Possible to convert 42MC-50MC FM?

[wa2ise]

I have this Wmweson prewar AM/FM set, and I use a modified ham radio block converter intended for 2M to 6M conversion (144 to 50MHz). Changed it to do 100MHz to 45MHz.

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).

A modified old style TV set tuner (not PLL tuned) might work. Set it to channel 6, and move the LO up about 10MHz to get it to tune the FM band, and the tuner's IF output should produce 45MHz FM radio stations.

[wa2ise]

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).

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.

[vintagecollect]

That VCR converter is interesting, I'm going to build that compact DIY converter , will update on results later. I'm interested in DIY as can be put in a small box and tucked behind my Brewster tuner set. Your posts are good W2ISE, PLEASE REPLY TO pm.

It appears there was a lot of interest in early FM 15 to 20 years ago. Several old articles done including the well laid out one I mentioned. Not too much as of recently? Perhaps more of an old timers wanting to rig these for use. Never heard anyone using a prewar restored fm radio.

ONLY saw one at old friends house 8 years ago, he has since passed away. The power transformer was bad as I checked it for him 20 years ago. It sat in their living room as a fine piece of furniture as had fancy cabinet with matching burl grain doors. I remember wanting to see set run, knowing the FM was probaly obsolete. Had weird ultra futuristic gray plastic and metallic knobs and look of benzel. Made radio look more like a 50s or late s 50s set. Definetely 1941, had only obsolete band, saw ad for exact set somewhere in Life magazine- full page.

Have since early FM interests me. These sets must of been rare in general. Most must of been scrapped. Pic of Brewster tuner set restored by someone as older project. original cabinet in very good shape which doesn't show age of 70 years.

if anyone else using prewar fm please post pics!