On 9/7/2011 8:54 AM, Jeff Liebermann wrote:
On 07 Sep 2011 13:27:08 GMT, wrote:

If you do not short the center conductor (on the DUT) to ground
immediately before connecting to the analyzer you risk discharging a
large "capacitor" directly into the instrument.

Good point except that none of the 3 analyzers that failed were
(allegedly) attached to equipment. They were attached to antennas.
Antennas normally do not have BFC's (big fat capacitors) attached, but
do build up static charges. With the humidity currently at 60% or
more, I don't think that's likely.


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.



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.

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.




If I am at an antenna
farm I am grounding all my test gear prior to putting it into service.
There is a Ground lug on the 259B right next to the SO239. They
provide a Type N adaptor with a new meter, too, BTW.

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.

On Wed, 07 Sep 2011 10:48:55 -0700, Jim Lux
wrote:

but just the clear sky current could provide some charging.

There is a earth-sky current in the femtoamperes per cm² that has a
constant potential gradient on the order of 600V/m (or something like
that). This current is the return path for all lightning strike
charge transfers, world-wide.

Few dipoles are co-planar, parallel wrt ground.

Actually, humidity doesn't affect the charging all that much. What
humidity affects is the leakage current across dirty insulators.

Which could easily overwhelm this femtoampere charge where a gigaOhm
leakage is trivial (zealous Hams using teflon technology?).

Actually measuring this current (ca 1970s) required using two
polonium-210 coated probes (what are still available as static brushes
for vinyl records) feeding FETs.

The following link:
http://www.angelfire.com/electronic/...rad/brush.html
illustrates what the brush is like, and its electrical attributes.
Another source, the manufacturer (which deeply hides the polonium
reference):
http://www.nrdstaticcontrol.com/doc/microbalance.pdf

73's
Richard Clark, KB7QHC

On 9/7/2011 11:47 AM, Richard Clark wrote:
On Wed, 07 Sep 2011 10:48:55 -0700, Jim
wrote:

but just the clear sky current could provide some charging.

There is a earth-sky current in the femtoamperes per cm² that has a
constant potential gradient on the order of 600V/m (or something like
that). This current is the return path for all lightning strike
charge transfers, world-wide.

a few pA/sq meter and a kV/meter field is how I always remember it (in
round numbers) It's small, that's true.


Few dipoles are co-planar, parallel wrt ground.

Actually, humidity doesn't affect the charging all that much. What
humidity affects is the leakage current across dirty insulators.

Which could easily overwhelm this femtoampere charge where a gigaOhm
leakage is trivial (zealous Hams using teflon technology?).

Well.. Consider a 20 meter long wire hanging 10 meters above the
ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg
isolation isn't hard to get with clean insulators. That 20 m wire is
like a 850 pF capacitor. If assume, say, 25 pA charging current, you
get a volt every 42 seconds. After half an hour or so, you're up to 40
volts or so..

Granted it's not a lot of Joules.. (heck, probably not even a microjoule)..

So fair weather charging isn't likely to kill your MFJ..

Back to the dust/rain/induction charging, which can certainly get the
levels needed.

In article ,
Jim Lux wrote:

Well.. Consider a 20 meter long wire hanging 10 meters above the
ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg
isolation isn't hard to get with clean insulators. That 20 m wire is
like a 850 pF capacitor. If assume, say, 25 pA charging current, you
get a volt every 42 seconds. After half an hour or so, you're up to 40
volts or so..

Granted it's not a lot of Joules.. (heck, probably not even a microjoule)..

So fair weather charging isn't likely to kill your MFJ..

Back to the dust/rain/induction charging, which can certainly get the
levels needed.

I've observed clear-air charge on a TV antenna (about 30' above ground
level) which was sufficient to create a visible spark when I touched
the center connector of the coax to a grounded static-drain block.

No rain at the time, no appreciable amount of dust (SF Bay area)...
just clear air with a mild breeze.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 9/8/2011 12:24 PM, Dave Platt wrote:
In ,
Jim wrote:

Well.. Consider a 20 meter long wire hanging 10 meters above the
ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg
isolation isn't hard to get with clean insulators. That 20 m wire is
like a 850 pF capacitor. If assume, say, 25 pA charging current, you
get a volt every 42 seconds. After half an hour or so, you're up to 40
volts or so..

Granted it's not a lot of Joules.. (heck, probably not even a microjoule)..

So fair weather charging isn't likely to kill your MFJ..

Back to the dust/rain/induction charging, which can certainly get the
levels needed.

I've observed clear-air charge on a TV antenna (about 30' above ground
level) which was sufficient to create a visible spark when I touched
the center connector of the coax to a grounded static-drain block.

No rain at the time, no appreciable amount of dust (SF Bay area)...
just clear air with a mild breeze.


There could actually be a fair amount of particulates without you being
aware of it. I used to work for a company that made things that created
fine particles in air and we tried to remove the particles as well
(often using electrostatic techniques).

For very small particles, they don't scatter the light very well so you
don't see them. Ultimately, you get small enough: molecule sized and you
get blue sky, but even fairly large particles (on the order of a
wavelength of light in size) are basically invisible as such, but do
increase the attenuation, and do scatter some light so you get
decreasing visual contrast at long distances (called atmospheric
perspective in the computer graphics biz) One way that cinematographers
can make a room seem bigger is by putting a very small amount of haze
into the room, because that makes distant things less contrasty, which
your brain turns into "farther away".

Some numbers:

At 1 mg/cubic meter of 1 micron diameter particles, you won't see any
noticeable haziness. That's about 2E15 particles per cubic meter, and
each one can have a max charge of about 1E-13 coulomb. So you can
potentially move 200 coulombs with a cubic meter of air. That gentle
zephyr blowing by at 1 m/sec can move a lot of cubic meters in a fairly
short time. Say you have a 1cm diameter antenna element.. it will
intercept 0.01 cubic meters/sec of that breeze.. 2 Coulombs/sec - 2
Amperes...

In reality, of course, the particles won't have that much charge
(they'll repel each other, for one thing), and not all of the particles
will touch your antenna, especially once it starts to charge, and so
forth. When I was working with a Vollrath Electrostatic Charging scheme
(like a Van de Graaff generator using dust instead of a belt) the best
kind of charging current I got was 10-100 microamps with dust flowing in
a 4" diameter pipe at several meters/sec.

But, the real thing is that you can get particulate charging in what
seems to be perfectly clear air.

Compressed air system run into this kind of thing... you can have fine
oil particles from the compressor, or condensed water particles from a
sudden expansion of the compressed air, both of which might be
invisible, but which can build up a surprising charge.

Dave Platt wrote:

In article ,
Jim Lux wrote:

Well.. Consider a 20 meter long wire hanging 10 meters above the
ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg
isolation isn't hard to get with clean insulators. That 20 m wire is
like a 850 pF capacitor. If assume, say, 25 pA charging current, you
get a volt every 42 seconds. After half an hour or so, you're up to 40
volts or so..

Granted it's not a lot of Joules.. (heck, probably not even a microjoule)..

So fair weather charging isn't likely to kill your MFJ..

Back to the dust/rain/induction charging, which can certainly get the
levels needed.

I've observed clear-air charge on a TV antenna (about 30' above ground
level) which was sufficient to create a visible spark when I touched
the center connector of the coax to a grounded static-drain block.

No rain at the time, no appreciable amount of dust (SF Bay area)...
just clear air with a mild breeze.


Were there any elevators nearby?

"Dave Platt" wrote in message
...

snip

I've observed clear-air charge on a TV antenna (about 30' above ground
level) which was sufficient to create a visible spark when I touched
the center connector of the coax to a grounded static-drain block.

Didn't Art Bell, W6OBB, former host of Coast to Coast AM, report 300 volts
on his loop antenna? Even with low current, a kiss from that voltage will
make you fall out of love.

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.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On 9/7/2011 10:01 PM, Jeff Liebermann wrote:
On Wed, 07 Sep 2011 10:48:55 -0700, Jim
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.


It has to do with the leakage currents discharging you when it's more
humid. Interestingly, humid air has a higher breakdown field than dry air.



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.

And, you can take ESD hits that degrade, but don't destroy, the part.
I've got some LNAs in my desk drawer that appear to work just fine,
except the NF is a bit higher than it used to be.

On 9/8/2011 1:30 PM, Jim Lux wrote:

And, you can take ESD hits that degrade, but don't destroy, the part.
I've got some LNAs in my desk drawer that appear to work just fine,
except the NF is a bit higher than it used to be.


How do you know it was ESD that caused the degradation?