"G "Guglielmo" Evans G4SDW" wrote in message
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"G "Guglielmo" Evans GW4SDW" wrote in message
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Does anyone have experience and/or recommendations
for analogue and digital I/O interfaces based on the Universal
Serial Bus (USB)?

Just an idea for the genesis of a homebrew spectrum analyser.

Next consideration....not having to hand any components or
experience of the broadcast TV band (0.4 - 1GHz?) I wonder
what tuners and mixers are fitted to modern TVs and if anyone
can recommend a tuner separate from a main board that
might be used.

Also, where tuners are driven by I2C and similar busses, are
they channelised to fit the standard TV channels, or do they
have a delta frequency, say, 10kHz, that might be useful
for a spectrum analyser?

Maybe you could look at tuner boards form an old VCR, On VCR's Circa 1990
the tuners were a separate board, Older tuners were simply fed by a PWM
output from the display / timer CPU that was then fed to an amplifier/
smoothing stage that then gave a 36V down to 2V DC voltage to select
frequency, they were analogue tuners, so not stepped, there was usually
another line to the tuner to disable the AFT lock that was used when
scanning for new channels.
We used to take the VCR tuner board, put it in a box with a PSU, pin the
AFT lock line to 5V to disable AFT then use a 10K pot with a 2K or 3K
fixed R on the 0V leg, the wiper to the collector of the transistor that was
after the PWM input line.
The modules used in the VCR's were usually Mitsumi or Alps, and if you get
hold of an European one. then you can tune VHF and UHF with it, but you will
need to apply 5V to the band switching pins on the tuner. and yes it can be
used as a basic spectrum analyser, but you may have to find a way to disable
the AGC circuits.
Also the tuner boards rely on the RF output modulator / pass though unit on
the back sockets of the VCR having considerable gain, without the
modulator, the signal would be weak.