, and intermodulation distortion to name a few.