SSB grounding

[Afriki]

Hi
I am installing a new ICOM M-802 with a AT-140 tuner on my 43' monohull. My question is about the location of the tuner and the lengths of the antenna inside the boat and length of the ground from the tuner to my dynaplate:
Location 1: grounding copper is approximately 6' long and the part of the GTO-15 that runs inside the boat before it exits up through the deck is about 11' long
Location 2: grounding copper is approximately 12' long and GTO-15 inside the boat is about 5' long
Which do we think is better?

[Bycrick]

Put simply, the antenna SYSTEM, includes everything from the counterpoise, ie the from sea water or other sufficiently large conductor, to the end of the driven element. So almost anything big enough will radiate some power in some direction(s). It’s theoretically easy to characterize the performance of a free-standing, 1/4-wave, end-fed vertical antenna. But, when you tilt it, make non-resonant, feed it somewhere in the middle, don’t have a perfect counterpoise, and surround it with other conductive wires, the real-world performance will be anybody's guess. Ideally, the tuner would be at the bottom of the bilge, directly connected to sea water and the "antenna" would stick straight up with nothing conductive near it. But that’s hardly practical. In both of your two examples, you have a fair length of potentially radiating conductors inside the boat where they can couple to other circuits.

[Frankly]

A number of years back I did away with my jumbo Dynaplate and now use my center board SS tube with no significant change in HF radio operation. There are lots of things that can serve as a ground around the transom of a sailboat (assuming back stay antenna). Might want to rethink the ground connection and try to get that tuner as close as practical to the above deck radiating element. Also recently did away with the BS lower insulator to no obvious degredation (just insulate the wire). Try to not have anybody in the cockpit when transmitting anyway.


Frankly

[S/V Illusion]

Originally Posted by Afriki

Hi
I am installing a new ICOM M-802 with a AT-140 tuner on my 43' monohull.
Location 1: grounding copper is approximately 6' long and the part of the GTO-15 that runs inside the boat before it exits up through the deck is about 11' long

Tuner should be as close as practicable to the antenna. The reason being all of the GTO radiates, I.e., is part of the antenna. Between attenuation and stray RF, you want to minimize that length particularly inside a boat

Location 2: grounding copper is approximately 12' long and GTO-15 inside the boat is about 5' long
Which do we think is better?

A longer ‘grounding’ strap can serve as a counterpoise which is good. A shorter GTO length is also good as mentioned above.

[Lazerbrains]

On my last boat I installed a KISS SSB grounding system - very easy to install and it worked fantastic.

[Bycrick]

It’s quite true that any wire connected to the ANTENNA connection of the tuner is part of the antenna, above or below decks. What is often ignored is that anything connected to the GROUND connection of the tuner is also part of the antenna and can also radiate. One can even find high voltage points on radio station ground systems which can be several hundred feet in diameter.

[S/V Illusion]

Originally Posted by Bycrick

It’s quite true that any wire connected to the ANTENNA connection of the tuner is part of the antenna, above or below decks. What is often ignored is that anything connected to the GROUND connection of the tuner is also part of the antenna and can also radiate. One can even find high voltage points on radio station ground systems which can be several hundred feet in diameter.

Typically, that “ground” connection is grounded obviating any danger

[Bycrick]

Your statement is an illusion (forgive the pun). RF is distributed along the "ground" connection in exactly the same manner as it is "ground" connection. That’s why a center-fed dipole works.

[Brian.D]

Read this. After reading it, read it again. Then one more time for clarity.

[Afriki]

Thank you all for your replies. Brian D, I had read that article a few months ago but upon rereading it he does mention that the longest the distance between the seawater ground and the tuner should not exceed 15'. My Location 2 is 12' away from the dynaplate (and I may try the rudderstock which is about 7' away). The consensus also seems that it is important to have the tuner as close to the vertical antenna as possible, so again, Location 2 seems better.

Cheers, Ian

[Brian.D]

The consensus for tuner location is correct. Your antenna will start radiating at the GTO-15 port on the tuner. So your total antenna length starts at that port.

As for the length of the ground connection, many here have had success with the length being longer. Also, others here have used a length of GTO-15 as part of their ground system. My thinking is that Gordon does not want the ground wire/path to be a part of the "other side" of the antenna, but wants the saltwater to be the entire "other side" of the antenna. It may affect how the tuner will tune, JMHO.

[Lou-In-NJ]

One last comment Afriki, is that these types of antenna arrangements are "unbalanced" which means there is only RF current on the center conductor of a coax, and the shield side goes to , and only acts as a counterpoise, i.e. reflection of the current on the center conductor causing the electromagnetic radiation. In other words, it is NOT a dipole (center-fed, or otherwise) antenna, which by definition has currents on distributed on two connections, and simply connecting the shield of the coax to a length of wire, does not mean you have created a dipole. I say all this because salt water is a very good ground plane, and in a small boat and limited expanses, you are aiming to have a ground-plane antenna since you usually don't have the expanse for a half-wave dipole like the old ocean-liners with their antennas stretched between smokestacks and masts. And yes, your tuner should be as close to the antenna as possible, otherwise your coax between the A.T. and your antenna becomes too much of a radiator itself and will likely lead to excessive RF loss and a poor radiation pattern.

[Afriki]

Thanks to all again