[Elecraft] static buildup on antennas

[Don Wilhelm]

Gary,

The type of transmission line does not matter, there will be static 
buildup on the antenna wires, pure and simple.  That is conducted into 
the shack by the transmission line, whether that be coax or balanced line.

I am sorry I did not make that clear previously.  Most transceivers use 
coax input, and as long as the problem is solved before the coax reaches 
the transceiver, there is no remaining problem.

Yes. a resistor across the balanced feedline will be sufficient.

73,
Don W3FPR

On 9/10/2012 2:19 PM, 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?  Is the problem with discharges from precipitation and other static
> electricity sources with that feed configuration the same as for coax feed?
> (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)?
>
> 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?
>
> 73,
> Gary VE1RGB
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Latham
> Sent: September 10, 2012 2:35 PM
> To: Elecraft at mailman.qth.net
> Subject: [Elecraft] static buildup on antennas
>
> An antenna can get charged up in different ways. First, the earth has a
> fair-weather electric field of about 100 v/m near the ground. This field
> has a very high source impedance, so most things simply look like short
> circuits. If, however, an antenna is left disconnected that is not
> shorted, it will come to equilibrium with this static field and charge
> up according to its capacitance. The charge will probably bleed off, but
> not always. During high winds, especially with dust or snow, or even
> rain, the charge on the antenna can become very much larger. The reason
> for this is that not only can the particles, charged by friction,
> transfer charge to the antenna, but also particles leaving a conductor
> in the presence of a static field carry charge away from the conductor,
> leaving the opposite charge on the conductor. This is why the exhaust of
> a helicopter or aircraft can charge it up.
> Because antennas are raised above the ground, the fair weather electric
> fields can reach high values at the top of towers or other supports, and
> the horizontal elements of wire antennas as well. For example, a 30 m
> tower can have a field near its top of 3000 v/m. In addition, there is a
> shape factor that can raise this value even further. Then, any sharp
> point can go into corona discharge, so small currents will flow. This
> means any wire ends not covered with tape or blobs of insulating goop
> will generate small steady currents.
> All of these static effects can easily be taken care of by simply
> putting a 5k resistor to ground at the antenna terminations, either at
> the antenna itself or at switching points, etc. A good friend and I have
> K2's and suffered routine blowouts of the swr sensor diodes for these
> reasons until we put 1/2 w 5k resistors on the inputs. no more problems.
> During a thunderstorm, the static electric fields near the ground can
> get as high as 5000 v/m or even more, depending on the arrangement of
> the clouds with respect to your location. This means that the buildup of
> charge on antennas as described above can reach really high values.
> However, this static buildup will still be sufficiently taken care of by
> the resistance trick as above.
> Now we come to the other problem, induced pulses from lightning. As you
> all know, the lightning discharge, whether in cloud or to ground is from
> our point of view a huge antenna. The radiation peaks at about 1-5 MHz,
> but there are components for various reasons well into the VHF region.
> Proper antenna mast and antenna treatments can be found in the
> literature so I won't go into that. Find some good articles and follow
> their advice. One main thing to remember is to keep all mitigating
> switches, arc points, and their grounding stuff outside the shack. In
> case of a direct hit to any part of the antenna system, you don't want
> it inside!
>
> I hope this helps somewhat. More on the earth's fair weather field can
> no doubt be found online.
> 73, Don
>
>