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use standoffs between SSB coax and backstay??

Discussion in 'Boat Electronics' started by Gordon Wedman, Nov 5, 2003.

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  1. The other day I was wandering around one of our marinas trying to steal
    ideas from other boats and I came across an aluminum pilot-house sloop that
    may have come over from Europe. I noticed that the SSB coax was held away
    from the backstay turnbuckle and wire by ~1 inch plastic spacers. I've
    never seen this before and the previous owner didn't do it on my boat. I've
    been thinking of upgrading the ancient SSB system on my boat and was
    wondering if these standoffs were something recommended.
    Anyone know about these? Thanks
    Gord
     
  2. I think I read somewhere that the high voltage GTO wire should optimumly
    approach the backstay at right angles. Something about when the lead
    runs close and parallel to the grounded section some power is leached
    off. Not real practical in most cases though. Stand offs about 1 1/2"
    long keep the lead wire away from the stay enough to prevent significant
    loss and are a pretty good way to keep things neat but probably not the
    most electrically efficient.

    OTOH, if you have this RF hot wire running up the stay where anyone can
    grab it, why have a lower insulator in the first place? I am
    considering not grounding the backstay chainplate and feeding the tuner
    directly to one of the bolts. Just have to remember to yell "If you
    have to pee off the stern rail Don't hold the backstay!" before sending
    any e-mail. :)

    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  3. It was probably GTO-15. I would hope that who ever went to the trouble
    of adding the standoffs would know the difference. GTO is hard to tell
    from RG59 from a distance. Neon sign suppliers even have it in
    decorator colors.

    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  4. GTO-15 is 15KV insulated wire and fairly standard for tuner to backstay
    leads. More for safety than efficiency. The whole idea of elevated
    lower insulator on the backstay is to prevent some dumb crew member from
    grabbing a hot lead and getting an RF burn. The GTO limits that
    possibility. The stainless strap approaching at an angle is probably
    more efficient and neater looking but gives no protection. West Moron
    dropped it from the Catalog this year but used to sell it for $1/ft. It
    is standard material in neon shops for $.50/ft and from HVAC dealers as
    spark igniter wire for $.25/ft.

    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  5. Thanks to all for the discussion. For the minimal effort and expense it
    sounds like a good way to save a bit of transmit power.
    Sorry about the reference to "coax". As I'm not very knowledgeable about
    these things I couldn't really state what type of wire it was and just
    guessed coax. Thanks for pointing out the correct wire to use. I don't
    think my boat currently has this.
     
  6. It isn't the RF leaking out that GTO-15 is used for.....

    Real Marine Radiomen use PhospherBronze Antenna Wire and GTO-15
    as short jumpers where human contact is possible.......

    GTO-15 is, highly insulated stranded copper wire, used to connect
    antenna tuners to antennas in the marine enviorment. It has 15000V
    insulation to prevent flashovers and arc's to ground, from the high
    voltage companents of the voltage feed longwire antennas. The 1"
    insulators are designed to move the RF antenna away from the Grounded
    Backstay and reduce the RF coupling between these two components.
    1" isn't enough to really do the job. 6" would be much better considering
    the length of the two components, and their parallel coupling.

    GTO-15 is fancy sparkplug wire....

    Bruce in alaska
     
  7. Harry Krause

    Harry Krause Guest

    You'll find a lot of GTO-15 at neon sign shops. It's heavy voltage cable.
     
  8. Woody

    Woody Guest

    If you are talking coax, and it is properly impedance "matched" at both
    ends, proximity to objects (metal or not) will have no effect. There is
    (should be...) no RF on the outside of the shield.

    OTOH...
    Most comments reference a single feed wire to the stay. In that case
    isolating the wire from nearby objects is very important for proper
    function.

    Woody
     
  9. Kris VK4CPG

    Kris VK4CPG Guest

    It is practically impossible to match coax cable to an end-fed antenna for
    various bands, without traps or impedance matching tricks at the end of the
    coax. The outer insulation and even the core insulation of coax is normally
    not high voltage proof, so don't rely on it, certainly not near an "earthed"
    wire.
    Special marine antenna cable can be bought but is expensive. I used
    multicore green earthing wire and spacers. These can be made of 5cm pieces
    of white conduit pipe (UV stabilised) with two holes on each side to fix a
    tag to the feeder wire and the backstay. Wrapping around both, fixes it
    well. Perhaps shrink tubing would even make it more "professional". The wire
    has been there for more than 5 years and the plastic has not deteriorated.
    The inside wires were getting black, so soldering on both ends is necessary.
    I am now going to replace it by special multicore UV stable HV cable, neatly
    tied to the backstay.
    It is still the question if spacers are electrically better than tying a
    cable close to the backstay. The coupling between the feeder and the rest of
    the backstay makes the antenna anyway into an a-symmetrical off-centre fed
    thingie that may radiate well on one frequency but miserable on another. The
    tuner will make the whole system resonant but that does not guarantee good
    radiation or prevent RFI. Sometimes a dummy load would perform the same way.
    With spacers, a 600 ohm feeder could be created (at least for some length)
    to keep stray radiation at lower levels but it must be symmetrically fed and
    commercial tuners don't do that.
    Probably the best is trying it out, as there is not much calculation that
    can be done. Thick marine antenna cable tied to the backstay makes the
    system at least wind and foolproof. And pray for no RFI into the GPS and
    mobile phone antennas.
     
  10. I doubt the boat in question was using coax. I just didn't know the
    correct term to use for this type of wire and used "coax". Subsequent to all
    the original discussion I had a closer look at the wire used on my boat
    (installed in 1983) and I see that it is, in fact, GTO-15. Says so right on
    the insulation.
    Now I just need to buy a decent SSB to hook up to the backstay after
    selling the old Motorola 11 channel unit.
     
  11. Yachtfunk

    Yachtfunk

    1
    0
    Jul 14, 2009
    Standoffs and GTO-15

    When installing equipment capable of
    transmitting HF frequencies, one needs to
    carefully think about where HF is radiated, thus
    one needs to decide where certain distances
    need to be kept short in order to avoid loss
    of power or interference. Connecting the tuner
    to the antenna, it is necessary to emphasize
    that the feeder is already part of the antenna
    – system. Therefore, the tuner will try
    electrically to adjust the length of the antenna
    - including the length of the feeder - to the
    used frequency. At last year’s ARC, we were
    surprised to see that many so called “experts”
    working for shipyards had installed coax
    cable between the tuner and the antenna.
    That is one of the major problems that keeps
    the tuner from adjusting the antenna system.
    A lot of the power emitted on the way to the
    insulated backstay will be reflected inside
    the coax, back to the tuner and will finally
    be diverted to ground. The tuner will never
    be able to properly adjust the system unless
    appropriate cable is installed. Yachtfunk.com
    recommends GTO-15, a high-voltage cable to
    connect tuner and antenna. The GTO-15 will
    then have to be kept at a distance to the uninsulated
    part of the backstay with the help of
    standoffs. A feeder directly connected to the
    un-insulated backstay would lead to a loss
    of power and can cause interferences with
    other electrical systems onboard. Basically
    we can say that whatever kind of antenna is
    used onboard, it should be mounted as far
    away from any metal objects on the vessel as
    possible for the best performance possible.
    Distance also plays an important role with
    regard to the installation of the tuner – it should be placed as close as possible to the
    ground-plane.

    More Info´s by yachtfunk.com

    sea u
    Joerg
     
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