VHF Radio Troubleshooting

[BrianW]

I have an Apelco 5160 VHF radio in my Hunter 26. I receive transmissions very well, but do not seem to transmit out very well. With a radio check, I mostly get no response but I do get an occasional positive response from 100 yards. On channel 16 at 25 watts, when I key in the mike, I see the "transmit" icon on my radio display. I can also change channels and the transmit power (25 watts/1 watt)with the mike's channel switch . I disconnected and reconnected the antenna connectors on the radio unit and at the base of the mast with no improvement. I would very much appreciate some troubleshooting tips on how to narrow the possibilities, especially whether it's the radio or the antenna. The radio unit has a hard-wired mike cord (no plug). The very last two options I prefer are taking the unit to the shop and especially stepping or climbing my mast to check the antenna. What can I do to check things out before getting to the last two options? Unfortunately, the cost of a shop visit just to check the radio out is almost half the cost of replacing the 10-year old radio. Thanks for your input. BrianW

 

[Don S/V ILLusion]

it's probably the antenna

With the exception of the amplifier transistors, the components in a transceiver are shared between the receiver and transmitter sections meaning that if it receives okay, it should transmit okay as well. This is only a general statement so don't take it as literally as is stated; just an overview of how transceivers work.The likely cause is the antenna and more specifically, the connections to the antenna and the coax. A transceiver may "hear" quite well but, because the transceiver is designed to cut back power to protect itself with antenna problems, the symptoms you describe fit pretty well.Unfortunately, the most common problem also happens to be in the most inaccessable location. As the antenna to coax connection is subject to weather, it is typically the source of your problem. Only two ways to check:1. put an SWR meter between the radio and coax and observe reflected power when transmitting, or2. visually inspect the connection at the top of the mast.Before doing either, I'd suggest two other things:1. check continuity of the inner conductor and braid on the coax - there should be none (not a definitive test), and2. connect the radio to a different antenna to ensure it is the antenna or coax causing the problem.

 

[Ken Palmer]

Wait a minute...

There are some vhf antennas that will normally show a "short" from center of coax to the shielding. That is because resistance is not the same as impedance, and you cannot measure impedance with a VOM. Your best test is with a SWR meter. If you don't have one, perhaps you know a ham radio operator that might have one to borrow, or better yet, test the radio for you.

 

[BrianW]

Thanks Ken & Don!

This advice is exactly what I needed! Maybe a little above my capabilities, but very useful in steering me in the right direction. Thanks, BrianW

 

[Paul H]

Radio Problem

Brian, had the same exact problem with my unit on our H26. I checked all the connections at the mast base and going into the VHF. Everything seemed ok. I didn't have a SWR meter available to check the signal. I thought of the other radio idea also but I couldn't get anyone to volunteer to let me possibly fry their unit while I was testing. I ended up buying a new unit. It seems to be working fine. I've tried some long distance transmissions and they could hear me and I had good transmission strength. I replaced it at the end of last season so when I take her out this spring I'll know for sure.Paul HS/V Linda Belle95 H26

 

[Brian D]

Good advice all around...

I'd like to comment on Don's second group of tests, in particular to item #1. The use of a DVM or VOM to test continuity is a valid test. Most commercial antennas are of the 1/4 wave or 5/8 wave type and do not match the 50Ω requirements of the radio. Therefore, a matching transformer is installed so the radio sees the correct impedance. With that, the DVM test will confirm that the shield and center conductor are good. Most radios will receive with just a piece of wire stuck in the center pin. Reception is improved with the use of a ground plane, or any ground for that matter. I agree that the best test would be to get a good working antenna and try that. Even at ground level, you should get good results.Try using a hand held radio, find someone who is not on Channel 16, and give them a call. Then call them on your base unit and compare the results. Try the base unit with a good antenna and the mast mounted antenna. That should eliminate if it is a radio issue or an antenna issue. Moving your radio to another boat might not work due to electrical connection differences.