Help with SSB Installation

[peterbringloe]

If anyone can help me improve the performance of my Icom M710 SSB radio I would be most grateful. I installed it myself about a year ago and used it to fairly good effect from the Uk down to the Canaries and across the atlantic. But it was noticeable that our transmission distances were inferior to other boats' rigs. Now it is pretty useless - both receiving and transmitting. Assuming that the tranceiver and tuner are working properly I gather that the installation boils down to these three issues:

1. Ground - It is a steel boat, and my installation included grounding both the tranceiver and tuner with a braided strap (about 1.25" wide and silver coloured) to a stringer which was taken back to metal and drilled. Both tranceiver and tuner are grounded to the same place, each length is about 1 metre.

I consulted a marine elecrtonics company in Road Town Tortola and was adviced to improve the grounding of the tuner and make the strap as short as possible. And on their adviceI bought a 4" copper strap from them (3' long) and connected it to two bolts fixing a harness line padeye in the cockpit. They said that the gounding of the tranceiver was less important, unless interference was a problem, so that remains in the original place with the original braid strap.

2. Antenna wire and connection to backstay. I have an insulated backstay and am using the inner only of heavy duty coax. The road town people said that it would be ok as they did the same when the did not have an appropriate cable, except they advise stripping off the outer completely. I have not done this. The inner of the coax is connected to the backstay (10mm) with stainless steel bulldog clips not jubilee clips. And I have remade the connection as best as I can. Incidentally, I find the terminals on the tuner both for the antenna and ground to be too small and light to be confident about a good connection.

3. Voltage. I understand that the Icom 710 is set up to operate at 13.8 volts. In order to achieve this we run the engine for transmitting and check the voltmetre for 13.8 or better. The tranceiver is wired directly to the batteries (4 x 110 amphour) using the supplied cable.

Any advice would be most welcome.

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[coco]

Since the impedance of your antenna cable probably does not match the impedance of the antenna at the feeding point, you should use an antenna tuner. Just connecting the coax to the backstay usually leads to a very poor SWR hence a weak signal. You might want to look here for more advice: http://cruisenews.net/cgi-bin/mmham/webbbs_config.pl and http://www.vrona.com/ssb_ground_2.txt

There is some good advice to be found.

Cheers
JP

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[Strathglass]

On a steel boat you are unlikely to have earthing problems.

Your supply sounds ok. Have you measured the voltage at the transmitter ( not at the batteries) when you are transmitting?

I assume that you have the correct Icom lead, including the coax feed between the TX and the Tuner.

If all the above are correct then look at the lead between the tuner and the backstay. THIS IS PART OF THE AERIAL.

I presume that the tuner is mounted as near the backstay as possible in order to reduce the length of this wire. You should not be using a piece of coax here. But can use the inner from a piece of heavy coax.

Hope that gives you a start.

Iain

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[peterbringloe]

Thanks very much for the website info. My installation does include a tuner - Icom AT-130.

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[IanBBA]

Peter, a couple of thing:-

1) Is the tuner actually tuning? I assume it's an AT120, AH2 or similar; it should clatter like blazes while tuning. If not, check the control wiring.

2) Ideally the tuner should be mounted as close to your backstay as practical in a location that offers good protection. Icom ATU's are designed for outside use but better protected. The wire to the backstage should be short, direct and unscreened. The earth as you mention is important; best being short and a wide copper tape or braid.

3) You will hear a lot about VSWR. Great thing about Icom auto-tuners is that ypu don't need to worry about this if the tuner is working, it is earthed properly and the connection to the antenna is as short as possible. However it would be useful to check the VSWR into the tuner when it thinks it's tuned.

4) Check your backstay insulators are in good condition.

5) Your M710 should work fine at 12V.

6) Are you sure it is the transmitter and not the receiver? Look for sources of 'noise' generating interference such as fluorescent lights, switch-mode battery chargers, fan motors.

7) I am very familiar with the M700 but not M710. The microphone may be faultly; has it been dropped? SSB transmitters give low transmit power if the microphone 'volume' is low. When you talk, is there a meter that moves; does it peak at the right level?

8) If all this fails, take the fit to your local dealer; after all you want t to work properly when you really need it!!!

Ian.







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[Bergman]

Agree with all comments above.

Would only add that a VSWR meter between the transciever and atu is almost essential. Without this you are working blind.

The range of tuning of auto atu is limited and the VSWR may be greater than the transciever can handle. In this case the transciever will automaticaly reduce the output power to protect its PA.

One possible cause of VSWR problems could be the length of coax between the atu and the antenna. With just the inner used you have effectively put a capacitor between the antenna and earth. Worse still, the length of coax will form a resonant trap at a wavelength roughly equal to 4X its length (in meters). I would prefer a length of ordinary wire, heavily insulated of course. Alternately use coax with outer and inner strapped together and of course both insulated from earth.

One further thought is the joint between the backstay and the feeder wire from the atu. Can be subject to corrosion and start playing at being a diode which doesn't help the cause.

Best of luck



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[Birdseye]

Lot of good advice above.

For connecting the set to the aerial, I used old fashioned copper cored spark plug wire from a motor factor - good insulation and a nice thick multi stranded copper core. Coax is less good and if, for example, you get water by capilliary action up the braid or in the insulator (if you've used air cored) you will degrade the signal.

Dont worry too much about voltage - the difference in performance on the receiver will be small and not much more on the transmitter

Try using the set with everything else switched off. On my set, the agc reacts to the background noise level and reception suffers. If your engine or fridge etc is generating noise (and I'd be surprised if they werent) then receiver performance will suffer. Same if you are using in an electrically noisy marina/ harbour.

Personally, I found earthing made damn all difference - to the point where I now dont bother.

So to summarise, I recommend you replace the coax altogether, remake all the aerial connections and try when everything is switched off and you're peacefully at anchor somewhere isolated. Try at the right time of day since propagation varies during the day. And get someone else to try at the same time as a datum - since conditions vary day to day. If it still doesnt work right, think about having the set serviced and / or the atu checked out professionally.


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[MainlySteam]

Peter. With a radio such as the 710 in a metal vessel you should be able to work the world when propagation allows - for example, I have no problem working European amateur stations from our boat here in New Zealand when propagation allows (most days, 150 watt radio, 8m vertical antenna).

I have a background in radio, including installations on metal vessels where I have run into most of the difficulties there are. I would be happy to provide some troubleshooting information but it would be too lengthy to post here. So, if you wish, please send me a personal message. If you do so, to get started would you let me know if your yacht's DC negative is isolated from the steel hull and (if you know this) whether the IC-M710 is one with its rf ground isolated from its internal DC negative or not. This will give me a grasp on the likelihood of common mode rf currents existing and which can affect radio and tuner operation (as well as affect the accuracy of any measurements made with an SWR or power meter, for example).

Also, just to clear up some of the existing points -

The use of coax from the tuner to the backstay is ok as long as the braid is either removed (and the jacket slipped back over and sealed to provide UV protection to the inner insulation, or the braid is left on but is NOT connected in any way to the centre conductor or to ground (it could be connected to the centre conductor at BOTH ends, but that of course, only leaves you with the coaxial cable's sheath as poor insulation against the rf voltage inside). I would strip the braid out, but that can be hard to do, or impossible, without destroying the outer sheath if the length is long.

The wire from the tuner to your backstay connection is part of the antenna. This is a particular issue in metal boats, as unlike plastic or timber vessels the part inside the boat is screened by the grounded hull from the outside world and all radiated from that bit is lost. Preferably the length inside the boat should be as short as possible and at very worst no more than 5% of the total length of the antenna from tuner to the top insulator of the backstay. The section inside the boat should be kept away from the metal hull as far as is practicable (although not a big issue if the length is short as long as the insulation has some air clearance to avoid the possiblity of arcing in the case of insulation breakdown). The section above the deck to the connection above the bottom backstay insulator must be kept well clear of the backstay (100 mm or more if possible) to minimise capacitive coupling to the lower and grounded to hull part of the backstay. Again this is of particular importance with metal boats, but I do see many installations with no (ie clipped to or wound around the backstay) or little seperation.

Your rf grounding sounds ok, and despite many claims to the contrary, a good ground of sufficient area at the tuner is essential to the good performance of a vertical or random wire antenna (as a backstay is). A good ground is, of course, easy to achieve in a steel vessel. However, I would remove the ground strap from your radio to the hull (completely) and leave it off unless there is a deterioration in performance (even less power on transmit than you now have or more noise on receive) - it probably won't fix the problem but it may make finding the problem easier, as if common mode rf currents are an issue it will be contributing to those.

I expect that I may have told you at least some things you know already, apologies for that, but I have just stated what has come to mind for completeness.

John

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