Hello once more!
I’m building my Raspberry Pi ADS-B tracker and I am going to use a collinear antenna on top of a 3meter mast. After the Raspberry Pi I will have a direct ethernet connection with my ethernet switch (with something like 20m Cat6 cable).
I’m thinking that I have to use a Lightning Arrestor/Protector after the antennas N connector. Something like this one: http://www.rfcnn.com/upload/photo/3915735e2bb0b34612073abaf6633b3e.jpg
Is this a good idea or not? Do you think that a lighting strike on an antenna like that is possible or not? Will I have signal reception issues using this protector?
I think the only way to know its impacts on the reception will be to try it to see if it attenuates the signal. A lightning strike is always possible, it can damage things via a direct hit or unexpected paths.
I recently had a lightning strike a tree over 300 meters away that took out my Raspberry Pi power supply. The Pi and radio dongle were not affected as the voltage surge apparently came through the electrical service ground connection, so don’t overlook protection for the power source.
I have one fitted and i cant tell its in circuit.
Hi, reviving this thread with a specific question of advice on hooking up the lightning arrestor. I’ve purchased this arrestor:
https://www.amazon.com/dp/B078NT5M37/ref=sspa_dk_detail_1?th=1
I plan on screwing it to the bottom of my 1090 outdoor antenna (the Flightaware one in camo green). The antenna/arrestor will be mounted to the side of my house peeking above the roof using a satellite mounting arm like this:
https://www.walmart.com/ip/Antop-Antenna-Inc-J-pole-Outdoor-TV-Antenna-Satellite-Mount/927625211
(not that specific one but close enough).
I’m going to run a 9-gauge aluminum wire down from the base plate of the mount to a grounding rod (with as few bends as possible and no sharp ones at all).
Here’s the question given the setup: shouldn’t I be able to run a wire from the lightning arrestor to the same location where the aluminum grounding wire attaches to the base of the J-pole? This would be a distance of maybe 30 inches, max. If the base plate is grounded I would think it’s OK to ground the arrestor to the plate?
Thanks much for any advice/feedback.
Unless the j-pole is attached to something metal i would run the ground wire strait to the arrester.
Your better approach is to have the “surge” arrestor located just before the coax enters the house.
The straight run of coax coming down from your antenna is capable of acting somewhat like the winding of an alternator for a nearby stroke of lightning, resulting in a current on the coax.
Equally, certain atmospheric conditions can result in high amounts of charge building up on antenna systems.
The surge suppressor, mounted low on your feedline “hopefully” would bleed off of those types of damage causing electrical charges before they get into your equipment.
Other potential sources of damage is current coming in through lighting caused inductance currents on the various telecommunications infrastructure such as: telephone, cable TV, internet services.
Often referred to as “backdoor damage”. To minimize such risk, I have protection devices from the company APC on all of my incoming telecom lines.
However, with a direct lighting hit - all bets are off.
The amount of voltage and current is unimaginable. If you realize that the stroke of lightning travels hundreds or thousands of meters of open air… the arrestor doesn’t stand a chance and would be vaporized in a millisecond, along with everything connected to it.
Crazy idea asked in brazen ignorance: what if I wrapped a piece of 10 gauge aluminum wire around the cable just before it enters the house and ground that back to the plate as well? Would that not serve the same purpose since, theoretically, the charge would be building up on the exterior of the cable?
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Contains:
(1) Building Lightning Protection System (BLPS) for the Protection of Building and Persons Occupying it.
(2) Lightning & Surge Protectors for Electrical and Electronic Equipment
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Unfortunately I don’t think that latest suggestion would deal effectively with any equipment hazardous voltage that is inside the coax.
The design of of the surge arresters I have used generally is with a small replaceable cartridge (think of it as something like a fuse) and with an overall design that would permit voltage over a certain threshold to bleed off to ground. That voltage threshold usually is well high enough to allow use of bias-T voltage injectors to power amplifiers that some people mounted up close to their antenna.
However, once the danger threshold is exceeded, the surge device protects the equipment by shunting to ground, requiring the replacement of the cartridge.
Companies such as Alpha-Delta or MFJ have an offering of surge arresters which are available with popular SO-239, N and F connectors. Depending on the risk of lightning a one’s location, these items certainly may be worth the investment. They are available through communication dealers, ham radio dealers etc.
- “Alpha Delta F Connector Coaxial Surge Protectors are rated for 200 or 2,000 watts at frequencies up to 3 GHz. They are not DC-blocked, so they will pass control voltages in applications requiring the coaxial cable to carry both RF and DC voltage. They can be easily mounted for the most effective grounding with their 1/4-20 in. stud in a single hole, or as a bulkhead through the grounding panel.”
Besides being an ADS-B hobbyist, I work in information technology, and have been a “ham” for over 25 years; while living in an area prone to very intense summer storms, frequent lightning (and the occasional tornado), so I have taken a lot of effort in things like surge protection and systems grounding.
I just see the link that user abcd567 has put up for reference - a good explanation of protection of systems and the various paths that lightning induced damage could occur through.
There are many great resources on this topic - including the US national ham radio organization “ARRL” which has many document visible from a quick Google search… http://www.arrl.org/lightning-protection
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Now to be clear, I’m looking for a second block of some kind that I can use with my SMA/N connectors so that I can arrest anything inside the cable.
The question I have is mostly theoretical – given that:
- The antenna is grounded.
- A lighting arrestor is directly below the antenna between the antenna and the cable.
- The length of the distance the cable travels to get inside the house is roughly 5 feet.
I’m wondering just how much energy would actually get inside the cable?
Assuming “enough to be a problem” is the answer, my next question is why a grounding block is seen as a solution in these cases? I keep looking at grounding blocks for Coax/F connectors and it looks like the inner connection itself is actually shielded from the metal of the grounding block, meaning that any energy inside the line would pass through anyway? Again I could easily be wrong, but it appears that the block is solving the problem for an external charge and therefore my idea of a coiled single strand of 10-gauge copper would be an adequate substitute for the grounding block?
But wouldn’t the lightning arrestor between the antenna and cable negate this?
With a direct lightning bolt of 10 Billion Watts passing through, everything in its path (the antenna, the surge divertor, the coax, the receiver) will all melt & vaporize in fraction of a second.
However induced charge due to clouds overhead, or a distant lightning strike is much low in intensity, and is diverted to ground by surge diverters, keeping the installation safe.
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A couple of points regarding GDT’s:
- The strike voltage is typically in the order 90~140V
- The response time is (relatively) slow, allowing surprisingly high voltages to be seen by the “protected” equipment.
BOURNS Datasheet has good info
Collinear antenna will be shorted at the top.
There is a lot of confusion here. GDT’s won’t protect against a direct hit, but they are protecting the input from induced over-voltages from close-by hits and to discharge static electricity build-up.
However, all the receivers have inside a diode that is faster in reaction time, but that can be overwhelmed in some conditions.
The only protection against direct hits is a grounding wire, minimum 6AWG sized, connected to the mast and ground side of the antenna.
If a lighting hits the antenna, it won’t hit just the central wire, it will definitely jump to the ground that is close proximity. Remember, that strike traveled 300-1000 yards in air, for it it doesn’t matter one more inch of air. Even the cable insulation around the central wire is nothing for that level of voltage.
The ground wire has to be as straight as possible, no sharp bends, because those will act like inductance, limiting the discharge path of the strike (that has a sharp rising front).
If the antenna looks like a DC short (CoCO w/ shorted top, J-Pole, folded dipole, butterfly, patch etc.), can a GDT offer any addition protection?
Not all CoCo are shorted at the tip. And spider antenna (lambda/4 wires) is not either.
But yes, if it is DC shorted, there is no need for the GDT.
There is always a need for ground connection. Unless you like to have a lighting strike brought in the house by the cable.
