Antenna static electricity discharge.

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vk3tjs

Guest
After our on air discussion about storms, electricity discharge I found an interesting article covering various ways of solving the issue and protecting the equipment.
 
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VK3ZYZ

Guest
The choke looks to be the way to go.
It would be interesting to test a few and see what changes to the antenna tuning result.
 
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VK3YNV

Guest
The magazine article I referred to was in Critical Comms Magazine Nov/Dec 2020,

On a normal fine, sunny day the earth has a slight negative polarity, and the electric field so created is about 300 V per metre. As a thunder cloud forms, separation of electric charge in the cloud creates a surplus of negative charge in the base of the cloud and over a period of many minutes this will build up to create an electric field in the order of 10 kV per metre. Imagine the electric field as essentially horizontal lines, as per Figure 1.
https://www.criticalcomms.com.au/co...iocommunication-sites-872304496#axzz6dYmeNUid

I've got some Gas Discharge tubes I use on RS485 comms networks, they are cheap enough and it would make for a nice simple lightning arrestor PCB, I'm thinking coax in/out and a hefty ground connection. Maybe a choke for the DC ground path.
 
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VK3ZYZ

Guest
It will be interesting to see what power they will work to.
They are way more robust that NE2s or similar Neon tubes.
 
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VK2RK

Guest
The choke looks to be the way to go.
It would be interesting to test a few and see what changes to the antenna tuning result.
The use of a choke at first may appear to be a good solution, however the shortfall is that the reactance will vary with operating frequency, the best method is the neon globe, its capacitance is so low that the reactive effect will be negligible.
Note that the neon striking voltage depending on the construction is from 40 to 100 volts, when it ignites its resistance is virtually zero.
On some designs, diodes have been used as protection, but this has also a problem, that it degrades the inter-modulation rejection ability of the front end in the radio due to the creation of second order harmonics of the received signal or any adjacent strong signals, turning the diodes on.

Another preferred method that has been used in many solid state radio front ends is the use of an incandescent globe, when cold the filament has a very low resistance, when there is enough current the globe filament heats up and the resistance increases, limiting the current into the RF amp.

Using a fixed resistor to ground is a solution that I don't like because the voltage will increase as the current increases, thus the stronger the field the greater the voltage.

None of the above will protect against a direct lightening strike, only offers protection against static build up in aerial systems, with lightening one is dealing with fast rise time events, thus the protection device must have fast response time.
A device suitable for this application is the MOV (Metal Oxide Varistor), even here we have a trade off, that as the MOV does its job it degrades and becomes inoperable, requiring replacement after any strike events near or far to retain the assumed protection.
Ray mentioned gas discharge tubes, these work in a similar manner to neons, but can handle larger currents, the principle is the same, the ionization of a gas at a required voltage, when this happens the device assumes a very low resistance.
 
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VK3ZYZ

Guest
If anyone is interested, I have a couple of thousand MOVs of 275V rating.
Also, a selection of other voltages.
 
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BillC

Guest
In the old days some longwire instalations used a static bleeder to discharge such voltages to ground . The gadget consisted of a porcelain body with two sawtooth plates adjusted for a couple of thou. separation, one plate on the line the other plate on the ground cable.This thing would crackle and fizz away with ever increasing intensity in the presence of a storm until a nearby lightning strike would discharge the immediate area, after a short time the process would start again and would continue until such time as the storm moved away. Maybe a spark gap discharge could be used to advantage in parallel with other devices in the "ALL IN ONE DISCHARGE BOX"
 
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VK2RK

Guest
In the old days some longwire instalations used a static bleeder to discharge such voltages to ground . The gadget consisted of a porcelain body with two sawtooth plates adjusted for a couple of thou. separation, one plate on the line the other plate on the ground cable.This thing would crackle and fizz away with ever increasing intensity in the presence of a storm until a nearby lightning strike would discharge the immediate area, after a short time the process would start again and would continue until such time as the storm moved away. Maybe a spark gap discharge could be used to advantage in parallel with other devices in the "ALL IN ONE DISCHARGE BOX"
This uses the principle set by the Paschen curve, here is a link to better understand " https://en.wikipedia.org/wiki/Pasch... at standard conditions,is therefore 3.4 MV/m. "

The method you mention has one flaw that been in an open air environment, the gap strike voltage is variable, things like humidity and air pressure have an effect on the strike voltage taking place due to the ionization of the air (gas) in the gap.
The evolution of sealed devices came about due to this problem, a known gas with a known gap provides a predictable exact strike voltage.
 
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BillC

Guest
Thanks, It sounds as though a vacuum / gas filled device would do the trick.
 
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