"tony sayer"


** I take 88.5 should be 88.05 ????

So the tuned frequency drifts up by only about 100 kHz as it warms up -
NOT 500 kHz.

Despite appearances, the FM4 is NOT frequency locked with a digital
frequency synthesiser, like most other tuners with a digital readout.

Tuning frequency is controlled by analogue circuitry via "varicaps " -
so
cannot be entirely drift free.

What is that locked to if anything, or is it free running with AFC?.


** Correct.

Just the DC bias voltage applied to the varicaps and internal temperature
set the frequency.

Likely some temperate compensation involved too.


Doesn't seem to be an FM4 circuit in the web anywhere.....


** Here's one:

http://www.dc-daylight.ltd.uk/Valve-...ic-circuit.pdf


The mysterious MP4480 uP ( a programmed Texas TMS1000 ? ) makes deciphering
it a bit interesting.




........ Phil