Spring Stay Puzzle

[Renoir]

Your insulator can facilitate a dipole drive. A balun is installed to hang below the insulator, the coax is installed so as to angle back towards the mizzen to clear the main roach, barely. The compromise is to not have the coax downlead perpinducular to the beginning of the dipole yet, as has been pointed out, all sailboat antenna installations are compromises. The proof is whether or not the final installation works well or not. The dipole length consists of the spring stay plus the mizzen and main masts (assuming both are aluminum).

For 35 to 50 ft boats the installation may yield dipole dimensions which happen to work well on the 20 and 40 meter bands. If the dimensions are too small for these useful bands then small air inductors are placed in series with the balun output wires to the insulated leads tuned to give the correct performance. If the dimensions are too large capacitors are placed (selected to give the correct response) in series with the balun output leads. Obvouosly it takes two people using a noise bridge and an SSB receiver to achieve the tuning in place (who know what they are doing).

When done correctly the performance can be outstanding. Brion is correct in that most fixed receive long distance (DX) antennas are horizontally polarized and, therefore, for direct radiation from a transmit antenna, a horizontally polarized signal helps to maximize receive signal to noise ratios. Such compromise dipole installations typically have side lobes almost equal to the two direct lobes giving you four quadrants of directional transmission such that the lobes essentially touch each other yielding an overall omni-directional capability.

[Russ L]

Thanks for jumping into the discussion Renoir and good points.
So, for Bill's situation, with the pieces in place he will have a quasi inverted dipole. A local live-aboard HAM uses an inverted dipole on his sloop. I have learned that if you take a challenge into a meeting of HAMs you can come away with almost as many opinions as there are members attending.
What effect will a furling gear have on the forestay leg? Should the forward lead be "earth"?
He can be transmitting very easily & cheaply with the current set-up. I believe he should try your suggestion first.
Cheers, Russ

[Russ L]

For Bill's rig, in the most recent discussion, we have been assuming a plastic or wood boat and unbonded rig.
We do not want to 'connect' the ends of a dipole antennea together ...

Cheeers, Russ

[Renoir]

One cannot truly view a bonded rigging as a dipole with the ends shorted. You just have to try it first on the different bands to see what is the impedance presented. In some cases it just works great, in others not. Sometimes one merely has to install a knift switch in the one of the bond wires to open the while transmitting and close it in storms.

[billknny]

Gee, I thought I was asking a simple question! NowI know the reason that I became a chemical engineer instead of an electrical engineer!

Let's see if I have understood the things discussed.

With an insulator at the center of the spring stay, I can run a coax from the antenna tuner up to the insulator where I connect it to each side of the insulated spring stay with a balun (had to look that up, but still don't really have a good feel about what it might look like!). This makes a large dipole antenna witht he main mast as one leg and the mizzen as the other.

It sounds like there is a difference of opinian on the effects of the lightning gound on the mast, which theoretically would ground the two ends of the dipole, which even I know would not be a great idea!

All this might be of theoretical interest since it sounds like the lead of the coax can't go back to the mizzen along the spring stay. If it deviates much from that, it will interfer with my mizzen staysail, which I am loath to lose the use of!