SeaTalk interferes with SSB on certain freqs

[Rhumbline]

I have an annoying problem on my SSB installation where the (Raymarine) SeaTalk bus is interfering with my SSB reception. Whenever I turn on my instruments I hear a strong chirping on specific frequencies, particularly annoying on the maritime marine ham nets on 14300 and 21412 kHz. The antenna tuner is located near the autopilot control head. It would be a major effort to reroute these cables/devices. Can I put some clip-on RF bead(s) on the SeaTalk bus cable to eliminate this RFI, and if so what choke value do I need? I believe the SeaTalk is running at 4800 baud. The interference occurs more-or-less periodically across the HF spectrum but I haven't been able to determine any exact spacing of the frequencies. It seems loudest on 14300 mHz.
Since SeaTalk is a popular interface and the interference occurs on the principle marine ham net frequencies I am surprised I haven't found comments about this on the web.
Rig is an Icom M710 and the instrument pack is about 10-yr old Raymarine C-series.

Bill, AI6MB
s/v Vector, C&C 38

[transmitterdan]

I doubt that old style Seatalk I which is a single wire slow speed network is causing the noise. It may be something else such as the autopilot computer. I would try putting ferrites on the 12V power cables feeding the autopilot. Also, try to ensure that the 12V power wires are run very close to one another. Even a twisted cable might help. It may be that the noise is emitted by the processor in the AP unit. It's a bad practice to power the AP computer using the Seatalk bus cable. If that is how it's powered consider powering the AP direct from the batteries. On our boat I power the AP from the battery via a 40A relay that is switched on from the DC power panel at the nav station. That way we can have instruments but keep the AP powered down until we need it.

Can you switch on the instruments without powering on the autopilot? That may be instructive as to the true source of the noise. The Seatalk network is running even if the AP is powered down.

Also, think about the depth finder as a potential noise source. Those are much more powerful than a Seatalk I bus.

[Paul Elliott]

Originally Posted by Rhumbline

Can I put some clip-on RF bead(s) on the SeaTalk bus cable to eliminate this RFI, and if so what choke value do I need?

Step 1: Get some clamp-on chokes that do a good job for HF frequencies. I talk about this in a presentation made to the Singlehanded Transpac racers, pdf here: http://www.sailvalis.com/presentatio...ons%202012.pdf

I use Fair-Rite "Type 31" material. See page 14 of the presentation for more details.

Step 2: Try putting the ferrites on any cable you suspect, as close to the source as practical. Wind three turns through the core if you can. Again, I touch on this in the presentation.

Step 3: Test. See if it made a difference. Turn things off and back on to help isolate the problem. If it helped, but not by a lot, use an additional ferrite. Add one on the other end of the cable and see if that works. Try other wires. Signal leads are usually the worst offenders, but power cables can also be a problem. Essentially any wire that is connected to a digital (or other radio-noisy) device is a potential radiator.

There are other ways to reduce RF interference, but ferrite clamps are usually the easiest and they often work very well. Buy a bunch of the ferrite clamps and experiment. You may find that multiple Seatalk devices are radiating this interference. Trial and error is the usual approach. If you can still get a hand-held transistor AM radio, you may find that it is a useful "sniffer" when tuned to a quiet frequency. If Seatalk signals are being picked up on your marine SSB, the interference is probably hitting lower frequencies as well.

Go slow and steady, and take careful notes.

[Rhumbline]

Thanks for the reply. It's the autopilot 'head' that's close to the tuner, not the drive motor. When you mention '40 amp relay' I assume you're talking about the motor, and not the AP head or computer. The motor is definitely powered separately, but the control head/computer (ST 4000) is powered from the 18AWG wires that interconnect all the instruments. This is a bundle of about 5 wires that I think interconnect all the instruments. I didn't do the wiring (the instruments came with the boat I bought from a friend) I don't think I can turn the AP off separately; some instruments are on a breaker labeled 'electronics' and some are on a breaker labeled instruments' and I need both on to have a functioning autopilot, and the RFI is present regardless of which breaker is on (that's why I assumed it was somehow coming from the SeaTalk bus).
It makes sense that the RFI is coming from the AP computer. Do you think it would help to put a choke on the wire bundle (sheathed, straight wires no twisted pairs) going into the AP head/computer? or fabricate a grounded metal box to shield the back of the AP head?
It's not that major a problem since I'm not on the radio when I'm at the helm. Thanks for your insights.

[transmitterdan]

I don't know how your system is wired. The autopilot has two parts that both have computers inside. One part is the control unit with a LCD display. The other part is the actual autopilot computer. It is a plastic box that has no display. That is the unit that runs the motor. Which one is close to your tuner?

Typically there will be two power circuits and it sounds like you have that. The instrument displays are powered with one breaker and some other "electronics" are powered by the other one. For now it doesn't matter but you should try to determine what devices are powered by what breakers. Write it down so you can refer to it later.

Some Seatalk instruments such as AP control, wind, depth and speed are powered by the 3 wire Seatalk cable. This is the one that plugs into a slightly curved connector. There are 2 such connectors on most instrument display units. They run in a daisy chain. You can try putting Ferrites on those cables at multiple locations.

Here is another thing you can try. Carefully unscrew and unplug the RF cable connector from the back of the SSB radio and unplug the tuner control cable. Turn the SSB on and listen to see if you still hear the noise. If you still hear it then the noise is not from the tuner. Plug it all back in carefully. Don't try to transmit with the cables unplugged. After you plug each cable in turn on the SSB and listen to see which cable affects the noise more. It could be either the RF or the tuner control cable.

[Rhumbline]

Thanks, I'll try your suggestions. From what I've read on the internet (reader beware) the computer is not a separate box on this autopilot, but is located in the unit with the LCD display. Regardless, the tuner is near the display/control box and the antenna feed line is routed a foot or two away from the control head.
Unplugging the tuner from the ssb is an easy test. I'll try that first. I've ordered some ferrites (Fair-Rite) that another helpful poster suggested. When I gather some results I'll post to this group.
Thank you Cruisers' Forum members for all this info!

[TLSparks]

The Chirp is the fathometer pinging. I have the same thing and just live with it. Shame on me. I suspect it is probably coming in through he power supply, but have never investigated the problem. Sounds like a good project.

The fathometer chirps at 200K or less so I would try a mix type 75 ferrite beads instead of the normal mix type 31 we normally use for RF. The type 75 has the highest permeability (most opposition) and the lowest frequency blocking capability so it might work.

A few other things: You should be connected to the battery directly via a fuse within 7 inches, not the breaker panel. Twisting your power cable will reduce the coupling from outside sources into the power cable. Looping the power cable through the core increases it's effectiveness by the square. e.g. 1 = 1X, 2 = 4X, 3 = 9X. Loop the core as many times as possible at the back of the transceiver and or use multiple cores.

It is also possible the signal is coupling into the transceiver via the antenna and the control cable. I guess I will order some type 75 cores and investigate.

[TreblePlink]

As was mentioned above, use large high permeability ferrite torroids and make several turns through them for each cable treatment. A single pass probably won't make enough difference at 14 MHz.

[toddster8]

This thread is interesting to me, since I have kind of the same sort of interference but also different. It is definitely the Sea Talk bus making a rhythmic pattern of "clicks," but is stronger at the lower frequencies - still present but almost unnoticeable above 8 MHz. There are still a couple of things on my list to try but actually I've put off troubleshooting this for the last few months - however, those long winter nights are coming around again.
The problem with "just turning off" the offending device, is that the worst culprit is the AIS/GPS unit - which is required to operate the radios correctly. The other Sea Talk devices produce the same rhythmic signal, but at much lower intensity.
I don't have my troubleshooting notes with me today, but IIRC, a small fortune in chokes has had little or no effect. The most effective reduction I've achieved (somewhat accidentally) was tying the SSB chassis ground to the AIS cable shield.
Anyway, my troubleshooting plan is reducing the system to the minimum wires required to operate the radio, then adding only the AIS unit, one wire at a time. I've already run through this exercise once, but that's still a lot of wires... I think the next thing on my list was to try eliminating or shielding the terminal blocks that I've been using to connect them all. I've also been reluctant to trim the multi-conductor cables (because what if i have to re-route everything) so there is a lot of excess cable coiled up and stuffed in the back of the cabinet...

Edit: I guess I should clarify that the interference appears to be NMEA 0183 and Sea Talk 1 communications. Somewhat interesting in that you can hear the pattern of clicks change as the different devices are booting up, then establish communication with one another.

[TLSparks]

Keep in mind we are not trying to eliminate the 14M, We like that one coming in. We want to eliminate the lower frequencies from the fathometer coming into the transceiver box. I just ordered 10 of the 75 mix. Should be a fun exercise.

[alctel]

I get this loud high pitch chirp/squeal on 14300 as well, as well as a couple of other frequencies, even with everything else on the boat disabled. I wonder if it's local interference (I always forget to test when I'm out)

[TreblePlink]

Originally Posted by TLSparks

Keep in mind we are not trying to eliminate the 14M, We like that one coming in. We want to eliminate the lower frequencies from the fathometer coming into the transceiver box. I just ordered 10 of the 75 mix. Should be a fun exercise.

If it's coming into the transceiver on the power leads (usually won't) then you want to reduce everything above DC. This is easily cured by internal bypass capacitors, already done by the mfr.

Usually however, the transceiver is hearing harmonics (multiples) of the offending data line or power supply. That is to say it's coming in through your antenna because the offender is actually radiating it (a harmonic at 14.3) and the SSB antenna is close enough to hear it.

When the offender is found (important) and treated with ferrite torroids, although preventing all radiation is best, your focus will be on the problem receive frequencies - 14.3 MHz etc. 75 mix should be fine. Even if you run your coax through a torroid a few turns, (common mode suppression) 14 MHz receive will remain unaffected. Use as many turns through the torroids as you can.

[TLSparks]

ALCTEL
It is possible, lots of noise in a marina. I do not know what your sound is, but in a marina it could be noise from other boats, refrigerators, electronics, water makers, LED voltage regulators, etc

Disconnect the Antenna and see if that is the source of the noise. I suspect it is, but if it is coming in via the power or control cable you should be able to narrow that down anyway. Unfortunately the antenna's job is to bring in MF and HF signals. In AM / SSB not all the signals coming in are what we want to hear.

If you can send me a recording, I might be able to tell you what it is.

If it is coming in via the antenna, you might try using a portable radio and search for the signal source. You might be able to find it.

[transmitterdan]

Originally Posted by Rhumbline

Thanks, I'll try your suggestions. From what I've read on the internet (reader beware) the computer is not a separate box on this autopilot, but is located in the unit with the LCD display. Regardless, the tuner is near the display/control box and the antenna feed line is routed a foot or two away from the control head.
Unplugging the tuner from the ssb is an easy test. I'll try that first. I've ordered some ferrites (Fair-Rite) that another helpful poster suggested. When I gather some results I'll post to this group.
Thank you Cruisers' Forum members for all this info!

For sure the ST type AP LCD display is not the AP computer. The AP computer is somewhere else usually installed close to the rudder drive unit. You should look for it so you know where it is.

[bluewatervet]

Bill, Some more 'offending signal tracking down' ideas & techniques. Suggestions by others here that the noise may be from the marina/nearby vessels is a very excellent point to keep in mind. If you can motor out away from the marina and test, that is a very good "process of elimination" technique as a initial step. If that simple test fails, it gets tougher fast as shown by all the various suggestions for fixes by others here. Power-up the ICOM & tune to where you have the unwanted noise, then disconnect both ends of the antenna RF coax cable btwn ICOM radio rig and the tuner. If noise stays same, then your offending signal is very probably getting into the radio via the ICOM DC power (or ground) systems. First try to run on marina AC power with board inverter's completely off, not even idling. Then run the ICOM on boat DC only, with marina AC cable disconnected from the boat completely. Then try with your generator and/or main engine also secured. If stuff is sharing circuit breakers/switches, then pull off power leads or pull fuses, etc. to work your way through all your DC powered electronics and other AC or DC powered appliances. Keep notes when the offending signal changes noticeably. Possible noise source clue each time signal changes. Connecting ICOM rig directly to battery bank (with own inline fuses on dedicated positive/negative wires) is another excellent isolation idea...use heaviest copper wire gauge you can reasonably employ. Even consider ICOM powered with a separate temporary power source (no transmit!). Twisted power wires also excellent recommendation....either for AC & DC for all electronics. When using ferrites, more turns the better as clearly noted by others, and they may be needed at 'both ends' of offending cables. Note they can be bought with plastic snap-close housings, so if enough wire slack is available you can avoid any connector removal/replacement. Cables for control signals btwn ICOM rig & antenna tuner are a good first bet for suppression beads. Sneaky interference source hunting trick is to use a loose coax cable in place of the normal ICOM antenna run, and with the rig tuned to a strong offending signal, use the stripped back center conductor (...leave 3 inches or so with insulation still on & taped-up bitter end) as a hand-held pick-up probe to 'sniff around' the boat. Loudest picked-up signal 'almost always' near the offending source; but note interconnecting cables between devices can & do conduct interference very well...at times very long distances. And then they can & do effectively become an antenna to radiate outward what originally was just a conducted interference signal..!!! Start with DC power cables, then AC cabling, control cables from bridge/helm displays to outlying devices, the radar, autopilot, traducers, and so forth. Keep a checkoff list so you know what you have eliminated! One more thing to keep in mind: When listening on the Maritime Net, a lot of times you are listening to a very-very weak signal depending which regional net control station is currently running the net. And they tend to have powerful rigs and direction antennas....while replying stations are more like you, low power by comparison, less punch in other words. In that case, your rig is operating at 'maximum gain' and that is when offending signals can & do seem huge. If the interference varies widely in strength, that is a very important clue btw. So tune off that net frequency and listen to a somewhat stronger signal as shown on the S-Meter of the ICOM (....on the 14.150 to 14.350 mHz range there's usually both day and night weak & strong amateur SSB radio operators from near and far...use them as test signals). Key point here is there is a practical limit, a trade-off if you will, on just what you can keep out of your rig's antenna input. Oh, forgot to mention there are Internet LAN 'extenders' ever more present out there. They typically have a repetitive tick-tick sound or pattern buzzing sound, and can be very strong depending on your distance from them. This is BPL (broadband over power-line) technology. If your marina or a nearby neighborhood condo complex is using that stuff, it is next to impossible for the average radio user to filter out..!!! For your & other marina slips sake I sincerely hope this is not your interference source.... Good hunting!! George