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Author Topic:   VHF Marine Antenna Check
BellBoyBob posted 04-21-2007 11:23 PM ET (US)   Profile for BellBoyBob   Send Email to BellBoyBob  
Hello. I have the Shakespeare entry-level 8-foot antenna that is mounted and used in conjunction with an ICOM 402a VHF radio. While out on Irondequoit Bay (Lake Ontario at Rochester, NY) trying out the new equipment, I found that I was unable to hail anyone, nor monitor anyone. The automated weather channel, easily heard in my garage, required the squelch to be opened practically all the way to be heard on the water. Granted, it is very early in the season for small craft conversations--I saw one or two boats out on the water while I was cruising--I would have thought I might pick up on some commercial conversation. When I mounted the antenna and its cable, I did not take into account the cable slack I would need when the antenna was hinged down. I know I put a good deal of stress on the antenna cable at the antenna when I lowered it the first time. I am concerned that I might have severed the internal connection in a place I cannot see (within the fiberglass shaft). The antenna cable is secure at the antenna. Is there a way to test the antenna to determine if it is operating properly?


jimh posted 04-22-2007 01:07 AM ET (US)     Profile for jimh  Send Email to jimh     
You can make a very rudimentary test of the antenna by measuring its DC resistance. You need to know what the normal reading should be, and then you can compare what you get now, after the damage. Typically the normal reading is usually either just about a dead short or an infinitely high open circuit. It is hard to say which is appropriate for your antenna. Even if you know what the expected readings should be, this is not a fool proof test, as either an open or a short in the transmission line could mimic a working antenna.

A second method to test whether or not the antenna is working at all is to use the receiver as a detector. Generally the noise from the receiver will increase when an antenna is connected. Turn the squelch off so that the receiver is putting out noise. Disconnect the antenna. Adjust the volume to a comfortable audio level on the noise and listen carefully to the receiver output. When you connect the antenna to the receiver the noise level should increase very slightly. This is also not a fool proof test.

A third method to test the antenna is to use the transmitter and a good quality directional wattmeter or directional bridge indicator. Measure the VSWR on the transmission line. If the VSWR is not below 2:1, the antenna is very likely not working properly. Most boaters will not have a directional wattmeter or directional bridge, and in all honesty I do not recommend buying one of those cheap $35 meters. Borrow a decent meter from a radio technician who works with VHF radios, or ask him to check the VSWR for you.

You have already conducted one of my favorite tests: reception of distance weather stations. In most locations you should be able to receive at least one NOAA Weather Radio broadcast. These stations usually transmit with impressive antennas and high power, so should be able to receive them at ranges of up to 60 miles. Because of our location near Canada, we can often receive five or six weather broadcasts simultaneously on the ten weather channels, including several from Ontario and Ohio. (In Michigan we do consider Ohio to be a foreign country. This is because Ohio thinks of itself as a sovereign nation.)

The best test is probably to conduct a two-way test with another station which is at least five miles away. Do not be fooled by tests at short range. Even a radio which has practically no power output at all or an antenna which is completely useless will be able to communicate with another station at short distances.

ASIDE: Anecdote from many years ago: We were cruising with another boat for a week in Lake Huron. We were in frequent radio contact, but generally only a few hundred feet apart. One afternoon we became separated by a few miles, although still in sight of each other. We were sailing along a stretch of rugged coastline heading up the Bruce Peninsula in early June. On the other boat, unknown to us, there was a serious health emergency. They tried to contact us via radio. They discovered we could not hear their calls because their VHF radio was broken and was transmitting with only a few milliwatts of power. This was a total surprise because we had been chatting with them all week on a routine basis, but never more than a few hundred feet apart. We kept sailing on, wondering why the other boat was falling farther and farther behind. We kept calling them on the radio, and getting no reply. Fortunately, the health emergency was resolved, no one was seriously hurt, and they eventually caught up to us to tell us about their radio problem. It was quite a surprise because we had been working each other via radio without any problem. The Moral of the Story: if you get a radio check, be sure it is with another station a few miles away.

SECOND Anecdote: Just a year or so ago we had a similar instance. We were out in Lake Michigan with another boat, the wind picked up, and the waves grew. They developed a problem with their fuel system and tried to hail us on the radio. It turned out their radio was also defective, and, again, we had been working them just fine from a short range. But once they got about a mile away--we could see them clearly--they were out of radio range and we just barely picked up their call about the fuel system problem.

On open water with a good radio and antenna on each boat, it should be very simple for two boats to communicate at five mile separation. If that does not work, one of the stations probably has a problem. So that is a good test, as long as you have another boat to work with and that boat has a good installation.

BellBoyBob posted 04-22-2007 08:51 AM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Thanks very much for the ideas. I will try the actual station test at longer and longer distances to see what kind of range I get.
Mardav posted 04-23-2007 07:31 PM ET (US)     Profile for Mardav  Send Email to Mardav     
If the boat is on a trailer, stop by your favorite marine store and try out a handheld radio; have someone monitor the handheld in the store, and you drive say a mile away and call them on the boat's radio, you can repeat as needed to determine range. West Marine has allowed me to do this on a couple of occasions (and I have purchased a handheld or two from them also). Just a thought.
HAPPYJIM posted 04-24-2007 05:35 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     

I remember overhearing radio techs talk about NOT transmitting with the antenna disconnected because of burning something out. I'm not radio savvy but that stuck in my mind from 30 years ago. Are the new radios protected or is is just the nature of modern electronic VHF radios?

jimh posted 04-24-2007 07:54 PM ET (US)     Profile for jimh  Send Email to jimh     
I recommend never operating a transmitter without a proper load connected.

Modern radios MAY survive some situations where there is an improper load by sensing an improper output voltage condition and shutting themselves down, but I would not intentionally test that property by intentionally transmitting with no antenna connected.

towboater posted 04-25-2007 02:56 AM ET (US)     Profile for towboater  Send Email to towboater     
Thx Jim, I understand half of that, & certainly, it is twice as much as I knew about testing antennas prior.

Sounds like the antenna is shot. but...The problem could be in the coax connection.
BellBoy mentions this is new equipment he installed. Now, did he soldier the coax connector or drill big holes?

Many times Ive just unscrewed a weathered coax connector, cleaned it, screwed it back in and the radio came back to life.

BellBoyBob posted 04-27-2007 10:44 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
It was the coax connector indeed! I bought one in addition to the one provided by Shakespeare because I could attach it without soldering. My connections clearly were inadequate. I attached the original one that required soldering and went out on the bay this morning. I conversed clearly with the CG staion six miles away and they informed me I was being heard 5 by 5. So, I am in business.
Thanks again,

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