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Since the passage from Hawaii to Juan de Fuca I've been plagued by intermittent the following intermittent problem in my HF - Pactor Modem setup that I use for my Sailmail communications:
"Communications with the PTC-II have been lost (modem-ready signal has gone false, power may be off. Terminal window will be closed."
These were a real pain because the computer would refuse to terminate the Airmail3 process, I would then have to reboot and start again. Sometimes it would take 2 or 3 retries but eventually I would get through the session. It would be unnerving because there was the risk that this mysterious problem could go 'hard' at any time and leave me without the vital weather and other services of Sailmail. Then the problem would go away for a while only to return later. Changing computers and the laptop-Pactor cable made no difference. Cleaning and reseating the cables to the Pactor modem seemed to help sometimes but in retrospect it was little more than a ritual intended to appease the Gremlin God.
The problem went 'hard' last night, even after our recent error-free days during our visit to the island. In desperation I Googled the exact message and found the analysis of the problem buried deep in the Sailmail/Airmail3 FAQ. I've attached relevant sections of the FAQ in both Open Source (ODF) and MS WORD formats.
Looking at the analysis I don't think that last night's hard failures were a coincidence. The 'expert' who set up the system in Hawaii decided to use the water vane of the Monitor wind steering as the earth, independent of the boat's ground system. (To avoid ground loops?) This made sense at first because of the large surface area presented by the stainless steel paddle. But it didn't take me long to figure out that I don't always have the paddle in the water. Worse, the join between the paddle and the Monitor frame to which the tuner is grounded is a loose one that jumps around while the Monitor is doing its thing. I then used two bare ground wires to provide additional grounding from the tuner to two of the keel bolts. Strapping would have been better than wire, but there was no way that I could work strapping through the bends, nooks, and crannies leading to the keel bolts.
I figured that I could get a lot of assistance by the fact that the wires were usually bathed in water, improving the connection between the ground wires and All of the keel boats. Except that last week I cleaned and dried out the bilge, and I am thinking that this, with the fact that I have completely removed the Monitor paddle have caused a grounding problem which has led to RF interference to the laptop's USB cable.
Today I plan to service all ground connections from the antenna through the tuner and to keel bolts to see if that helps.
However, there are other recommendations that I would like to follow, namely (1) two RFI chokes, at each end of both the laptop-modem USB cable and the modem-HF cable, (2) place a T4 Line Isolator on the coax cable between the tuner and the HF radio. The "expert" seems to have installed only one RFI choke per cable, and no T4 line isolator.
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The Sailmail FAQ cited in the message above stated the following:
Similarly to the above question, this is caused by your own transmit signal getting back into the computer, and scrambling the USB or serial interface to your PTC-II modem. This is a serious problem which must be addressed. It may be exacerbated by a change of USB port, but the cause is RF radio signal where it doesn't belong. See Airmail help for "RF interference" for info. In short, make sure your ground connections to the tuner are adequate and in good shape, surface corrosion of the copper foil won't hurt but corroded connections are a problem. Also check the antenna connections, from tuner to backstay. It is recommended to disassemble, clean and check all of those connections annually (e.g. when hauled). Then check the ferrites on the cables from radio to modem, and computer. There should be a clip-on ferrite on each end of the two cables from modem to radio, and the USB cable from computer to modem. For the USB cable it is often necessary to use a larger ferrite (with a 0.4" hole) clipped around a loop of 3-4 turns of USB cable in order to completely block the RF. Also we recommend a ferrite line isolator in the coax connection between radio and tuner, at the tuner end. This is supplied by some dealers, and is excellent insurance against RF.
---------------------------------------Jak replied that he would be able to bring some clip-on ferrite RFI chokes and a T4 line isolator as recommended in an article that I found on the web. I then spent a few days on the internet learning what I could about positioning HF tuners and grounding them on boats.
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| Corrosion Around Connection Hole at Top Left, Another at Right After Sanding |
I must have changed my mind a half dozen times about whether or not to move the tuner from the lazarette, where it could be immersed were the cockpit ever to fill with water to the security of the quarter berth area. In the end I considered to tradeoffs of moving the tuner too high. Moving the tuner would result in a longer GTO cable from the antenna to the tuner as well as a longer grounding run, each introducing their own problems.
I found the following article extremely useful: http://www.kp44.org/ftp/SeawaterGroundingFor_HF_Radios_byGordonWest.pdf
I found his test results amazing.
Another writer stated that all communications setups must be considered temporary rather than permanent. Every cable and connection must be checked regularly - at least once a year. This immediately changed the way I look at the system, which I haven't looked at since it was installed in Hawaii exactly 24 months ago.
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| Cleaning in Progress |
The AT-130 is housed in a durable, completely weather-resistant acrylic case with rubber gaskets. This allows it to be conveniently installed near the antenna element base. An ICOM power point presentation states: Tuners are designed to resist moisture, but not a good idea to expose to frequent splashing water.
Given the imperatives to place the tuner as close to the antenna as possible and also to minimize the length of the grounding run, the tuner will stay in the lazarette, riding about 6 inches above the floor and hopefully protected from all by a cockpit filled with water (which has never happened). And even if the tuner is immersed there is a good chance that it will survive.
Then there is the issue of grounding points. First of all, for all of the variety of opinions on the subject flat copper ribbon (or rigid copper tubing) is non-negotiable: round wire presents too much impedance to the RF ground signals. This means that the two solid ground cables that I ran from the tuner to the keel bolts were probably a waste of time and maybe introduced more noise into the system. The technician who installed the system deemed a two copper tapes running to the Monitor wind steering frame adequate. I've read that people have had success grounding to aluminum toe rails, stanchions, and even water tanks. I'm going to try grounding to the fairly substantial stainless steel cockpit frame as well as the Monitor windvane.
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| Clean Copper Tapes, New Holes at Near Ends |
Today I unbolted the tuner off its mount and removed the two copper tapes that ran between it and the Monitor wind steering. The copper at the point where it bolts to the tuner was corroded so badly that I'm wondering how the HF radio worked at all. I spent spent several hours sanding the corrosion off the tapes. The literature states that corrosion on non connected sections of the tape is OK, but I decided to get rid of as much of that green oxide as possible.
One of the complaints about the AT-130 tuner is that the bolt to which the ground tapes must be fixed is small and obstructed. I couldn't agree more. I cut off the tuner end of the tapes and prepared new holes using a drill rather than the fold 'n scissors technique that the "expert" recommended. The idea is to have as tight a fit around the small bolt as possible.
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| Tuner On Its Side |
The last photo shows the bottom of the tuner. The ground bold is the small one above the black control cable. Note the two ferrite RF chokes on the black cable. To the right is the black engine exhaust hose. At the far right are the two disconnected ground cables that lead to the keel bolts.
Tomorrow I hope to purchase two more copper ribbons for grounding to the cockpit frame.
1 comment:
You are working hard lone sailor. Take care.
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