Quote:
Originally Posted by vintagecollect
Hey pentode, please post a pic of your 1025M PLEASE
thanks for tip pentode. What channel covers the other end of fm dial, channel 7?
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Here is my Stromberg Carlson set. It appears that Stromberg Carlson and GE were the first manufacturers to go ito FM in a big way. Stromberg Carlson launched an FM receiver in 1939, one year before FCC FM commercialization.
With the TV tuner set to channel 6 and the local oscillator adjusted upward, The radio will receive 88 MHz to 96 MHz corresponding to 50 MHz to 42 MHz on the old band. Note I reversed the old band from 50 to 42. This is because the TV tuner oscillator is set to 138 MHz. This is how it is calculated:
Channel 6 local oscillator = 87.25 MHz(ch6 snd) + 41.25 MHz (TV snd I.F.) = 128.5 MHz
Low Band FM converter osc. = 88MHz (new band low end) + 50MHz (old band high end) = 138 MHz
Further: Converter osc. = 96MHz (new band 88 + (50-42)) + 42 MHz (old band low end) = 138 MHz.
What this means is that with the local oscillator in the tuner adjusted 9.5 MHz higher to 138 MHz, the old band FM radio will receive the low end of the new band. It must be noted that the old band was 8MHz wide and the new band is 20 MHz wide, so that only a portion of the band is covered with one TV tuner channel setting. It follows that if you can rebuild the tuner to cover the entire band with three separate channel selections of the tuner, each with a progressively higher local oscillator setting. Eg 138 MHz osc. for 96 to 88 MHz, 146 MHz for 104 to 96MHz and 154 MHz for 112 to 104 MHz. Or else you can over lap. Then again you may be able to get the fine tuning control of the tuner give you extra range.
Note that I have also adjusted the TV tuner RF stages for the FM radio band. In that way you can receive more distant stations. I find with the TV tuner, the old Stromberg Carlson can receive distant stations as well as a new FM radio.
Note the inverted calibration. This is because when the local oscillator freq. is set above the incoming signal freq. the RF frquencies are inverted. Recall with analog TV, the broadcast video carrier frequency is lower than the broadcast Sound carrier frequency. The higher local oscillator inverts the arrangement in the video IF.
I hope this helps.
Cheers,
Terry