On Wed, 07 Sep 2011 10:48:55 -0700, Jim Lux
wrote:
Actually, humidity doesn't affect the charging all that much. What
humidity affects is the leakage current across dirty insulators.
P-static is a nice example of static charging in rain at 100% humidity,
for instance.
It's true that dry dust or blowing snow are more notorious for charging,
but just the clear sky current could provide some charging.
Well, what I've noticed is that when the humidity is low, I throw
lightning bolts when I walk across the carpet or slide across the car
seat. When the humidity is higher, then I don't have those problems.
I don't know how this correlates to charge buildup on an antenna, but
my guess(tm) is that there would be some connection.
Also, any antenna design, that
would fry an analyzer, might also fry a radio front end. It's
possible, but unlikely.
I don't know about that. A LNA with a FET front end might be an example
of a ESD sensitive thing, but for HF, where we're usually more concerned
about instantaneous dynamic range and strong signal handling, a more
robust front end is common. One of those +20dBm LO mixers, for
instance, is going to be quite robust.
In a past life, I helped design a marine HF xceiver, which had a +7dBm
mixer (SBL-1) in the front end. Between the antenna and the mixer,
was a low pass filter with no capacitors to ground. There were a few
failures, most of which were due to nearby lightning hits. However
some of these failures were blamed on static buildup.
The higher level mixers will certainly survive a bigger blast through
the antenna. But that's because there's a torroidal isolation
transformer between the antenna and the diode ring. See typical
+23dBm mixer at:
http://www.minicircuits.com/pdfs/RAY-1+.pdf
Also note that the maximum RF power is 350mw, which is well within the
range of what can be delivered by a good solid ESD blast via the
antenna. I don't think it will fry the diodes, but might blow the
tiny wire used in the torroids into a fuse.
I can think of a lot of antennas that won't be too hard on a radio front
end that would cook a delicate detector diode hooked directly up to the
antenna.
Ok. I'll admit that the MJF-269 diodes, which are directly connected
to the antenna terminal, are more easily fried than a receiver front
end, which has a mess of circuitry, and possibly an antenna coupler,
between the antenna and the front end.
I carry a neon lamp line tester in my tool box. It's useful for
checking AC power, but also for detecting high voltages on antenna
terminals. It's amazing what I find at broadcast sites.
There's a whole literature on making neon lamp blinkers with an antenna
and a ground.
These days, it's called "energy scavenging" or "RF energy harvesting".
http://www.eweekeurope.co.uk/news/scavenging-free-green-power-from-radio-waves-35622
I used to have a 4 watt fluorescent lamp on top of my mobile antenna
that flickered with the transmitted envelope.
--
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