VHF radio trouble shooting

[Gone Fishing]

Last Spring I bought 2 ICOM 402 radios and I’ve had trouble transmitting with both of them. They start out transmitting OK but as I continue to transmit, the power goes away and people can’t hear me. I sent them back to ICOM and they checked out OK. I’m guessing my problem is either connections (I don’t believe I used marine stainless connectors) or possible my new Digital antennas. I think that a SWR meter might be a good resource to find the problem if it is the antenna but probably won’t tell me much if it is a connection problem (by the way, I’ve never used one). Any thoughts? I ran 14 gage power wire directly to the battery and I’m still having the problem. The battery is powering my other electronics with no problem and is powerful enough to start my 350 small blocks so I can’t believe that is a problem. I really need to get this resolved and I’m not very good at electrical. Any help would be appreciated. Goosebuster79 (marine electronics tech) where are you? I have a case of your favorite beverage in my fridge. ;)

[double trouble]

VHF Antennas

* Which antenna is right for me?
This is a big question, and there's no easy answer. It has an answer file all its own. See also Shakespeare's Audio Fact Books web page for digitized sound samples that you can download.
* Can I cut the coax on my VHF antenna?
Yes, if you need to. However, you should leave at least three feet of coax. Note that this is not true for all antennas. CB antennas' coax should not be cut.
* How can I check the antenna to make sure it is working?
You should transmit to a friend's receiver, and have the friend assess your transmission for quality from a variety of known distances. Note than the US Coast Guard frowns on radio test calls made to them. To help you measure the efficiency of your antenna/radio system more scientifically, Shakespeare makes an antenna / radio tester. The ART-2 will test the output power of your transceiver, as well as the VSWR of the antenna.
* How do you install the PL-259 connector?
An instruction sheet for installing the PL-259 connector is included with the antenna. Follow the instructions and consult the diagrams. Shakespeare's new PL-259 connector includes special washers and spacers to reduce the complexity of the installation. For true ease of installation without soldering, check out Shakespeare's innovative Centerpin® PL-259-CP and PL-258-CP connectors.

NEW! Downloadable PDF Instruction Sheets for PL-259 Connectors: RG-8/X - RG-58
* Will metal or other objects that are close to the antenna affect it?
Yes they will. It is best to locate the antenna at least three feet from any metal objects or other antennas.
* Can I mount the antenna beside the radio?
No, it must be at least three feet away from the radio, so transmission will not interfere with the radios reception (usually resulting in a squeal in the speaker).
* Do I need a ground plane for the antenna?
No, Shakespeare VHF marine antennas are designed with independent ground planes built in.
* What is the antenna's wavelength?
It can range from 1/4 wave to 5/8 wave, depending on the length and style of antenna. Please see the antenna specifications section for information on your particular antenna.
* How high must the antenna be?
There is no particular height requirement, but remember, the higher the antenna, the better the reception.

* What range can I expect from the antenna?
Here is the formula to determine range:

[gitfiddler]

test it in low power and see if you lose transmit. That will draw up to 6 amps in high power. you might have a bad antenna conection but if it starts out ok and goes out after some time I would look into power and connections. Does that unit have a protection ckt for high swr? that could point to connections or transmission line.

[Take Five]

Try a different battery. It is amazing how much power a vhf needs to transmit and I suspect that your battery is not keeping up with it.

Wayne

[Gone Fishing]

Does that unit have a protection ckt for high swr? that could point to connections or transmission line.

First off, thanks for the replies. I don't see anything pertaining to protection for high swr. For what it's worth, here are the radio specifications:


General
Frequency range:
Tx: 156.025 - 157.425 MHz
Rx: 156.050 - 163.275 MHz
Mode:
16K0G3E (FM)
16K0G2B (DSC)
Usable channels: All international, USA* and Canadian* channels, plus 10 Weather channels.*
(* USA version only)
Power supply requirement: 13.8 V DC ±15%
Current drain (at 13.8 V DC):
Transmit: 6 A (at 25 W output)
Receive: 1.2 A (at max. audio)
Operating temp. range: -20°C to +60°C; -4°F to +140°F
Antenna connector: SO-239 (50 ohm)
Dimensions (projections not included):
153(W) x 67(H) x 141.6(D) mm
6 1/32(W) x 2 5/8(H) x 5 9/16(D) in.
Weight: 900 g; 2 lb


Transmitter
Output power: 25 W or 1 W (at 13.8 V DC)
Modulation system: Variable reactance freq. modulation
Spurious emissions: Less than -70 dB
Adjacent channel power: 70 dB


Receiver
Receive system: Double conversion super-heterodyne
Intermediate frequencies:
1st 21.7 MHz
2nd 450 kHz
Sensitivity: 0.25 µV (at 12 dB SINAD)
Squelch sensitivity: 0.2 µV typical
Adjacent channel selectivity: 70 dB
Spurious response rejection ratio: 70 dB
Intermodulation rejection ratio: 70 dB
Audio output power: 4.5 W typical (at 10% distortion with a 4 ohm load)
Audio output impedance: 4 ohms

[gitfiddler]

Try it in low power it might be pulling too much current for your battery. And check your ant connections. If it starts out working fine and gradually goes away something is heating up or opening up. Put a volt meter across the battery when you are keyed up(when it is acting up), if the voltage dips too much i'd lean twards a battery problem.

[Gone Fishing]

My batteries are getting a bit old but since they would start the engines, I figured that it would certainly power a vhf. It looks like the low end power requirement is 11.73 volts. I guess that voltage is possible when my main engines are off. I'll check into it. Thanks for your input gentlemen. :)

[double trouble]

your antenna might not match up with this radio or as said before you have a battery or antenna connection problem.transmission takes full power, 6 amps, so i guessing that is a battery problem.try using your vexilar battery hooked up direct to the radio.see if this corrects the problem.easier than carrying some big heavy battery arround.

[Jason Adam]

I would test the voltage at the radio connector as you TX. If it drops off when "the power goes away", it is probably a problem with your source(battery). Since you're having the problem with both batteries, its probably not the radios. I would also not think it is the connectors. I would definitally look at your power source.

[Gone Fishing]

The more I think about it, the problem happened when I was running on my kicker or anchored down, meaning my big engines were not running. I more than likely had my live well pump running along with 2 sonar systems, 2 GPS’s and a stereo. The extra draw from transmitting could have very well caused a drop below 11.73 volts in a marginal battery. I’ll check it out. Thanks again.

[goosebustr79]

This weekend? Maybe I can stop by with the meter. Most of these guy's are on the right track? Batt's are more than likely toast. We really should install an isolator and an electronic's bank on that vessel of your's. You have alot of equipment and you really need a distibution point. Also I told you before what i thought of those antenna's. We will SWR them and see what we come up with. BOAT, Bust Out Another Thousand! We should think about getting you some new batt's at the very least. Are those the same batt's that were in the boat when you bought it from Jim? Get in touch with me!

[Gone Fishing]

This weekend?
Are those the same batt's that were in the boat when you bought it from Jim? Get in touch with me!
I just got the radios back from ICOM and don't have them reinstalled yet but it doesn't take long to do. I'm working on a dog kennel this weekend but I could break away if necessary. And yes, those are the same batteries that came with the boat from Jim. I'll start there and keep you posted of my progress. Thanks for the response! :)

[Jason Adam]

The more I think about it, the problem happened when I was running on my kicker or anchored down, meaning my big engines were not running. I more than likely had my live well pump running along with 2 sonar systems, 2 GPS’s and a stereo. The extra draw from transmitting could have very well caused a drop below 11.73 volts in a marginal battery. I’ll check it out. Thanks again.

If you had the radar alone running, or even really all those electronics going without a radar, you were putting quite a hurting on the batteries. Add to that trying to TX on your 25W VHF..... I'm saying batteries.

If you plan on trolling alot without charging, you should consider setting up a starting battery or batter bank, and a separate, isolated deep cycle(house) bank for running electronics off of. You will trash your starting batteries quick if you keep running them down while using all your toys with no charge to them.