SeaTalk interferes with SSB on certain freqs

[TLSparks]

I hope you are remembering all ferrites are not created equal. Most of the snapons at Ham stores are mix type 31 which work great to keep the RF out of things when RF penetrates wires. If there is a chirping it may be at a lower frequency not covered by the Mix 31. That is why I recommended the mix 75. I was not able to find snapon 75s.

[TreblePlink]

But we don't care about frequencies we aren't listening to. We're hearing harmonics of the lower frequencies, not the lower frequencies. So we focus on the frequencies we're listening to.

Small point, as the treatment is usually the same. For choking, all that is required of the ferrite is high permeability, not Q, so choice is not nearly as critical as use in a tuned circuit.

[TLSparks]

That is true Treblepink as long as the signal is coming in via the antenna. A pulse signal clearly has a significant number of odd harmonics. If it is riding on the power supply DC, then it could be mixing in any non-linear stage and provide the sum, difference and the original high frequency. It is also possible to ride into the transceiver via the control cable on that DC. That is where the type type 75 may block a lower frequency getting in and heterodyning in the receiver.
T

[TreblePlink]

Have you seen many problems caused by power or control cable ingress? Just about everything I've seen is radiated noise that is picked up by the antenna ...

[Rhumbline]

OK here's a little more info. It's definitely not coming from the marina. We have other types of (white) noise issues there. Turning off the instruments stops the interference immediately. Disconnecting the tuner from the M710 doesn't help either. Hooking up my backup Icom 718 to a long wire routed far from the tuner (with no tuner - receive only) with an AC supply (or boat's DC, no difference) still picks up the noise. I doubt it's the depth sounder because I've heard that periodic chirping on other boats. It's not so much a 'chirp' - more a continuous 'diddle-little-little-little' sound that overpowers other RF signals on selected frequencies. I can't figure out any common harmonic frequencies. I've tried a clip-on type 15 choke on various wires coming out of the AP control head with no noticeable difference. I'll try other chokes on all instrument cables but that'll be a bigger job. For now I'll just turn off the instruments/ap when using the radio on the affected frequencies and continue looking for the culprit. It's just a bad coincidence that the interference is loudest on 14300 and 21412 marine nets. But the 15m band is pretty dead these days so 21412 isn't that important.
I'll order some type 75 chokes and try them - but the rfi is apparently being radiated throughout the boat since the long wire on the 718 under ac power still picks up the noise.
Thanks for all the posts. Lots of good & interesting info here!

[Rhumbline]

According to a Raymarine tech, "...Please note that the ST4000/ST5000 and ST4000+/ST5000+ combined an autopilot course computer and autopilot control head into a single product."
Is there another computer associated with the autopilot?

[TLSparks]

Originally Posted by TreblePlink

Have you seen many problems caused by power or control cable ingress? Just about everything I've seen is radiated noise that is picked up by the antenna ...

Clearly the majority of the noise on HF SSB comes in on the antenna. You can significantly reduce the signal picked up from own ships antenna using cores, but it is also possible for signals to come in via the DC in the power cable and the power being fed to the tuner. The designers of the M802 are focused on MF and HF frequencies.

I plan to investigate as it is clearly only a theory at this point. I have just listened past the fathometer noise in the past and I have all the cores on my coaxes and control cable already. May not be the case, but worth the effort. It is winter in the NW, not much else to do anyway as the wife is a fair weather sailor. My parts should be here in a week or so and I will get back to this blog then.

[TreblePlink]

Rhumbline,

Good progress. I would try individually turning each instrument on and off to try to find the worst offender, then focus on that. I'm not familiar with a ferrite type 15 core - that sounds like an iron powder mix - and if so, will not have nearly enough permeability to do the job.

Ferrite type 31, 75, or 77 are good. Because you often need several turns through the torroid to get enough inductance, and you need the center hole large enough to get a connector through, I use BIG torroids. There are some clamp-around types that can work, but often they don't have enough inductance.

[bluewatervet]

Originally Posted by TLSparks

I hope you are remembering all ferrites are not created equal. Most of the snapons at Ham stores are mix type 31 which work great to keep the RF out of things when RF penetrates wires. If there is a chirping it may be at a lower frequency not covered by the Mix 31. That is why I recommended the mix 75. I was not able to find snapon 75s.

-------------------
Roger that Sparks! Try PALOMAR's Ferrite Snap On Pack under their SKU FSCP-75-8 ..... their kit of 8 pcs which is a bit pricey, but offers a range of diameters that would be very handy depending on cable sizes etc. I'm sure you could get a particular size from them, in single quantity.

...George (...and no, I have no affiliation with the company!!!)

[Rhumbline]

OK, I think I may have found the smoking gun. The noise is coming from the sailing instruments, which pretty much means the masthead wind instruments. In tracing the wiring, the shielded multi-wire cable that runs down the mast from the wind instruments was cut at sometime beneath the salon setee when the mast was removed for rigging rework. When the mast was restepped the cable wires were reconnected via a regular electrical connector block rather than a proper RJ-type connector that would maintain the shielding. On early Raymarine equipment this shield carried the only ground connection, so the ground connection was broken on this shielded cable. That's my current theory anyway, and I'm sticking to it until I rework this connection with a proper connector/plug and find the problem still exists :=)

[TreblePlink]

When you re-work the splice, use the opportunity to insert a ferrite torroid over the cable with multiple turns.

[transmitterdan]

You should be able to reconnect the shield at the terminal block. I doubt that having a couple inches of exposed wiring at the terminal block is an issue. But not having the shield (screen in Raymarine speak) connected could definitely cause a problem. Not only with noise but also with flaky wind readings.

[alctel]

Originally Posted by 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.

Some good ideas here, thanks.

I'm actually moving the install to clear the power leads from other wires, but once I put everything back I'll give some of these a go.