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SSB on junks (including antenna location, ground plates...)

  • 13 Mar 2013 20:03
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    Reply # 1241951 on 1230219
    Anonymous member
    Thanks for the photo, David, and all the other info on this topic. 
    I'm following in your wake...
    Kurt
  • 12 Mar 2013 07:24
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    Reply # 1240332 on 1230219
    Deleted user

    In the chimney is your best option. Because you have an alloy mast radiation out to the mast could as you say be an issue but if you have sufficient non conductive length between the top of the antenna and the mast you could probably get around this. I don't know how tall your mast is but provided you have more than 8 metres of actual antenna length you should have an effective long wire antenna. I thought about having something which I just hoisted when I needed to use the radio but in the end decided it was a lot more simple to have something I left in place permanently.

    I have found with my antenna, and the spare halyard which is in the same location, that if they come down to the toe rail anywhere ahead of the mast they do get caught in the upper luff area of the sail when the sail is squared off on the opposite tack, if that makes sense. So mine attaches to the toe rail directly athwartships of the mast. That puts a very slight limitation on my downwind sailing in that the sail cannot be allowed out so far as to be dead square when on the port tack, sail to stb'd, but it doesn't seem to affect anything.

    I have placed a photograph of Footprints' rope antenna in the Technical Forum Illustrations.

    Last modified: 12 Mar 2013 18:43 | Deleted user
  • 12 Mar 2013 03:49
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    Reply # 1240248 on 1240132
    Deleted user
    David Tyler wrote:I was actually thinking of attaching the feed at the bottom, and leading it along the boom and down by the mast. Not dissimilar to the geometry when using the bermudan boat's backstay. Still no good?
    Well, that's certainly more doable.

    The question then would be chafe at the mast (would it get pinched by the boom?) and slack/fouling as the boom moves up and down if the topping lifts are not perfectly static (e.g. on mine they will be running lifts).  The other concern is if the boom angle changes much when reefing (e.g. on a fanned sail?) then the lift lower sections may slide a bit to rebalance the bundle's weight and could possibly yank/snarl the antenna.  But... if you genuinely have a straight shot of line to the top that isn't served up in purchases along the way then that could definitely be made to work.  It wouldn't be ideal (that horizontal, then vertical sort of "kink" in the run will change the effective radiated energy and probably cancel out some of your power and give the antenna a directional nature) but it could certainly serve as a usable antenna and I daresay it's a lot better than many installs I've seen.

    It does lead to another possibility, though, and that's the idea of a second "lift" dedicated to this antenna, one that is on a separate halyard, and probably with a heavy bungee at the top so that as the boom bounces a bit the line would not be strained.  This could then be let out if dropping the sail bundle and would allow for scandalizing the sail or taking a reef upwards with running lifts if one so chose, without serious problems.  It would require two additional blocks on the boom to allow the antenna to slide through as the boom position adjusts but otherwise I cannot see anything seriously wrong with trying the idea. 

    But this is all theory.  I won't be trying it as I want to keep my antenna tuner against one or the other hull interior as it's rather large and needs good support, but if one had an area near the partners belowdecks to mount it, it could be a very good idea to try.
  • 12 Mar 2013 01:39
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    Reply # 1240132 on 1230219
    Anonymous member
    I was actually thinking of attaching the feed at the bottom, and leading it along the boom and down by the mast. Not dissimilar to the geometry when using the bermudan boat's backstay. Still no good?
  • 12 Mar 2013 00:07
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    Reply # 1240043 on 1239787
    Deleted user
    David Tyler wrote:I'm not an SSB user, so this may be a dumb question, but why can't the standing part of one of the topping lifts be used? Made of load-bearing wire, with insulators, like a backstay antenna, or made of  wire inside braid, but using a strong braid, not polypropylene?

    It would be a great idea, David!  Unfortunately the way SSB antennas work, there is an antenna tuner at the base of the antenna which matches the ground portion and the radiating portion to reduce reflected power back to the radio unit.  If we were to use a topping lift (or any other portion of the rigging where the "starting point" is at the top of the mast), a radiating part of the antenna must go all the way up the mast, then come back down the standing rigging.  This part going up the mast will likely be out of phase with the part coming back down and, for those of us with metal masts, will dissipate a large portion of it's radiated energy into the mast and/or develop nasty frequency-related side effects.  SSBs are a bit weird when it comes to antennas and it's definitely best to keep them spaced out a bit from any other metal that is parallel or roughly so to their path.  

    The other option is to put the tuner at the top of the mast, which would both add weight and probably put the tuner out of commission relatively quickly from exposure to the elements.

    So, since neither option is very good from an SSB perspective, we tend to avoid them.

    However, there are other problems as you pointed out, with the usual locations.  If I cannot clear the luff of the sail when the sail is swung well to port, then I'll have to consider other options such as a "temporary hoist" antenna and/or the "forestay" antenna shoved out on a pole to clear the luff of the foresail.  I'd rather not have the antenna run and tuner be all the way in the bow, though, but that seems to be plan B for a permanent mount.  It might make more sense to integrate the antenna into a "running backstay" type system which can be eased when on a run to allow the sail to come well forward, but taken in a bit on the opposite gybe to clear the luff.

    I'll ponder it for a bit more.  Keep up the interesting thinking!
  • 11 Mar 2013 18:41
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    Reply # 1239787 on 1230219
    Anonymous member
    I'm not an SSB user, so this may be a dumb question, but why can't the standing part of one of the topping lifts be used? Made of load-bearing wire, with insulators, like a backstay antenna, or made of  wire inside braid, but using a strong braid, not polypropylene?
  • 11 Mar 2013 17:03
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    Reply # 1239677 on 1230219
    Anonymous member
    Be careful to ensure that the antenna stays well aft of the luff of the sail when squared off on starboard gybe. If it catches on the forward end of any of the battens, and you then gybe, it will ruin your entire day.
  • 11 Mar 2013 15:20
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    Reply # 1239598 on 1230219
    Deleted user
    So I've figured out an interesting place to put the antenna which might work very well..

    In the "chimney area" on the starboard side of the mainmast, but running out to the toerail slightly forward of athwartships.  This should give some good separation between the aluminum mast and the antenna.  I expect there will still be some directionality to the signal based on the mast but since it is not a tuned radiating element it will likely be less significant.  This will allow the JR sail to swing well forward of beam on starboard anyway and will be the most "out of the way" solution I can think of for a semi-permanent hoist antenna.

    I will likely make this out of antenna wire run up a polypro single-braid line so that I can hoist it with the ghoster halyard and put it away when necessary.
      
    Thoughts?
  • 04 Mar 2013 18:41
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    Reply # 1233321 on 1230219
    Deleted user
    For your information Kurt and anyone else who is trying to figure their way through an SSB or Ham radio installation I found some very helpful information on the sgcworld.com website. Specially the HF Users Guide which you can download from the publications section of the web site.
    Last modified: 05 Mar 2013 05:04 | Deleted user
  • 04 Mar 2013 07:39
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    Reply # 1232909 on 1230219
    Anonymous member
    Nearly blew it.

    I had thought of using 20mm^2 cable for the antenna. I went today to buy it, and I'm glad it just looked wrong. I resolved to find out what smaller size would be adequate, and now I notice that Footprints has 4mm^2 and it works well. Phew. I avoided a big fat and costly mistake. Now a little more study, and up she goes.

    Thanks to David and you all.

    Cheers,
    Kurt
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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