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 Post subject: ESD Protection
PostPosted: Fri Aug 04, 2017 9:42 pm 
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Joined: Fri Aug 04, 2017 9:33 pm
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I have made a 54 foot Dipole antenna for my RTL-SDR to receiver HF and it will be connected all the time. I want to know what I should do for ESD and Lightning protection. I will be running the cable to a ground block to ground the cable.


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PostPosted: Sat Aug 05, 2017 12:58 pm 
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Spark vs. lightning strike differ in duration and the amount of energy contained

While Lightning is deadly, ESD is mostly not to humans, and only to sensitive electronics. You will have to read up a bit to understand and decide what you need. Therefor there is imho no easy answer and will depend on your living circumstances. Here is what I know and hopefully others will amend/correct my post where necessary.

ESD or electrostatic discharge is described here https://en.wikipedia.org/wiki/Electrostatic_discharge.
The static electricity necessary for an ESD can be produced e.g.
- by body movement, shoes on a carpet,
- when you rub a balloon on a wool pullover
- through a trickle charge of AC devices not grounded (e.g. TV, monitor, notebook, PC).
- or at an antenna output when a thunderstorm is nearing, which is basically clouds rubbing and charging each other until they discharge through an enormous spark more commonly known as lightning bolt. Even a short ¼ Ground wave with many meter of coax acting as capacitor can produce a continuous spark discharge under such weather conditions.

When discharged through/into sensitive semiconductor devices, a spark destroys the today less then a µm fine structures of the electronic die in an electronic chip.
If the circuit cannot/does not have protection, designers add fast switching diodes e.g. across the (Rx-) input to short/limit the impact to ground. However diodes cannot protect in all cases of ESD, e.g. when the spark has to much energy or is to short to be grounded by diodes.

Surge protector devices are mainly to limit surges on power lines https://en.wikipedia.org/wiki/Surge_protector and will imho be not of much help, if at all, since they are intended to absorb much energy but are to slow to react to short sparks.

As said above most antennas, even a ¼ wave ground plane together with a transmission line acting as capacitor, both will charge until the voltage will discharge to ground or is discharged by a spark.

I know the below listed designs to limit such electrostatic voltage used in the past, but since the structures are very fine today some may bring more peace of mind than protection:
- Old receiver designs had a NE-2 or similar neon lamp (often called also neon bulb) or some similar form of protection. Unlike a spark plug that need kV to discharge the gas in the bulbs ignited around 120 V https://en.wikipedia.org/wiki/Neon_lamp
- a spark gap consists of two conductors, preferably sharp pointed needles, separated by less than a mm to act as discharge. I remember having read under dry conditions it takes about 2000 V to conduct in air, polluted air will reduce the voltage. Similar discharge can be seen in variable conductor having air as dielectricum during transmit.
- a preselector, filter which has a inductor in between antenna and ground which conducts the antenna to ground
- a resistor attennuator in front to maintain a low resistance connection to ground.
- or use preamp to take the ESD, this is what happened in most older Rx designs using transistors, the preamp was blown but most of the rest of a Rx, if not all survived

Lightning protection https://en.wikipedia.org/wiki/Lightning_strike has the prerequisite that you have an adequate ground system to take the large amount of energy contained in a lightning bolt.

While a lightning road will protect your house, it will most likely still create a lot of damage through secondary effects. Consider a lightning a part of a transformer which induces, due to the large current conducted during a lightning strike to earth, also voltages into “nearby” wires and will most likely damage sensitive electronic circuits in operation. I experienced a strike in a 3 story stone house, I heard pieces of a slate shingle fall to ground, while the microwave stopped working and the TV on standby switching power supply was damaged.

Lightning arrestors can help, but it depends on the sensitivity of your circuits and the energy they are confronted wit. Lightning arrestors are described here https://en.wikipedia.org/wiki/Lightning_arrester and use for long wire ant. here http://www.eham.net/ehamforum/smf/index.php?topic=89184.0

PS.: Maybee you can change your posts title to reflect that you are interested in ESD vs. lightning protection for long wire antenna


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 Post subject: Re: ESD Protection
PostPosted: Sun Aug 06, 2017 8:35 pm 
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Joined: Fri Aug 04, 2017 9:33 pm
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Well for the ESD Protection should I use a resister or a TVS(Transient voltage suppression) Diode connected to ground to drain the static buildup and what value should I get? I'm thinking I might also add a Gas Discharge Tube for added protection as well. Do you guys have any other ideas?


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 Post subject: Re: ESD Protection
PostPosted: Thu Aug 10, 2017 1:52 pm 
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Joined: Mon Nov 19, 2012 11:54 pm
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Resistor to discharge slow static build up, GDT or diode for extra protection, and a lightning arrestor for lightning.

Make sure your mast/coax is grounded and you really should bond the grounding rods between antenna ground and electric ground with copper strap to ensure they are at the same potential. This requires digging.


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