[Elecraft] Insulated Backstay

[brianb]

Don,

I did this for a time on my 34' boat. It worked with the SGC tuner (not 
too suprising) and I made contacts. It had the added advantage of 
lighting all the LED's on the boats power panel, a great indication of 
radiated power, and woke up the off watch crew that were sleeping with 
their hand against the chain plates where the standing rigging feeds 
through the deck. Oh, and the other cool phenomena was the way the 
autopilot would go offline on voice peaks leaving the boat to round up 
with the spinnaker wrapping and flayling away against the head stay.

Brian n6iz/mm  s/v redsky 


Don Melcher wrote:

>Mike
>
>The 23' feet dimension is specified because that is the shortest length
>the tuners like the SGC230 and Icom AT120/130/140 AH2/3, etc., will load
>on 2 MHz and 2.182 MHz is the "distress" frequency on Marine MF - though
>not monitored much outside the US any more.
>
>I have done computer modeling of a typical cruising boat - a Valiant 40
>- and found that actually the BEST antenna was to only insulate the
>bottom of the backstay and load the whole rig, AS DISCUSSED in the
>current editions of the ARRL Antenna Book. But I got tired of arguing
>with people that this would actually work - "But it is a short!" - as I
>was advocating it long before the Antenna Book, and gave up. And - in
>some cases it didn't work very well - on a ketch rig or with a "split"
>backstay. On a sloop, with a single wire from the mast to the stern - it
>is killer. In a lot of cases, we simply ran a 6 gauge wire back from the
>base of the mast or the forestay to the ground of the tuner and jumpered
>all the fitting toggles with wire for good continuity - forming a big
>"loop". The one insulator was because without it, there would be a lot
>of leakage from the chainplate at the feed point to ground after the
>stern gets coated with salt spray (but some installations worked OK
>without it anyway - Brian may recall Bill Parks' Islander 36 Stray Cat
>Blues about 2 or 3 races ago and his effort before that - Bill
>introduced the idea to me when he was interviewing me for an article in
>Latitude 38. It was in a book that was published some years ago on Ham
>Radio and Cruising and the author discussed not using insulators - at
>first I too said it wouldn't work - then I thought about it for a
>while).
>
>For an insulated stay. a length of 45' seems to be (a stretch of the
>word) "optimal" in that it is efficient on the lower frequencies yet not
>too long so it maintains a decent angle of radiation on the higher
>frequencies. In reality - an insulated backstay is a pretty poor antenna
>when you look at the pattern as on most bands there are two pretty deep
>nulls about 120 degrees off the bow. Fortunately - they are fairly
>narrow. But you won't be able to achieve that length on a W32. A 23'
>whip as typically used on a power boat and most multi-hulls has an
>almost perfect omni pattern and a good launch angle - of course -
>assuming the boat is upright in the water - which is often NOT the case
>under way.
>
>IN short - no matter what you do - it is a compromise and you would have
>to work REALLY hard to screw it up so it wouldn't work as long as you
>follow good engineering practices. I have never seen an Icom tuner fail
>to load anything on any frequency - not the same can be said for the
>SGC230 (but that seems to be a different problem where it just won't
>tune sometimes without being reset) or certain SEA tuners (the 1635 will
>not load a 1/4 wave on 4.146 MHz - the check-in frequency for the PacCup
>race - go figure - and that is EXACTLY what they cut the backstay to on
>a Santa Cruz 52 - I received panic calls from three boats just before
>they were leaving on past Pacific Cups who had that tuner installed by
>someone because it - with the companion SEA235 radio - was light weight
>- didn't bother to check if it would work). SEA's other tuners (like the
>1631) do not appear to have this problem and like the SGC, will work
>with any radio. 
>
>As far as grounding - there are many methods - but the only one I can
>say WILL work is bronze plates (drag is NOT an issue on a Westsail 32) -
>I recommend 2 of the 3" x 12" - and I have close to 500 installations
>now with no RFI problems running 150 watts using e-mail to back that up.
>
>I am not saying other methods WON'T work - just that it is difficult to
>predict the results and it can be a tremendous amount of work and
>expense with poor results. One thing that has been determined is SOME
>sort of direct sea-water contact is needed.
>
>Don Melcher
>W6CZ
>HF Radio On Board
>www.hfradio.com 
>
>
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