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FM Alignment of 48-482
#1

I am trying to finish up the alignment of one of these and am having trouble with getting the oscillator set to the proper frequencies at both ends of the dial. The instructions have you align at 88Mc and 105Mc. You adjust the oscillator coil at 88Mc and the trimmer cap at 105Mc. I find that I have to keep compressing the windings of the coil at 88Mc and keep withdrawing the trimmer cap at 105Mc. On each iteration I get closer but I have reached the extent of how close together I can get the windings of the coil. It seems that the oscillator should be running on the low side of the received signal (i.e. received frequency-I.F.). With this case I would need the oscillator to run at 78.9Mc for 88Mc and 95.9Mc for 105Mc. I have been checking the frequency of the oscillator with a coil of wire wrapped around the 7F8 tube and connected to my frequency counter. With the coil compressed I can get 78.9Mc with the dial set at 88Mc but when I set the dial to 105 I get about 93Mc from the oscillator. I spread the coil windings out as much as they would go and withdrew the trimmer cap as far as it would go to see if I could get the oscillator to run on the high side (received frequency+I.F.). At 105Mc it will oscillate at about 118Mc but at 88Mc it will only oscillate at about 88Mc so it does not seem that high side oscillating will work. Has anybody else had any problems with getting the FM dial to align on one of these sets? I know it isn't going to be completely accurate but I would think I could get it closer than 3Mc.

Sean
WØKPX


Messages In This Thread
FM Alignment of 48-482 - by Sean - 11-21-2009, 11:06 AM
Re: FM Alignment of 48-482 - by Ron Ramirez - 12-01-2009, 08:29 AM
Re: FM Alignment of 48-482 - by Terry Judkins - 12-03-2009, 10:53 PM
Re: FM Alignment of 48-482 - by Sean - 12-05-2009, 05:21 PM
Re: FM Alignment of 48-482 - by DCASAZZA - 12-10-2009, 09:38 AM
Re: FM Alignment of 48-482 - by Don Lind - 12-12-2009, 02:27 PM
Re: FM Alignment of 48-482 - by Sean - 01-05-2010, 09:50 AM
Re: FM Alignment of 48-482 - by Ron Ramirez - 01-05-2010, 11:08 AM
Re: FM Alignment of 48-482 - by Sean - 01-09-2010, 02:08 PM
Re: FM Alignment of 48-482 - by Ron Ramirez - 01-09-2010, 03:06 PM



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