Cable Connectors for NMEA cables

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Didleydude

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Have just fitted an NMEA cable to a new Navman DSC VHF radio.

It's currently rigged using standard electrical block connectors and it all works ticketyboo!

The NMEA cables are very thin and as I pick up the standard shelf stuff from Maplins/Halfords/Chandlers etc I get the sense that even the tiniest connectors/heat shrink tube are too big in diameter.

I've searched high and low (Googled-out) for some very small watertight butt or bullet connectors and/or heat shrink tubing or similar so that I can ensure watertight connections. But I always draw a blank feeling the connctors are too big.

Bullet connections would be best to enable easier disconnection if I need to get to the back of the radio or remove etc.

Anyone passed this way before and can suggest a supplier/solution?
 
Navman have a non waterproof colour coded connection box for their products.

'D' type computer connectors could be used, fiddly to solder and not waterproof.

Hi-fi speaker in-line male/female look better to me, again not waterproof but perhaps splash protected?
 
What I have done .....

(Based on a rummage of my odds and ends bins .....)

On a previous installation:

A Megallan GPS mounted on fwd cockpit bulhead. The data and 12V cable descended into cabin and there was plugged into a "BT Telephone" socket. One of the ones with screw terminals inside. It had two sockets. A bare ended telephone cable was plugged in to find out which terminal went where (plus colours of wires were visible in the plug). Then 12V supply was fed in and connected to 2 of the terminals applicable ... the data cable form GPS suitably crimped with BT plug ... so now 12v is supplied. Data leads were also in the crimp - so other terminals now had data supplied.
A cable from PC / any other item was then fitted with BT plug and plugged in to receive data ....

Standard multi-core telephone cable was used and I never suffered due to lack of screening ...

The above of course was inside cabin and not water-proof ... but simple to make and would be simple to repair / replace.

Later set-up was based on bin again with RS232 9 pin sockets and plugs ... and an electrical distribution box ... Data came in via serial plug to box ... and 2 sockets passed it out to other items ...

Yes - I experiment with connections and things ... bit of a hobby ... no expert - just interested in finding solutions for my use ... (FYI - the telephone cable set-up is still in working condition 5 years after I made it ... the serial split box is supplying my PDA with GPS data still .....) /forums/images/graemlins/tongue.gif /forums/images/graemlins/cool.gif
 
Radio control models...

Radio control models use some fairly tiny connectors and miniature heat-shrink tubing. Try a good model shop.
 
If you are starting from scratch you might consider screening the cables, not so the NMEA works better, becuase it won't care, but to keep the electrical noise down in the boat.

You may want to install HF or NAVTEX (or whatever else in a few years time) later and all will work better in lower electral noise environment. Unscreened NMEA cables give off a lot of noise.

Peter
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Arrrrr ... so it's actually more noise FROM NMEA cable .... not outside affecting the NMEA ?

I was always under impression that NMEA was not so strong a signal and ws affected by other electrical stuff around it such as engine alternators etc. and radios.

Would I be correct in assuming that NMEA is probably the signal that would be most upset by receiving noise on a boatn and that other are really not that bothered about getting noise from NMEA ? I ask in absolute honesty ...
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Well, I think its this way round:

NMEA is a pretty hefty signal. Its really slow baud rate. Its a few volts with a low source impeadance so it gets a good fan-out - able to drive lots of listeners. Its got some error detection so listeners can drop damaged sentences. Its got some error correction in that data is repeated very frequently so dropped sentences can get picked up again good a few seconds later.

All that adds up to a pretty robust system.

It does give out some awful noise though. Try holding a transistor radio on LW or MW near an NMEA cable. Alternators do too, thats true, but there are well tried stratagies for dealing with that such as capacitors. Those stratagies won't work with NMEA without rounding off the nice sharp square waves it needs to work.

Don't get too worked up however. Electrical noise may not be a problem for you. Its really only if you are expecting NAVTEX to work near the edge of its range or you are planning to use HF or you like listening to BBC on LW.

Peter
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Absolutely agree. In a former life I worked a lot with RS232 and cannot ever remember having problems with noise pickup at the sort of baud rates and cable lengths used on NMEA networks on boats.
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Explains why my telephone cable set-up works well - despite some comments I rec'd from "experts" ...

Great ... thanks.

I feel a bit better now about the thick, stiff cables on my plotter now !!
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Thanks for the ebay link. I did look at these and two thoughts occurred to me.

1 They seem ideal for the waterproofing side of the matter
2 They seem to be more of a permanent connection (frankly though, I can't quite see how the conncetions are made).

So I steered away from them.

The question has sparked off other stuff that is useful though.

Shmoo - Thanks. It never occured to me to screen the NMEA cables...any detailed views on the screening methods as I have complete access and might as well go the whole hog if I can!
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Hi Nigel,

If any data cable isn't screened then it will provide a source of noise.
I prefer to always use (both professionally and for the boat) Belden 3 pair twisted foil shield data cable with a drain wire for all serial connections.
Not cheap but excellent cable.
It is quite important to use the right cable as the twist ratios vary according to it's use...ie the twist ratio is not the same on telephone CW1308 than say CAT5 or Serial data.
The twist is designed to cancel out generated noise, although for short runs like on a boat it's rarely a problem.
The best way to stop NMEA cables from being a source of noise is to use a ferrite choke, either toroidal or cylindrical clamp, and earth them at one end only.

Serial data cables can be affected by external signals such as high power transmitters...which can cause packet losses.
For instance it's always a golden rule that we never run data cables or telephone cables in the same duct as mains cabling. There always needs to be some degree of separation, otherwise you can get mains hum causing havoc under some circumstances.

Steve.
 
Re: Cable Connectors for NMEA cables ... NMEA noise ??

Hi Steve ... no problem ... as said the runs on the boat are short and reasonable power still at ends so not had a problem.

Interesting about the domestic telephoine and not run in same conduit ... that mimics a problem in my old apartment when ADSL was installed. Until then the phone was OK and fax etc. worked fine. They cam and fitted the splitter on the line with filter .... ADSL worked fine - but telephone was humming its head of and fax refused to work. I called Lattelekom back to sort it ... they tried everything and eventually seperated the extension tel cable out of the domestic conduit and the hum and fax sorted out "nearly" back to before ... there was still hum - but they reckoned down to the poor filter supplied ... well it was more like a cross between hum and white noise ... luckily at very low level.

Cheers
 
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