Chartplotter to VHF

[Giblets]

I need to connect my chart plotter to my DSC VHF radio.

Would I be correct in assuming that NMEA Rx sends the GPS position from the plotter to the VHF and NMEA Tx sends a received position from the VHF to the plotter, NMEA ground being common to both?

I have managed to work out on the plotter how to set up the NMEA 0183 connection and how to send the correct NMEA sentence required by the VHF but just need to confirm the sending & receiving bit.

The radio has NMEA Rx+, Rx-, Tx+ and Tx-/ground whereas the plotter has NMEA Ground, NMEA Rx and NMEA Tx. I'm not too sure if the Rx- and Tx-/ground on the radio are one and the same.

TIA

Pete

 

[timbartlett]

I need to connect my chart plotter to my DSC VHF radio.

Would I be correct in assuming that NMEA Rx sends the GPS position from the plotter to the VHF and NMEA Tx sends a received position from the VHF to the plotter, NMEA ground being common to both?

No

The radio has NMEA Rx+, Rx-, Tx+ and Tx-/ground whereas the plotter has NMEA Ground, NMEA Rx and NMEA Tx. I'm not too sure if the Rx- and Tx-/ground on the radio are one and the same.

TIA

Pete

In principle, there are two separate communications going on here, each using two wires. The wires labelled Tx+ and Tx- carry the data out of one device, while the wires labelled Rx+ and Rx- carry data into the other device. So:
(1) Always connect Tx to Rx
(2) Always connect + to + and - to -

So (still In principle)You need to connect:
-- PlotterTx+ to RadioRx+
-- and PlotterTx- to RadioRx -
and if you need to send data from the radio to the plotter, also connect:
-- Radio Tx+ to PlotterRx+
-- and RadioTx- to PlotterRx -

In practice, it is quite common for the "ground" wire to fulfill several different purposes -- it is often combines the Rx- and Tx- and sometimes the power supply negative as well.

It would be easier to explain with pictures: try here: http://www.timbartlett.co.uk/briefing.html#NMEA_0183

 

[Giblets]

Tim, many thansk for your reply. (BTW your web site link worked OK but it throws up a lot of gobbldy gook characters. )

Below are the two respective wiring diagrams of the GPSMAP 551 plotter and the NASA SX35 radio.

So far as I can see the plotter uses a common ground but the radio has two separate grounds.

My interpretation of the wiring required is:

GPS Blue Wire to VHF Brown Wire

GPS Brown Wire to VHF Orange Wire

GPS Black Wire (Ground) to VHF Red wire & Shield.

There is a seperate power supply to the VHF.

Pete

 

[timbartlett]

Tim, many thansk for your reply. (BTW your web site link worked OK but it throws up a lot of gobbldy gook characters. )...

...My interpretation of the wiring required is:

GPS Blue Wire to VHF Brown Wire

GPS Brown Wire to VHF Orange Wire

GPS Black Wire (Ground) to VHF Red wire & Shield.

There is a seperate power supply to the VHF.

Pete

I see what you mean about the gobbledegook: I just tried it, and got the same. But the pictures were OK, and the text was OK apart from where some of the punctuation had been relaced with foreign-looking symbols. Hope it was OK for you too...

That wiring is exactly what I made it, too. If only NMEA had specified a standard colour-coding, eh? ... but they didn't.

 

[AngusMcDoon]

It would be easier to explain with pictures: try here: http://www.timbartlett.co.uk/briefing.html#NMEA_0183

From your website...

The NMEA0183 code consists of groups of low-voltage electrical pulses, delivered in groups of eight,

'eight' should be 'ten'.