VHF - can hear but not be heard at a distance

[waterman46]

Originally Posted by MathiasW

That was my original thinking, which made me wonder!

Now, we both use the same make and type of radio, a B&G V50. So, nominally, they should be identical and I doubt that tiny production variances will cause such an effect. Nominally, both radios should have the same sensitivity in the receiver as well as transmitter, unless one is faulty.

As to different transmission powers on both sides - is that actually possible at all on channel 16? I thought it is always set to HIGH and there is nothing one can do about it. The only thing here could be that my radio is somehow slightly faulty, but then again, I did measure 25 W as output, so it is not per se broken.

The third possibility is how loud I speak into the mic, and the forth possibility is a different squelch level set.

All those make a lot of sense to me, but again, I am not a super nerd on this topic and I certainly do not have the expertise like John, so I may well be overlooking something fundamental...

Cheers, Mathias

From this and your other posts I politely would say that it seems like you don't want to accept the possibility (probability) that all is fine at your boat but the other guy has a problem with receive, not just from you but in general. If you have any other friend that can help, it would be good to run a signal check with him. Or just go to ch68 and ask for a radio check.

[team karst]

The radios in question do have a LOCAL/DISTANT feature.

[continuouswave]

In an over-the-air test of signal strength made with just two stations, and one station tells the other their signal is weak, it is impossible to deduce if the problem is at the station sending or the station receiving.

If three stations participate in the test, then the ambiguity can be resolved.

[MathiasW]

Originally Posted by waterman46

From this and your other posts I politely would say that it seems like you don't want to accept the possibility (probability) that all is fine at your boat but the other guy has a problem with receive, not just from you but in general. If you have any other friend that can help, it would be good to run a signal check with him. Or just go to ch68 and ask for a radio check.

Hmm, not sure why you read this conclusion out of my posts. I only want to rule out all other possibilities, but then I am happy to accept it is the other vessel that is having the problem...

And yes, I will try calling him when there is another vessel nearby him, so that I can compare the two. And a radio check I will also do.

[MathiasW]

Originally Posted by Dieseldude

Considering that theory, losses should be equal in both transmit and receive directions. However radio signals can behave unpredictably in unique situations. Losses in any component of a medium is considered in dB's, whether cable or connector. But dB loss alone is just one part of the story. No two different medium components will have perfect continuity as seen by a signal. For high frequencies, discontinuities such as poor terminations or a crushed cable can cause reflections back toward the source. Transmission lines can have strange two way flow of signal due to reflected signal. Defective termination of connectors is a common cause of such trouble. Terminating coax cable is a precise mechanical procedure and a craft. It can be subject to bad practices. The pros can be in too much hurry. The DIYers may not be skilled. But lack of skill can be compensated by using good info and taking time to get it right.


To understand reflected signals, basic AC theory and impedance must be understood. Radio signal, being high frequency AC can bounce back toward source if impedance of any two components do not match.



Discontinuity caused by a crushed cable for might only be found by careful inspection. Or it can be located with a fancy device called a time domain reflectometer, which no DIY boater will own.


Received signals are quite weak, so reflected received signals will not harm a receiver. Transmitted signals of your radio are quite strong, so can damage the transmitter "finals". That is high power output transistors.


To understand reflected signal, basic AC theory and impedance must be understood. If impedance of any two components is not identical, a portion of signal will bounce back to source. The power of the bounced signal can overheat radio output transistors, causing decreased efficiency and damage.



Ok, this attention is only on transmission line and connectors. In my work as Electronic Tech aboard research vessels, I have seen many cabling problems caused by poor workmanship. I was a generalist tech, not specifically a radio tech, but I solved a lot of radio problems. Don't want to lead you down a wrong path. Your problem could have other causes, some of which I had suggested in earlier post.

Digging in my memories from decades ago, it seems the one-dimensional transmission line can be characterised as such:

On input side: exp(i k z - i w t) + r exp(-i k z - i w t)

On output side: t exp(i k z - i w t)

So, on input side I have an incoming wave and a reflected one. On the far side I have only a transmitted wave.

Furthermore, |r|^2 + |t|^2 = 1

Now, this was for, say, transmission, so the input side was the radio, and the output side the antenna = so TX. But similar equations also hold for RX, just that the waves run in the opposite direction (replace k with - k) and I have a reflected wave on the antenna side now, and only a transmitted wave at the radio. The reflection and transmission coefficients are r' and t', respectively.

Again in my recollection we have |r|^2 = |r'|^2 and |t|^2 = |t'|^2, so the situation is symmetric.

From this I conclude that a faulty connector, or for that matter anything in the transmission line will affect RX and TX equally. So, I do not need to check faulty connectors on my vessel, nor on my sister vessel to find the reason why I can hear them, but they cannot hear me. It cannot have anything to do with the connectors.

Also, as to suggesting to check the connector at the top of the mast as well... If I insert my SWR metre at the bottom of the mast, where I have another connector, it is measuring the entire system, radio to antenna, is it not? If I see almost no reflected wave there, then my connector at the top of the mast must also be good, because any reflection it will cause will be seen down at the mast foot as well.

You see, I am desperately trying to avoid manual work, if I can help it...

As I can rule out a faulty TX of the radio (I did measure 25 W as it should), for now it boils down to squelch settings, distant / local settings on the radio (I have not heard back from the sister vessel what setting they are using), faulty receiver on my sister vessel, or simply volume of my voice or rather lack thereof...

Cheers, Mathias

[Dieseldude]

VHF marine radio is FM, and radio sets generally lack field strength meters. Signal quality relies on frequency deviation. AM totally relies on signal strength. This means that the microphone sensitivity and voice intensity play a direct role in perceived signal strength. It has been assumed that the user has held the mic at a normal distance. So this is a potential problem. The mic itself may have a sensitivity issue. Any chance of grabbing a spare mic ? Not a bad idea to have a spare aboard anyway. If I recall correctly, the watt meter reading was quite good, so this could be a clue to a mic issue, as FM power output is relatively constant regardless of intensity of modulation which is controlled by the mic.

[Dieseldude]

Originally Posted by MathiasW

Digging in my memories from decades ago, it seems the one-dimensional transmission line can be characterised as such:

On input side: exp(i k z - i w t) + r exp(-i k z - i w t)

On output side: t exp(i k z - i w t)

So, on input side I have an incoming wave and a reflected one. On the far side I have only a transmitted wave.

Furthermore, |r|^2 + |t|^2 = 1

Now, this was for, say, transmission, so the input side was the radio, and the output side the antenna = so TX. But similar equations also hold for RX, just that the waves run in the opposite direction (replace k with - k) and I have a reflected wave on the antenna side now, and only a transmitted wave at the radio. The reflection and transmission coefficients are r' and t', respectively.

Again in my recollection we have |r|^2 = |r'|^2 and |t|^2 = |t'|^2, so the situation is symmetric.

From this I conclude that a faulty connector, or for that matter anything in the transmission line will affect RX and TX equally. So, I do not need to check faulty connectors on my vessel, nor on my sister vessel to find the reason why I can hear them, but they cannot hear me. It cannot have anything to do with the connectors.

Also, as to suggesting to check the connector at the top of the mast as well... If I insert my SWR metre at the bottom of the mast, where I have another connector, it is measuring the entire system, radio to antenna, is it not? If I see almost no reflected wave there, then my connector at the top of the mast must also be good, because any reflection it will cause will be seen down at the mast foot as well.

You see, I am desperately trying to avoid manual work, if I can help it...

As I can rule out a faulty TX of the radio (I did measure 25 W as it should), for now it boils down to squelch settings, distant / local settings on the radio (I have not heard back from the sister vessel what setting they are using), faulty receiver on my sister vessel, or simply volume of my voice or rather lack thereof...

Cheers, Mathias

OK, if you are measuring 25 watts transmit power, and reflected power is a small fraction of that, we can assume cable, connectors and antenna are ok. I just posted a bit about potential voice an mic issues.

[team karst]

Yeah, that was me some years ago. Repeated calls to a bridgetender went unanswered. Finally i switched radios. I replaced the mic element a week later and all was well.

[MathiasW]

Originally Posted by Dieseldude

VHF marine radio is FM, and radio sets generally lack field strength meters. Signal quality relies on frequency deviation. AM totally relies on signal strength. This means that the microphone sensitivity and voice intensity play a direct role in perceived signal strength. It has been assumed that the user has held the mic at a normal distance. So this is a potential problem. The mic itself may have a sensitivity issue. Any chance of grabbing a spare mic ? Not a bad idea to have a spare aboard anyway. If I recall correctly, the watt meter reading was quite good, so this could be a clue to a mic issue, as FM power output is relatively constant regardless of intensity of modulation which is controlled by the mic.

Mic, that is a good idea! For a start, perhaps I can switch the mics of my sister vessel and mine temporarily... I have a remote handheld to use alternatively, that one could also be at fault...

[Cynara]

I've been following, but lost track.

When did this start. Did you do anything to the boat between the time it was working and stopped working

[MathiasW]

Originally Posted by Cynara

I've been following, but lost track.

When did this start. Did you do anything to the boat between the time it was working and stopped working

I first noticed this during our Atlantic crossing with the ARC+. A year later I replaced the antenna cabling with low-loss cabling and also had to do new connectors at the time. That was also the time when I did all the measurement with the SWR metre. Since then, I have noticed it a few more times. Not often, though.

[thomm225]

Originally Posted by MathiasW

I first noticed this during our Atlantic crossing with the ARC+. A year later I replaced the antenna cabling with low-loss cabling and also had to do new connectors at the time. That was also the time when I did all the measurement with the SWR metre. Since then, I have noticed it a few more times. Not often, though.

Interesting.....

maybe should have mentioned that 86 posts or so ago.

It only affects the entire thread that you did a change to the original installation........and that those you were trying to communicate with may have been out of range or there was interference from others

[MathiasW]

Originally Posted by thomm225

Interesting.....

maybe should have mentioned that 86 posts or so ago.

It only affects the entire thread that you did a change to the original installation........and that those you were trying to communicate with may have been out of range or there was interference from others

Are your trying to be un-insulting and helpful again???

I did mention this very early on in my extensive reply to John. But of course, to detect this, it would require careful reading and not just blabbing without any content as you do!

And no, the others where NOT out of range. I could hear them after all. My point was - and is - that I was irritated that I could hear them but they could not hear me. With all the stuff that is symmetrical for RX and TX, there are not so many explanations available for this particular observation. In particular, replacing the antenna cable may have worsened or improved my installation, but it would have done so equally well for RX and TX. So cannot be the reason. But as a professional, I am sure you know this.

So far you have consistently failed to present any reasoning that can explain the observation made. Instead, you moaned about tests you are forced to take etc etc, apparently being a grumpy retired radio technician. A lot of blah blah that is not relevant at all.

Greetings to all TROLLS!

[thomm225]

Originally Posted by MathiasW

I did mention this very early on ......... it would require careful reading

apparently being a grumpy retired radio technician. A lot of blah blah that is not relevant at all.

Jesus.

I think I would have shot myself if I had spent my whole life as a radio technician. BORING.

Too simple.

I majored in History btw. BA History! Division 1 College. USA. GI Bill.

I was a tech for 20 years (Radar/IFF/Simulators/Computers)

My first computer class was in 1982.

Today I'm a manager of techs and still working.

Recently I was required to earn a Comptia A+ Certification due to new rules for cyber security

So it could help your troubleshooting technique to get the certification also. There are just two rather long 90 minute exams involved and you have to recertify every three years.

https://www.comptia.jp/pdf/comptia-a...objectives.pdf

https://www.comptia.jp/pdf/comptia-a...objectives.pdf

[Cynara]

Our boat was commissioned in 1977.we had them install a Hi Gain Hi Seas VHF. It was the first that didn't have crystals. It was great for 3 years. They put a 6 foot fiberglass antenna on it. We were off the west end of Catalina island, about 30 miles from Long Beach California. We were rolling so bad that the antenna ripped itself off the top of the mast. We lost the antenna wire inside the mast and had to take it down to reinstall the antenna. We used a Metz antenna, installed it our selves. The radio worked great until I sold the boat in 2016. The radio was on 12 hours a day, not always transmiting.

We went cruising in 1985 until 1988, then it was on 24/7. About 1/2 way through it always had some static like the squelched failed. We got used to it, then about a year later it fixed itself. Strange I know. Anyway it was still working in 2016.

VHF radio is pretty simple, except in today's world they can also have circuitry for DSC and AIS. If the antenna isn't right you could have issues regardless of the SWR meter. Go back and resolder the connections. There should be a max of 4. The one from the back of the radio. 2 if you have a connection at the base of the mast and one at the top at the antenna. That is my story and I'm sticking to it.