FCC Drops Morse Code Requirement!

[JouvertSpirit]

k1vsk,
Antenna height is more important in VHF propagation than HF. Not saying that it's not important for both types, just more of a factor in VHF. Antenna height is always relevant.

I'm not sure what you are saying about having a horizontally polarized antenna on a sailboat but it seems a bit of a stretch. There are plenty of COTS marine SSB antennas available that are vertical whips and have excellent propagation characteristics, right?

[hellosailor]

K1, i think you misreaed Jouvert's comment about "cabin top" as I first did, thinking he meant a horizontal antenna. He's talking about a vertical alongside the mast, supported/spaced off from it.

Jouvert-
Bad idea. The mast is a ground, so you are erecting your vertical next to a ground and transmitting 'into' ground. Ignoring that, you'd still wind up with a highly directional antenna, placing a second wire alongside the antenna starts turning it into a Yagi if it doesn't just dump the energy into ground.

With a horizontal antenna (typically a wire dipole) the distance above ground also does matter. If the antenna is within about 1/10th of a wavelength to the ground (i.e. 4-10 meters!) the ground affects the radiation pattern and you get an "NVIS" near-vertical-incident-system which sends your signal basically straight up, to bounce straight down, making great contacts within 200-400 miles around you--but not taking off to roam the world. So anything mounted horizontally on a sailboat would be quite problematic for long range communications.

If you wanted to erect a vertical, folks do that. Typically a 20+ foot tall pole on the stern quarter, as far away from everything else as possible. If you remember to take that down before rough seas...it can certainly work. Or, I suppose, you could turn the world upside down (so to speak) by putting the mast on an insulated step, adding an insulated mast truck to keep the standing rigging isolated, and driving the mast itself as a vertical antenna.
Before anyone calls me crazy and points out the mast should have a lightning ground directly to the keel...Yes, it should. So instead of disconnecting the antenna cable before storms...This would require connecting the lightning ground before storms instead.

Hmmmm....Only one way to find out, right?

[k1vsk]

[quote=k1vsk]"For HF propagation, antenna height is not as important as for VHF."

JouvertSpirit
Common misconception since people know that VHF is line-of-sight so one normally deduces, incorrectly, that for HF SSB, height must be irrelevent...

you'd want a horizontally polarized antenna for HF to be as high as possible.
So, if i explained it clearly, you can see that your antenna idea won't work unless you can elevate the horizontal antenna high up the mast. An impractical concept, hence,...


I guess I wasn't clear enough in the above.

Any HF vertical behaves similar to it's VHF cousin in terms of omni-directional radiation pattern but will be affected by nearby metallic objects (read- mast) moreso than a VHF antenna so putting it near a mast would not be a good idea. Both it's radiation pattern and impedance will change with proximity to a mast or shroud. How much is a crap shoot.

Probably the best place, which would be a compromise in any case, would be off the stern in close proximity to the waterline.

[JouvertSpirit]

Thanks for the insightful replies on the antenna mounting choices for HF! I never thought about the fact that the mast is a ground when running an antenna next to it (assuming a metallic mast).

Now I'm thinking about a wire antenna hoisted with a halyard (or maybe a permanent wire antenna connected to the top of the mast and angled off to the rear) with the base connected to a junction box mounted somewhere on the cabin top with standard coax type connectors on the inside (preferably near the nav station). And the wire antenna at an angle away from the mast. Thoughts? Or is the description too vague?

[k1vsk]

Not vague at all - you just described a random length sloper antenna which is a tried-and-true design. The only siggestion I'd make is that you feed it at the top rather than the bottom which is the tradional way to achieve max voltage lobe and good radiation pattern.
There is no magic bullet when it comes to antennas - they all work with some providing a marginal improvement in one respect or another such as impedence matching, radiation pattern, receive noise reduction from static, etc. The point is they are all compromises but you probably already know all this so have fun experimenting

[btrayfors]

JouvertSpirit,

Your intended antenna will work well, as you describe it. I've used one for 17 years on my boat, and have described it on numerous occasions in the past.

You can see the antenna here: http://gallery.wdsg.com/Maine-Trip-2...ckland1?full=1

Look at the little white "loop" in the center of the pic. It's actually not a loop. The antenna itself goes to the left, while the other white wire is the GTO-15 wire which connects the base of the antenna to an SG-230 automatic antenna tuner just beneath the deck.

The antenna itself is made of s/s lifeline, insulated, and about 40' long. It is nearly indestructable.

While there are theoretical advantages to top-feeding as VSK suggests, the practical and design considerations on a sailboat obviate this option, IMHO. Consider that this is an end-fed, random wire antenna. The antenna begins right at the antenna lug on the tuner, i.e., the wire connecting the tuner to the antenna is, itself, a radiating part of the antenna. Obviously, therefore, it is impractical and undesirable to run a large radiating portion of the antenna up your mast -- either outside or inside -- for top-feeding.

The only other ways to do it would be to use coax and ground the braid to the mast at the top; use balanced twin-lead or open wire transmission line, and a current balun; or mount the tuner itself near the truck of the mast. None of these is really practical for ocean-sailing, IMO.

So, feed this antenna at the bottom, just as you would a "standard" insulated backstay. Make your connections tight and waterproof. Be sure to pay attention to the need for a good RF ground system (another topic in itself).

After living with one of these "alternate backstay" antennas for the past 17 years, I'm convinced that they are actually preferable to conventional backstay antennas because:

1. they are cheap and easy to build;
2. they are rugged;
3. they work every bit as well as an insulated backstay antenna; and
4. they are easy to raise and lower for periodic maintenance.

Good luck,

Bill
WA6CCA