[Boatanchors] Ferrite Chokes

[James Liles]

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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