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 <[email protected]>
To: BRAZOS VALLEY AMATEUR RADIO CLUB <[email protected]>
Cc: Jonathan Guthrie <[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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Jonathan Guthrie KA8KPN
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