[Elecraft] static buildup on antennas

[gary bartlett]

Thanks, everyone.  Perhaps I should have emphasised the word *balun* in my
original post by describing what I was using.  I modified an MFJ-949
transmatch by replacing the original 4:1 balun by a 9:1 Guanella.  One
terminal of each side of that balun transformer is/was tied to ground in
either case.

73,
Gary VE1RGB

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Fred Jensen
Sent: September 10, 2012 5:01 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] static buildup on antennas

Comments interspersed since you asked questions.

On 9/10/2012 11:19 AM, gary bartlett wrote:
> Can someone comment on this issue as it relates to balanced wire antennas
> like dipoles fed with ladder line and matched to a K3 receiver through a
> balun?

Doesn't matter, so long as the antenna is not at DC ground.  A grounded, 
shunt fed tower is at DC ground.  A dipole strung between it and an 
organic tower isn't.

> Is the problem with discharges from precipitation and other static
> electricity sources with that feed configuration the same as for coax
feed?

Essentially, yes.

> (Yes, I recognize, lightning would be a different issue.)   For that
matter,
> how does the K3 transmatch figure into the equation in terms of protecting
> the receiver from unfriendly charge build-ups (both when the radio is
> powered up and when powered off)?

Powered or non-powered, doesn't matter.  My K3 has a static bleed 
resistor inside, I also have 100K's [I think, maybe 50K] on coax tee's 
on the antenna connectors.
>
> If the concerns are the same for both types of transmission line, what is
> the protection configuration external to the radio for the ladderline
> situation?

Well, pretty much the same only not quite as convenient as the 
PL-259/coax tee solution.  Just put a 100K to ground from both sides of 
the balanced line.  If you have a balun in your configuration, it's 
possible that it will DC ground your antenna through a center-tap.  It's 
easy enough to test.

We can talk this into way more of a problem than it really is, as Don 
mentioned, and possibly is happening.  The so called "fair weather 
field" of 100-200 V/m means nothing, its source impedance is so high 
that it delivers essentially zero current.  I'm 6'2" [1.87m] so standing 
outside, the potential of my head should be a few hundred volts above my 
feet.  In fact, I'm a short circuit and it is zero or extremely close to it.

Precip static is a problem only if your antenna input on the radio is DC 
insulated from ground.  The individual charges deposited in the antenna 
are very tiny but they add up in the input capacitance and the potential 
slowly ratchets up.

The no-more-stress solution is just put a bleed resistor on all your 
antennas, leave it there, and move on to working NH8S on all bands. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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