Experiments
Andre Kesteloot
andre.kesteloot@ieee.org
Sun, 24 Nov 2002 17:01:43 -0500
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MarkusVester@aol.com wrote:
> 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
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MarkusVester@aol.com wrote:
<blockquote TYPE=CITE><font face="Arial"><font size=-1>Dear group,</font></font>
<p><font face="Arial"><font size=-1>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.</font></font>
<p><font face="Arial"><font size=-1>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).</font></font>
<p><font face="Arial"><font size=-1>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.</font></font>
<p><font face="Arial"><font size=-1>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...</font></font>
<p><font face="Arial"><font size=-1>73 es best wishes</font></font>
<br><font face="Arial"><font size=-1>de Markus, DF6NM</font></font></blockquote>
<br>
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