Grounding a roof mounted PVC CoCo antenna?


#1

I’m considering mounting my PVC enclosed 8 segment CoCo antenna on the roof and have been thinking about the need for lightning protection. My instinct is to stick a grounding rod in the ground and connect it to the coax outer conductor with a grounding block as you would a regular TV antenna.

The more I think about it, i’m wondering if it’ll do any good. The house is surrounded by huge oak trees, the antenna barely peeks over the roof line, and of course grounding the coax outer conductor doesn’t actually ground the (plastic) mast.

Then again, with a large enough electrical potential, anything is a conductor, so better provide a safe path to the ground.

Any thoughts?

Thanks!!


#2

I’m thinking that using a grounding block is better than nothing. Also, in the case of lightning damage it might help with your insurance claim if you show that you installed a grounding block as a precaution.


#3

I’ve grounded the bracket that holds the steel mast to the wall using a 6mm copper conductor to a 1.2m earth spike.

This does earth the outer of the coax.

A side effect is that it also will provide a ground path for the static build up which seems to cause the Pi to sacrifice it’s Ethernet port if there is no grounding.


#4

We send a lightning arrestor with FlightFeeders but these can easily be bought online or a local electronic store. The main thing is to find one with the right impedance and connector to minimize insertion losses.

The lightning arrestors we use are gas discharge tube. They only conduct electricity once it reaches their breakdown voltage. This will ground the entire wire (inside and outside conductors) and hopefully shunt most of the power to ground instead of inside the home.
en.wikipedia.org/wiki/Surge_protector


#5

[quote=“david.baker”]We send a lightning arrestor with FlightFeeders but these can easily be bought online or a local electronic store. The main thing is to find one with the right impedance and connector to minimize insertion losses.

The lightning arrestors we use are gas discharge tube. They only conduct electricity once it reaches their breakdown voltage. This will ground the entire wire (inside and outside conductors) and hopefully shunt most of the power to ground instead of inside the home.
en.wikipedia.org/wiki/Surge_protector
[/quote]

Can you please give a link to the specific lightning arrestor you use? Thanks.


#6

I received from Flightaware, with the FlightFeeder, this high quality L-com surge-protector.

l-com.com/surge-protector-n- … -protector


Lightning Arrestor
#7

Thank you! That looks like a nice piece of hardware.


#8

[quote=“david.baker”]We send a lightning arrestor with FlightFeeders but these can easily be bought online or a local electronic store. The main thing is to find one with the right impedance and connector to minimize insertion losses.
[/quote]

Maybe one of those could be added to the optional section of your RPi shopping list at
flightaware.com/adsb/piaware/build


#9

All - Thanks for the fantastic feedback on my original question. I ordered the above recommended lightning-arresting grounding block. An insertion loss of 0.4 db seems well worth the added protection.

I also agree on the need to create a consolidated list of optional components. I needed to order a bandpass filter, as the cell tower at the top of the hill about 1500 feet away overwhelmed (and pretty much blinded) my RTL. I’m using the VBFZ-1065.


#10

Beyond just being a good idea (to have a surge / lightning protector) … you may want to consult your electrical code - in many cases this would be mandatory.

Even if you have trees and other objects nearby that are higher … you can think of lightning as having lots of fingers - while a tree may take the bulk of a strike other objects in the area would also be affected.

I would always advocate surge suppression for all external antennas. When choosing the location for the surge suppressor make sure that the ground wire from the suppressor to earth is as straight as possible - avoid coils and sharp bends. If the suppressor is on the outside of the building a small coil or two of the coax before it goes into the building can also help minimize lightning following the feedline.

For more reading:

PolyPhaser White Paper

Detailed Report on Surge Arrestors

Bob W1QA