[Boatanchors] Ferrite Chokes

Mon Jul 16 18:01:35 EDT 2012

If you mean parallel to and under the antenna that will provide the most 
coupling. Any angle perpendicular will have minimal coupling. This is no 
different than running a dipole for another band to an existing one and 
sharing a common feedline.

One of my antennas, a sloper for 80 and a 40M inverted vee hanging from it 
has the feed line coming down and away at about 45 degrees from vertical and 
about the same in relation to the 80M wire has no apparent common mode/RF in 
the shack on either band using a pair of  those large 31 mix toroids wrapped 
full with RG-6 quad shield. This is mainly used for up to 200W carrier of AM 
from the vintage station.

On another tower there is one feedline to inverted vees for 160, 80 and 75, 
however that coax comes straight down a tower leg and a similar balun is at 
the feed. With about 450' of 3/4" CATV hardline it has every opportunity to 
be troublesome so I added another balun at the house entrance and to the 
shacks ground rod. This is used for the modern gear up to 1500W CW/SSB and 
sometimes when I run the TS-950SD and linear at around 1500W PEP on AM.

----- Original Message ----- 
From: "James Liles" <james.liles at comcast.net>
To: "Geoff" <geoffrey at jeremy.mv.com>; <boatanchors at mailman.qth.net>
Sent: Monday, July 16, 2012 4:09 PM
Subject: Ferrite Chokes

> Hi Carl:
>
> If you run the coax at a 45 degree angle from the antenna I believe you 
> can expect RF on the coax.  If the choke is at the antenna, the RF induced 
> on the coax will be reflected by the choke at the antenna and forced back 
> to the source.  Don't much care though, if the coax angle is within 15 
> degrees from 90 or over 1/4 wave away from the antenna.
>
> My suggestion to Keith was "if you are real fussy about your antenna" use 
> a balun at the antenna because it eliminated the RF on the shield problem. 
> And then if the coax was run away from the antenna at an angle that 
> deviates much from 90 degrees, add the choke at the entrance to the shack 
> to kill what is induced on the coax by the antenna.
>
> The balun at the antenna provides the first line of defense.  The choke at 
> the shack mitigates any induced current from the antenna to coax from 
> getting into the shack.
>
> Hope this and the last post make sense --- don't know how else to explain 
> it.
>
> Have a great day and Kindest regards Jim K9AXN
>
> -----------------------------Original 
> Message----------------------------------------- 
> From: Geoff
> Sent: Monday, July 16, 2012 1:16 PM
> To: James Liles ; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Ferrite Chokes
>
> It doesnt matter which way the coax is run, the first line of defense is 
> at
> the antenna unless you like the feedline to continue radiating.
>
> Wrapping the coax around 2 of Fair-Rite part 2631803802 at $6.94 each from
> Mouser will be more effective than twice the cost of snap ons.
>
>
> ----- Original Message ----- 
> From: "James Liles" <james.liles at comcast.net>
> To: <boatanchors at mailman.qth.net>
> Sent: Monday, July 16, 2012 1:09 PM
> Subject: [Boatanchors] Ferrite Chokes
>
>
>> Hi again Keith:
>>
>> Don't know how difficult it is to get to the antenna feed point but here 
>> is
>> a thought that you might entertain if you are really fussy about your
>> antenna.  Simply add a mast mounted or hanging  balun.  That way both 
>> halves
>> of the antenna wire will participate.  Couple of advantages.  The antenna
>> will be a bit less susceptible to noise and there will be a very slight 
>> bit
>> of gain from driving both wires.  Also would significantly reduce RF on 
>> the
>> shield --- wouldn't have to use the cores at the antenna.  If the coax is
>> not 90 degrees from the antenna, I would still use the snap on cores but 
>> at
>> the entry to the shack.
>>
>> Just a thought --- the cores will be just fine though.
>>
>> Good luck Keith and let us know how all works out.
>>
>> Kindest regards Jim K9AXN
>>
>> --------------------------  Original
>> message ----------------------------------------
>>
>> Message: 1
>> Date: Mon, 16 Jul 2012 11:25:36 -0400
>> From: "Keith Densmore" <kmd at xplornet.ca>
>> Subject: Re: [Boatanchors] Ferrite Chokes
>> To: <boatanchors at mailman.qth.net>
>> Message-ID: <FC2A0A80A16645AABA4B7B15F935A631 at keith3dc125020>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>>>>> Might be interesting to put the antenna up without any choke or
>>>>> ferrite and see how it works out......
>>
>>
>> Thanks to a kind suggestion from one of the list members, I have ordered 
>> a
>> set of beads from Palomar. The advantage of these is I do not have to
>> disassemble the coax connectors to install.
>>
>> I used to use a multi wire dipole without balun, located not too far from
>> the house without any RF feedback issues. Not so with the Off center fed
>> dipole which is totally unbalanced, and without a choke causes lots of RF
>> back into the shack. I guess there is no such thing as 'free lunch'.
>>
>> 73
>>
>> Keith ve3ts
>>
>>
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