Quote:
Originally Posted by wa2ise
Another method that did not work out well was to use an old cable TV descrambler box to tune in a 6Mhz section of the 100Mhz FM broadcast band (cable channels 95 to 98 or so), and to grab the box's tuner's IF output and feed that to the prewar FM set. But reception was rather noisy, suspect that the box's local oscillator has lots of PLL phase noise, which translates to added crud on teh FM signal. It doesn't bother TV sets as most use intercarrier FM IF strips (the phase noise is the same on the picture carrier and the sound carrier, these two carriers are beat together and the phase noise cancels out).
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Tried the same thing with an old VCR, and got much better results. Its local oscillator must be much quieter, as converted FM radio stations fed to the 45MHz FM set sounds a lot better. I connected a special output (via a 470pf high voltage cap) jack to a coax cable that connects to a special port on the VCR's tuner module (probably intended to feed a stereo TV IF amp, filter and demodulator). You want to be in front of the video IF filter, but just after the mixer stage of the tuner. This feeds the 45MHz FM prewar radio. One has to set the VCR to tune CATV channels, and then tune in channels 95, 96 or 97, depending on which segment of the 100MHz FM band you want to block convert. WSBS-FM, 101.1 comes in at about 47.7 with the VCR set to cable channel 97. Or about 41.7 on channel 96. WAXQ 104.3 comes in at about 44.5 on channel 97. Note that the order of stations will be flipped as you tune up the 45MHz FM dial.
You can also pick up the weather reports transmitted around 182MHz at about 46.5Mhz when setting the VCR to cable channel 21. And around that for fire and police, all these will be at much reduced volume as they are narrow band FM.
The VCR is an RCA model VR657HF.