Oh, I see.
My goal has always been to have a system where I didn't have to ground
my antennas during a lightning storm. Having done the broadcast
engineering thing, I know it's an achievable goal. It may not be worth
the expense, but it's what I want.
On 5/24/2016 3:51 PM, WILLIS COOKE via BVARC wrote:
A resistor will bleed off a static charge which will reduce the chance
of a direct hit. I lightning arrestor will arc and bleed off some of
the static electricity before the charge reaches a maximum. Nothing
will protect you from a direct hit, but both are a good idea. A
better idea is to ground your antenna during a storm. A choke will
ground your antenna to DC charges if the wire is big enough to not
burn up when the charge gets large. Nothing will help stupid.
Willis 'Cookie' Cooke,
------------------------------------------------------------------------
*From:* Jonathan Guthrie via BVARC <[email protected]>
*To:* [email protected]
*Cc:* Jonathan Guthrie <[email protected]>
*Sent:* Tuesday, May 24, 2016 1:36 PM
*Subject:* Re: [BVARC] Bleeding static from antennas (RF choke)
A resistor won't do a dang thing to protect you from lightning. You
need a lightning arrestor for that.
On 5/24/2016 1:31 PM, WILLIS COOKE via BVARC wrote:
The reason for using a 3 megohm at 5 watt resistor is so that it will
not burn our with a proximal lightning strike, but it will not allow
a buildup of static electricity until you get an arc. This is a
reasonable loss at any RF frequency and will prevent a large voltage
from accumulating. If you wish to add a choke, put it in series with
a 1 meg or larger resistor, nominally about 3 megohm with a large
wattage to prevent burning out if the current gets too large during a
storm. The choke alone is used if you want to insert a control
voltage, 12 or 24 dc to power a tuner or such between the choke and
ground. You can use a large resistor as well for lightning
protection, but it will not protect the antenna tuner if used for
control insertion.
Willis 'Cookie' Cooke,
------------------------------------------------------------------------
*From:* Jonathan Guthrie via BVARC mailto:[email protected]
*To:* BRAZOS VALLEY AMATEUR RADIO CLUB mailto:[email protected]
*Cc:* Jonathan Guthrie mailto:[email protected]
*Sent:* Tuesday, May 24, 2016 12:29 PM
*Subject:* Re: [BVARC] Bleeding static from antennas (RF choke)
The idea is that the choke passes essentially no current at the
frequency of operation, but is essentially a dead short at DC.
Unless I'm remembering the formula wrong, which is always a
possibility, the choke has a reactance of about 28k ohms at 1.8 MHz,
which means that it would have about 10 mA through it if you had it
across a 50-ohm feedline being driven at 1500W. I'm pretty sure that
would work without letting the smoke out. Since that's the most
difficult case (higher frequencies have more reactance and, hence,
less current) it should work on most any band. Up until you hit the
resonant frequency of the choke, anyway.
Another technique you can use is to put a large resistor across the
feedline. Since you're only trying to prevent tiny amounts of charge
from accumulating, that should work, too. 300K or larger should be
able to dissipate the power from a legal-limit signal. Unless I did
the calculation wrong.
On 5/24/2016 11:52 AM, n5xz via BVARC wrote:
Would this be suitable for legal limit (or more)?
Did a search on the choke: https://www.tubesandmore.com/products/P-C1535B
Travis
K5HTB
________________________________________
From: BVARC mailto:[email protected] on behalf of Sam Neal via
BVARC mailto:[email protected]
Sent: Monday, May 23, 2016 7:50 AM
To: BRAZOS VALLEY AMATEUR RADIO CLUB
Cc: Sam Neal
Subject: Re: [BVARC] Bleeding static from antennas
Hello,
Consider placing a 2.5 mH RF choke from the antenna to ground. Keep
it in a
dry place. Many of the old boat-anchor transmitters did this from the
antenna
coax connector to ground to protect the operator or anyone from
touching the
antenna should the RF coupling capicator between the tube plate and
the pi-net
tuner open up placing B+ on the antenna.
73,
Sam Neal N5AF
Sent from my Verizon Wireless 4G LTE smartphone
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