I hoped you'd have some thoughts here, Bruce, because you've always made a
lot of sense in this general area.
For Fintry, for use primarily for SailMail and talking to Herb Hilgenberg,
would you use a whip or a wire? While we could shout for help on 2182 and
everything else available, little else will happen below 4mhz.
Wire would be between jackstaff and masthead, about 48' total. see
http://www.mvfintry.com/pix/felev800.png for a profile drawing, although the
jackstaff doesn't show. If this is your choice, where would you put the
insulators? The tuner would presumably go at the base of the mast.
For a whip, I've been looking at the Comrod AT100, which is easy to get in
the UK.
http://www.comrod.com/v2/Marine/pages/mar_1.asp
Fintry is steel, with an aluminum wheelhouse, so grounding is easy.
Thanks,
--
Jim Woodward
www.mvFintry.com
"Bruce in Alaska" wrote in message
...
In article ,
(Jim Woodward) wrote:
A few thoughts from a user. There are several experts in this group
and I, too, would be interested in their thoughts, as I have not yet
made this decision for Fintry. The masthead wire is cheaper for us,
as it doesn't need to support anything but its own weight and to pull
the mast up from the lowered position.
1) Since the whip is a constant price, for a sailboat it becomes more
attractive as the boat gets bigger and the insulators for the backstay
go from expensive to outrageous.
2) The insulators interfere with several useful rigging options,
including hoisting a special sail on the backstay to prevent the boat
from tacking about her anchor. You want to think about possible
interactions between the top batten, the roach, and the upper
insulator.
3) The backstay rig is up and out of the way, but its feed wire is
potentially dangerous while transmitting. The feed wire is easier to
protect on the whip.
4) Many whips (particularly the cheaper ones) require a two point
mount -- base and two or three feet above the base. Others can be
mounted on a flat surface, but make sure it's strong, as there's a lot
of leverage in a seaway. (It's not called a whip for nothing.)
5) I get mixed reports on which will give better results. Many of the
people who answer the question have a horse in the race.
6) While Shakespeare is the "standard" yacht brand -- that is, West
Marine sells them -- you may want to look at Digital Antenna and
Comrod.
http://www.shakespeare-marine.com/antennas/ssb.htm
http://www.digitalantenna.com/ssb500.html
http://www.comrod.com/v2/Marine/pages/mar_1.asp
7) If you lose your mast, you still have the whip (yes, of course the
falling mast may wipe out the whip). This might just be when you want
to phone home. With the backstay rig, you have to have another way as
a backup (another antenna or some other long range device --
Inmarsat-C, for example).
Jim Woodward
www.mvFintry.com
1 & 2. Backstay antenna systems are very nice, and handy, but as you
point out do have some limitations. Whips are usually a poor substitue
for a good wire antenna, as they try to approximate a long wire by adding
coil impedance to replace the wire length.
3. What you need is Proper Antenna Leadin Wire. The "Big Boys" use
GTO-15 type wire. It is esentially Sparkplug Wire, with 15000 Volt
insulation, and was specifically designed for this service.
4. Whips just are to compromised on most installations to provide
acceptable radiation efficency, when compared to a wire antenna.
5. Schakkyspeer has always provided what the asteticlly pleasing
noncommercial boat owner looked for in an antenna. The thing that
always drove my recommendations was. "Do you want it to look good,
or do you want it to work." Many a vessel owner said the former, but
came back a year later and replied the later, after a year of less than
stellar results. They also complain about the costs of "doing it right"
the second time around. I alwasy just pointed out that they had made
the intial desission against my advice and got what they paid for.
It is so much easier to do antenna designs as the vessel is being built,
rather than retrofitting it later.
6. Again you will not find a lot of Schakkyspeer HF & MF Antenna's on
Commecial vessels as these guys depend on their radio's for business,
and that means it has to work ALL time. In the North Pacific most
of the guy's are using Morad Antennas for whips, or just wire antennas.
7. Years ago I oufitted a few Racing Sailers with emergency wire
antennas, that used Helium ballons to hoist the 75 ft wire. Worked
great for one guy who was demasted 500 miles south of Kodiak, AK, and
had to limp into Yakatat on the AUX. Had a Ham aboard who knew how to
string a wire.
The most important thing to remember in HF & MF antenna design, is
"What is the Radiation Resistance of the Antenna at the Lowest Frequency
that one is entending to operate." If you don't plan on using 2182 Khz,
that is one thing, but if you need MF coverage, Grounding Design is
CRITICAL for best operation. Metal Hulls are easy, wood or plastic is
a horse of another color, BIG TIME. when your out on the High Seas and
in trouble, this is not the time to find out your systems is "In the
****ter", and always has been.......
Bruce in alaska
--
add a 2 before @