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Troubleshooting and install tools

A year or so ago, NMEA began offering courses to technicians in the proper operation of basic tools and hardware used to install and troubleshoot marine electronics. Last month we discussed one of the topics—cable connectors and in March rolled out the first round of troubleshooting tools. This week is the second round of specialty tools that help you get a fix on things like proper VHF installations and voltage/current put out by a USB port. The article is excerpted from an article written for Marine Electronics Journal by instructor Johnny Lindstrom. Where the information gets a bit techy, we provide some background.

By Johnny Lindstrom

We broke training down into several general categories: DVM (digital volt meter), RF tools—watt and SWR meters, NMEA Data and Networking (PC tools, cable testing) and Miscellaneous. [The SWR meter or VSWR (voltage standing wave ratio) meter measures the standing wave ratio (SWR) in a transmission line. The meter indicates the degree of mismatch between a transmission line and its load (usually a radio antenna). Technicians use it to evaluate the effectiveness of impedance-matching efforts—Wikipedia.] In the process we demonstrated the numerous uses of the ubiquitous digital volt/ohm meter, illustrating how to measure volts, ohms and current.  

RF (radio frequency) tools

Following the training outline used in NMEA’s Marine Electronics Installer course for proper VHF installation testing, we were able to show how to test the VHF using a dummy load, and then again with the antenna in circuit.
First we measured the transmitted power into a dummy load using a standard Bird watt meter to confirm proper output power from the transmitter. Then we did the same test with the antenna in circuit.  During each test we used the DVM to measure the supplied power to the radio to confirm proper wire size and secure connections.

We also used a pretty cool tool that measures both forward and reflected power and displays them on an easy-to-read LCD screen digital VSWR meter. The Nissei RS-50M would be easy to carry in one’s tool bag and is a little more robust than a traditional Bird meter.

I have also done the test with the antenna disconnected to simulate a number of antenna problems that can occur.  Note the forward and reflected power indications—if they’re pretty extreme I’d say it’s a sure sign of a problem.

[Forward power is the power (voltage/currents) generated from a transceiver that is transferred thru the coaxial lines, meters, etc., that are connected to the antenna. We also have a reflected wave that occurs due to the mismatch from the line to the antenna. The reflected waves are the waves (currents) that are returning to the transceiver due to a mismatch (antenna not being 50-ohms Z). The ratio of the forward vs. the reflected power is called VSWR or SWR. This ratio is calculated by comparing the forward to the reflected waves. A meter will display this reflected power as SWR on the readout—Tech Times blog.]

Data troubleshooting

Here’s two data troubleshooting tools for NMEA 0183 and then NMEA 2000.

The first tool in testing data, like most things, is the trusty multimeter. This will at least show you that there is activity at some level on the line, but won’t show you what that activity is.  For this we need a tool that will let us "see” the data.

A PC running PuTTY, a simple "free” terminal emulation program, will allow you to "see” the NMEA 0183 data in human readable form that lets you know exactly what is on the line.  If you are working on a data issue or just completing an installation and want to confirm the data present, your PC is an invaluable tool.

Next is a nifty little device that will not only "read” NMEA 0183 data sentences but will also generate them. This feature can be used to very quickly and easily confirm a port or device is operating properly.  Another feature is that the AMI300 will also act as a single "trace o-scope”—very clever.  This feature will let you confirm wave forms of a variety of signal producers.  I used it the other day to confirm proper wave form on a fuel transfer pump on one of our 125-foot yachts, and it worked great!

Maretron N2KMeter

A primary tool is the Maretron "blue meter.”  It’s specifically designed to confirm the values on the bulk of the necessary "CAN” signaling voltages used in NMEA 2000, along with "bus” traffic and "bus” errors.  Combined with a multimeter and a test terminal strip, it is the basis for troubleshooting the vast majority of NMEA 2000 issues.

Another tool that comes under the heading of "nifty” is the USB analyzer.  It will confirm voltage as well as current being produced by a USB port.  Check to see if there’s a difference in voltage and current for, say, charging your smartphone using a laptop (not plugged in to AC) and a wall wart-style of USB charger.  Being able to read current draw of various devices on a USB bus is useful in tracking down some of those pesky intermittent issues with USB devices.  A common fault is that the connected devices consume more power than the port can deliver, which causes problems.

About the author
Johnny Lindstrom runs the electronics shop at Westport Yachts in Washington state. He also teaches NMEA’s technical installer courses and is past chair of NMEA.

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