[TenTec] [Fwd: Line Isolator Balun (sorta) question.]

[Dr. Gerald N. Johnson]

The purpose of these "baluns" is to attenuate any RF current on the 
outside of the shield. That helps cut feed line radiation when the coax 
is hooked to an antenna. Sometimes that helps cut TVI and received 
interference from local sources. Sometimes that hurts working stations 
that need the vertically polarized component from feedline radiation.

Unless the radio and amplifier and such are not shielded, beads on those 
jumper cables will have no detectable effect. If the coax connectors 
don't make good braid contact they will have some effect, but not much 
benefit over having tight and well crimped or soldered coax connectors. 
UHF connectors have a history of poor ground connections if not kept 
really tight.

73, Jerry, K0CQ

On 8/6/2010 11:38 AM, Jim Lowman wrote:
> Background -
>
> QST Magazine, and various commercial entities, tout the benefits of a
> 1:1 line-isolation balun - sometimes simply made by slipping a number of
> ferrite beads over the coax feed lime. and securing them with heat
> shrink tubing.   (e.g., Palomar Engineers, BuxCom, and other vendors
> sell these as an inexpensive kit.)
>
> Several articles and commercial vendors suggest using line isolation
> baluns ( which are often made of ferrite beads)   on  feed lines in the
> shack - including the short jumper cables running between rig and amp,
> and between amp and tuner,  and so forth.
>
> Questions -
>
> 1)   What if I put those ferrite beads on ALL my coax jumper cables as
> they run between rig and amp and tuner ?   Any downside to this ?
>
> 2)   What if I installed those beads on outside coax cables, at the feed
> point, as suggested in the many articles I have read.   Any downside to
> this ?
>
> 3)  What if I do both  1)  and   2)...   and install them all over the
> place ?
>
>                THANKS in advance for your insight.
>
> ======================  James - K8JHR  ========================
>
>
>
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