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VHF Radio Range Problem

Discussion in 'Boat Electronics' started by MazingTree, Jun 6, 2005.

  1. MazingTree

    MazingTree Guest

    I suspect that my Marine VHF radio is a little lacking in range, even on the
    25W setting.

    It's an older style Navico, I only get about a 10 mile range out at sea,
    Yacht to yacht, although I can just reach the Coast Guard from around the
    Eddystone (about 15 miles to the coast) This woulnd't seem so bad, except
    my brand new ICOM M31 portable gives exactly the same range, both
    tramistting and receiving, and that's using it down at deck level, and at
    only 5W output! whereas my Main boat VHF has an aerial on the top of the
    mast.

    Does anyone have any thoughts about what range I can expect yacht to yacht
    on a 32 footer sailing boat with mast head antenna with 25 Watts.

    I am considering purchasing the ICOM M421, do you think this is the best
    bet, or could the aerial be faulty. I have checked all the deck level
    connections and these seem OK.

    Tips and hints welcome.

    Cheers,

    John
     
  2. Richard

    Richard Guest

    I had the same problem on my Pearson 303. I was told that the antenta wire
    going up the mast had chaffed through and was shorting out. I replaced the
    wire and now it works fine. It is the original radio from 1985 on the boat.
     
  3. MazingTree

    MazingTree Guest

    Ah that's encouraging. Another reply in UK.rec.sailing (didn't see the
    electronics group!) concurs with this thought. I think I shall replace the
    antenna and aerial, unless I can get the Vtronix Antenna apart to replace
    just the cable. Sounds worth doing first anyway.

    John
     
  4. I would suspect the antenna and or coax cable in your case. Sounds like
    a simple case of old tired coax, or detuned, ort failing antenna.
    Here in the North Pacific, we usually are getting 50+ miles boat to
    boat with 25 Watts and 10db antennas on 0ver 300 ton Coastal Freighters,
    with some paths reaching out to 90+ miles. Of course your milage may
    vary, as to Actual Tx Power, and Receiver Sensitivity, and Antenna
    losses.


    Bruce in alaska
     
  5. If your boat is fiberglass or wood, make certain you have a ground plane for
    the antenna. The earth connection of your transceiver needs to connect to
    large matt or screen on the hull which is connected electrically with the
    water. Some boat builders bond the screen into the deck. As a check, borrow
    a VHF base station antenna and see if it performs correctly. If it does, you
    have found your problem. Now fixing it, is another matter.
    Steve
     
  6. krj

    krj Guest

    Used my VHF for a 1300 nm contact today.
    krj

     
  7. Larry W4CSC

    Larry W4CSC Guest

    Ok, let's splurge and drop by Waste Marine for a Shakespeare VHF power/SWR
    meter. It's a little white meter with a switch and adjustment control on
    the front and two coax connectors, one on each side. $30. You'll need a
    short coax jumper to go from the meter's transmitter connector to the VHF
    transceiver. If you also buy two right-angle PL-259/SO-239 connectors to
    make the coax jacks come out the back of it, instead of the side, you can
    make a neat permanent installation of the meter on the panel next to the
    radio so you KNOW it's actually transmitting and that the antenna is OK at
    any time you don't get an answer.

    Use is simple. To check the antenna out, put the meter switch in the SET
    position, key the transmitter on some channel in the middle of the band
    (NOT CHANNEL 16!) and rotate the little adjustment control until the meter
    is at the SET mark at full scale. Now, switch to SWR position and read the
    SWR scale on the meter, while still holding the transmitter keyed. A
    perfect antenna, which rarely exists, will show no movement of the needle
    off the 1 on the SWR scale, indicating no reflected power back from the
    antenna. All the power is going out on the air. Any reading on SWR below
    2:1 (the 2 on the SWR scale) is fine. 2:1 means you're losing 10% of your
    power back from the antenna. At the antenna it's worse than that but noone
    can really tell the difference out on the horizon between 25W and 15W. If
    the SWR is higher than 2:1, especially if it goes way up off the SWR scale,
    which only goes halfway up at 3:1, the antenna or the cable is
    TOAST...probably from a lightning hit or broken coaxial cable.

    Worst case....SWR sucks over 3:1....what now?......

    Now we get out the bosun's chair and have the galley slaves haul us, and
    our SWR meter, up the mast to the antenna. Move the jumper coax cable from
    the transmitter jack to the antenna jack as up at the top it will be
    jumpering the meter to the antenna. Unplug the coax cable off the antenna,
    after the galley slaves secure the line to a cleat, please, and connect it
    to the transmitter jack on our meter. Connect the open end of the jumper
    coax to the antenna. Move a galley slave to the radio and have him/her
    turn it on. Repeat the SWR set and measurement procedure above. If you
    have to significantly move the SET control from the position you had it at
    the transceiver end of the coax....or.....if you get little or no reading
    at all....the coax is TOAST. Replace it and start measuring again.

    Ok, what if we get good power level up the coax? Switch to SWR position
    and read the SWR under the antenna, now. It would normally be a little
    higher than what you'd measure at the transceiver on a good antenna because
    the reflected power that makes the SWR position run is attenuated by the
    cable when we measured it back at the radio. That'd be normal. Again, the
    SWR here should be less than 2:1. If it's high, the antenna is toast! Go
    to your favorite marine "discount" dealer and order a Metz Manta 6 VHF
    antenna, not that piece of plastic crap with COAX RUNNING OUT OF THE
    PLASTIC they'll invariably try to pawn off on your. The Metz is guaranteed
    for life. They'll send you a new one if you ever tear up this one. It's
    the best antenna for sailboat masts....damned near indestructable. it
    comes with a right-angle stainless bracket to mount it to the mast if your
    current one isn't compatible.
    http://www.metzcommunication.com/manta6.htm
    You won't need the handrail mount. Mounted on the handrail sucks.
    ALTITUDE IS OUR FRIEND ON VHF!
    Daytime, normal weather....50' mast to 50' mast...probably 15 miles...a
    little over the visual horizon from the top of the mast. VHF is line-of-
    sight to the radio horizon. Mathematically it's:
    http://continuouswave.com/whaler/reference/VHF.html

    As you can see from that, the major concern is "path loss" and antenna
    height. The 3dB Metz gives you double whatever power is at the end of the
    cable atop the mast in Effective Radiated Power (ERP) The 6dB antenna is
    too tall to make sense up there...easily destroyed plastic.

    Before we spend hundreds on a new radio, let's get the antenna checked out
    with the cheap meter, first. If the SWR is reasonable, under 2:1, when you
    test it at the radio, THEN we'll flip the switch to POWER mode and read the
    handy little wattmeter, which is "fairly accurate" at LOW SWR READINGS,
    being most accurate at 1:1 with no reflected power. Check the 25W high
    power and 1 watt low power in this meter mode. As the SWR increases, this
    reading increases, so don't get way excited if it reads 30 watts at 2:1
    SWR. It was calibrated into a perfect dummy load at the factory.

    Now, of course, if you're reading ZERO and can't get the meter to SET in
    SWR mode....then we've got a bad transmitter. Your choice to repair or
    replace. If it's old, dump it.
    They stopped making my beloved M-59 the jetboat jumping waves couldn't
    destroy...dammit. Lionheart has an M-602 on the mainmast Metz and an M-59
    on the mizzen lower down. Captain Geoffrey likes the way the M-602 matches
    the M-802 HF panel...(c; There's no difference in the range of the big
    expensive 602 and the old M-59 I can tell. M-59 has new clothes. They
    call it the M-302, now. If you don't need the extra toys of the M-402,
    like remote Commander mic, etc., it has the same radio operation.

    Any Icom is fine. M-127s, the Radio Of The Year back in 2000 and before,
    is a great radio. They're still available, but discontinued, now. Gotta
    keep cranking up those model numbers, you know!

    As the range webpage shows, 10 miles is pretty fair, boat 2 boat on VHF.
    The investment in the little SWR/Power meter will help you find out the
    true health of the radio/antenna/cable combo....Everyone should buy one.
     
  8. Larry W4CSC

    Larry W4CSC Guest

    The end-fed halfwave antennas, such as the Metz Manta-6 do not require any
    ground or groundplane at all. The antenna rod, itself, is a total 1/2
    wavelength dipole, but fed from the bottom end. No ground is necessary.

    http://www.metzcommunication.com/manta6.htm
    Guaranteed for life....
     
  9. MazingTree

    MazingTree Guest

    The Antenna system is a Vtronix Great Hawk, the one with the Wind indicator
    built into it. Since I first posted, I have spoken with their technical
    man, and he was very helpful, and explained that it's fitted with a special
    solderless connection to enable the cable to be unscrewed and checked. from
    my description to him, it sounds like the aerial has been up the mast for a
    long time though, so I may swap the antenna anyway, whilst I am up the mast.
    He says it is possible after a very extended period of time for the antenna
    to become faulty due corrosion and possibly water ingress.

    John
     
  10. MazingTree

    MazingTree Guest

    Yes I am sure you are correct, according to the Vtronix Hawk information,
    this is an end fed dipole, and so needs no ground.

    John
     
  11. MazingTree

    MazingTree Guest

    Excellent post - Thanks. I think I follow it all, and it makes logical
    sense. I had searched for some time for a Meter to mesaure output power,
    but must have been using the wrong terminology because I couldn't find
    anything.

    My Antenna, is a Vtronix Great Hawk, which appear to be very popular over
    here in the UK, and appears well made, with a special solderless cable
    fitting, and appears to be well engineered. It also houses the windex, so I
    may stick with this type. Price is similar to the Metz it would appear.

    I wonder if you SWR meter can be purchased from the UK. I'm off to find out
    now!

    thanks,

    John
     
  12. MazingTree

    MazingTree Guest

    Larry,

    Would have the URL for Waste Marine, I can't see this listed in Google?
    I wonder if you have a typo, it seems an odd name for a company selling
    marine equipment :)

    Cheers,

    John
     
  13. Hi John,

    Waste Marine is a common pun on a very big company in the USA with
    _many_ stores called West Marine. Their website can be found at

    http://www.westmarine.com/

    Of course, on our side of the Atlantic we've never heard of the bloody
    outfit...

    Vriendelijke groeten,
    Kees
     
  14. John,

    Type "swr meter vhf site:uk" and up they pop. Most of them seem radio
    ham oriented, but I was quickly able to find one that's GBP 29.95, which
    sounds reasonable.

    -- Kees
     
  15. Oops, that should have read ''Type "swr meter vhf site:uk" into Google''
    of course...

    -- Kees
     
  16. Larry W4CSC

    Larry W4CSC Guest

    Sorry I didn't notice you were in the UK, John. If you know any ham radio
    operators, they'll know, too, where to purchase a similar VHF SWR meter.
     
  17. Larry W4CSC

    Larry W4CSC Guest

    Just make sure they are for the 156 Mhz range in their specs. Many ham
    radio SWR meters are only for frequencies below 30 Mhz...the HF band.
     
  18. Larry W4CSC

    Larry W4CSC Guest

    Shakespeare manufactures marine antennas in the US. Go to Google and
    search for:

    Shakespeare ART-2 Antenna Radio Tester

    There are lots of dealers. I looked at Shakespeare's website and see they
    have a new model out, the ART-3, but have never seen one. The ART-2 has
    been out for many years. It's all you need.

    http://www.google.com/search?hl=en&q=Shakespeare+ART-
    2+Antenna+Radio+Tester&btnG=Google+Search

    The PDF catalog is at:
    http://www.shakespeare-marine.com/catalog/fullline.pdf
    Click on "Radio Accessories" in the control panel of the Adobe Acrobat
    Reader. It's the 2nd unit down on the left.
     
  19. Larry W4CSC

    Larry W4CSC Guest

    Sorry for causing the confusion. You haven't missed anything having never
    been in an overpriced West Marine store.
     
  20. Larry W4CSC

    Larry W4CSC Guest

    I don't like it. Solderless usually means corroded within 5 miles of the
    sea.
     
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