Advanced VHF Radio Troubleshooting

Many boaters complain about the reception or transmitting range of their installed VHF Radios but are at a loss how to evaluate their systems and make the necessary changes to optimize their performance. Below I identify the four (4) key issues that I’ve seen multiple times over the years. Some of these will require test equipment not usually carried by cruisers, but often available in many areas, if not from local marina workers. In those cases, I’ve suggested where to find a helpful local radio enthusiast. Most of these issues also apply (differently in some cases) to HF Radios as well, but that’s another article.

Low Operating Voltage

This is the most common problem and has several causes, besides low battery voltage (a systemic issue and not limited to the VHF Radio). Measure voltage AT THE RADIO, not at the electrical panel, WHILE transmitting on high power on an unused channel such as VHF 24. You will need to either strip back some wire insulation on the power supply wires or

(recommended) install a terminal strip such as a two- pole “euro strip” pictured to the right. This permits the voltmeter probes to be placed on the screw heads as the radio is powered. Look for a drop of less than 3%. (A drop from 12.6 to 12.2 volts is OK, but below 12v would indicate a problem with the supply wiring). Check for wire sizing using the ABYC 3% Table. If wire is correctly sized, look for corroded fittings and clean replace as indicated, then retest. All fittings should be marine grade, ratchet crimped, and “pull tested” to make sure of a good connection. Heat shrinking every connection isn’t overkill.

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Measuring Voltage at the Radio

Problems with the Radio Itself

These are easy to test if you have a wattmeter and a dummy load. A dummy load is just a large 50ohm resister that substitutes for an antenna cable and antenna, but doesn’t transmit. They are available from ham radio stores for less than $50; every boat should carry one.

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Watt meters (usually combined with “SWR” meters, can be purchased for well under $100. I think every boat should have one of these as well. The same dummy load and Watt/SWR meter can be used for HF/SSB radio diagnostics as well. Many times, I’ve been unable to assist cruisers remotely because they couldn’t rule out a radio problem, which these two items and a couple of jumper cables would have solved. Together, they will allow you to verify that

the radio is putting out its specified 25-watt power into the antenna cable. I’ll explain the SWR functions below, but for now we’re just measuring the radio output without the antenna in place. Like with the voltage check, when the meter is wired as shown and you transmit on high on an unused frequency; the meter should register 25 watts.

Be sure your wattmeter is rated for VHF output up to 170MHz. Some cheaper CB models often are designed for HF frequencies below 30mhz and won’t accurately measure the frequencies used by Marine VHF (156-162MHz). Good, reasonably priced models are the MFJ-822 and MFJ- 260C below.

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Testing a Radio with a Wattmeter and a Dummy Load

Transmission Line Failures

There are three issues that I frequently find with “coax” transmission lines. First is undersized cabling that is not well suited for the VHF frequencies. While it’s easier to run thinner cable, the power loss through “attenuation” is just too great. The common CB style RG58, for example, will lose almost 3db, or 50% of the transmitting power, in just a 50′ run, assuming a perfect antenna. Even the ubiquitous RG8X will lose the same 50% in a 100′ run. I strongly recommend a minimum of RG213, and, if possible, the outstanding LMR400 Ultra Flex which has the lowest loss of any standard sized “large” coax. You need every available watt reaching your antenna, not being consumed by poor cabling on the way from the radio.

The second issue is poorly crimped or soldered connections. Unless you are very experienced soldering the PL259 style connectors common on marine VHF radios, I strongly recommend having them professionally terminated. At the very least purchase a wire with one end done professionally and run it DOWN the mast and make the lower connector yourself at the nav station and not hanging at the top of the mast. Also, give yourself a few feet of extra cable to cut off and start anew, if you don’t get it perfectly the first time. I’ve been a ham radio operator for 50 years, have literally soldered thousands of PL259’s, and still mess up 1 in 10. If you really want a high-end system, use waterproof “N”-Connectors and have them crimped and heat shrunk using the correct ratchet tools. Of course, you would need to order your antenna with an “N” connector in lieu of the much more common SO-239. Regardless, after you snuggly make the connections, cover them with “Coax Seal” to keep out moisture. Corroded connectors are the Number 1 reason for VHF radio failures.

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N Connector

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The third possible problem would be damage to the antenna feeder itself. Whether by chafe, kinking, or water intrusion, it is possible, but rarer, that the wire itself is the problem. This is most easily tested using a device known as a Time Domain Reflectometer, or TDR. The TDR, attached to one end of the open cable (remove the antenna from the top first) can identify a range of problems including impedance mismatch, a kinked or damaged dialectic, or water intrusion in the cable itself. You probably don’t have a TDR aboard, but a local ham radio club will surely have a member with a TDR who would be happy to play with it aboard with you. A cold beer is usually all the thanks needed. If you do need to replace the cable through the boat or up a mast, take the opportunity to upgrade to the best cable you can find and afford.

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Antenna Failures

Lastly, antennas themselves do fail over time, especially ones with base loading coils like the common 3db 3′ whips found on many sailboats. The same Watt/SWR meter we used to check the radio can help here by verifying 25 watts and a low (less than 1.3:1 SWR, or Standing Wave Ratio). These can be tested most easily with an antenna analyzer, another tool most don’t seem to have aboard. However, again, your friendly local ham radio club will have many members who have them. Just disconnect the coax from the radio, connect the analyzer in its place, and you can read the antenna system impedance and resonant frequency. Of course, this assumes the cable and connectors (above) are all serviceable.

Getting Help

A few times in this article, I’ve suggested soliciting the assistance of a local amateur, or “ham” radio operator. I suggest this because, while most boatyard folks have very limited knowledge of radios in general, most radio hobbyists do. Marine and Ham radios work the same way, use many of the same modes of operation, and use adjacent frequencies. A technically oriented ham, familiar with Ham VHF radios (also FM), will easily be able to troubleshoot and help with a marine VHF radio. Almost every town has a ham radio club and I’ve never failed to find a member happy to help out a resident or visiting boater. In the USA an extensive list can be found at Other countries have similar listings, and like so many things, Google is your friend. A quick email will often lead to more help than you need, with friendly folks dying to try out their latest diagnostic equipment. Oh, and they’ll probably ask you to join their club! Indeed, I strongly encourage cruising boaters to study for and obtain a General Class ham license and join a local club. Besides being a great source of radio information and help, it’s a great hobby in and of itself.

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Author: Scott Berg has been sailing, racing and cruising for the past 50 years and has experience on a range of power and sailing vessels. Scott is the owner of Chardonnay Boatworks, a full-service marine repair and consulting company focusing on the repair and re-engineering of sail and motor yachts. He frequently lectures on marine electrical systems, electronics, and yacht systems and off shore sailing. Scott is a current member and past president of the Seven Seas Cruising Association (SSCA). He also holds a USCG 100T Masters license, an Amateur Extra Ham License, and currently lives on his 60’ Seaton Ketch, Chardonnay.

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