Dipole Bleeder Resistor

[VK4GJW]

Evening all. Was wondering what the general consensus is on the use of static bleed resistors between the elements of a dipole antenna? I was thinking in the order of 10-100K Ohm, 1/2 to 1 Watt. No, this is NOT for lightning protection! For that I disconnect the antenna completely! Just for static buildup caused by wind across the dipole antenna, what with all our dry conditions and all (having said that it is currently bucketing down rain at the moment! ).

[VK4UH]

I cant see that fitting a resistor ACROSS the two halves of a dipole can do anything to bleed off static charge, building up from any source, If the antenna is isolated from ground.

What is needed is a high resistance path to earth of about 500K -1M from all part of the antenna.

If one side of the dipole IS grounded eg via coax braid then a high resistance across the feeder will provide DC/static ground for the other half of the antenna

Alternatively a simple inductance to ground may be a better option, the reactance at the design frequency being 10 or more time higher than the feed impedance of the dipole.

If you are using a balanced dipole, eg with open wire feeder, then there may not be a DC path from either side to ground for static to bleed off. Then you need a high resistance or high inductive reactance to ground from both sides of the feeder

As stated this may reduce static "noise" on receive during hot dry windy days or during "static rain" where the raindrops themselves are charged as they fall.

This technique cannot reduce the amplitude of lightning crashes (noise) and certainty provides no protection from lightning strike or damage

[VK4GJW]

I probably should have described my antenna better. It is an Inverted V 40Mtr dipole, with the centre at 10Mtrs above ground. It is coax fed, with a 1:1 balun at the apex. So being coax fed it is not entirely isolated from gound, all be it that that ground connection is via the coax. Having said that, I have no ground connections in my shack (desk, and in a rental property!) and no earth rod installed outside. I have had the antenna up for over 18 months now with no problems, so maybe I should leave well enough alone. I do disconnect EVERYTHING when storms are approaching and departing, which includes the coax AND the mains plug from the wall!

[VK3ALB]

A 1:1 balun is a DC short and generally has a path to ground. There's no need for any kind of resistor.

[VK4TI]

"VK4GJW"I probably should have described my antenna better. It is an Inverted V 40Mtr dipole, with the centre at 10Mtrs above ground. It is coax fed, with a 1:1 balun at the apex. So being coax fed it is not entirely isolated from gound, all be it that that ground connection is via the coax. Having said that, I have no ground connections in my shack (desk, and in a rental property!) and no earth rod installed outside. I have had the antenna up for over 18 months now with no problems, so maybe I should leave well enough alone. I do disconnect EVERYTHING when storms are approaching and departing, which includes the coax AND the mains plug from the wall!""


The balon will take of the static bleed however if using a vertical a decent ferrite core choke would help . I hope you have the coax grounded at tower base and window entry ??

[VK3ZAZ]

A 1:1 balun is a DC short and generally has a path to ground. There's no need for any kind of resistor.

I am with you
want to bleed static use spark gap like we do in broadcasting,
better still when clouds arrive pull out lead from radio and throw out the window.
some hams do weird science..

[VK4WDM]

VK4ZAZ wrote:

want to bleed static use spark gap like we do in broadcasting,

In the days when open wire line was the only feeder hams could afford spark gaps were often used on both wires just before they entered the shack. Some hams used actual engine spark plugs with the top terminal connected to the feeder and the bottom end connected to a ground wire with a nut. This also provided a convenient anchor point for the feed line. You had to be careful to make sure that the gap was wide enough so that RF would not arc over during tune-up. This setup was more for lightning protection rather than static bleed.

But I agree with Steve, to be on the safe side, disconnect if in doubt.

73

Wayne VK4WDM

[VK4UH]

All good Greg

I agree entirely with Lou 3ALB as above

With the antenna system you describe the balun you have will provide a path for DC (static charge) to bleed off from both sides of you antenna and down through the coax braid to ground

Even without a dedicated RF earth spike (which is an RF path not for a DC or static) there will still be a path via the mains earth at least for static to bleed away.

A valuable question none the less

KJ VK4UH

[ZL4DK]

This is an extremely good question and I think something overlooked in a lot of antennas. I have seen sparks leaping a couple of inches from a the disconnected end of a long wire antenna under certain wind conditions. The effect is not just limited to HF, I have also seen sparks jumping from the inner to the outer of a disconnected PL259 connector on a 2metre 5/8 whip (this was with wet conditions on a hilltop).

It is concerning what equipment this could be damaging. Many preamps have a capacitor on the input with no DC path to ground. I have seen one preamp design that specified an optional resistor to ground to drain this charge (I think the value was in the 10k-100k ohm range).

It would seem that antenna designs that avoid this problem are a good idea. Yes a wound 1:1 balun will provide this DC path; however a choke type balun (i.e. several turns of coax on a former) does not. A coax 1/2wavelength 4:1 balun also does not. I have sometimes added a wire from the braid at the end of a 4:1 balun to the cold point on the centre of a folded dipole to cure this problem (this should not alter the tuning or SWR of the antenna if it is working properly).

Also a good idea I have seen is the addition of a shorted 1/4 wavelength coax Tee at the input to a preamp.

I would be interested in other ideas and experiences on this topic.

Regards
David ZL4DK

[VK4GJW]

While everyone has stated that my 1:1 balun will provided a DC earth, it wont. It is in fact a Guanella 1:1 coax balun, so the point is still valid, that I need a shorting resistor between the two antennal elements.

[VK2ZRH]

If it is a Guanella 1:1 balun (in other words, an unun), one leg of the bifilar winding goes from one 'wing' of the antenna to coax common (aka 'ground'), while the other leg of the bifilar winding goes from coax centre wire to the other 'wing' of the antenna. All you need is a bleeder resistor between the two 'wings' of the antenna.

Posted in the interests of clarification.

[VK3ZAZ]

While everyone has stated that my 1:1 balun will provided a DC earth, it wont. It is in fact a Guanella 1:1 coax balun, so the point is still valid, that I need a shorting resistor between the two antennal elements.

The pic below has dc static bleed of one side and if u want to shunt your rf signals with a resistor go for it mate!

Ive had dipole for decades and never provided for the issues you seem to have generated in your mind.
do your own research and decide.








http://vk6ysf.com/balun_guanella_current_1-1.htm

[VK5APN]

Or build one of these for a DC path to ground. Either the 1:1 or the 4:1

Cheers

Wayne

[VK5ZLR]

I too have seen my pigtails arcing over under certail wind conditions. Can't any harm in putting 100k or 1M across it, the loss due to resistor is going to somewhat less than infintessimal, but not actually zero......

[VK4TI]

I added a substanual ferrite cored choke to my 43ft vertical and stopped some problems , didnt help most of the noise though