LF: Re: Transistor riddle, VLF

[MarkusVester@aol.com]

Dear group,

thanks to Alan for pointing out Bob Pease as the original source of the experiment. I think DL2NDO mentioned it when he told us about it a few years ago, I just didn't remember.

Yes, that's the clue to the voltage inverter: photocurrent in the c-b-junction. You really don't need a microscope to see its origin, though a small magnifier helps. Just look at the chip in the dark and turn on reverse-bias, and you will see a faint glow of orange-coloured light. It is quite pretty on a larger transistor like a 2N3055, the structured rim of the emitter zone is seamed by luminescence. - But the voltage conversion is not very efficient: 0.3V x 0.4uA output from a 2N5322 fed with -9V x -4mA (yes, PNPs can do it just as well).

For a moment I had also considered rectified zener noise, but I think polarity would be the other way round: RF rectification in a diode generates reverse, light "rectification" forward voltage. - Today I connected a scope parallel to the 2N2222 e-b-junction in pursuit of Rik's observation, and yes, there it was: Slightly above the threshold of avalanching, there were three discrete bands of instability, up to 50 mV pp. I couldn't trigger the timebase properly so it was not periodic; the display looked a bit like a train of pulses clipped between two levels, as if someone turned the avalanching on and off at random. A pair of 300 ohm headphones in place of the biasing resistor revealed it as wideband (and apparently very non-gaussian) noise.

Boys, lets get back to business ;-) ... Apropos headphones: they remind me of an experiment Geri and I did some time in 2001: We connected them to my LF antenna through an old TV line-transformer acting as a resonating inductance, tunable by the width of its airgap. Then we listened to the high-pitched beeps of the russian Alpha beacons, without any amplification or frequency conversion. Had I tried this 40 years earlier, perhaps I could have _heard_ SAQ on baseband...

73 es best wishes
de Markus, DF6NM