Radar Arch Grounding

[svcattales]

Wow! The the inputs on this question turned into a full seminar on rf grounding and lightning protection. Thanks for the education. Rick, in one of your inputs you seemed to indicate that I needed more than one RF connection to seawater. Did I understand this correctly? If so, where should they be located and how should the 14-2 bundles be connected? Based on some of the discussions, copper sounds like a better RF ground than bronze and might also have better anti-fouling characteristics. Since I'm starting from scratch, should I look for some copper plates? Also you mentioned mounting the tuner ON the arch. My whip antenna is mounted within a foot of the bottom of the arch leg with a plastic standoff near the top of the arch. With this setup, I can mount the tuner below deck and only need about 24" of GTO wire to connect. I would prefer to keep the tuner below deck since it would be in the way if we put it ON the arch. Would this set-up limit the output of antenna?

[Rick]

I had incorrectly visualized from your description that the whip was mounted on top of the arch which would have made the arch a natural platform to form an rf ground for the whip. As it is no matter what you do you will lose energy into the arch. Yes, you certainly can place the tuner below decks although with a good installation you should not fear mounting one above decks (they are usually designed to do this) unless you just don't like the sight of it being there.

The main point is that a good rf ground be provided to the groundling lug of the tuner. If below decks it is not, therefore, as critical (except for lightning protection) to make the arch an antenna rf ground because it is not geometircally immediately below the drive point of the whip.

If you desire the arch to be a good rf ground and the arch has four "legs" then each leg should be directed as straight as possible via the #14 wire bundles to a thru-hull, if possible.

Copper is not as passive as is the alloy used in bronze thru-hull fittings. I don't know that the benefit of a slightly imporved resistance to marine growth is worth the expense of having to pay for expensive thick pieces of copper which can still erode away without the benefit of good zincs. Keep in mind that Old Ironsides did not originally have to live in a hot marina with other vessels generating all kinds of electrical effects with onboard electrical systems, etc. In addition, they did not have the benefit of good bronze metalurgy and understand just how to make a good passive marine bronze.

[svcattales]

Rick, thanks again for your detailed instructions. A copper plate may work initially until it starts to dissapear. Guess i will stick to bronze. I may go with a small dyna plate since it makes for an easy installation.