VHF - can hear but not be heard at a distance

[MathiasW]

Originally Posted by thomm225

Looks like they will be able to have fun with this one for a while. It's not like when a tech comes to work and has 6-8 Tx problems to fix along with 4-5 RX problems plus the Radar Scope is missing IFF and so on during his one shift.

No these guys get to have real fun on a single problem with all sorts of outlandish fix it ideas. It is fun for some folks though with time on their hands I reckon.

Looks like they believe also sorts of things can interfere with VHF TX up to and including LED's and Solar Controllers!!

As if most every sailboat out there doesn't have these things but somehow don't have VHF TX problems. Hummmm.....??

Think shielded cable! Maybe that's why it's used on VHF Radios close to other electronics ...........radios, radars, etc

I wonder did some one other that a tech make some changes to this VHF and antenna install ...... to make it better?

Thank you for this most helpful comment. Why don't you go and play somewhere else? Or are all other kids already banning you from playing with them?

And yes, I did modify the installation, and yes, I do consider myself a techi who knows at least as much as a normal installation guy from the average marine electronics company, who is doing VHF installations infrequently, and next to his butter and bread LED and other stuff installations. Nothing against technical experts in the marine business, by all means, but many of them never get feedback on whether their installation actually worked or not, whilst I have to live with the result of my modifications... And finally, I do like most of the installations my electrical provider did. So nothing against him. It was a good installation to begin with, and I tried to fiddle around with it.

It is this asymmetry in tx and rx that intrigues me and I am trying to learn from this. Called curiosity...

And it does have a safety implication, if others cannot hear me as well as I can hear them, so it is worth chasing.

So, thank you very much!

[MathiasW]

Originally Posted by Cadence

Check your coax shielding for good connections the crimps or the Ferrals themselves. As I said just a WAG. Do you have an SWR meter? Not expensive and might be a good investment.

Ah, ok. Got you. Thanks. And yes, I do have a reasonably good SWR meter and with that I had detected the 8 W loss at the mast foot of the original installation...

Now the loss is almost zero at the mast food, as measured by the SWR meter. But I did not measure at the mast top in 25 metres height. Not pleasant whilst at anchor...

And I did notice this asymmetry before I made any modifications to the cabling, so I do not believe it is in the connectors.

Still not sure, how this should affect tx more than rx, but I will brew on this a bit more...

[team karst]

Lets see; other boat can Tx to the OP boat. But OP can't Tx to the other boat. My $ is on other boat has local interference. As mentioned before, solar controllers, and many other possibilities. btw, what comm R U using to know these results? satellite, internet, 2 or 4 MHz ssb or ?

[PippaB]

Originally Posted by MathiasW

....In particular so as they have the habit of leaving on their navigational LED lights when at anchor? And those, I believe, they did not shield? So, most definitely, when I communicated with them - or should I say tried to - their nav lights in the top of the mast were on, whilst mine were off....

I can only say that we have an ~4-year-old LunaSea LED tricolor + anchor light and it ruins our AIS reception (even though it was specifically advertised not to do so). When we are at anchor we used to leave it on all day because it has a photo sensor, and even without that the LED uses so little power, but even with the photo sensor turning off the LED it would kill our AIS reception. Turning off the power to the light fixture and everything worked fine.

So, instead of a TX problem on your side it could be an RX problem on their side. Certainly I would test that theory as it is pretty simple to do.

[waterman46]

There should be no concern about antennas, transmission lines, bearings, distance, weather, and on and on to answer this question. Reciprocity of transmit and receive RF paths, all the way from the VHF tranceiver of station A to the transceiver of station B, rules out any of these factors as affecting this issue.

For example, a lossy transmission line, a heeling boat and a poor antenna all affect both reception and transmission equally.

If station A can hear B, but B cannot hear A, there are only two possibilities. Either the transmitter of A is lower in power than transmitter B, or the receiver of B is less sensitive than receiver A, or a combination of these two situations. Note that it doesn't matter if the two VHF sets are the same or different models, and they don't have to have the same output power and sensitivity to achieve sucessful communication. For any given value of transmission path losses, its the *combination* of output power and sensitivity of both transceivers that makes two way communication possible.


You can waste a whole lot of time trying to figure out which of the above is actually the problem. If I had this concern, I would take my VHF to a technician who can very quickly measure the output power and sensitivity over all channels. And the tech can also make adjustments of the audio levels so that you will be assured your transmissions will be clean and the voice quality the best.

[MathiasW]

Originally Posted by team karst

Lets see; other boat can Tx to the OP boat. But OP can't Tx to the other boat. My $ is on other boat has local interference. As mentioned before, solar controllers, and many other possibilities. btw, what comm R U using to know these results? satellite, internet, 2 or 4 MHz ssb or ?

Hmm, I seem to be a bit thick today... What do you mean by "what comm are you using to know these results?" And then refer to satellite, internet, or ssb?

My observations are for the plain old VHF. But I do have satellite and ssb, yes, and sometimes I am lucky and even have internet...

[MathiasW]

Originally Posted by PippaB

I can only say that we have an ~4-year-old LunaSea LED tricolor + anchor light and it ruins our AIS reception (even though it was specifically advertised not to do so). When we are at anchor we used to leave it on all day because it has a photo sensor, and even without that the LED uses so little power, but even with the photo sensor turning off the LED it would kill our AIS reception. Turning off the power to the light fixture and everything worked fine.

So, instead of a TX problem on your side it could be an RX problem on their side. Certainly I would test that theory as it is pretty simple to do.

Thanks a lot for sharing this experience! I can definitely confirm that my sister vessel was having the same problem with another LED on the mast. So yes, indeed worth following up.

Perhaps on your side you can try adding these ferrit clip-ons that help suppress interferences. My sister vessel was very happy after they added it to the wires for their LED.

Cheers, Mathias

[team karst]

Originally Posted by MathiasW

Hmm, I seem to be a bit thick today... What do you mean by "what comm are you using to know these results?" And then refer to satellite, internet, or ssb?



My observations are for the plain old VHF. But I do have satellite and ssb, yes, and sometimes I am lucky and even have internet...

How do u run this experiment without 2 way comms? Ie. How does he know u r transmitting??

[team karst]

Originally Posted by waterman46

….
If station A can hear B, but B cannot hear A, there are only two possibilities. Either the transmitter of A is lower in power than transmitter B, or the receiver of B is less sensitive than receiver A, or a combination of these two situations. ….

Local interference is 3rd possibility. Quite likely actually. Signal to noise is the operative metric. Signal can be ok, but if you push that denominator too high, then comm is lost.

[MathiasW]

Originally Posted by waterman46

There should be no concern about antennas, transmission lines, bearings, distance, weather, and on and on to answer this question. Reciprocity of transmit and receive RF paths, all the way from the VHF tranceiver of station A to the transceiver of station B, rules out any of these factors as affecting this issue.

For example, a lossy transmission line, a heeling boat and a poor antenna all affect both reception and transmission equally.

If station A can hear B, but B cannot hear A, there are only two possibilities. Either the transmitter of A is lower in power than transmitter B, or the receiver of B is less sensitive than receiver A, or a combination of these two situations. Note that it doesn't matter if the two VHF sets are the same or different models, and they don't have to have the same output power and sensitivity to achieve sucessful communication. For any given value of transmission path losses, its the *combination* of output power and sensitivity of both transceivers that makes two way communication possible.

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

[Cadence]

Originally Posted by MathiasW

ok, thanks, but how would this affect tx and rx differently? I am looking for some effect that is detrimental to rx, but not to tx...

Get a HAM to explain it. Receiving does not rely on you getting the signal out of antenna were as transmitting does.

[MathiasW]

Originally Posted by Cadence

Get a HAM to explain it. Receiving does not rely on you getting the signal out of antenna were as transmitting does.

John?

[JPA Cate]

Checks for local interference being in the way of the other boat's receiving you could include him turning off his solar controller and then on. See if having it on wipes you out for him. It is a data point.

If the problem is that you have many wires all near to one another at the masthead, you've got too much parasitic absorption and it is weakening the signal you put out. So, gird your loins, and get up the mast with your SWR meter. That's a tall stick. But, while thinking about the problem is fun, I think you need more data to clarify the situation.

Agree it is a safety issue.

Ann

[team karst]

Originally Posted by Cadence

Get a HAM to explain it. Receiving does not rely on you getting the signal out of antenna were as transmitting does.

Receiver noise figure includes the antenna performance. Now, some bands, such as the lower frequencies below 20MHz, lets say, are not as critical as VHF and above. But to say marine VHF Rx performance is independent of the antenna is not true. Weak signal enthusiasts spend lots of time optimizing antennas. Matching, beam width, gain, avoiding noise sources (like the sun), all at play here.

[MathiasW]

Originally Posted by JPA Cate

Checks for local interference being in the way of the other boat's receiving you could include him turning off his solar controller and then on. See if having it on wipes you out for him. It is a data point.

If the problem is that you have many wires all near to one another at the masthead, you've got too much parasitic absorption and it is weakening the signal you put out. So, gird your loins, and get up the mast with your SWR meter. That's a tall stick. But, while thinking about the problem is fun, I think you need more data to clarify the situation.

Agree it is a safety issue.

Ann

Thanks Ann, I think I will do the easy tasks first - particularly those that only involve work on my sister vessel...

But at some point I might need to bite the bullet...