SV: [PCR-1000] ZAPTRAP

Sun, 17 Aug 2003 21:43:34 +0200

Yes, an inductance is used in many GP-antennas between radiator and
ground. One problem is that
bursts from nearby lightnings (a broad spectrum of HF) also is blocked
by the inductance and therefore
not bypassed to ground. They therefore is tranfered directly to the
front-end of the recieiver and
often kills the components. Another problem is selfcapacitance in the
coil, which forms a serial resonance
at a certain frequency and shorts this frequency to ground. It=B4s good =
to
know this serial resonance and to
know that around this frequency the antenna is not working.
Same problem with many of the DC-grounded antenna systems, dipoles and
so on.
They are fine regarding bleeding off DC-voltages but offers little or no
protection to lightning burst.
Again, antiparallel diodes, MOV:s or the gasfilled lightning protectors
will do the job.

/Folke

-----Ursprungligt meddelande-----
Fr=E5n: [email protected]
[mailto:[email protected]] F=F6r Tim Tapio
Skickat: den 17 augusti 2003 16:31
Till: [email protected]
=C4mne: RE: [PCR-1000] ZAPTRAP

Hey folks,

Happened to open an antenna book the other night....we're kinda goofy
thinking of diodes, etc.  Better way is to use a coil.  It would
represent a high impedance to the rf signal yet be a direct ground for
DC.  You'd have to figure out the reactance of the coil for the
frequencies you're looking at to make sure if was a high enough
impedance to block your rf...or you could do the scientific method of
"try it and see".  Not sure if Radio Shack still has any coils or
not....they're pickings have been slimmer and slimmer over the years....

73 de Tim

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Folke
Sent: Friday, August 15, 2003 6:35 PM
To: [email protected]
Subject: SV: [PCR-1000] ZAPTRAP

The DC-voltage that can apear during certain weather, hailstorms and so
on has a polarity, yes. Which specific polarity between antenna and
earth at the different wheather types and situations? Sorry I don=B4t
know. The voltage induced by nearby lightnings are more like AC and with
only one diode only one half periode would be clipped. Besides diodes
VDR:s MOV:s and small neon lamps are used for this purpose.

/Folke

-----Ursprungligt meddelande-----
Fr=E5n: [email protected]
[mailto:[email protected]] F=F6r Tim Tapio
Skickat: den 15 augusti 2003 23:56
Till: [email protected]
=C4mne: RE: [PCR-1000] ZAPTRAP

I understand the reasoning behind the dual diodes, but I still have the
question as to whether static has polarity.  I don't know the answer.

73 de Tim, AG4QE

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Folke
Sent: Friday, August 15, 2003 11:59 AM
To: [email protected]
Subject: SV: [PCR-1000] ZAPTRAP

The reason for two anti-prallelled diodes is to take care of both
polarities of statics and induced voltage in the antenna. If you get in
contact directly with lightning voltage, please don=B4t worry about
polarity, any kind of diodes, cables and other stuff use to vaporize any
way.... The weather station doesn=B4t care about loss of high freqs as a
radio, then it is OK with a power diode. The method of disconnecting and
grounding cables outside the building is the best protection.

/Folke

-----Ursprungligt meddelande-----
Fr=E5n: [email protected]
[mailto:[email protected]] F=F6r Tim Tapio
Skickat: den 15 augusti 2003 17:50
Till: [email protected]
=C4mne: RE: [PCR-1000] ZAPTRAP

Are you sure?  Does static have a positive or negative relationship to
ground?  Lightning flows from ground to cloud, negative to positive (I
don't believe it though).  Someone else mentioned the capacitive effect
of the diodes at higher frequencies, suggested using standard 1N4148
switching diodes.  The stuff in my weather station has a 5 amp diode
(didn't see any
numbers) but that is not RF.

The main importance is a good ground and if it is highly likely for
lightning outside, discount from the radio...and ground it or disconnect
outside.  I run all my coaxes through bulkhead connectors on a 1/4"
copper bar outside with three ground rods attached (12' apart) and #6
wire to connect (small but better than nothing).

73 de Tim, AG4QE

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of [email protected]
Sent: Friday, August 15, 2003 4:43 AM
To: [email protected]
Subject: [PCR-1000] ZAPTRAP

Hi all,

Just for the record, since no-one has mentioned it, you need 2 diodes,
in parallel, one each way, between line and ground.

73, Heath.

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