RF Earth for Raymarine Autopilot

[robbieg]

Looking at the installation instuction manuals on the Raymarine site it seems that some of their kit (SPX 5 Wheelpilot) and C70 display should be earthed with a 4mm sq wire (about AWG10?) to ideally an RF earth or if not as very much second best the battery negative. This is despite the units being connected to 12v and so being connnected to 12v negative in any event. Dire consequences are threatened if tihis is not done.

Any electronic experts enlighten me why this needs to be done and why do they require such a large earthing wire. I've wired in earlier Raymarine models and this wasn't required so presumably a new requirment. Presumably most folk must take the earth to 12v neg since I guess not many boats have an RF ground. Any idea if an anode stud would do as an earth if you don't have an RF ground?

 

[William_H]

The term "RF earth" is the best indicator. The a/p may be susceptible to interference from a radio transmitter. Especially the SSB HF transmitter if fitted. Possibly but not likely from VHF transmitter.
On the other hand the system may be inclined to radiate RF interference which could interfere with radio reception. Perhaps unlikely.
So the manufacturer may be simply covering themselves from criticism if interference occurs either way.

An RF ground is more effective if the wire is large because ery high frequencies tend to travel along the surface of conductors hence use of flat strap for SSB round. An "RF ground" can be also a way of describing a connection using one or more capacitors in the wire so that only RF (AC) and not DC (or 50hertz) are conducted.

So I dunno I very much doubt any harm could be done without the "RF ground" so I would be inclined to try it out without. good luck olewill

 

[whipper_snapper]

I am about to install an SPX5 and I worried briefly about this.

I do have an RF ground, but I am certainly not intending to trail a lead from the autopilot to it! I will take it straight to battery neg. I do not expect problems from this. As said above, this is probably Raymarine covering their backs in case of RFI issues.

 

[meandraft]

I am about to fit an SPX10 AP and also noted the requirement for an RF ground. I don't understand the point of running a seperate cable right back to the battery negative terminal when you could make a short lead from the negative supply to the RF ground within the course computer unit. Does this not achieve the same thing?

 

[whipper_snapper]

It probably does achieve the same thing, but I suppose you are increasing the risk of picking-up or dumping RF onto your supply. If it is a big issue to get to battery neg, I would take it to a major neg busbar.