Re: [IRCA] [NRC-AM] Grounds, coax, leakage

[Russ Edmunds <wb2bjh@xxxxxxxxx>]

--- Patrick Martin <mwdxer@xxxxxxxxx> wrote:

> Russ,
> 
> In the case of all of the antennas here, the coax runs horizontally
> out
> to the antennas, mostly under the house (no vertical movement except
> where it comes into the house from underneaith, right up under the
> table
> the receivers sit on. Otherwise the coax in on the ground or buried
> to
> the antenna input at the matching transformers.  But I fiqure I
> should
> get a better grade of shield to get rid of unwanted signals on the
> coax
> as much as I can anyway. Getting CBU-690 at S9 with the coax
> disconnected from the antenna was quite a shocker. 
> 


*** Let me clarify something here. The coax doesn't have to be vertical
nor have a vertical component, so the fact that your coa is essentially
horizontal, while good, isn't a guarantee of no unwanted pickup.

But given Craig's experiences, I'm somewhat skeptical that you will
gain any noticeable improvement, and probably not enough to be worth
the effort and cost. 

The main reason I say that is because I don't see that you've yet
conclusively identified the problem yet. It may not be a problem with
the coax shield or even the coax at all. If fact, I'm not even
convinced yet that you have a problem to begin with.

Wire or wire and braid, even coax, has some innate amount of rsistance
for any given length. It seems that's within reasonable tolerances,
especially as measured with an consumer-grade meter. Further, when you
take your measurement, you're measuring the resistance of the center
conductor in one direction and the braid in the other - by necessity,
and so the real effective resistance that matters to you is probably
half of what you measured, because the active length of your coax is
half of the lngth you measured.



Russ Edmunds
Blue Bell, PA ( 360' ASL )
[15 mi NNW of Philadelphia]
40:08:45N; 75:16:04W, Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
AM: Hammarlund HQ-150 & 4' FET air core loop


       
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