[TowerTalk] Coax, conduit and toroids

Ian White GM3SEK gm3sek at ifwtech.co.uk
Wed Jun 27 01:50:55 PDT 2012

K8RI wrote:
>> Is it a good idea to create a coil of coax in or near the base of the tower,
>> run through ferrite toroids? I do this at the base of my vertical, but I'm
>> not sure if it's as useful for a horizontal antenna.
>I have a one of these current chokes/baluns on each of my sloping 
>dipoles. On 75 I still had so much feedback that all the LEDs in the 
>shack would light by the time I reached a KW out let alone 1.5 KW. I 
>added a second choke in the 75 meter feed line at the tower and it 
>cleaned it up to where I can not detect any common mode voltage making 
>it back to the shack.  If you need one, use one, if you don't then save 
>your money.

The problem may be that he needs to decide right now, while he is 
installing the coax.

On the other hand, large ferrite cores will be very expensive imports in 
ZL, so it won't be cost-effective to scatter lots of them around "just 
in case".

One option might be to look up K9YC's recipes for ferrite chokes using 
the big #31 clamp-on beads, and make the air-cored coil at the base of 
the tower when installing the coax. Very little is lost by doing that 
much in advance.

Later, if a "serious" common-mode choke does turn out to be necessary at 
the base of the tower, then simply snap the big bead onto the coil that 
is already there.


73 from Ian GM3SEK

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