Author Topic: AM RF rejection - how to help needed  (Read 523 times)

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Offline AllTheGearNoIdeaTopic starter

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AM RF rejection - how to help needed
« on: April 05, 2020, 12:27:08 pm »
Although my main interest is collecting and repairing test equipment I do on occasions dabble in radio repair. I would like to do some before and after testing and see how a particular radio compares to the manufacturer’s specifications. If you cannot measure it how do you know you have made an improvement etc.

  I’m today playing with a fairly typical domestic receiver of the 60s and 70s and need some practical advice on how to test the AM rejection against manufacturer’s specifications sheet.

The radio specifications quotes”  40db  {Signal to noise ratio greater than 50db}

My IF is 470khz.

Having tuned in the radio to the signal generator do I then increase the frequency off generator by  2 x IF  and make measurement with the modulation on and off to get the signal to noise ratio.

Where do I make the measurement I am guessing it could be at the output of either the IF stage or speaker dummy load. I should keep the signal level very low to avoid activating the ALC ?


Is the 40db part of the specifications telling me the amplitude of the image Frequency should be 40db down on the level at the frequency the radio is tuned too.


I have never done this before so just need some help with the basic setup and getting the procedure correct. I do have basic test gear including RF test sets.

Thanks regards Chris




« Last Edit: April 05, 2020, 12:53:03 pm by AllTheGearNoIdea »
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Offline iMo

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