Testing signal from GPS aerial

skyflyer

skyflyer

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I have a legacy Standard Horizon chart plotter (175c) with an 'active' GPS Antenna. In practice this means that the antenna has a +12v and ground feed into it and two wires come out with a signal to the plotter.

Recently I have been getting 'no fix' and the plotter shows no satellites and no input data from the port that has the GPS info.

The question is how do I determine whether the fault lies in the plotter or the GPS antenna?

It struck me that maybe there should be a specific voltage on the feed from the GPS that I can test.?

Obviously one option is to borrow another plotter or antenna but that will mean a lot of rewiring to test it
 
Yes anticipate a voltage of between 12v and 5v on one of the wires to the active antenna. However failure of GPS is most likely is an antenna connector problem assuming the wire is not damaged. good luck olewill
 
Voltage between green and black on the GPS cable is the NMEA signal and you should see a fluctuating value, not more than 5V. If you're not getting that then either connections, cable or antenna are bad.

As Will says, check all the connections or even just remake them for certainty. Trim back the wires if there's any sign of corrosion.

Apart from trying another antenna, you could test it by connecting to a PC either by serial port or USB converter.

Might also be worth checking antenna itself for water ingress. If there is, then probably best to remove it and dry out with the rice/warm place technique. You can cut the cable below deck at a convenient point to avoid a complete re-run and rejoin later. It may still not work of course!

If the antenna is finished, you can still get the Standard ones or use an Evermore SA-320 type but make sure it's not the USB one. There are other cheaper NMEA ones you can use below deck as well.
 
slightly confused! The active antenna (Standard Horizon's description of their product) is powered by 12v, and presumably outputs NMEA sentences as stated in replies above. However I assumed that rather like AC current the constant fluctuation between 0v and 5v would be too quick to show on a multimeter, but that one might get an evarge of 2 or 3 v?

Looking at replacement active GPS antennae they seem to mainly require 5v power.

How does a 'non-active' GPS antenna work? If the chart plotter is set up to receive a signal from an active antenna, resumable a non active one will not work?

Connection runs I will re-check but I suspect its condensation somewhere as the problem does seem to disappear after the unit has been on for a while.
 
skyflyer said:
However I assumed that rather like AC current the constant fluctuation between 0v and 5v would be too quick to show on a multimeter, but that one might get an evarge of 2 or 3 v?
Click to expand...

In practice, an analogue multimeter on an NMEA signal tends to show a fairly distinctive swinging pattern. You're right that we wouldn't be able to see the transitions between individual bits at 4800 of them per second, so I assume this is the gaps between sentences.

Pete
 
Sounds a bit like a similar issue I have been chasing with a Standard Horizon CP180 with the separate active antenna. Ours would show no input data from the GPS port either, this would go on for days then it would suddenly work again for a few days. I stripped everything out of the boat and sent it to Standard Horizon and it came back as no fault found as it worked ok for them for a couple of weeks. Immediately on install it failed again, however it works fine at home on the bench. You should be able to see the comms on the GPS port monitor on the plotter,

In the end I decided that the active aerial was failing due to some issue with the boat power as this was the only difference between running it on the bench and running it on the boat. The active aerial is similar to a GPS "puck" device, ie. it is a complete receiver and NMEA generator in one. I think it was effectively "crashing" or locking up when on the boat power (electrically noisy environment). It had not failed previously but perhaps the components inside are ageing.

I spoke to Standard Horizon and they said that the GPS port is simply a 4800baud NMEA connection so that any feed at the correct speed into this port will work. The Standard Horizon active aerial has now been discontinued (some people are advertising them but when you call they find they cannot get stock) so I simple purchased a Digital Yacht Active Aerial and wired it in. Any 4800baud NMEA source will do so you could buy a cheap GPS puck from Ebay if you wanted a cheap fix. (I still have the standard horizon aerial if you want one to test but it is, of course, faulty intermittently)
 
Last edited:
mlines

As you know the SH aerial has 4 wires (that are used), whereas the simple cheap pucks have only two - could you explain what you wired to which terminal etc?

Thanks
 
The SH aerial has 4 wires but only 3 are used.

6-Pin connector

Pin 1 - RED +10v to +35v
Pin 2 - GREEN - GPS RX+
Pin 3 - BROWN - GPS TX+ (NOT USED)
Pin 6 - BLACK/YELLOW/SHEILD - GROUND/COMMON

The Red and Black are self explanatory. Green is the NMEA input @ 4800 baud.

The Digital Yacht is a balanced source but the instructions give this diagram which worked just fine

gps.png
 
skyflyer said:
slightly confused! The active antenna (Standard Horizon's description of their product) is powered by 12v, and presumably outputs NMEA sentences as stated in replies above. However I assumed that rather like AC current the constant fluctuation between 0v and 5v would be too quick to show on a multimeter, but that one might get an evarge of 2 or 3 v?

Looking at replacement active GPS antennae they seem to mainly require 5v power.

How does a 'non-active' GPS antenna work? If the chart plotter is set up to receive a signal from an active antenna, resumable a non active one will not work?

Connection runs I will re-check but I suspect its condensation somewhere as the problem does seem to disappear after the unit has been on for a while.
Click to expand...

You will see the voltage fluctuations on a digital meter. Presence of any intermittent voltage at least shows something is going on.
I suspect the 5V antennas are intended for PC use. Plenty of 12V ones available.
Beware the difference between an antenna advertised as 'active' rather than being capable of NMEA output (which is what you need). Different things. If the lead doesn't have bare wires or a serial connector, it probably won't be suitable.
As suggested previously, do try drying out the antenna. If that helps, you could try locating it inside to avoid future ingress. Probably sensitive enough to work OK.
 
Thanks again, mlines, but I think we are at cross purposes!

The Digital Yacht GS150 is £150+ and has four wires (it seems from your diagram) which is similar to the SH antenna and thus I can see would work. However you suggested it might be possible to use a "GPS puck" off ebay, which have only two wires.

As far as I can work out the difference between these etwo types of antennae is that the active one does the position processing within the antenna and transmits an NMEA position to the plotter, whereas a passive one is just an aerial that feeds a signal to the plotter and the GPS trigonometry calks are done within the plotter?

If so then the very minimum this device needs is an NMEA Gps position signal?

Interestingly the plotter can show the number of satellites being received and signal strength etc so presumably that information either comes from the integrated processor in the active antenna via NMEA (is there an MMEA sentence for that?) as well or else the raw signal is also transmitted to the plotter so it can evaluate those criteria?
 
skyflyer said:
The Digital Yacht GS150 is £150+ and has four wires (it seems from your diagram) which is similar to the SH antenna and thus I can see would work. However you suggested it might be possible to use a "GPS puck" off ebay, which have only two wires.

As far as I can work out the difference between these etwo types of antennae is that the active one does the position processing within the antenna and transmits an NMEA position to the plotter, whereas a passive one is just an aerial that feeds a signal to the plotter and the GPS trigonometry calks are done within the plotter?
Click to expand...

Correct. And the plotter expects an NMEA signal, which is output by a GPS puck (for example, the BR355) costing about £25 - £30. Branded ones will be no better, just more expensive.

GPS satellite information is indeed transmitted over NMEA, my AIS display can show that data and it is fed by a BR355.

You will need a 12v -> 5v power supply; you can build one for pennies with a voltage regulator and two capacitors, but nowadays something intended for USB is probably the easiest way.

Pete
 
Brilliant - thanks guys; basically then I've been looking at a raw antenna when what I really need would be better called a 'receiver'!
I've got 'pucks' from two older GPS pucks (VERY old!) and they are coax only hence the confusion
 
just found this from one of my redundant but working old units - I'm guessing thats an NMEA connector, all I need is to work out the pinouts and I can at least try it and work out if its the plotter or the antenna that is the issue.

2hmezk6.jpg
 
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