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How do you properly ground a dipole (RX only for VHF scanning) to protect it against ESD/lightning?

In my set up i'm putting a dipole on my roof. I've connected the two dipole elements together with a 100k resistor, and have a balun and amplifier just under the roof, then 20m of coax to my receiver. So to protect the balun and amplifier I need ESD to shunt to ground before it reaches the amp.

Should I ground the antenna via the mast and some heavy gauge wire leading to a grounding rod? And then connect the shield/gnd element of the dipole to the grounded mast? I could then also use a gas discharge tube on the line before the balun and amp.

But if I do this, won't I affect the dipole by essentially lengthening the ground side element via the mast and grounding rod?

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  • $\begingroup$ Every metal mast should be grounded at the base. Let it be your lightning rod. I never connect my coax to the top of the mast, nor do my antennas extend above it.. Proximity to the mast is an issue if you are mounting the dipole vertically. Your balun should be the highest point of the dipole and below the top of the mast. And btw, I recommend discone antennas for scanning - they are wide-band. Mine's on a PVC mast. Dipoles are tuned to a specific frequency - the one VHF dipole I use is for NOAA WX Radio, mounted vertically on the side of the house (wood). I ground everything at the radios. $\endgroup$ – SDsolar Apr 3 '17 at 18:33
  • $\begingroup$ friendly reminder: please accept an answer or clarify what is not satisfactory about the answers you've gotten. This site stops working if askers don't give feedback!! $\endgroup$ – Marcus Müller Apr 15 '17 at 10:24
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The typical amateur radio / SWL budget will rarely allow for sufficient protection from a direct lightning strike. More often than not, the measures taken help minimize damage from a direct strike but more importantly they mitigate damage from near lightning strikes and static build-up.

If the goal is to bleed static and minimize damage then mast should be grounded (this is also an NEC requirement). The grounding should be carried out with a heavy gauge conductor (minimum of #6 by NEC) leading to a ground rod. The efficacy of the ground can be improved by using wide copper straps. The ground rods should be tied to the house system ground rod(s) with a minimum of #6 AWG wire.

The cellular industry has promoted bringing the coax down to the ground level and installing a lightning arrestor bonded directly to the ground system at this point. This is considered a best practice for amateur radio installations as well. If you cannot route the coax in this manner, installing a lightning arrestor in the coax at the mast and bonding it to the mast ground may provide some level of protection.

Be aware that your mast mounted pre-amp is considered lightning fodder. There is little that can be done to protect it from a near lightning strike when it is located so far from an effective ground. Some people advocate the use of an RFC (radio frequency choke) inductor across the input. This will offer some degree of protection but due to the rapid current rise (di/dt) during near lightning events, it is not likely to stop all damage.

Your resistor across the dipole legs will prove helpful to bleed of static that is generated by winds and nearby storms. You should periodically inspect this resistor as it too will be sacrificial in the event of a nearby strike.

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    $\begingroup$ W8JI has some additional information on resistor selection. It's for Beverage antennas, but should mostly be applicable to other types. w8ji.com/beverages.htm $\endgroup$ – Phil Frost - W8II Apr 13 '17 at 16:49
  • $\begingroup$ Thanks for this answer! I edited it just to remove your signature from the bottom, since the site already shows your name and profile link below. $\endgroup$ – natevw - AF7TB Apr 14 '17 at 18:48
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Simply grounding things by connecting them to some ground rod arbitrarily stuck in the ground will not protect anything from lightning: in fact it may make lightning damage more likely. The protection comes not from grounding the antenna per se, it's having a single point of entry to the station. For detail on how to ground things and for lightning protection generally, see:

How can I protect equipment against a lightning strike?

If you aren't going to go through the trouble of having a single point of entry as detailed in that question, my recommendation would be to not ground the antenna at all, or ground it with a separate system which is disconnected when not operating. Disconnecting the antenna will provide a degree of protection, but a direct strike will have no trouble blowing past the few feet between your station and the disconnected feedline. You can solve that problem with insurance.

If you are going to properly ground the antenna to a single point ground, assuming you are using a coax feedline, use a balun and ground the coax shield. Otherwise you'll unbalance the antenna. If you are using a balanced feedline it's probably still best to run coax from the transceiver to the station entrance ground, then have a balun outside. It's difficult to make a low impedance connection to ground with a balanced feedline.

You also say you've connected the dipole halves with a 100kΩ resistor. This is already an effective bleeder for static buildup, without any need for a discharge tube. Though if you want to include a discharge tube at the station entrance also it can't hurt.

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You should ground the shield of the coax before or at the connection point to the balun, not between the balun and antenna. Remember that the balun conversion between the balanced dipole antenna and the unbalanced coax cable.

Also remember that grounding does not protect you or your equipment from a direct lighting hit.

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  • $\begingroup$ Proper grounding does protect from a direct hit. That's why broadcast stations on mountain tops or tall buildings can get hit multiple times per year without damage. $\endgroup$ – Phil Frost - W8II Mar 31 '17 at 12:10
  • $\begingroup$ Oh, I wish I had your budget to do a proper grounding but my guess is that most hams can't afford the same kind of grounding that goes into broadcast antennas. Even then broad cast stations are getting damages from lighting. [search key: "off-air due to lighting strike"] $\endgroup$ – Claus Mar 31 '17 at 17:34
  • $\begingroup$ BTW, most commercial buildings and towers have lighting rods that are at a higher point than the antenna itself in order to direct the lighting away from the antenna. Although I'm not an expert in this area, this seems to be more effective than antenna grounding for direct lighting hits. Of course antenna grounding is still useful. $\endgroup$ – Claus Mar 31 '17 at 17:47
  • $\begingroup$ Gas discharge lightning protection tubes are really not that expensive when you compare to buying a really high-end shortwave listening radio. If you're hooking up a Radio Shack special and you can get more cheaply then it might not be worth it. When you have a few thousand dollars worth of radio gear it is completely worth it. Also you cannot depend on electrical ground because you could be on a battery system or their are not the shortest path. $\endgroup$ – Rowan Hawkins Mar 31 '17 at 23:24
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    $\begingroup$ Good grounding isn't so much an issue of budget as it is technique. Most of the protection comes not from expensive protection devices and 100s of kilograms of copper, but just bringing in all the cables at one point, and having a good ground at that point. $\endgroup$ – Phil Frost - W8II Apr 3 '17 at 13:37
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Here is what is advertised (and recommended by Elmers in my ham club) to connect your coax to a local ground. It is called a Lightning Arrester.

It has an internal spark gap that will only be jumped by a high voltage coming in from your antenna.

There is no direct connection that will have any effect on the antenna, as long as this on at the near end of the coax, and not right at the antenna.

Lightning Arrester

They are available from the usual sources.

I recommend grounding this the same place your radio chassis is grounded. That way this is nothing but a pass-through connector with an internal spark gap.

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    $\begingroup$ That little screw terminal alone will provide effectively no lighting protection at all. By grounding this to a water spigot, etc, you are creating a low impedance path between two ground rods which will not be at the same potential when there's a nearby strike, a low impedance which goes through your equipment. This is a recipe for bad times. $\endgroup$ – Phil Frost - W8II Apr 2 '17 at 12:38
  • $\begingroup$ How could it go through the equipment when it will only jump the internal spark gap during a strike? $\endgroup$ – SDsolar Apr 2 '17 at 20:45
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    $\begingroup$ It won't jump just the spark gap. Do you think that puny terminal lug and that teeny spark gap will really contain an entire lighting bolt? And what about the non-zero impedance of the connection to ground, and of the soil? Why would all the current go through that ground lug, especially when the wire attached to it is much smaller and thus higher impedance than the coax shield? How will this device help with the difference in potential between two ground rods: one at the electrical panel, another at the antenna? $\endgroup$ – Phil Frost - W8II Apr 3 '17 at 13:28
  • $\begingroup$ I agree about the shield, hence my comment that it should be grounded to the same place as the radio. (So, what two rods are you referring to?) Meanwhile, just think a minute about what you're saying. Do you REALLY expect your dipole to be your primary method of lightning protection? Next time you see a large rocket launch, notice the towers all around the rocket. They discharge the air to prevent strikes on the asset. Look up lightning rods - a la Ben Franklin. THAT's the best way to perform lightning protection. But the OP simply asked how to ground a dipole. So there you are. $\endgroup$ – SDsolar Apr 3 '17 at 18:16
  • $\begingroup$ Thanks for editing your answer. I think you should make clear that the place the radio chassis is grounded is almost certainly the electrical service ground. If one has the good fortune to have a feedline which runs past the service panel, that's an excellent place for grounding. If not, a new common ground point must be established for the station. $\endgroup$ – Phil Frost - W8II Apr 4 '17 at 12:22

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