BoatBanter.com - View Single Post - non-insulated backstay on metal boat

Larry

wrote in news:1180601311.461858.45960
@r19g2000prf.googlegroups.com:

Does this sound like a good idea?

Well, not really.

I did it with shrouds for a while and it did work, somewhat. I could
tune it but radiation proved less than the insulated backstay when my
captain switched boats. Here's why....

If we feed the backstay (or shrouds) from the insulated-by-fiberglass end
on the stern, the instantaneous antenna current goes, for this instant,
up the backstay and we'll call this radiated wave because of this
current, "in phase". At the top of the backstay, connected to the mast,
the instantaneous current now flows DOWN the mast, OUT OF PHASE with the
backstay current, creating a wavefront that is "out of phase" with the
wavefront created by the backstay.....cancelling lots of it because there
is a significant difference in distance and angle with the backstay.
This creates a radiation pattern that has many small lobes and many deep
nulls, all rotating around as the boat swings, which is not good. The
current will also flow down all the shrouds and forestay, making the
radiation pattern even more complex.

It'll radiate, but not as good as an insulated backstay, which is really
cheap to accomplish.

I'd rather be feeding the mast from the bilge with insulators on all
shrouds and stays, myself, using the iron or lead keel as a significant
ground plane, but that's not very practical as it would be hard to
accomplish and even harder to keep from corroding into oblivion. All
boat antennas are a great compromise. It's amazing they radiate on HF at
all...(c;

Larry
--
W4CSC