VHF Radio Problem

[Ted]

Problem: When I transmit a message on my fixed mount VHF radio, the volume level of the message that is received by other people is very low. The messages that I receive are very loud and clear. The weather channels are also fine.

What I've tried: (Unsuccessful results)
Replaced the radio with an identical radio.
Replaced the antenna by hooking it up to a short cable from the radio to the new antenna thus bypassing the cable within the mast and the old antenna.
Checked the coaxial connections for corrosion.
Battery bank is fully charged.

Questions:
Can a poor power supply connection to the VHF radio cause this problem? (I haven't checked that yet)
Can a bad coaxial cable or bad antenna cause this problem in the transmit mode but not in the receive mode?

Snow has halted progress but in the meantime, I'm looking for other ways to throw more money at this problem. Thanks.

 

[Brian D]

This is FM, which means that a signal is transmitted regardless if there is any information sent. Because the audio level at the receiving end is low, it would mean that the input audio level at your end is low. This could be a microphone or an internal amplifier. Now, you said you changed radios and it was doing the same thing? If that is the case, then it could very well be coax related. Too much attenuation. A paper clip can be used to receive.

What you can try and do is get a light bulb. 50 watts should be fine. Connect it to your antenna output with a coax. If you key the radio and it shines then the radio is working. You can also try running a pig stick antenna up the mast with the main halyard. Connect this antenna to the radio and key it. See if the results are the same. If so, then yeah, the radio might be the culprit.

I have experienced poor DC power with this thing called motor boating, The radio sounds like a low power motor boat engine, or an outboard.

 

[Ken Cross]

The radio should have poor performance if the antenna isn't mounted. If you have good sensitivity (able to receive distant transmitters) there is nothing wrong with the antenna. If that is the case, transmitter or microphone are the likely culprit. I assume you don't have a radiotelephone license based on your question. If that's true, don't try to fix it yourself unless you like government fines or other legal problems. Just send it off for repair or replace it.

Not trying to be a downer, trying to save you some trouble.

Ken

 

[Don S/V ILLusion]

Low audio on FM means low deviation on the transmit signal. Bad coax or low voltage typically will not affect deviation.

 

[Ken Cross]

I should have clarified. The same technical details of a receiving antenna are present with a transmitting antenna. This is that affect the performance of one also effect the other with the exception of internal arcing, which would be extremely unlikely and part of the basic design

Ken

 

[Skipper]

Microphone technique might need analysis.
Many people hold the mic too far away, which would cause low volume on the receiving end. It should be about 1" to 1.5" from your mouth, and angled to prevent "p" popping and breath noise (pic).
You can even angle it so far as to talk across it (pic) if it doesn't cause wind to hit it.
You probably know this..... But just in case

 

[Ted]

What you can try and do is get a light bulb. 50 watts should be fine. Connect it to your antenna output with a coax. If you key the radio and it shines then the radio is working.

Brian, Can you clarify this statement? Do I disconnect the antenna completely and just run the coaxial cable to the light bulb? Wouldn't there have to be two connections to the bulb in order for it to shine? Am I missing something?

 

[Bill Roosa]

Did you use the same mike on both radios?

 

[Ted]

Bill, I used different mics. They are hardwired into the radio.
Skipper, I was speaking directly into the mic and within a inch of it. My voice volume was about as loud as it is when my daughters would come home late from a date without checking in. Don't miss those days. Thanks for the illustrations.

 

[Ted]

I assume you don't have a radiotelephone license based on your question.

Is it that obvious??? Thanks for your comments, especially the helpful ones. LOL

 

[SG]

The radio should have poor performance if the antenna isn't mounted. If you have good sensitivity (able to receive distant transmitters) there is nothing wrong with the antenna. If that is the case, transmitter or microphone are the likely culprit. I assume you don't have a radiotelephone license based on your question.

Please, don't try to transmit without an antenna connected to the VHF. If you do so, I'm told you'll probably fry your VHF. They make "emergency" antennas (as if you lost your mast). You can try to borrow one and then transmit (on low power, at first). You should pick-up a signal in the cockpit without any trouble. Then try "full power".

Ted:

By the way, DID YOU SEE IF THE SAME THING HAPPENED ON LOW AND FULL POWER? You may have the ability to receive (which isn't related to what you're putting out). You m might be fine on the one-or the other.

 

[Ted]

I only tried transmitting on low. The receiving radio was only 100 yards away.

 

[SG]

Might be different on Full (say 25 watts of supposed output)

It is also possible you have a high gain powerboat antenna. Aside from being mismatched with some cables to the masthead, simplistically it has a narrower transmission Angle relative to the horizon. High gain antennas are used on powerboats which theoretically are more stable. (They also are often closer to the water surface.).

 

[Brian D]

Brian, Can you clarify this statement? Do I disconnect the antenna completely and just run the coaxial cable to the light bulb? Wouldn't there have to be two connections to the bulb in order for it to shine? Am I missing something?

Here you go. Give this a read, it also has an image of how to set this up. Just read the section on The Light Bulb Test. All you are going to do is connect the radio to a light bulb. It will act as an antenna. Push the PTT on the microphone and the bulb should light up. Hi power bright, low power dim. No need to talk because, again, this is FM and a carrier (RF energy) is present regardless of any voice or data present. And one more thing. This is still acting like an antenna, a poor one, but an antenna none the less. So be aware of the frequency you are testing. If you have a handheld, you can monitor your test.

http://www.sgcworld.com/lightbulbtesttechnote.html

 

[Ted]

Thanks for the link Brian. It makes sense now.
SG, I'm using the correct antenna. Thanks