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wrote:
Hi All,

I have an older TV set with the UHF tuner going up to channel 83. The
tuner is a mechnical type.

The output of the tuner goes back into the VHF tuner and you select the
U on the VHF tuner to operate the UHF channels.

In down conversion of the UHF band, what is the IF frequency of the UHF
tuner? The set is an old RCA.

pdrunen

Same IF as VHF: 45.75 MHz.

When the VHF tuner is set to "U", its local oscillator is disabled,
and its RF amp & mixer amplify the IF out of the UHF tuner
without doing any frequency conversion.

Those mechanical UHF tuners have no RF amp stage, and
use a diode mixer, therefore no gain. The VHF tuner
makes up for this by acting as an IF preamp before passing
the IF signal to the IF stage.

This configuration is likely due to the lack of cheap, low-noise
UHF transistors in that time period, along with there being
much fewer UHF stations on the air, so the UHF tuners
went unused in many sets. By the time digital-controlled
tuners became commonplace in the late 80's, the UHF
tuners got real RF amp stages, and didn't pass their
IF outputs thru the VHF section for amplification.

Mike
WB2MEP