M802 SSB transmission problems

[Paul L]

Is your antenna cable from the radio to the antenna tuner run clear of all power and instruments wires, Ie not in the same cable runs or near? If it has to cross a cable it should be at right angles and not run close and parallel.

[Brian.D]

I already mentioned common mode currents as a culprit. You need to choke the source, not the destination. Get yourself a choke balun from balundesigns. This will prevent any stray currents from getting into your system.

Also - https://www.google.com/search?client...ents+on+yachts

[Auspicious]

Originally Posted by alctel

I've choked all the wires leading to the autopilot (there are a lot of them) and it's still happening - would it be worth putting the autopilot computer unit into a metal box and seeing if it still happens? If so, would steel be ok?

Yes, you can try that. It needs to be a box and not just a cover. The least expensive approach may be to buy an appropriately sized "project box" from an electronics supply house. Steel or aluminum are fine. I'd test it before painting or applying other coating. Ground the box. The problem is that if your autopilot has an integrated flux gate compass you're going to generate new problems.

On the other hand the problem may be an external flux gate compass. You may have to relocate that or reroute the cable between the flux gate compass and the autopilot computer.

Originally Posted by Paul L

Is your antenna cable from the radio to the antenna tuner run clear of all power and instruments wires, Ie not in the same cable runs or near? If it has to cross a cable it should be at right angles and not run close and parallel.

This is a bit of valid conventional wisdom that leads to great frustration. Sometimes you simply can't. You have to do the best you can. As much separation as practable and shielding may be the best you can do. That certainly works on most boats.

Originally Posted by Brian.D

I already mentioned common mode currents as a culprit. You need to choke the source, not the destination. Get yourself a choke balun from balundesigns. This will prevent any stray currents from getting into your system.

For less than half the cost you can buy six or seven type 31 ferrite beads and heat shrink over them at the tuner end of the coax between radio and tuner. This duplicates the deservedly well regarded RadioWorks coax isolator. This approach also avoids two additional connections in the coax.

[Brian.D]

If cost is going to be an issue, the just buy 50' or coax and make a poor man's choke by wrapping 10 turns into an 8" diameter. Done.

One more thing I should mention. A bad ground connection could also result in common mode issues. I would recommend removing your RF ground from the tuner and cleaning it up. Then reconnect. Follow that ground to the next point in the path and clean it up, and so forth until you have cleaned all the physical connections. Make sure the ground lug on the turner is also tight.

And get a decent RF Common Mode Choke. JMHO

[alctel]

Originally Posted by Paul L

Is your antenna cable from the radio to the antenna tuner run clear of all power and instruments wires, Ie not in the same cable runs or near? If it has to cross a cable it should be at right angles and not run close and parallel.

The coax runs parallel to a few wires, but is around 6 inches away. The line from the tuner to the antenna doesn't run parallel to anything, and is only close to one other line which it crosses at a right angle

Originally Posted by Brian.D

I already mentioned common mode currents as a culprit. You need to choke the source, not the destination. Get yourself a choke balun from balundesigns. This will prevent any stray currents from getting into your system.

Also - https://www.google.com/search?client...ents+on+yachts

I have a line isolator, the radioworks T4 T-4

That should do the same job, right?

Since cleaning up the ground/antenna connections and putting a ferrite on the USB cable I've had no more problems with the PC crashing at higher frequencies, the autopilot is the only thing left.

[alctel]

Originally Posted by Auspicious

Yes, you can try that. It needs to be a box and not just a cover. The least expensive approach may be to buy an appropriately sized "project box" from an electronics supply house. Steel or aluminum are fine. I'd test it before painting or applying other coating. Ground the box. The problem is that if your autopilot has an integrated flux gate compass you're going to generate new problems.

On the other hand the problem may be an external flux gate compass. You may have to relocate that or reroute the cable between the flux gate compass and the autopilot computer.

Thanks, I will give that a shot. When you say 'ground the box' do you mean RF or DC ground? (I guess RF ground but I don't want to presume)

Compass isn't integrated and I haven't noticed any issues with it while transmitting.

[Brian.D]

Yes, the T4 Line Isolator is the same as a RF Choke. I personally don't like ferrite beads, but if you have some, put them on the power line at the radio. As close to the radio as you can. Also, try reducing your output power. See what level the autopilot starts to go bonkers.

[Jim Cate]

A pair of bypass capacitors on the DC power leads to the a/p brain box is another easy fix to try. Simple .1 or .047 microfarad ceramics would do the job and cost pennies. Inside the box if possible...

Jim