Old Sonar FR-105 tuning

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skip0157

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Does anyone know if it's possible to tune an old Sonar receiver by ear? Specifically I would like to tune the coils for a center frequency of about 154 MHz. without sending it to a radio shop.
 

pro92b

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It is difficult to tune by ear because using off the air signals does not allow you to control signal strength or duration. Signal strength variations common in off the air reception will also make tuning difficult. It would be best to use a signal generator and voltmeter to align the radio. The Sams Scanner databook SD-1 covers the FR-105 and includes alignment instructions. I can scan the relevant pages in SD-1 if you want them - it would take a day or so for me to do it.
 

skip0157

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Yes, please send it if you can. Also, I did notice that one of the coils is stiff. Do you know of any way to make it turn any easier? I don't want to ruin it because of it's age. Thanks!
 

RFI-EMI-GUY

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Yes, please send it if you can. Also, I did notice that one of the coils is stiff. Do you know of any way to make it turn any easier? I don't want to ruin it because of it's age. Thanks!
A common problem and one that will result in breakage. You might try some light penetrating oil. Just a tiny bit. Netting the crystals on channel and zeroing the discriminator are probably the only tuning required.

The original technique for tuning radios of that era was to use a dead carrier (CW) and quieting. If you get too far out of wack tuning the radio, the quieting will improve, but distortion will be excessive, The "new" tuning method uses 12 dB SINAD reference so that the modulation is properly aligned.

Parts do age and you might encounter difficulties. If you do, concentrate on power supply capacitors first.
 
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