Static electricity on antennas

[MW0KXN]

I thoroughly enjoyed reading kite-lifted-long-wire-antenna-operation on the reflector which got me thinking more widely about static electricity build up on antennas. I have heard a steady ticking/ clicking on my radio on a couple of occasions, which alarmed me at the time, I made a hasty decent from the summit, and thought no more of it.

We are generally very poor at risk assessment. If we unknowingly put ourselves at great risk a couple of times with no adverse consequences, we tend to assume that the same situation is safe to repeat. No matter how many times you survive walking across a busy road blindfold, it does not make it safe, and should not be recommend to others.

What are the real risks to me and my equipment from static electricity while operating on a summit using portable, wire, antennas for HF and VHF, at a height of less than 10m, and what could/ should I do to minimise risk?

If I am going to ask this question it seems only fair to do some reading first.

A bit of Googling unearthed a fantastic archive film from the US Department of the Interior, The Amazing Power of Static Electricity, it doesn’t answer all of my questions but it is 20 minutes of pure joy to watch.

My personal experience from UK school physics lessons in the 1970’s suggested that it is/ was safe to use a Van de Graaft generator and children holding hands to create large electrostatic sparks. Van de Graaff Electrostatic Machine Safety suggests that there is a ‘Genuine Hazard’ if Van de Graaft generators are used with Leyden jars, capacitors or human chains. From what I have learnt, I think that charging up a person to create a spark restricts the maximum stored energy to a safe level, limited by the capacitance of the human body (up to 400 picofarads). Discharging a stored charge through a person is a completely different situation and should not be assumed to be safe.

Static electricity - Wikipedia is another good read and provides some interesting references.

Wolfson Electrostatics website news has a section towards the bottom of the document ‘Can shocks from static electricity damage your health?’ which states:

The effects of electrical current passing through the human body are covered at length in the International Electro Technical Commission document IEC 479-2:1987. In this document it indicates that a transient or capacitive discharge, as is the case with static electricity, requires energy in excess of 5 Joules (5000mJ) to produce a direct serious risk to health… it is practically impossible to store this level of electrostatic energy on the human body …. Footnote: In some industrial processes, discharges of several Joules due to static electricity can occur under extreme conditions. In such cases the static charge accumulates not on the human body but on highly polarised materials where the effective capacitance is very high. These situations can give rise to extremely energetic discharges resulting in severe physiological effects.

If I assume that my antenna connector/ radio internals provides an air gap of 10mm or less, I think this limits the maximum static voltage in the antenna to 30kv (I can not justify this assumption). A 30m length of 0.5mm radius wire, 3m above a ground plane has a theoretical capacitance of 165 picofarads. If this is representative of my antenna, it can store a maximum of 0.075 Joules of energy which is significantly less that the 5 joules quoted to produce a direct serious risk to health. It may still be sufficient to produce a direct serious risk to my radio though.

Edit: My assumption of a 30kv maximum assumes that the potential is across the contacts of the antenna connector. Without bonding of the antenna or radio the entire antenna could float to a voltage only limited by environmental leakage.

Lightening is a whole different scenario. I suspect that the clicking sound is also warning me of potential lightening and is still a good reason to get off a hill.

Further questions:

• Do people have experience of radios being damaged by static build up?
• Do you use an earth stake (tent peg) connected to the outer of your coax?
• Is it worth connecting a spark gap and bleed resistor across all SOTA antennas?

SOTA is a hobby and I don’t want to kill myself doing it, or mislead others about the risks and safety of operating a SOTA station. I am an amateur asking questions, you need to do your own research and make your own choices.

73 Kevin, MW0KXN

[MM0FMF]

@MW0KXN

Do people have experience of radios being damaged by static build up?

Yes, but not when SOTAing.

@MW0KXN

Do you use an earth stake (tent peg) connected to the outer of your coax?

No.

@MW0KXN

Is it worth connecting a spark gap and bleed resistor across all SOTA antennas?

Maybe. But it’s more a case of knowing when such conditions arise and not operating. It’s more of a problem in the centre of large land masses (like mid US or Central Asia). Does happen in the UK .

With reference to a kite supported antenna… There’ll be no more static acquired by a 1/4wave 20m “kite vertical” than a normal 1/4 wave 20m vertical on a pole. It’s when you have an 80m or 160m antenna that you’ll be catching more static.

However, the problem of bleed away is over stated. You need a resistor that gives a DC path whose impedance will not upset your antenna. Here you go… pick 3W, 910K and get 100 of them for £6.50. One end to the antenna, one to a peg in the deck. Simples.

1/6W 1/4W 1/2W 1W 2W 3W 5W Carbon Film Resistor ±5% Range of Values 100KΩ-910KΩ...

[G4AZS]

This is my only brush with serious static, and as Andy mentions above, I should have known better and stayed off the hills, it was a really silly decision to carry on. The equipment survived, perhaps helped by being metal cased, current tracking around the outside and to ground.

Abrupt end to CW from GW/SW-015!

My apologies for suddenly going QRT today from GW/SW-015 at around 14:16, after completing a QSO with Vlad, OM1AX. Others were calling, but lightning threatened. First today I activated GW/SW-009 Mynydd Troed, including 24MHz S2S contacts with Mike 2E0YYY/P on G/SP-015 and Carolyn GW6WRW/P just across the valley on GW/SW-041. Carolyn mentioned the growing static crashes, and we agreed that it was time to get off the hills. I just had my gear packed, when the rain arrived. It looked like a pas…

I don’t intentionally earth anything during activations.

73
Adrian

[G8CPZ]

The size and frequency of static discharges (or static shocks, if you are involved) due to friction depend hugely on your location and the weather, specifically the humidity. When was the last time you got a static shock outside in the UK? [Me and the Missus can’t remember].

I would be more concerned about static discharges operating where it’s dry most days than where it’s damp a lot. I’ve just checked the humidity today in my Cumbrian village [75% - 84%, and it’s not raining yet!] and in Phoenix AZ. [25% to 12%].

[MW0IDX]

I haven’t used bleed resistors or an earth stake while activating. My only experience of static damage was when I activated Allt Fawr many years ago during the winter with lots of snow around. My HF radio suddenly went deaf and a 2m beam antenna that my mate (GW0VMW) was using started crackling loudly. Needless to say we downed antennas quickly and beat a hasty retreat!

[M1EYP]

Yes.

I have experienced static noise build up, sometimes accompanied with getting a small shock from the case of the radio, a few times. That is the cue to abandon the activation, but dismantling everything very carefully, using dry non-conducting material to insulate my hands against connectors etc.

As others have said, it’s better to use the weather forecast to avoid being out in such conditions.

I once spectacularly failed in this regard. To me, it looked like a passing electrical storm was going to give me a wide berth and I pressed ahead with an August overnight SOTA camp. I now know not to do that again, and thank goodness I am still here to be able to learn from my mistake.

12-08-20: The 2020 Perseids 144MHz Meteorscatter s2s event

[image] Worst storm in living memory apparently.

[MW0KXN]

Thanks for the link to your original post Tom. That sounds terrifying and I’m very keen to try to avoid anything remotely like your experience if I can, bleed resistor or no bleed resistor!

[MW0KXN]

@G8CPZ

I would be more concerned about static discharges operating where it’s dry most days than where it’s damp a lot.

This seems to fit with Rogers comments and some of my experiences which were on cold windy winter days.

My most striking case of static noise was on a warm summer’s evening on the coast with cloudless skies and a gentle breeze. I didn’t know what it was at the time, but now feel sure that it was static build up. I suspect the sea spray may have been responsible.

[M0WIV]

There are videos on YouTube showing static build up just before lightening strikes. I found this one after a quick search but there are others. Of course you do need hair on your scalp for this test.

Woman nearly electrocuted on Mount Princeton

[G0EVV]

I have had a few experiences of aerial static and its effects.

1. Back in the 1970’s I had a push button medium wave receiver in my car. The BF981 in the front end was twice destoyed soon after the radio emmitted a wailing sort of sound. This radio was of course not 50Ohm inpedance, being connected to a short mobile whip. Solution, a 1000Volt 0.1uF blocking capacitor and 10k to ground in the low capacitance screened aerial cable.

2. A low band AM tranceiver connected to a 1/4 wave GP in falling snow. Again the wailing noise and blocking. No permanent danage done.

3. Wailing noise and blocking of an FT 857 connected to a 40m dipole in misty conditions on an activation. No damage done.

Before embarking on additional static removal circuits, check your radio circuit diagram, many include such circuits.

Although aerial static may damage the rig, it is not life threatening. The difficulty for Activators is that high levels of static can also be the pre-cursor to a full lightening strike that will be life threatening. So if static is encounterd , take steps, big ones, down hill.

Regards
David
G0EVV

[G4OIG]

I’ve experienced static on quite a few activations, probably because I am generally prepared to operate in poor weather conditions and don’t worry unduly about getting wet. The worst experience for me was when Paul G4MD and I activated Gathersnow Hill GM/SS-077 and it started snowing. I received one heck of a shock when I heard the static noise and decided to disconnect the 2m antenna having just qualified the summit. Before that experience I had never associated snow with static as all occurrences had previously been in rain or mist. I suppose in all I’ve had maybe 4 or 5 shocks in all and thankfully no failure of the radio equipment.

[VK2AOH]

Over the years have had a few encounters with static electricity buildup. Usually on hot dry days where there is an approaching thunderstorm.
One evening whilst on Mt Nangar was using a vertical aerial with ground plane wires. So floating above ground.
In the evening a mist rolled in and heard the tick tick coming from the KX3. Abandoned the activation and hastily disconnected the aerial using a handkerchief as a insulator.

Shone a torch on the aerial and could see tiny mist droplets dancing all around the aerial wire.

73’s Wal VK2WP

[MW0KXN]

@MW0KXN

If I assume that my antenna connector/ radio internals provides an air gap of 10mm or less, I think this limits the maximum static voltage in the antenna to 30kv (I can not justify this assumption).

My assumption of a 30kv maximum assumed that the potential is across the contacts of the antenna connector. Without bonding of the antenna or radio the entire antenna could float to a voltage only limited by environmental leakage.

I have added a note to the main posted, clearly flagged as an edit.

[G8ADD]

I have had encounters with static electricity on mountains, and in any gathering of climbers it is a topic that will.arise from time to time, with descriptions of hair raising, St Elmo’s fire, buzzing noises from your equipment (particularly ice axes and walking poles) and one particularly lurid description of a summit cross in the Alps outlined in blue fire. You can get static build-up in blowing powder snow without a cloud in the sky! The conventional wisdom is to get off the mountain ASAP, but if you can’t (stuck on a ridge with no safe descents nearby or on a stance of a major rock climb) then move your metal equipment as far away from you as possible and wait it out. Most mountain encounters with static are harmless to people, but of course most mountaineers don’t have to worry about radio equipment!

[MW0KXN]

@G0EVV

Before embarking on additional static removal circuits, check your radio circuit diagram, many include such circuits.

Thank you for the excellent and informative reply David.

My much loved Kenwood TH-K20E handheld offers no DC path to ground and has a 50v rated chip capacitor across the antenna.

Good enough for the stock rubber duck. I hadn’t even thought to look before fitting an alternative antenna.

My also much loved QRP Ham Radio Kits DB4020 offers no DC path to ground but has 630v capacitors in the LPF and has a narrow gap between the BNC terminals providing a spark gap of kinds.

My Xiegu X6100 is a mysterious black box, and as it is still under warranty, I have no idea what is inside.

Once things start sparking, I imagine that blocking capacitors will offer no impedance to the spikes and I will have high voltages running right through the circuit. It’s a miracle that any of my radios are still working.

Having now checked the circuit diagrams I will build a short BNC to BNC cable with a bleed resistor, and a clip on earthing strap for non-rocky summits.

[MW0KXN]

@G4OIG

Before that experience I had never associated snow with static as all occurrences had previously been in rain or mist.

Thank you Gerald.

Rain, mist, or snow are encountered so frequently on UK summits that it seems likely that I will encounter static on my antennas again and am very grateful for the excellent advice and sharing of experiences on this post.

Several comments have confirmed that the ticking noise I have heard is due to static and a warning of potential lightening. I am now also aware that wailing noises and desensing are a symptom of static.

I had not even considered the possibility of static on VHF antennas.

Lowering the antenna (kicking it down if necessary) before attempting to disconnect the antenna from the radio is obvious now that I am comfortably sat at my computer, but is not necessarily the instinctive reaction when on a hill, unless you have thought about it before.

[MM0FMF]

@MW0KXN

considered the possibility of static on VHF antennas.

Quite a lot of VHF and up antennas will be DC shorts so the issue is a non-issue with them.

[G8CPZ]

@G4OIG

Before that experience I had never associated snow with static

It’s not really surprising. Snow is formed in clouds from ice crystals pushed together that then become heavy enough to fall. So, the same triboelectric charging mechanism [that I described in a post above] for ice crystals and air within clouds applies to snow flakes and air around you and your antenna at the summit - but on a smaller scale.

@G8ADD

You can get static build-up in blowing powder snow without a cloud in the sky!

Yes, for the same reason.

[G0EVV]

In dry air at 1 Bar the breakdown voltage between spheres is about 1kV per mm. (edit to add distance Sri)

[G8CPZ]

@MW0KXN

My personal experience from UK school physics lessons in the 1970’s suggested that it is/ was safe to use a Van de Graaft generator and children holding hands to create large electrostatic sparks

That’s because kids were still considered expendable in the 1970s. By the time I was teaching high school Physics in the 2010’s only the teacher was allowed to take those risks.

For example, Health & Safety rules meant we could no longer let the ‘students’ (as we called them by then) handle iron filings for looking at magnetic field patterns around magnets. The iron filings were in a clear solution enclosed in a see-through plastic case - but results not as good as the old method.

Re the V de G gen, high voltage but very low current. As the old saying goes “It’s the volts that jolts but it’s the mils that kills”.