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Old 13th Jun 2019, 8:19 am   #25
Martin G7MRV
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Join Date: May 2008
Location: Selby, North Yorkshire, UK.
Posts: 949
Default Re: No LW/MW receive - Sony ST-S311

Quote:
Originally Posted by Radio Wrangler View Post
The 5v everywhere thing could just be where the internal bias system sets things for analogue inputs and outputs.

-35dBm would be 4mV PD in 50 Ohms. With AM inputs being high Z, it's likely got 8mV at the input. Specs for the chip are in dBuV so call that +78dBuV

The datasheet quotes power consumption with 107dBuV and with no signal. so 78dBuV is within the ballpark.

Ah, at 80dBuv it quotes <1% THD and "detection output" between -15.5 and -9.5 dBm... whatever detection output may mean.

It should be working properly at that RF level, though the numbers above are for 30% mod.

As a reality check, as a kid in Almondbury, my crystal set gave audio out the headphones which could be heard several feet away from the phones, if tuned to Pole Moor at the other side of huddersfield. So the RF level must have been in the 100mV region and normal radio sets in the area handle it.

S-meter output... 0 to 0.5v quiescent about 4.5v with 107dBuV RF... pin16 That ought to be checkable to see if the thing is running and AGC is alive.

Datasheet application circuit number 1 gives quiescent DC volts for all pins.

I wonder if a zap has discombobulated only the RF amp stage and just left the chip very deaf? so your -35dBm is only just lifting the rest of the receiver structure out of its floor. The S meter pin voltage as you vary the RF might throw light in this area.

David
Cheers David,

well the s-meter output isnt! There is no output from it!

'scoping the IF oscillator resonator I could barely get a trace at all, but it must be running as I can see the 450kHz signal cleanly on the IF filter. But thats all I can see - a nice clean 450kHz sine wave! No modulation at all, whatever I set the mod level to on the test set. Im pretty sure as well that in a working set I shouldnt be seeing that IF oscillator signal, even low and badly distorted (almost a double triangle wave!) at the output to the audio stages!
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