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Old 20-01-2016, 09:31   #1
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Backstay Antenna and radar

Hello, I'm installing a new Icom 802 ssb on my 38' sailboat and will use my backstay as an antenna. My radar is mounted off the backstay with a swivel mount about 10' high. I also have solar panels mounted on either side of backstay.
My ideal installation for the lower isolator would be to mount it just above my backstay adjustor. This would make my backstay antenna pass within 6" from my radar. With this installation, I would have a Teflon or PVC tubing on the backstay in the cockpit area. The other option would be to install the lower isolator above the the radar mount, on the backstay, and run the gto15 wire along the backstay up to it.
Any thoughts on either of these installations? On the first install, I'm wondering about the affects of the antenna with the radar when transmitting.
I've added some photos.
Thank you!
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Old 20-01-2016, 12:04   #2
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Re: Backstay Antenna and radar

Actually, I don't like either option. Maybe because I don't like either radar mounts or anything else mounted on the backstay. But, that's just me.

Yes, I'd be worried about proximity and such, mainly de-tuning. While you could run the longer GTO-15 to above the radar mount, GTO-15 is a part of the antenna -- a radiating part!

Two options, depending on how your LH38 is outfitted (with bimini, solar panels, etc.):

1. Forget the backstay, and run an "alternate backstay" from near the truck of the mast to one side of the pushpit. This works very well and is very robust (build it with 1/8" or 3/16" s/s insulated lifeline), but you need to have clearance for the roach of your main; or

2. A marine SSB whip antenna.

The first is to be preferred if you can mount it.

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Old 21-01-2016, 01:51   #3
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Re: Backstay Antenna and radar

We have a similar set up with our radar on a quest pole that the backstay runs through. For our ssb we put on a GAM electronics antenna. People who do not use them but are "experts" in the field say they do not work. We find that interesting as we were told many times we had one of the strongest signals in the Caribbean and we sailed from Mexico to Colombia over to Jamaica and down to Trinidad. We also had great signals all the way across the Atlantic and twice a day used Winlink to get gribs and update our position report.
Now in the Med we use it and are using stations in Switzerland, Russia and Bulgaria.

You have to do whatever but we love our GAM antenna - we also have a 802 with a at 140 tuner.
good luck
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Old 21-01-2016, 11:52   #4
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Re: Backstay Antenna and radar

Alls Well,
I'm with Bill, in that I don't like all that stuff on the backstay....but, that doesn't mean you can't make it work...

Bill's "alternative backstay antenna" is always a viable option, and in your case may in fact be the least expensive!

{I don't come from a racing background, but rather am a cruiser / ocean voyager....so please forgive me if I say something wrong...}
But, I have yet to ever see any cruising boat, ever adjust their backstay....and never saw the need for an adjustable backstay on any cruising boat....(I understand that some older fractional rigs might work best with adjusting stay tension, but even then most cruisers never do it, so why have it...)


And, please remember that the GTO-15 wire IS part of your antenna, as is the remote tuner....so, the further away you can install your HF radio antenna (SSB antenna, tuner, GTO-15, backstay, etc.) from everything else electronic on-board, the better off you will be...
Of course, it's a sailboat....so you cannot get things much farther than a few feet, and of course many compromises need to be made....just think it all thru before you make decisions, otherwise it'll cost you extra $$$...


Plan A:
--- So, if you remove the adjuster, you can simply feed the chainplate with GTO-15 wire, and install an upper insulator on the backstay...

Plan B:
--- Or (such as, if you choose to keep the backstay adjuster), you could add a lower insulator a couple feet above the radar mount....and feed GTO-15 wire (perhaps supported inside a PVC tube, for rigidity / longevity) from the tuner / deck feed-thru, diagonally up to the lower insulator...(although this may cause some shadowing of your solar panels???)


Plan C:
Bill's "alternative backstay antenna"...

Plan D:
A stern-mounted whip...


In either plan A or plan B (or even if deciding on plan C, an "alt backstay ant", and possibly plan D as well), you should pass your radar control cable(s) thru ferrites, both right as the cable exits the radome and below deck / below the scan-strut....make multiple turns thru a couple Mix 31 torroids or use MANY Mix 31 clip-on ferrites....
And, do the same for your solar panel wiring...

Use of these ferrites will do two things:
-- reduce SSB transmit energy ingress into the radar system (and solar system)
-- reduce your SSB receive RFI, from the radar system (and solar system)
Failure to do this will lead to frustrations!!!!



Now, if you could mount the radar scanner on the mast, perhaps 15' - 20' off the water, remove the backstay adjuster, etc....well, then you'd be like most of the rest of the cruiser out there...and just need to wade thru the mass of info and learn about HF comms on-board...


I do hope this helps some??

For more helpful info, please have a look here:
Marine SSB Stuff (how-to better use / proeprly-install SSB, & troubleshoot RFI, etc.)


And, have a look at these videos...

M-802 Instruction Videos...
https://www.youtube.com/playlist?lis...rC-8QKVyMb4tVr


HF-DSC Communications Videos...
https://www.youtube.com/playlist?lis...ga2zYuPozhUXZX


Offshore Weather Videos...
https://www.youtube.com/playlist?lis...zdjTJjHlChruyY



Fair winds...

John


P.S. Chuck, just a brief side note...
The GAM Split-lead antenna is like many antennas, it can work great, or it can work horrible...

It is a "coupled" antenna, using capacitance to "couple" to / "slant-feed" / "couple-shunt-feed", your stay...(although being a "radiating part" as well as the couple, it does work acceptably for many to find it useful)

Coupled, slant-fed, shunt-fed verticals (and other arrays) have been around since the 1920's and 30's, and much professional research was done throughout the 30's, and much amateur research was done from the 50's thru 80's....and the results are always the same: sporadic...
And, with good results coming from only single-freq/single-band designs...

These are notoriously difficult designs to "broadband" efficiently/effectively....and this is a testament to how well our modern remote autotuners work!

And, this is why some love the GAM and some hate it....
And, BOTH groups are correct!

It is the inherent, sporadic and unpredictable results, that prevent most professionals from recommending this antenna to most sailors....
However, I have yet to hear of any "expert" that says they don't work...
Simple fact is, for repeatable and predictable results, the GAM split-lead antenna is not a good recommendation....(but, it can work well for some)



Those words above are the facts...now here is a very brief opinion...
In my personal and professional opinion, if the sailor cannot or chooses not to insulate his backstay....or if they cannot afford to insulate the backstay.....
He/she would find an "alternative backstay antenna" to perform as well and typically much better, than the GAM....
And, cost a lot less, as well...
(but, as I wrote above....they can work....and I've never heard any real antenna professional say otherwise....)
FYI, I've studied and taught antenna system design for > 40 years....and have used shunt-fed/slant-fed antennas myself, when no other alternative was viable/affordable....
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Old 21-01-2016, 12:16   #5
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Re: Backstay Antenna and radar

You know, the more you learn about something, the more you find out there just aren't as many absolutes, and it's not as clear cut as you first thought
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Old 21-01-2016, 12:52   #6
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Re: Backstay Antenna and radar

Quote:
Originally Posted by a64pilot View Post
You know, the more you learn about something, the more you find out there just aren't as many absolutes, and it's not as clear cut as you first thought
Very true! And, that's life.

One dramatic example I've seen is that of a newbie coming to India to live for the first time.

Stage 1 first week: You are absolutely overwhelmed by the complexity, the colors, the sights and smells and customs and on and on... You feel you'll never understand this country.

Stage 2 (after 6-12 months): You feel now you have a pretty good handle on things.

Stage 3 (after 10-15 years): You know now that you know absolutely nothing about India.

Bill
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Old 21-01-2016, 13:05   #7
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Re: Backstay Antenna and radar

I too dont like stuff mounted to the stays.

If you can get at least 29' of insulated backstay you should be good with a tuner.

There has been good feedback recently on dedicate ssb whip antennas.

Both will work. We also have a dynaplate and lots of copper foil. The counterpoise is as important as the antenna.

I prefer the backstay antenna, we have two one for the ssb and one for the ham. Anything that has multiple uses, ie backstay as antenna, we like.

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Old 22-01-2016, 12:33   #8
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Re: Backstay Antenna and radar

Here's another option. What about running covered dyneema as a backstay with gto15 internally? I know that it wouldn't last as long, but it would eliminate the insulators and I can carry a backup for less than the price of a traditional wire backstay.
Any thoughts?
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