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Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics
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  #11  
Old 12-08-2009
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NightOwl, you are right about the grounds. I used a 3-inch strip of copper run from the transceiver and the tuner down to one of my thru hulls. It works fine and took about half an hour to install. Total cost was about $50. I always tell people to try the easiest solution and work up. I got this tip from Gordon West. He insisted it would work, and for me, he was correct.


As for the tuner, basically it electronically matches the wavelength of the output to the length of the antenna. For the best performance from your antenna, the antenna needs to look like it is a quarter wavelength long. If you figure the a 2 meter signal will need an antenna that is about 115 feet long. At 30 meters, the antenna would need to be 41 feet long. No way one antenna can match the length. So the tuner makes the antenna look like it is the proper length.
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Old 12-08-2009
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Yes, there are conflicting thoughts about RF grounds. Those of us who've been experimenting with them -- both on boats and ashore -- for several decades, and who have used them and written about them extensively, have some pretty strong ideas about what works and what doesn't. Also, we have some clues as to WHY this is true.

I did a piece entitled "RF Grounds in the Marine Environment" on the SSCA Board some years ago. It was repeated elsewhere, but I'm sure you can find it on the Board.

Bottom line: lots of things work, some easy to install, some not so easy. Since I do SSB installations for a living these days, I've got a repetoire of possible solutions, depending on the boat, the circumstances (intended use), and the owner.

In a recent presentation for SSCA I enumerated some of the things which work well:
  • Copper strap to bronze thru-hull near tuner
  • Aluminum toerails (with sections linked together)
  • S/S rubrails (sections linked together)
  • Rudder and autopilot s/s framing complex
  • S/S radar and solar panel arch
  • S/S lifelines and pushpit/pulpit complex
  • Radials (wires or copper strips), tuned or untuned
  • Metal hull to deck beam
  • Large aluminum swim platform
  • Metal hull

If you want to go to the trouble of moulding wire mesh into the hull at layup time, or mounting bronze plates, etc.....those will work, too. But, they're unnecessary and overkill.

What is NOT a good idea is tying the RF ground to the boat's DC ground system, including the engine and/or any of it's component parts. The RF ground should be separate from other onboard grounding systems.

Do radials work? You betcha. Try it yourself. Hoist a random length of wire, over 23' long with a spare halyard. Affix it's lower end to the tuner antenna lug. Now, throw a 1/4 wavelength piece of insulated wire along your side deck, with one end attached to the tuner ground lug. For the 8mHz marine band, you'd need a wire (any kind) about 234/8 = 29.25' long.

This simple setup will tune very well on the 8mHz marine band, and will put out a pretty decent signal. Hams do this all the time. So do broadcast stations (which often use elevated radials). No need to have contact with seawater or even "couple to seawater".

Notice we're talking WIRES here for radials. But you'll find in just about every marine SSB book and in many instruction manuals statements to the effect that "wires don't work; you've got to use wide copper strips for radials". Balderdash. And, just one of the many myths and downright WRONG statements found in places where the authors are just parroting what they've read or heard elsewhere.

Lotsa ways to skin a cat. Read the ham stuff, experiment yourself, and talk to hams and marine professionals who've been there.

Bill
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Amen Bill !
I couldn't agree more. After being a ham radio operator, sailor, cruiser for over 40 years and tons of SSB installations, I think I can speak from experience. There is so much "balderdash" that just keeps on rolling from one to another. I have always used my KISS-SSB Ground Radial System and always chuckle with sadness when I read things like " you can not use round copper for the counterpoise", where did that come from? I think the cruising/sailing public is starting to see the light. It is not vodoo magic to get a decent SSB HF signal radiated out.
I have always used the radial type ground system "counterpoise" since being hit by lightning right at the top of my mast and not losing my radio gear since it was not grounded to the water. This happened in the third day of a 14 days passage from Samoa to Christmas Island, I was still able to stay in touch with my peers and the Pacific Seafarers Net. Carl KE7FGF
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Hmmm, just happen to have that antenna tuner too Thanks radio guy. I will let you know when I get the rest of this stuff together.
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Quote:
Originally Posted by btrayfors View Post

What is NOT a good idea is tying the RF ground to the boat's DC ground system, including the engine and/or any of it's component parts. The RF ground should be separate from other onboard grounding systems.
What problems does this present??
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Bill,
you mention some cheaper unities. I've never considered anything beyond the ICM-700, indeed never had any ref beyond those traditional ICOMs. What is the price for a working M-600 and a TK-707 ? And where to find it in US ?

tks
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Is it true that you can't, with a reasonable amount of ease and expense, connect an M700 to a Pactor modem? That you need an M710 or better? I'm sure that it can be done, but supposedly it is so expensive and difficult to do that the cost/benefit ratio is out of wack..... balderdash or true?
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Old 12-09-2009
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Originally Posted by lancelot9898 View Post
What problems does this present??
Mainly RFI concerns (radio frequency interference). Both ways -- from the radio to other onboard instruments and components, and from other onboard devices to the radio.

In other words, radios connected to the DC ground system tend to be noisier on reception and to have increased potential to interfere with other onboard systems when transmitting.

Bill
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Old 12-09-2009
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Originally Posted by negrini View Post
Bill,
you mention some cheaper unities. I've never considered anything beyond the ICM-700, indeed never had any ref beyond those traditional ICOMs. What is the price for a working M-600 and a TK-707 ? And where to find it in US ?

tks

Nave,

PM me. I've got several at the moment.

Bill
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Old 12-09-2009
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Originally Posted by mightyhorton View Post
Is it true that you can't, with a reasonable amount of ease and expense, connect an M700 to a Pactor modem? That you need an M710 or better? I'm sure that it can be done, but supposedly it is so expensive and difficult to do that the cost/benefit ratio is out of wack..... balderdash or true?
It depends, on your skill levels, intended use (PII vs. PIII), etc. One of the best sources for a discussion of the suitability of various radios for Pactor email is on the SAILMAIL website. But, even that is not gospel. For example, they say the TKM707 isn't suitable for email, but they include a technical note by a guy who's using his TKM707 very well.

In general, though, it's true that if you intend to use a Pactor modem many of the older marine radios are not easily adaptable for this purpose, due both to their T/R switching speeds and to the lack of dedicated connectors.

The Icom M700Pro, M710, and M802 work very well with Pactor modems, and connecting cables are readily available. So, too, do many ham radios, including the entry-level Icom 718.

Bill
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