Radio Scanner

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mossman

Joined Aug 26, 2010
131
Can someone explain in very general terms how a wideband superhet radio scanner operates? We're talking about an older scanner (80's), which uses discrete circuity, etc. (no microprocessor) to quickly detect signals and also calculates and displays the frequency on a digital display. My main question is not how the signal is detected necessarily (single conversion to 2 MHz IF), but rather how the scanner knows which frequency it is receiving (i.e., so it can display the frequency on the LCD).
 

nsaspook

Joined Aug 27, 2009
13,086
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Kermit2

Joined Feb 5, 2010
4,162
The radio MUST have a local oscillator for the mixer circuit, so that local oscillator must always remain above or below the received freq by the amount of the IF, in this case, 2 MHZ. What ever freq your local oscillator is feeding the mixer will determine what freq you are recieving.
 

nsaspook

Joined Aug 27, 2009
13,086
The radio MUST have a local oscillator for the mixer circuit, so that local oscillator must always remain above or below the received freq by the amount of the IF, in this case, 2 MHZ. What ever freq your local oscillator is feeding the mixer will determine what freq you are recieving.
In this model the readout was the 'frontend/PLL divider code' needed to generate that local osc frequency (10.7mhz/455khz IFs) not the actual frequency.
 
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