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Old 20-03-2011, 09:28   #1
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SSB Transmit Kills Autopilot

My old Icom IC-M800 is very well grounded and I get a lot of compliments on our ability to be heard well ("you're booming in here . . . "). And I took a lot of time to install my new Simrad Autopilot, carefully routing the cables away from any high-amperage sources. Now, however, when I transmit on the SSB radio, the autopilot goes into an alarm mode and the display says, "Lost Communications with Computer". Obviously, it no longer steers the boat and emits an annoyingly loud beep.

I have tried ferrite beads and running a seperate ground from the autopilot to the main ground buss but to no avail. Does anyone have any other suggestions? Thanks.

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Old 20-03-2011, 09:50   #2
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Re: SSB Transmit Kills Autopilot

Need full details of your install in order to make suggestions.

1. Power to the radio: How does it get 12VDC power? How long is the run? Direct to house batteries? Size of cabling? etc.

2. Ground system: What type of RF ground and connections are you using? Any interconnection between RF ground and other grounds (boat's DC ground? Bonding system? Lightning ground?)??

3. RF and control cabling: Type of coax between radio and tuner? Length of run? Proximity to other wiring?

4. Age and quality of all connections...DC, RF, control?

5. Existing RF transient suppresion: type and location of all ferrites, chokes, etc.

I know that's a tall order, but those are the major factors to be examined in tracing and eliminating your RF interference problem.

Bill
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Old 20-03-2011, 10:06   #3
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Re: SSB Transmit Kills Autopilot

Quote:
Originally Posted by btrayfors View Post
Need full details of your install in order to make suggestions.

1. Power to the radio: How does it get 12VDC power? How long is the run? Direct to house batteries? Size of cabling? etc.

2. Ground system: What type of RF ground and connections are you using? Any interconnection between RF ground and other grounds (boat's DC ground? Bonding system? Lightning ground?)??

3. RF and control cabling: Type of coax between radio and tuner? Length of run? Proximity to other wiring?

4. Age and quality of all connections...DC, RF, control?

5. Existing RF transient suppresion: type and location of all ferrites, chokes, etc.

I know that's a tall order, but those are the major factors to be examined in tracing and eliminating your RF interference problem.

Bill
Bill--

Could his radio be pulling so many amps that it knocks the voltage level below the reset level on his AP?
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Old 20-03-2011, 10:08   #4
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Re: SSB Transmit Kills Autopilot

"Bill--

Could his radio be pulling so many amps that it knocks the voltage level below the reset level on his AP? "

When we get the answer to question #1, we'll have some clue about this possibility.

Bill
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Old 20-03-2011, 10:13   #5
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Re: SSB Transmit Kills Autopilot

That's the ONE problem for which I never found an answer on our previous boat.
I had tried everything I could think of, and I'm a retired electronics tech and HAM.
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Old 20-03-2011, 10:23   #6
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Re: SSB Transmit Kills Autopilot

I would suggest as a possibility, assuming that the Simrod Auto Pilot has a function for a hand held remote controller, that the SSB transmission frequency is close enough to the remote's frequency to over ride the auto pilot and cause it to disconnect from the computer.
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Old 20-03-2011, 11:09   #7
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Re: SSB Transmit Kills Autopilot

EMI problems can be split into two types, radiated or conducted.
Either the energy radiating out of the antenna is being picked up by the conductors of the autopilot or the radio is conducting energy at spurious frequencies via the power or ground and this is being picked up on the ground or power of the autopilot.

Easiest way forward is to obtain or make a "dummy load" to terminate the radio firstly at the radio TX/RX termination output and test to see if the autopilot is affected, if so the problem may well be conducted*. Or if this test is OK a second dummy load test at the connection between feeder cable and antenna base, as a problem at this point would suggest routing or cable quality or mismatched termination impedance.

*If it is radiated the working assumption that we are starting from is that a Icom M800 and Simrad Autopilot can be co located without problems, it may be that you have to play around with some tin foil and moving the Simrad cables through 90 degrees (antenna polarisation) to see if that makes a difference.

If these tests or OK then you have to look at power feed or grounding return paths.
My next question would be does the problem go away when the engine is running?
If so I would be looking at the power feed if not then the grounding may need to be revised (at this point I would be curious was that seperate ground in lieu of or addition to the existing ground?)
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Old 20-03-2011, 12:44   #8
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Re: SSB Transmit Kills Autopilot

My thanks to all for taking the time to reply. It appears, though, that there is no 'silver bullet' with which to solve this problem. As I'm leaving Mexico for the Marquesas on Tuesday, I'm afraid my family and I will just have to hand steer whenever someone is on the radio.

Some of my thoughts on the issue, just the same:

I don't believe it's a problem with the power. The problem occurs with batteries fully charged (over 1,000 amp-hours in brand-new 6V golf carts) which feed a large buss with a 00AWG cable. The positive side of the radio is connected directly to the same positive buss. The ground buss to which the negative lead is connected is fed with another 00AWG cable.

I recently re-installed the transceiver (you may recall that this unit uses a remote control head that's fed with fiber optics) and I took a lot of care terminating the wire ends. As I said originally, the radio works great.

All of the cables for the radio (coax, control cables, etc) run above the headliner while all of the autopilot cables run below the floor boards. This means that they're all at least 6' from each other.

We have no remote option on the autopilot.

It would be my great pleasure to buy the solver of this problem two, very large, cold beverages. Hell, make it three!

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Old 20-03-2011, 13:06   #9
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Re: SSB Transmit Kills Autopilot

i think it may be somthing to do with the magnetic field/rf on the gyro/heading unit when you key the mike,had this problem between proximinity of the vhf and a wheel pilot, moved the gyro/control unit by 1 foot and was no longer a problem.

though 150 watts as opposed to 25w has got to have a bigger foot print.
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Old 20-03-2011, 13:33   #10
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Re: SSB Transmit Kills Autopilot

A large manufacturer of ocean trawlers in the Far East was having big problems with SSB to autopilot interference. They solved the problem by installing and using ONLY the KISS-SSB radial ground system, which is now standard on their yachts.

Does the problem occur on all bands, or just one or two?

You might try affixing 1/4-wavelength radials to the tuner ground lug and trying it out. Make the radials from any type of insulated wire, approx. 1/4 wavelength at the desired band. The formula is: Length in feet = 234 divided by the frequency in mHz. Example: for the 8 mHz marine band, you'd want a radial approx: 234/8 = 29 feet long. Length isn't critical.

Try one or two such bands on which you're having problems, and see if that solves it.

BTW, you'll want to disconnect all other wires from the tuner for these tests, and transmit ONLY on bands for which you have radials attached.

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