GAM Backstay Anetenna ?

[SkiprJohn]

Thanks again Bill.

[alanperry]

Question:
Why couldn't you use 40 ft of the GTO-15 wire for the whole thing? Instead of rigging something else up to connect to it? ie the SST lifeling idea???

[btrayfors]

Alan,

You could, of course, use virtually ANY type of wire in a temporary configuration.

However, it's my assumption that we're talking here about a real cruising boat that actually goes out sailing in rough weather, and which is located in a saltwater environment. These conditions...salt air, rough weather, constant motion, etc...are very hard on materials. I once built a temporary dipole antenna in the Virgin Islands out of 16-guage copper wire. It lasted exactly 10 days.

So, I recommend strongly that for a real seagoing antenna you use s/s lifeline. The insulated type is preferable both esthetically and, many people believe, because the insulation helps with reducing noise when it's raining, sleeting, etc.

Bill

[coot]

Originally Posted by swagman

Can anyone please provide advice on these guys, who claim to have a clip on backstay SSB Antenna that works? I've never seen these in Europe - and don't seem to be able to get a response from this firm despite one email and a phone message.

I don't know anything about this company, but in general I try to stay away from anybody who lists email and phone numbers as a contact, but does not answer messages left by those methods.

I see that antenna is available from hfradio.com for US$349.

So if this antenna works - and they are still in business - it might be an alternative. Any comments also really appreciated.

It looks like several people think it works. Gordon West seems to know his stuff pretty well; if you can independently confirm that he has tested this antenna and found it suitable, that would be a good recommendation.

I have some thoughts about how/why it could work, but you probably don't care. (For all the radio guys out there, I suspect that skin effect keeps the signal from coupling into the grounded backstay, and that is why there are two wires in the plastic sleeve -- it keeps the backstay in the center.)

I note the GAM web site says "high gain antennas" on the front page, but this backstay antenna is clearly not going to be high gain. That's no big loss -- you don't have space for a high gain antenna on a boat anyway. I wouldn't expect this antenna to perform any better than the "alternate backstay" antenna. You might prefer it for other reasons like convenience, though.

About antenna lengths: Whatever length you choose, it will be wrong for most of the frequencies your marine ssb can transmit on. The antenna tuner corrects for this wrongness. You don't need to understand how -- just that there are limits. btrayfors is suggesting that you start with a length that is "in the ballpark" and cut off bits of wire until it is within the capabilities of your antenna tuner. His numbers are a compromise between "too long" and "too short". Again, if the antenna tuner can correct for the wrong length, you don't care.

The formulas that Doghouse gave are for solving a slightly different problem. With those, you can compute the size of an antenna that works very well for one band only, and that does not need an antenna tuner. You probably don't want to go this route for a regular marine ssb install, though there are conditions where an amateur radio operator might find it desirable.

[hellosailor]

Coot, the GAM web pages only show that they've got the coax feed connecting to two wires that are in the sleeve running up the backstay, without any real details. That *may* mean this is a "zeppelin" aka Zepp antenna, i.e. similar to what was trailed on the airships. One wire would be a 1/4 wave (used as the ground/counterposie) the other a 1/2 wave. If you had a 40' backstay...it would probably work OK for 10-40 meter HF and depending on what else they did with it, who knows. Or it might be some type of folded dipole, that's also possible. Either one would work, either one is widely found on the web and would be compromised by being placed tightly against the backstay. But...it is a simple and robust way to hang one, and "robust" beats "efficient" if the efficient one breaks.<G>

I'm not sure I'd like or trust it without knowing what it really was, since pretty much anything can work as an antenna and sometimes even work well.<G> Every reference to sailboats and HF antennas on them seems to concede that the peculiarities of individual boat rigging make it almost impossible to be sure of what will work, let alone work well. I'd sure like to get the full context from Gordon West, too. (I found an email contact address for him, don't know how direct it is, but I've asked for his comment.)

[hellosailor]

Some clarification from Gordon West about the GAM. He said the great thing about it is the unique cover and fabrication, that it is robust and slides up the backstay easily, but also manages to stay put and to keep the two wires inside it separated.

In terms of what/how it is, he said apparently just two pieces of GTO15 high voltage wire with no magic gizmos or tuned lengths, one fed from each side of the feed wire, antenna tuner still required. And that his initial reaction to it was the same "it can't work". But SOME times it works great, other times not great at all. His advice was to get two runs of GTO15 wire (they're cheap) and run 'em up the backstay. If that works on a particular boat, then by all means use the GAM because it probably will work too. But whether this system works or not, apparently depends on the idiosynchracies of the particular boat's rigging, and there's no simple or easy way to tell if it will be great--or a dog. Simply because the rigging varies so much on each boat, and the impedance if each junction is unknown, and the lengths of each bit are going to be different, etc. So whether it works well or poorly on any given boat, can't be predicted and must be determined by trial on that boat. And at $400, that's why he suggests buying GTO15 and doing a cheaper trial first.

But if it does work on a given boat, apparently it is a very robust piece of work that will stay in place and keep working for the duration.

[kengoodings]

IMHO there will be quite a lot more stray RF zinging around the cockpit with this antenna solution than with an inslated backstay. The dual parallel wires simply couple the RF into the wire backstay. The resulting non-resonant antenna element will be comprised of the backstay, both antenna wires, the stern rigging tang, ground plane, the mast and effectively the whole rig...shrouds and all. With an insulated backstay, the 23 ft section that is between the insulators, together with the single conductor high-voltage feedline from the antenna tuner, is chosen to be harmonically related to the majority of the SSB channels desired. Extra metal hanging off the ends of the antenna....the mast, shrouds etc will all be directly RF driven from the tuner. There is enough parasitic RF current zinging around under an end-fed random length SSB antenna without actually connecting the antenna directly to the sailboat's rigging! I'll hoist a 23 ft wire on a halyard while saving for a pair of quality insulators.

[kengoodings]

There are wide variations in the wavelength of the MF/HF channels in the maritime mobile service, and the backstay "type" antenna is really an end-fed random length long wire antenna. This attached chart indicates some of the choices that you'll have to make when measuring up for a backstay "type" antenna on a sailboat.
Ken Silverheels III Toronto

[kengoodings]

Please excuse the apparent shouting....it was an inadvertent text size glitch Ken

[kengoodings]

Just off the cuff...using GTO15 wire for the whole antenna might be problematic....First of all, it's VERY $$$, may not have a strong enough tensile strength and flex strength, and would present quite a lot more "floppy" windage than a highly tensioned 5/16" backstay. Can you imagine the heavy icing that it would pick up in extreme conditions?

[Seastream]

I own a Catalina 320 and hold a ham license. I was looking at the GAM as a solution. Glad to stumble across this forum and suggestions re 'alternate backstay. I was unaware there was a 12 Mhz HF marine band. I thought the only HF marine band was around 2 Mhz. Please elaborate as to frequencies.

Bob

[btrayfors]

Bob,

All you wanted to know, and much more:

MF & HF Channel Information - USCG Navigation Center

Bill

[Healer52]

Brilliant! Thanks very much and sorry for bringing up this necropost, but this is exactly what I was looking for. I didn't want to weaken my backstay, which would have meant upgrading it's diameter and putting much bigger (stronger) insulators on it, with more windage and weight aloft...

This is what engineers (I used to be one before I went to medical school) call an 'elegant' situation. Terrific! Also easy to have a spare if needed (or run a second antenna along a shroud, for a secondary ham radio).

I've been a ham a long time and sometimes the simple solutions really are the best. Thanks again.

[btrayfors]

Originally Posted by Healer52

Brilliant! Thanks very much and sorry for bringing up this necropost, but this is exactly what I was looking for. I didn't want to weaken my backstay, which would have meant upgrading it's diameter and putting much bigger (stronger) insulators on it, with more windage and weight aloft...

This is what engineers (I used to be one before I went to medical school) call an 'elegant' situation. Terrific! Also easy to have a spare if needed (or run a second antenna along a shroud, for a secondary ham radio).

I've been a ham a long time and sometimes the simple solutions really are the best. Thanks again.

Guess that makes me one of the "necroposters" :-)

Glad it works for you, Rick. Here's an updated link to some pix which might help. The center pic shows the alternate backstay antenna on my boat, attached to the starboard side of the pushpit.

http://wdsg.com/gallery/main.php?g2_...=125&g2_page=2

Click twice on each pic for full resolution. Also shown in the pics are my dipole antenna...construction details are on page 1.

The black insulators shown and, particularly, the massive standoff insulators for the GTO-15 are really overkill. Dacron line works fine for insulators. And, for standoffs on clients boats these days I use 5/8" solid nylon rod lengths about 2" long with a hole drilled thru the middle, and plastic wire ties.

Have fun.

Bill

[Healer52]

Great work, thanks again, Bill.

In particular this seems a good option for the DSC antenna, too.