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Old 08-01-2018, 14:25   #1
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How to check VHF cable and connectors

I have a 25W VHF radio with a mast top antenna that doesnít transmit as far as my 5W handheld. The 25W is connected to the mast top via a coaxial cable and there are connectors at the mast base and top of the mast.

How can I check if the problems is with the
- radio
- connectors
- cable
- antenna

I have a multimeter but no other specialized equipment.

Thanks!
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Old 08-01-2018, 14:29   #2
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Re: How to check VHF cable and connectors

Probably the quickest way to find the most likely problem is to climb the Mast and directly inspect the seating of the VHF antenna. You'll probably see some corrosion and a simple clean up may solve the problem. While you're up there however, consider simply replacing your VHF antenna for a new one.
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Old 08-01-2018, 14:51   #3
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Re: How to check VHF cable and connectors

Hi Fuegomar, thank you for your response. I have installed everything new about a year ago: cable, connectors, antenna and radio and never got it to work properly. Thatís why I am looking to test and troubleshoot in order to find out what went wrong.

If there is something wrong with top of the mast equipment for example, is there a way to test and determine that from the bottom of the mast?
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Old 08-01-2018, 15:42   #4
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Re: How to check VHF cable and connectors

The best way to troubleshoot this is with an SWR meter. Here's the cheapest one I could find that covers the marine VHF band: https://www.hamradio.com/detail.cfm?pid=H0-001257 It's not a precision meter, but should work well enough for troubleshooting.

An SWR meter will tell you if you have a bad connection, cable, or antenna, but it won't tell you where the problem is unless you are willing to climb the mast and disconnect the antenna. We can talk you through the process if you like. A "dummy load" is very useful for this kind of testing: https://www.hamradio.com/detail.cfm?pid=H0-001070

A DVM may tell you if you have a short or open in your cable or connectors, but this is complicated by the fact that your antenna may itself look like a short or an open, depending on the particular antenna design.

Another useful bit of test equipment is a Time Domain Reflectometer -- this can tell you *where* the problem is. But this is getting way too technical, and I'll bet that fewer than 1% of marine radio techs have one of these, let alone boat owners.

If you know a ham radio operator, they usually have an SWR meter, a dummy load, and know how to use them. Perhaps you could borrow a ham for a while?
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Old 08-01-2018, 16:05   #5
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Re: How to check VHF cable and connectors

+ 1 on Paul's reply for an SWR meter.

I had the same issue after we pulled into Petersburg, AK for the winter - same test with the stationary radio vs the handheld you did with same results. The SWR I borrowed from a local electronics shop showed everything was fine down to the VHF unit. I had the tech from the shop came on board with a new VHF unit to test; we just hooked it up to my existing cable/antennae set up and it worked fine; transmit and receive.

Upshot is that my existing VHF unit is due for repair or replacement. A pretty easy way to see if you have a bad unit without having to go up the mast.
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Old 08-01-2018, 16:30   #6
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Re: How to check VHF cable and connectors

I forgot to mention that an SWR meter will tell you if the radio is actually putting out any power. This is step #1 in the troubleshooting process.
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Old 08-01-2018, 16:42   #7
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Re: How to check VHF cable and connectors

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Originally Posted by Paul Elliott View Post
I forgot to mention that an SWR meter will tell you if the radio is actually putting out any power. This is step #1 in the troubleshooting process.
not entirely. because low power output from the antenna (what the swr meter is showing) is not the same as low power output of the radio. they will only match with perfect SWR.

IE if you see 10watts on the SWR it doesn't mean you only have 10 watts coming out of the radio. it means 10watts is leaving the antenna. the rest is probably reflecting.

if you also measure 10watts with a dummy load and test cable then it's a radio issue.
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Old 08-01-2018, 16:59   #8
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Re: How to check VHF cable and connectors

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not entirely. because low power output from the antenna (what the swr meter is showing) is not the same as low power output of the radio. they will only match with perfect SWR.

IE if you see 10watts on the SWR it doesn't mean you only have 10 watts coming out of the radio. it means 10watts is leaving the antenna. the rest is probably reflecting.

if you also measure 10watts with a dummy load and test cable then it's a radio issue.
not entirely.

It depends on where the SWR meter is inserted and what is connected to the "antenna" port of the meter.

FWIW to the OP, all you can do is extremely basis fault analysis which the equipment you have listed and the most important one is your eyeballs. This might be enough to resolve your issue but if not, then take Paul Elliot's advice above and with a bit of reading (and thinking), an SWR meter and a dummy load, you can resolve it.
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Old 08-01-2018, 16:59   #9
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Re: How to check VHF cable and connectors

In order to test the radio without climbing the mast, you will need a VHF antenna and a separate VHF antenna cable. Disconnect the cable running to the top of the Mast and reconnect a VHF antenna with in the cabin of your boat. Although the equipment is new a fault may have developed within the choke of the VHF antenna at the top of the mast. The only way to determine the effectiveness of the antenna without climbing the mast is with an antenna analyzer. The antenna analyzer will sweep a low-wattage signal through your cable and antenna so as to find resonance in the VHF ranges. If you have transmitted into a shorted choked antenna then your radio is most likely overloaded in the final amplier stages and ruined or at minimum open fused. Although Standing wave reflector meters or swf meters are useful, they are not practical for your use. Swf meters are used to test the antenna with 1 watt to ensure resonance at the desired transmitting frequency before pumping power into the antenna and risking damage to radio and operator. A dummy load is used to test the output power abilities of the radio and to be useful must also have a means of measuring power output, often found on the antenna tuner.

I would bet your antenna is loose atop the mast and just needs some WD40 and a tightening however. If your radio is still working then you must still climb the mast. It's your destiny.
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Old 08-01-2018, 17:01   #10
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Re: How to check VHF cable and connectors

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not entirely. because low power output from the antenna (what the swr meter is showing) is not the same as low power output of the radio. they will only match with perfect SWR.

IE if you see 10watts on the SWR it doesn't mean you only have 10 watts coming out of the radio. it means 10watts is leaving the antenna. the rest is probably reflecting.

if you also measure 10watts with a dummy load and test cable then it's a radio issue.
OK, now you're getting all technical on us!

But the SWR meter will measure both forward and reflected power, so you can get a good idea of what's going on in most cases. With a little connecting and disconnecting you can tell if the transmitter is putting out, if your cable is open or shorted or lossy, and if the antenna is well-tuned for the frequency. Ultimately, these problems are usually pretty simple.
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Old 08-01-2018, 17:11   #11
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Re: How to check VHF cable and connectors

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................
Another useful bit of test equipment is a Time Domain Reflectometer -- this can tell you *where* the problem is. But this is getting way too technical, and I'll bet that fewer than 1% of marine radio techs have one of these, let alone boat owners.

...........
Off topic but thanks for the memories - I cut my teeth using valve operated bench mounted TDRs on open wire (aerial) copper pairs over 100 miles and finished using solid state portable TDR's on satellite coax feeders over a couple hundred metres. So many changes...

On topic, a SWR meter is small, easy to carry on board, doesn't need batteries and simple to use (once you are up to speed). Very useful to the cruising sailor who wants to maintain his/her own radios / antennas.
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Old 08-01-2018, 18:47   #12
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Re: How to check VHF cable and connectors

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I have a 25W VHF radio with a mast top antenna that doesn’t transmit as far as my 5W handheld.
... so at least you are transmitting.

Any radio will still transmit a signal even without a connected antenna. The radio will utilize the radio housing, power cable and sometimes the operator as an antenna. Your handheld across the room will receive the signal from your 25W radio transmission even if you disconnect your antenna.

You can measure the resistance between the coaxial cable ground and central conductor with your multimeter. It should be an open circuit. If it is closed then you have an antenna cable or antenna problem. A problem could still be present if the circuit is closed however.

Another consideration is the coaxial cable itself. Did you replace the coaxial too? If not and the cable is over 10 years old, then it may be at fault, either a broken signal wire (which would still give you an open reading with the voltmeter) or corrosion in the connections somewhere between radio and tip of the antenna, including the antenna base choke.

Maybe just using your handheld for now, with the most important concept is that you don't leave without a VHF radio.

Let me put in a plug for those considering getting your ham license. It's a good investment in ship to ship and ship to shore communication, and opens up lots of ways to utilize email (www.winlink.org) and to receive weather fax while at sea. It is far more reliable than iridium. Go to ARRL WEBSITE to find out more information.
Good luck!
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Old 08-01-2018, 19:17   #13
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Re: How to check VHF cable and connectors

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You can measure the resistance between the coaxial cable ground and central conductor with your multimeter. It should be an open circuit. If it is closed then you have an antenna cable or antenna problem. A problem could still be present if the circuit is closed however.
In most (?) cases, a VHF whip antenna will look like a short circuit and you will measure a low resistance between center conductor pin and shield at the far end of the cable. But this is not always the case and some antennas present an open circuit when measured with a DVM. If we knew the exact model # of the antenna we might be able to give the OP some guidance on this.
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Old 08-01-2018, 20:10   #14
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Re: How to check VHF cable and connectors

One quick check not yet mentioned: get an adapter and hook the handheld to the masthead antenna. See if it gets as good signal reports as it did when using the rubber ducky antenna. If it does, then it points towards the fixed VHF having low output.

But most often in situations such as you describe the fault lies in one or more of the coax connectors or in the joint between connector and shield braid in the coax... especially at the masthead, where corrosion often creeps into the connector or cable.

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Old 08-01-2018, 20:11   #15
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Re: How to check VHF cable and connectors

Actually, most any SWR meter you can locate, even an old CB radio one will work as a quick troubleshooting tool. It will not be accurate in the amount of power it measures, but it will tell you if you have a problem with the antenna system. System being the coax and antenna. If you can locate a 50 ohm dummy load capable of handling the rated 25 watts, you can put it in line in place of the coax/antenna and verify that the radio is putting out rated power. Modern VHF radios dial back the transmit power when the radio senses a significant miss match between what the radio is looking for and what it sees in the antenna system. Usually anything over about 2.5:1 and the radio starts rolling back the power. It is a protective feature of the radio to help keep the finals from burning out due to dissipating too much heat caused by the miss match. As others have said, the DVM will not be a whole lot of help in identifying the problem. It can show if there is a short or open in the coax, but the antenna will have to be disconnected first.
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