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

[Dr. Gerald N. Johnson]

The benefits on receive are that they can reduce the noise picked up by 
the outside of the coax. That noise can come from the house, or the 
neighborhood, or a vertically polarized storm many miles away, presuming 
your antenna is horizontal and discriminating against those noise 
sources. But if the DX signal was being heard by the vertical pickup on 
the feed line, it may get weaker.

The benefits on transmit are slight, unless that coax radiation has been 
putting more RF into nonham equipment like the neighbor's stereo. There 
is a chance of reducing the vertically polarized component of your 
transmitted signal improving the spacial "purity" of your signal, but if 
the choke is more dissipative than reactive the increase in the 
horizontally polarized component will be too little to measure at the 
distant station's location.

73, Jerry, K0CQ

On 8/8/2010 2:19 PM, Richards wrote:
> Hi Jim.... I am working my way through your piece, and getting the
> drift that  clamp-on ferrite beads do not typically hurt me, but unless
> I have A LOT of them, they won't help much (if at all).
>
> I did like this quote (taken slightly out of context, of course...) :
>
> 	Receiving Antennas benefit significantly from the addition
> 	of a common mode choke to isolate the antenna from its
> 	feed line. Both ends of the RG6 feed line to each of my
> 	Beverages takes 8 turns through one of the Big Clamp-Ons.
>
> And yet, if I read your Figure 35  on page 26 correctly  (unlikely, but
> I will try, anyway...)  it seems to say one needs A LOT of ferrite beads
> to make a substantial difference - on, say 40-10 meters, even more on
> lower bands - but the chart indicates numbers tested were like 20 and 40
> beads... and if those are the typical 1/2 inch long beads (or the .19"
> beads mentioned int he text),  then it seems one needs just 20-25 inches
> of beads to have some meaningful
> impact / effect.   THAT seems tolerable if one was going to use clamp-on
> beads - as did W0IYH using a string of clamp-on beads on his 10M
> antennas - with good effect  (acknowledging he preferred them over other
> types for convenience and specific reasons associated to a phased
> cabling already in place...)
>
> So, they seem to have some positive effect -  BUT AM I CORRECT THAT THEY
> HAVE NO SIGNIFICANT DELETERIOUS OR HARMFUL EFFECTS if placed on the coax
> near the feed point?
>
> I am especially interested in whether or not they might have more or
> better impact on a receiving antenna than on one I transmit with.   I
> use several receive only antennas, and anything to lower noise thereon
> is a bonus.   I would anticipate they would be more benign in a receive
> only setting than on a transmit -  receive setting.
>
> Any traction?   Or just wasting my time.
>
> =============================  JHR  =============================
>
>
>
>
> On 8/8/2010 1:05 PM, Jim Brown K9YC wrote:
>
>> benefit from reading my tutorial on coaxial chokes. Dissipation can be
>> made quite small if you make R large enough, and, as it turns out, it's
>> easy (and inexpensive) to do that if you understand the materials.
>>
>> http://audiosystemsgroup.com/RFI-Ham.pdf
>>
>>   =================================================================
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