[Premium-Rx] Re: gas discharge, lightening, etcos and High RF powers (Andreé Knott)

[refmon]

Hi,

I'm not sure I've latched onto the most directly related message here, but
it's at least related.  Just as a look from a different perspective, here
are a few url's on lightening strike prevention / suppression systems.
While the sheer scale of many of these solutions rule them out at most
armature and SWL stations, many of the theories and practices are valid and
helpful both in discouraging strikes to begin with, and absorbing the strike
when you do get whacked.  Take a look at:
http://www.abroyd.com/lightning_protect.htm , http://www.lpsnet.com/als.htm
, and other stuff that comes up under searches for "lightning prevention",
lightning suppression", and "surge suppression".

If nothing else, a tower with one of these lightning flowers (my word) is
quite a novel sight.

nice discussion...keep going.....

regards

John Collins
_______________________________________________
----- Original Message ----- 
From: "Gary Geissinger" <ggeissinger at digitalglobe.com>
To: <premium-rx at ml.skirrow.org>
Sent: Tuesday, June 03, 2003 03:19 PM
Subject: RE: [Premium-Rx] AW: Premium-Rx Digest, Vol 6, Issue 3 RE: Radios
and High RF powers (Andreé Knott)


Andree,

We used to use them in pairs; one biased one way and the other biased
opposite.  That way one or the other tube will catch the transient.

By the way, this is similar to the adjustable noise clipper in some tube
type military radios except they use diode tubes in pairs instead of gas
discharge tubes.

Regards,

Gary

-----Original Message-----
From: George Georgevits [mailto:georgg at bigpond.net.au]
Sent: Tuesday, June 03, 2003 4:01 PM
To: premium-rx at ml.skirrow.org
Subject: RE: [Premium-Rx] AW: Premium-Rx Digest, Vol 6, Issue 3 RE:
Radios and High RF powers (Andreé Knott)



Andreé,

I see a small problem with biasing a gas discharge tube. What happens if the
polarity of the surge you are trying to protect against is opposite to that
of your bias? Lightning induced impulses can be of either polarity.

Regards,
George Georgevits
Power and Digital Instruments Pty Ltd


-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org]On Behalf Of AKnott at WTD71.de
Sent: Tuesday, 3 June 2003 6:50 PM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] AW: Premium-Rx Digest, Vol 6, Issue 3 RE: Radios
and High RF powers (Andreé Knott)


If the ignition voltage of a gas discharge arrestor or neon lamp is too high
for your purpose, it is possible to bias the gas discharge device by a high
voltage (low) power supply (which should be "noise free") with fine tuneable
voltage fed through a good rf-choke (no series resonances throughout
operational frequency range) and a resistor which limits the current if the
gas discharge device "fires" to protect the gas discharge device and the
power supply as well. Possibly decoupling capacitors may be necessary to
keep the bias voltage away from the rf-frontend or parts which can be
touched.

The burning voltage of a gas discharge device is lower than the ignition
voltage. Therefore the bias voltage has to be lower than this burning
voltage, otherwise it will burn for ever. If the gas discharge device
"fires" there is still this burning voltage across the gas discharge device.
The following circuits have to cope with this voltage.

I saw gas discharge devices integrated into preselectors at certain points
of relatively high impedance. So the burning volage is lowered by the
step-down transformer the preselector includes. To explain this here is a
simple example. Think of a preselector of two inductively coupled parallel
LC-circuits (C is used for tuning). The input is coupled by a small coil
(few turns) inside the first parallel LC-circuit. The output is coupled by a
small coil inside the first parallel LC-circuit as well. So you see inside
the preselector there is first a step-up and then a step-down transforming
done. The "hot" end of each parallel LC-circuit is such a point of high
impedance. I saw gas discharge devices connected between such a point and
ground. Avoid long wires, take the next point (case of the preselector) to
ground.

If the light of the gas discharge device or the current of the gas discharge
device or the current of the bias power supply is supervised, it can be used
to switch in a power attenuator automatically if the period of activation of
the gas discharge device is longer than a certain time. This is done at
certain preselectors used in shipborn application. A military ship really is
the worst application you can think of. I saw such preselectors used on
ships which have several (parallel used) high power transmitters in the
range of HF up to SHF. Due to the small distance decoupling between antennas
is VERY low...

Yours
Andreé DD3LY





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