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Author Topic: Frequency Display For Surplus Receiver  (Read 3173 times)
A203
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« on: September 21, 2002, 07:17:09 PM »

Picked up an older military surplus VHF/UHF surveillance receiver.  It has a BNC connector for a 5-10 MHZ signal spectrum-display unit.  Is there any liklihood that a standard frequency counter connected to this output would read tuned frequency?  If not, any suggestion for where a counter could be connected to obtain a reading?
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KG4RUL
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« Reply #1 on: September 22, 2002, 07:21:01 AM »

The output that you are referring to is like a slice of spectrum.  It will always show you 5-10MHz window of the currently tuned frequency range and not the actual frequency.

Dennis - KG4RUL
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WB2WIK
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« Reply #2 on: September 23, 2002, 12:48:52 PM »

Depends on receiver design.  If you have the schematic and can figure it out, it's likely that there's a tunable oscillator (VFO) which relates to the received frequency by some offset (the receiver IF), and that oscillator's frequency could be read by loosely coupling to it and then adding and adjustment factor for the IF.

For an easy example: If the receiver is single-conversion and had an IF of 10.7 MHz, and covers VHF, then the tunable oscillator for the receiver mixer would tune the VHF band(s) 10.7 MHz offset (likely above) the actual receive frequency.  Thus, if the tunable (VFO) oscillator frequency was 150.00 MHz, the actual receive frequency would be (150.00 - 10.700) = 139.300 MHz.  Of course, the actual receive frequency could also be 10.7 MHz above the VFO output, in which case the receive frequency would be 160.700 MHz in this example.

But you'd need at least a block diagram indicating the receiver's conversion scheme...

WB2WIK/6
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