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Author Topic: Mobile Antenna (Sailboat)  (Read 1873 times)

Posts: 2

« on: March 27, 2003, 10:53:35 PM »

I recently purchased an ICOM 706 MKIIG and AH4 tuner, with the intent to install on my sailboat.  Having heard that a CB-type vertical will work well, I bought a marine-type Shakespeare "continuous load" 8' CB fiberglass vertical.  The antenna connection wire is coax.  In the past, I have used the continuous wire lifelines as a ground plane and it seemed to work well.  Excellent reports with less than 20W power.

My intent was to mount the AH4 tuner in the aft compartment, and the antenna on the stern rail of the boat, about 3 feet above the tuner. I will then run 3" copper strap inside the boat as a ground and attach it to a through-hull bronze fitting to bring it into contact with salt water, helping the ground.

My question is, is this antenna workable with this setup.  (I thought about the ICOM AB2B, but the price of $300 seemed very high compared with the $70 marine vertical).  I am reluctant to do the RS CB vertical, since salt water is extremely corrosive and will usually make short work of any non-marine antenna.  Shakespeare did also offer an end-fed version of the fiberglass CB antenna.

Second, how to connect the AH4 to the antenna?  Cut the coax short at the antenna and run high voltage wire?  Use the coax?  Mount the antenna on deck, to shorten the lead to the AH4 (could probably get down to 6" or so that way), at the expense of the nice lifeline ground plane?  

Extra kicker:  I am interested in the 706 for ham use on the boat.  However, it would be nice if this setup were capable of emergency use on the marine bands--just in case.  Are there any issues with frequencies outside the normal ham bands?

Lots of questions, so few answers.  I am recently returning to the ham hobby after many years away, so please bear with my probably-dumb questions.

Thanks, Mark.

Posts: 527

« Reply #1 on: March 28, 2003, 06:11:56 AM »

Almost any metallic item of length can be used for an
antenna. A simple wire suspended from the main mast,
the metal railing around the boat. Since you have a
tuner there are many possibilities. Just don't forget
to drop a ground wire in the water.
As to the Marine Radio band.... 156.800 mhz is
channel 16 . There are also several HF frequencies.
Using the 706 to transmit on these bands
would be in violation . However, listening is not
in violation.
The 706 is "Type Accepted" as an Amateur Band radio,
ONLY. To use it for any other service would be in
73 - Tim

Posts: 2

« Reply #2 on: March 28, 2003, 06:52:30 AM »

Thanks for the input.  Obviously I am aware of type acceptance and I intend to use the 706 only on the ham bands, as I indicated in my initial post.  However, in the event of a boat sinking in the middle of the Atlantic, with mast down and people hurt, it is a "Mayday" situation and "emergency" and it is a well-accepted premise to use whatever means necessary to save lives.  But thanks for the reminder.

I am really interested in how to connect this vertical antenna.  Any ideas, anyone?

Posts: 6168


« Reply #3 on: March 28, 2003, 10:12:14 AM »

Assuming the Shakespeare is just a loaded quarter wave, I would cut the coax off entirely and feed it with insulated wire (or salvage the center conductor out of the cut coax). The base would then be connected to your counterpoise/saltwater ground mount per your description. The distance between the tuner and the whip shouldn't be critical, I would do whatever is best mechanically. Since you already have the antenna and have decided where to mount it, you've eliminated a lot of variables already.  It's a matter of hooking it up and trying it out.  I can't seem to find any technical details on the AH-2b, but the AH-4 tuner requires a bit more than an 8' radiator per the spec sheet.  I don't own an AH-4 so can't speak of it's capabilities.  As far as marine freq TX, previous posts are correct.  For about $2K you could've bought Icom's marine HF SSB radio that is also ham-capable, if you really wanted the best of both worlds.  You get what you pay for, in a marine environment I suspect the 706 will meet an early demise due to it's lack of a sealed chassis.  It is basically consumer electronics grade construction.

Mark K5LXP
Albuquerque, NM

Posts: 10248


« Reply #4 on: March 28, 2003, 12:30:59 PM »

I'm not a sailor, but I have installed an IC706 and AH-4 for someone who is. We used an insulated back stay as a vertical. The tuner is located less than a foot away from the base of the stay. The tuner is grounded to keel plate using a 2" wide monel stap approximately 4 feet in length. The set up works like a champ.

Alan, KØBG


Posts: 496

« Reply #5 on: April 01, 2003, 01:31:25 PM »

Mark, I'm using the SGC autotuner on my 40' sloop here in Mobile, AL.  I'm tied to an insulated backstay, but since you are not wishing to tie to the backstay there are a couple of other ways.  

BTW, I'm assuming (yea, I know about ass u me ing) the AH4 is the long wire tuner?  If so, then there are a things you might do.  

IF your rigging is not grounded, then just tie the tuner to the rig and load the whole rigging.  You'll be surprised what that will do.  You can also use the SS CB whip.  With it you won't have any problem with corrosion.  Using a CB whip is about the least effective due to the short size.  Of course you will wish to use the keel (IF exposed) or a grounding plate as the ground for the tuner.

You might go to and serach around the site.  They have good info for connecting on a sailboat - and IF the AH4 is the longwire version, then the same advice applies.

Don't worry about the 706 not holding up in a marine use, I've had ham radios on board for the last 20 yrs and had very little problem with any of them - excpet the very first KW TS-430 I had.  That was a lemon from the start.

IF you can do the "Mars Mod" (only involves the removal of one diode for the MKIIG you can then use the 706MKIIG FOR EMERGENCY USE ONLY!!! A as you said as a backup VHF marine as well as a SSB marine radio.  I've tested my MKIIG into dummy load and the power output is not a problem.  On VHF freqs the power is still up the 25 watts allowed on marine bands... and on HF bands it's around 100 watts.  Less than the 250 watts (I think) allowed for marine radios.

Have fun and feel free to e-mail me if you wish to chat more.

Ken H>

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