2
$\begingroup$

Currently I am evaluating options for my antenna's in regards to lightning protection.

My setup is a physical disconnect of all my antennas using an outside "patch panel". So every time I power up my station, I have to go outside and physically connect the antenna feeds to a patch panel which brings the feed inside.

Theoretically this is probably the best protection, however it is getting a bit of a nuisance. So I am looking at alternatives. [emphasis added, due to comments]

One of the obvious choices would be a lightning protector, there are various models and types, and there is plenty of information available.

However I have found an Antenna Disconnect product which seems to be a good fit as well.

The link provided is only an example, there are others. Or even "home brew" circuitry which can be found by searching using a search engine.

My question: what would be the theoretical disadvantages of such a disconnect system ?

[edit 1] I am not in a high-risk strike area, however we do have 2-3 lightning storms annually. Direct strikes have not occurred in a 10-km radius for the last 10-years (which is obviously not a guarantee that they can not occur)

[edit 2] I am aware of electrical code.

Any comments welcome.

$\endgroup$
  • $\begingroup$ so, what does your external disconnect look like? You unplug some BNC connectors? $\endgroup$ – Marcus Müller Aug 17 '17 at 13:01
  • $\begingroup$ @MarcusMüller : PL259 on the cables, SO239 on the patch panel, cables are grounded when not in use... about 2m from the patch panel. I unground the cables, move them to patch panel, and connect them. Patch panel is grounded per electrical code (single point of entry). Does that answer your question ? $\endgroup$ – Edwin van Mierlo Aug 17 '17 at 13:04
  • 1
    $\begingroup$ yes, indeed :) Well, it'll be damn near impossible to top that level of separation :) at least not a prices below commercial lightning arrestors $\endgroup$ – Marcus Müller Aug 17 '17 at 13:06
  • 1
    $\begingroup$ I'd say it is not much better than a good DC blocked lightning arrestor. This gadget still depends strongly on a well designed grounding, bonding and LPZ system. A strike will jump over the insulation and the 20 kA will lift up the radio side of the device to some kV. Then unless your shack is well bonded to the same earth, and has no other unprotected wires entering the LPZ, some of this will run down the coax and blow your radio or computer. $\endgroup$ – tomnexus Aug 17 '17 at 20:27
  • 1
    $\begingroup$ "Patch panel is grounded per electrical code (single point of entry)" Does that single point include the ground for your electrical power? Or are your radios plugged into the wall as usual? $\endgroup$ – Phil Frost - W8II Aug 18 '17 at 0:37
4
$\begingroup$

what would be the theoretical disadvantages of such a disconnect system?

Firstly, keep in mind that antennas don't cause lightning damage: grounds do. It's not clear from your description if your patch panel is grounded at the same point as your electrical service or not.

If it's not, you have two separate grounds. This doesn't comply with the NEC, and it increases the risk of lightning damage since lowest impedance path from one ground (electrical service entry) to the other (patch panel) involves going through your equipment. See How can I protect equipment against a lightning strike? and an excellent example from W8JI where a strike on a tree 20 feet away arced back out of the ground to travel down a beverage antenna which was grounded on the far end.

Assuming you have a good single point ground, the purpose of the disconnect, surge protector, or any other device you might put at that point is not to handle the surge current, but rather to keep all the conductors at about the same voltage. Lightning is common-mode, so fortunately most of that energy will be flowing on the shield, leaving whatever protection device you choose with a relatively small amount of energy to deal with.

Just any method of disconnecting may not be effective: the voltages involved may still be high enough to arc across gaps. They are certainly high enough to blow past any solid state devices. W8JI recommends a double-make double-break relay, with the reasoning being that any arcs will most likely go to ground. He does not use coaxial surge protectors, and has never had a radio damaged.

Commercial installations operate continuously and don't disconnect the antennas. Most use a DC block surge protector like the Polyphaser IS-50 series. I don't have any relay control system so I use this approach. My first one I bought new, but I recently decided used units are probably fine too. Used they go for about $25 USD, which is about as much as I'd expect to pay for a disconnect device or the parts to build one. I like that there's no chance of forgetting to disconnect something.

Both these systems work, which I think shows that it's not the protectors or the disconnects, but rather the ground system that makes it work.

$\endgroup$
  • $\begingroup$ Thanks for this answer. Just to answer a question, my setup would be similar to the "Better but not Perfect" picture as shown here $\endgroup$ – Edwin van Mierlo Aug 18 '17 at 7:15
1
$\begingroup$

NEC Article 810 has all the answers you need. Here is a great overview from Mike Holt:

http://www.mikeholt.com/download.php?file=PDF/Radio_and_Television_2014NEC.pdf

Article 810 covers outdoor TV, Satellite, and Amateur Radio antennas.

$\endgroup$
  • $\begingroup$ Thank you for posting, but this does not answer my question. I am aware of electrical codes, not necessarily the one you linked, as I am not US based. While I am following electrical code, my question was about the theoretical disadvantages of an (electrically controlled) disconnect system. $\endgroup$ – Edwin van Mierlo Aug 17 '17 at 12:03
  • $\begingroup$ Ahh ok, I apologize. I did not know you were not in the US. The big disadvantage is finding a switch that would successfully protect against a realistic surge voltage caused by lightning. You can consider an airgap to have an impulse withstand of about 1kv per 1.5mm of airgap. Many protection switches have physical barriers between the contacts to increase the air distance between them. These kinds of switches will be somewhat expensive, but it's a balance of cost and convenience. Polyphasers on the antenna side are good, but ensuring adequate clearance is also a must. $\endgroup$ – user2104506 Aug 17 '17 at 12:09
1
$\begingroup$

There is not much that is better than "PHYSICAL SEPARATION" of feed-line from the station. What you're already doing is the best bang for the buck, ANY kind of a switch CAN "ARC OVER" with a very close or direct strike (I would trust "POLYPHASER" devices before I would trust the switch you linked to). If you are in a lightning prone or "HIGH STRIKE" area, I would not change what you're doing now nor would I trust any kind of switch or PolyPhaser alone to protect your station (I can do a lot of walking for $100). 73

$\endgroup$
  • $\begingroup$ why would you trust Poly-Phasers before this particual (or any such) switch ? If arcing is a concern then surely a Poly Phaser can be arced over as well ? $\endgroup$ – Edwin van Mierlo Aug 17 '17 at 11:49
  • $\begingroup$ I have seen first hand direct hit's where the polly's have done their job and protected the station,,,and I have also seen these switches fail and become a block of melted junk under the same conditions. $\endgroup$ – W9WLS Aug 17 '17 at 12:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.