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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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12th Jun 2022, 3:24 pm | #1 |
Octode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 1,002
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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. |
12th Jun 2022, 3:28 pm | #2 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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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 Aub
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Life's a long song, but the tune ends too soon for us all. |
12th Jun 2022, 7:20 pm | #3 |
Octode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 1,002
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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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13th Jun 2022, 1:48 am | #4 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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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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13th Jun 2022, 1:31 pm | #5 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,575
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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. |
15th Jun 2022, 12:46 am | #6 |
Heptode
Join Date: Jan 2008
Location: Ashhurst, Manawatu, New Zealand
Posts: 571
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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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15th Jun 2022, 2:35 pm | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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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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