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Old 29-05-2015, 09:29   #1
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Optimal SSB Antenna(e)

I am re-rigging my boat and am wondering what the best length is for an insulated backstay antenna.

Right now, it is 21 ft which favors the higher frequencies, but I am wondering if I should make it much longer (>35 ft) for lower frequencies and install a 20 ft (or so) whip on the stern rail and switch between the two depending on the RF frequency used. That way I would have greater efficiency across the HF bands and also a backup if the mast undergoes a gravity storm.

Radio is Icom M802 and AT-140 tuner. Intended use is circumnavigation.
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Old 29-05-2015, 10:26   #2
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Re: Optimal SSB Antenna(e)

Not sure your PSC is going to get caught between a stellar body and a singularity anytime soon (even on a circumnavigation). However, be sure your shrouds, forestay and backstay are strong enough to serve as inertial dampers.


Good plan to have a back up antenna, but, in practice, the longest backstay antenna you can rig (professionally done with the proper gear) would be as good as it gets.

A whip on the stern....will not have any inertial dampers...and so.....


If the AT-140 tuner will not tune all ham and marine freqs using a long backstay, the SGC-230 will.


Go with as long a backstay antenna as you can do. Make sure your counterpoise is well done...that is at least as important.


Hope this helps
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Old 29-05-2015, 11:19   #3
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Re: Optimal SSB Antenna(e)

An insulated backstay length around 40-45ft is a good compromise.

Also, important to keep the GTO15 feedline as short as possible. For many boats, esp. those without a backstay adjuster, feeding the backstay belowdecks at the chainplate is a good solution. This saves one insulator ($300) and is very robust. If you're worried about RF burns (a very remote possibility IMHO), you can put a length of PVC over the lower end of the backstay/rigging screw/etc.

For a circumnavigation and, assuming you're a ham, I'd seriously recommend a marinized 20-meter vertical dipole antenna. Nothing you can rig on your boat will be as effective over really long distances. I've written extensively about these in the past. Let me know if you need any details.

On my own boat (42' sloop), I have a backstay antenna, a vertical dipole antenna, and a mount on the stern rail for a Hustler whip antenna. Coax from these three is led below to an Alpha-Delta 4-position coax switch near the radios.

The Hustler mast and resonators (for 75m, 40m, 20m, 15m) are carried below, but can be rigged quickly.

Bill
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PS....I don't see any reason why the AT-140 tuner couldn't tune the ham bands as well as the marine bands. Every one I've installed (lots of them) on client boats was tested on the ham bands as well as the marine bands. No problem.

B
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Old 29-05-2015, 11:30   #4
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Re: Optimal SSB Antenna(e)

John,
Thank you for the reply.

Say I have a 33 ft (10m) backstay. This is 1/2 the wavelength for 15 MHz. At this frequency, won't I blow up my radio with the reflected wave?
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Old 29-05-2015, 11:34   #5
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Re: Optimal SSB Antenna(e)

Quote:
Originally Posted by btrayfors View Post
...For a circumnavigation and, assuming you're a ham, I'd seriously recommend a marinized 20-meter vertical dipole antenna. Nothing you can rig on your boat will be as effective over really long distances. I've written extensively about these in the past. Let me know if you need any details...
Bill
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B
Thank you. That is very encouraging. If you would point me to the written details I would be grateful?
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Old 29-05-2015, 13:08   #6
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Re: Optimal SSB Antenna(e)

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John,
Thank you for the reply.

Say I have a 33 ft (10m) backstay. This is 1/2 the wavelength for 15 MHz. At this frequency, won't I blow up my radio with the reflected wave?
Ha! Not likely.

First, the antenna length consists of the backstay length PLUS the feedline length...all the way to the tuner.

Next, physical length is not the same as electrical length. The electrical length depends on the type of conductor....stainless steel, copper, etc.

Finally, if you do find a frequency which the tuner doesn't like, you can adjust the length of the antenna itself or and/or the ground.

Bill
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Old 29-05-2015, 14:03   #7
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Re: Optimal SSB Antenna(e)

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Thank you. That is very encouraging. If you would point me to the written details I would be grateful?
Unfortunately, my website with the pix is not up.

If you'll shoot me an email direct, I'll send the info and pix.

Email is: bill at wdsg dot com

Bill
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Old 29-05-2015, 16:18   #8
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Re: Optimal SSB Antenna(e)

I would not worry about the exact length of the backstay, as an antenna. Use as much of it as can possibly can.


My only concern would be propagation...these days. And this is a good question for Bill...has HF propagation, especially on 10m gone way down these past couple of years???


[Sorry for any hijack, but this is actually pretty relevant]
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Old 29-05-2015, 16:42   #9
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Re: Optimal SSB Antenna(e)

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...My only concern would be propagation...these days. And this is a good question for Bill...has HF propagation, especially on 10m gone way down these past couple of years???


[Sorry for any hijack, but this is actually pretty relevant]
Yes. I have had a lot of opinions for shorter antennas which makes me wonder if people's experience at 10m is not all that good unless they optimize for it (with or without being aware of the reasons). Any experiences on this out there?
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Old 29-05-2015, 16:51   #10
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Re: Optimal SSB Antenna(e)

My understanding of the AT-0130/140 tuners is that within reason, it doesn't really matter how long your backstay antenna is, the tuner will deal with it.
We have only a double insulated backstay about 15m plus another 3 m to the tuner and it works well.
Of course propagation of RF signals varies at differing times of day and wrt sunspot activity, nothing is perfect. We use our SSB mostly for Sailmail and we can usually find a station/frequency that works.
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Old 30-05-2015, 10:43   #11
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Re: Optimal SSB Antenna(e)

John,

RE: propagation, I don't worry about it a lot. Reason: I can't do anything about it -- it is what it is! And, in the last year or two it's very often been terrible.

I'm gonna use a technical term, now: LOUSY TO ABYSMAL :-)

Problem is, bad propagation can and does happen on most all HF bands, not just 10 and 15 meters. Ten meters has been generally bad for years now, but there are good openings. A friend who had only a tech license was a 10m "expert", 'cuz he couldn't operate SSB on other bands! He'd come into the Club every week are two and rave about conditions on 10m. Happily, now he has his General class and he'll be able to work other bands.

Three things to remember about propagation:

1. On any given HF band and over the same path, propagation varies considerably from day-to-day, from hour-to-hour, and often from minute-to-minute.

2. Despite varying conditions, it is still possible to make solid HF contacts. We do that every day of the year on the Waterway Net (7268LSB beginning at 0745 Eastern Time). And, we've done this without break for over 50 years!

3. Your best bet regardless of propagation conditions is to make sure your installation is as good as you can make it.

This does make a difference.

Example from the Net this morning. There were two boats anchored in the Northern Neck of Virginia, next to one another. Both checked into the Net. One boat was very strong, here in the DC area and in Florida. The second boat was VERY weak, both here and in Florida. Both boats were using 100-watt class transceivers.

The only explanation is that the first boat had a better HF installation than the second boat. Installation quality does matter!

Bill
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Old 31-05-2015, 10:42   #12
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Re: Optimal SSB Antenna(e)

Propagation on 10m the past few years has been about the best it will be for another 9 years or so. We are just past the peak of a very anemic sunspot maximum, and it isn't going to get better for a long while.

10m can be surprising. Occasional openings over great distances, but hard to predict.

20m is the "bread and butter" DX or long distance band and where you will consistently find the most long distance activity. This is why Bill's recommendation for having a 20m vertical dipole is a good one. It will have a predictably good takeoff angle for long distance propagation. A vertical monopole of a random length, like a backstay, even if properly matched with an antenna tuner will radiate it's power, but not at the best angle for long distance communication at all frequencies. It may be great for one band, and lousy for another. The radiated power lobes for an antenna will vary in number and angle depending on the relationship between the frequency and antenna length. This is one reason why you may find that you can't make good contact with a particular station on a particular frequency, even though the propagation charts indicate you should have a good path. And also why the boat next to you may be making good contact with a given station, while you aren't having the same success at the same time, despite both of you having well installed radios and backstay antennas - the electrical lengths of the antennas might be different enough to have markedly different takeoff angles which may favor or disfavor a given distant station.

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Old 31-05-2015, 17:44   #13
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Re: Optimal SSB Antenna(e)

Hi Guys

I appreciate the response regarding propagation and apologize for any hijack (though I think it is relevant).

I changed QTH just over 2 years ago and was wondering if it was ME. I tried several different antenna options and finally settled on a big loop (70', horizontal....it's a long story).

To bring this back on topic for the OP...OP...when propagation is good...you really do not have to worry about having an optimal antenna. A 33+ft backstay on your boat will do just great. Your counterpoise is even more important, in terms of getting signal out. I was able to set up a simple, cheap one, following Gordon's West's advice, on my boat.

As Bill wrote, installation DOES matter.

And on the other side of it, when propagation is poor....it won't matter what radio or antenna you have, either.

To contribute: the counterpoise I set up was a sort of "belt and suspenders" one. I ran high quality copper foil through the bilge (probably 30ft) and also connected it to a bronze thru hull. At the time, you could buy a roll of copper flashing from HD very inexpensively.

My best to all

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Old 31-05-2015, 19:42   #14
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Re: Optimal SSB Antenna(e)

Thank you all for sharing you knkwledge and experience.

OK. Seems line the concensus is >33 ft. If I use a 23 ft backstay, what am I giving up?
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Old 31-05-2015, 21:48   #15
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Re: Optimal SSB Antenna(e)

You are giving up some radiation efficiency at lower frequencies. Somewhat higher losses in the tuner also at those lower frequencies. Will it ever matter? Who knows.


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