Sunday, December 10, 2017

Block diagram of the receiver

This is one possible layout. It has only one variable, that's the VFO. By using a band selector filter we get image rejection. The band select consist of a high pass or low pass filter. The second mixer/detector uses the same frequency Xtal as the filter. 

I have seen a set that used a NE602/612 for the second mixer/detector.

The tuning response will be determined by the VFO so a bandset and bandspread would be a good thing.

 This is a simplified diagram so it would be good only to understand the frequency conversions. I left the AF amp out and we may need an RF amp and an IF amp.

Now it is time to determine the receiver tuning range and the VFO frequency. Building a stable VFO will be the main project. 

How broad a tuning range do we want for the VFO?
How many bands?

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