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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 12th Jun 2022, 3:24 pm   #1
Cruisin Marine
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Default Use another receiver to check LO is running

Working on three radio's this week, all had various faults, when I wanted to check LO's were going, and I could not find my old diode probe!

Instead, for a quick quick check I just used another receiver close by and tune it offset by 455, 465, 470 kHz or 10.7 MHz away depending upon what your RX IF is, remember some LO's are High of the desired receive freq. and some may be low.
It is an amazingly QUICK way to see if the LO is oscillating.

Last edited by Radio Wrangler; 12th Jun 2022 at 7:23 pm. Reason: I sometimes spell that one wrong too.
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Old 12th Jun 2022, 3:28 pm   #2
Aub
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Default Re: Use another reciever to check LO is running

Yes it works. I've used that method to resolve SSB when there's no BFO.

Cheers

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Old 12th Jun 2022, 7:20 pm   #3
Cruisin Marine
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Default Re: Use another reciever to check LO is running

I mis spelt RECEIVER, "I before E except after C" apart from exceptions, what a crazy and wonderful language we have
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Old 13th Jun 2022, 1:48 am   #4
Graham G3ZVT
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Default Re: Use another receiver to check LO is running

40 years ago when peoples kitchen radios might still be valve, I could drive down any residential street mid-morning with my car radio tuned to about 100MHz and receive several strong carriers, some weakly FM modulated by Jimmy Young and his Radio 2 colleagues.

I am sure the chief modulation mechanism was acoustic microphony of the oscillator responding to the loudspeaker.
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Old 13th Jun 2022, 1:31 pm   #5
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Default Re: Use another receiver to check LO is running

Use of a receiver to verify operation of a fixed frequency oscillator is also a useful dodge, as some crystal oscillators, particularly higher frequency ones, will actually stop when you put a probe on them.

I usually use an SSB receiver tuned to within an audio frequency difference of the expected frequency so that the receiver produces a steady audio tone when the expected signal is present, and the tone disappears when the oscillator is switched off.
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Old 15th Jun 2022, 12:46 am   #6
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Default Re: Use another receiver to check LO is running

I've used a Degen 1103 (Chinese digital all-band receiver) to align all the oscillators in a Barlow-Wadley XCR-30 which was quite a challenge but in the end it all worked perfectly. The BFO of the 1103 allows setting a sig gen (Marconi TF995) carrier spot-on.
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Old 15th Jun 2022, 2:35 pm   #7
G6Tanuki
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Default Re: Use another receiver to check LO is running

Listening to a receiver's LO using another receiver set to SSB mode can also give you a quick-and-dirty assessment of the LO stability - a shift of 100Hz is easily detected by ear.

Smaller shifts and/or longer-term drifts are well shown by feeding the SSB receiver's audio output into the mic-socket of a PC and then using suitable PC software to produce a 'waterfall' display of the beat-note. This will highlight things like 50Hz hum-modulation or things like the dreaded 'switch the kettle on and it shifts 1KHz'. With a waterfall-display you can scroll back in time to see what the drift has been.

All assumes your main SSB receiver is unconditionally-stable though!
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