VHF - can hear but not be heard at a distance

[MathiasW]

I have a question regarding VHF...

Lately I did some tests with a sister vessel. The VHF radio installation was done by the same company, so we both have the same B&G V50 radio, same antenna, same AIS antenna sitting next to it. The only difference is that my mast is a metre or so taller and I replaced the antenna cable up into the mast as well as from mast foot to radio by a very high quality low-loss cable. I did this when I measured at the mast foot a loss of 8 W of the original 25 W at the backside of the radio. So, by the time the signal reaches the antenna, perhaps as little as 10 W would be left. (Did not dare measuring at the top of the mast and swinging left and right all the time...) With the new cable there is virtually no loss at the mast foot in my installation. So, I thought, great, it must be an improvement!

I can talk to commercial ships with tall antennas in 30+ nm, but when trying to talk to the sister ship in a distance of 16.5 nm I could hear them quite well, but they could not hear me at all. The line-of-sight cut-off is at about 17 nm between our two vessels.

This is puzzling me. I would have naively thought that reducing cable loss between antenna and radio would benefit equally well transmission and reception. I have tried to explain this with a signal threshold cut-off at the reception side, but I did not find this story convincing.

Can anybody offer an explanation?

Thanks, Mathias

[dougweibel]

Since you mention a separate AIS antenna i'll assume you do not have a splitter between your VHF and antenna. Other than a splitter there are not many problems that will affect the transmit and receive signal loss differently AFAIK.

Are you sure you didn't make a mistake and have your radio set on low power when running the test?

[sailormed]

How close were your boats. VHF signal going out above their antenna?

[Jim Cate]

Mathias,

Since you say that you have successfully talked to ships at 30 miles it seems that your transmitted signal is OK. This suggests that your sister ship may have a problem in her receiver if he can't hear you.

Another possibility is that the AIS antennae are distorting the radiation pattern in some directions and that during your test there was an unfavorable combination of distortions.
Antennae that are parallel and close together do influence the patterns... recommended distances are a meter or more separation.

Were the vessels in fixed positions during the test or under way?

Jim

[ka4wja]

Mathias,
Let's see if we can figure this out.
Btw, my first "from the gut" guess is that it is a receive issue on your sister ship. (but, there's a lot of info I don't have, so I can't be sure....yet)

[FYI, radio waves, and radiowave propagation, are reciprocal....meaning that your VHF transmit signal moves thru the air the same way that someone else's (your VHF received signal) does....BUT...
But, how the radio energy leaves the antenna, into the air, is highly effected by the antenna, its mounting and orientation, etc....as well as how much energy is captured by the antenna on receive....so to compare two antennas, they must be exact copies and must be installed/mounted/oriented exactly the same way...
Now, of course, we're on boats....boats move around....the antenna pattern can be effected by not just the boat's motion / heel, etc., but also by the wind "whipping" the antenna around...as well as differences in what else is near each antenna, etc...
So, while radiowave propagation is reciprocal between tx and rx, there are a lot of other things that are usually different. ]


BTW, it would help a lot if you would clarify where are you located?

Where are you doing this testing? Out on the open sea? Or along a coast? Or in port? in various ports? etc. etc.

What weather conditions, etc.?

How often has this occurred? Have you been able to regularly repeat these exact results, over-and-over again?

As well as actual info on these "antennas", where/how they are all installed, what exact coaxial cable you have now, as well as the other vessel's cabling....and if you are certain that all cable/connections were actually done correctly and proof-performance tested, etc.?

And, any other details you have that we do not....even things that may seem minor / inconsequential, can be important.

Originally Posted by MathiasW

I have a question regarding VHF...

Lately I did some tests with a sister vessel. The VHF radio installation was done by the same company, so we both have the same B&G V50 radio, same antenna, same AIS antenna sitting next to it. The only difference is that my mast is a metre or so taller and I replaced the antenna cable up into the mast as well as from mast foot to radio by a very high quality low-loss cable. I did this when I measured at the mast foot a loss of 8 W of the original 25 W at the backside of the radio. So, by the time the signal reaches the antenna, perhaps as little as 10 W would be left. (Did not dare measuring at the top of the mast and swinging left and right all the time...) With the new cable there is virtually no loss at the mast foot in my installation. So, I thought, great, it must be an improvement!

I can talk to commercial ships with tall antennas in 30+ nm, but when trying to talk to the sister ship in a distance of 16.5 nm I could hear them quite well, but they could not hear me at all. The line-of-sight cut-off is at about 17 nm between our two vessels.

This is puzzling me. I would have naively thought that reducing cable loss between antenna and radio would benefit equally well transmission and reception. I have tried to explain this with a signal threshold cut-off at the reception side, but I did not find this story convincing.

Can anybody offer an explanation?

Thanks, Mathias

1) First off, unless both vessels (yours and your sister ship) are identical and have identical equipment / systems, and all of the equipment / systems are used the same, at the same time, etc. etc., you cannot be assured of identical performance, let alone similar performance.

But, I do understand your concern regarding your VHF system performance, and I'd like to help you figure it out.

Also, be aware that while getting the most power out to the antenna is good, in general the difference between NEW cabling and connections, and OLD cabling and connections, is usually greater than the differences between normal coax cable (RG-213, etc.) versus low-loss cable (LMR-type cables)...it's not naïve to want to reduce losses in your system, it's just that with terrestrial VHF-FM, it's highly unlikely to ever be noticed, and usually not even measurable.

{further, even new cabling can have issues, as all it takes is one small screw-up on a connector assembly, to add significant loss into the system....and most marine electronics dealers will not test for this, 'cuz they don't know how or don't have the time....which is where you Mathias seem to be even better at this than most professionals are!}


2) I'm not clear about your (and the other boat's) antennas, so can you clarify the "antenna" situation?

You write that you both have the same antennas and the same AIS antenna sitting next to them? This means there are TWO VHF transmit / receive antennas at the masthead, and they are only inches away from each other? (this is not good....and, might be the proximate cause of your observed issue!)

So, to clarify things, can you tell me:
a) what antenna you have for your primary VHF, and where is it mounted?
b) what antenna you have for your AIS, and where is it mounted?
c) how far away are these antennas from each other?
d) what type, and length, of coaxial cable connects each of these antennas down to their equipment (radio and AIS)? And, is there a cable-connection at the base of the mast, for each of these cables?

...AND...

e) what antenna does the other boat have for their primary VHF, and where is it mounted?
f) what antenna does the other boat have for their AIS, and where is it mounted?
g) how far away are these antennas from each other?
h) what type, and length, of coaxial cable connects each of these antennas down to their equipment (radio and AIS)? And, is there a cable-connection at the base of the mast, for each of these cables?


3) RFI effecting VHF freqs used to be almost unheard of....but, unfortunately now-a-days it does happen....(just last week a gentleman here on Cruiser's Forum, mentioned his solar chargers' RFI wipes out his VHF aviation band reception).

So, this is good guess of what might be effecting the other boat's inability to hear you, when at 16.5nm, but you are still able to hear him.


4) Of course, there could be other possible causes (other than the antenna issues I asked for clarification of, and other than receive RFI on the other boat)

a) Is the other boat's radio adjusted properly? Is his squelch set too high?

b) Is your radio's output correct? 25 watts? (+/-)

c) Is your audio too low? Are you not speaking loudly enough? Or opposite, are you shouting and over-deviating?

d) Are you sure there isn't a radio problem on the other boat? (new radios CAN have problems right out-of-the-box, you know?)

e) Are you certain that the cable/connector assembly was done correctly? And, that you are, in fact, getting decent transmit power up to your antenna? You wrote that you didn't want to go up the mast to check it...but did the professional that installed it, actually test it? (this is part of the proof-of-performance testing, and should be written in your ship's log and/or radio log)

f) Are you certain that there are no obstructions (other than this other "AIS" antenna), either something else on the masthead (masthead tri-color light, etc.)....or a land-mass, etc. that can be effecting one vessel's transmit signal?


5) Notwithstanding what I wrote up top, regarding radiowaves being reciprocal, please be aware that even on VHF, even if you are line-of-sight, there are rare times when atmospheric conditions CAN enhance (or degrade) a radiowave path where you'd be able to notice, i.e. your signal isn't getting thru and someone else's is....(again this is rare, but it does happen)



I think if I can get a bit of clarification and some more details, we should be able to figure this out.

Fair winds.

John

[MathiasW]

Thanks for all the feedback!

No AIS splitter indeed. And I was moving, the other vessel was at anchor.

The AIS antenna is too close to the VHF antenna, this is a known problem, but it is the same for both vessels. But it could be, of course, that the vessels at anchor had a different orientation to me.

We were 16.5 nm apart, but since I could hear the other vessel, line of sight was still ok.

Cheers, Mathias

[ka4wja]

Mathias,
I see we each were typing out our posts close to the same time, as my post was just 3 minutes ahead of yours...

So, I'm, going to wait 'til you get a chance to provide a bit more info, before I form a certain answer / solution for you...
(but, first off....the "AIS" antennas ARE causing antenna pattern issues!! and, secondly, you were both not out at sea, one at anchor and one moving, that is a big fly in the ointment)

Let me know the answers to questions I posted above, and we'll get things sorted out in short order.

John

[MathiasW]

Originally Posted by ka4wja

Mathias,
Let's see if we can figure this out.
Btw, my first "from the gut" guess is that it is a receive issue on your sister ship. (but, there's a lot of info I don't have, so I can't be sure....yet)

[FYI, radio waves, and radiowave propagation, are reciprocal....meaning that your transmit signal moves thru the air the same way that someone else's (your received signal) does....BUT...
But, how the radio energy leaves the antenna, into the air, is highly effected by the antenna, its mounting and orientation, etc....as well as how much energy is captured by the antenna on receive....so to compare two antennas, they must be exact copies and must be installed/mounted/oriented exactly the same way...
Now, of course, we're on boats....boats move around....the antenna pattern can be effected by not just the boat's motion / heel, etc., but also by the wind "whipping" the antenna around...as well as differences in what else is near each antenna, etc...
So, while radiowave propagation is reciprocal between tx and rx, there are a lot of other things that are usually different. ]


BTW, it would help a lot if you would clarify where are you located?

Where are you doing this testing? Out on the open sea? Or along a coast? Or in port? in various ports? etc. etc.

What weather conditions, etc.?

How often has this occurred? Have you been able to regularly repeat these exact results, over-and-over again?

As well as actual info on these "antennas", where/how they are all installed, what exact coaxial cable you have now, as well as the other vessel's cabling....and if you are certain that all cable/connections were actually done correctly and proof-performance tested, etc.?

And, any other details you have that we do not....even things that may seem minor / inconsequential, can be important.



1) First off, unless both vessels (yours and your sister ship) are identical and have identical equipment / systems, and all of the equipment / systems are used the same, at the same time, etc. etc., you cannot be assured of identical performance, let alone similar performance.

But, I do understand your concern regarding your VHF system performance, and I'd like to help you figure it out.

Also, be aware that while getting the most power out to the antenna is good, in general the difference between NEW cabling and connections, and OLD cabling and connections, is usually greater than the differences between normal coax cable (RG-213, etc.) versus low-loss cable (LMR-type cables)...it's not naïve to want to reduce losses in your system, it's just that with terrestrial VHF-FM, it's highly unlikely to ever be noticed, and usually not even measurable.

{further, even new cabling can have issues, as all it takes is one small screw-up on a connector assembly, to add significant loss into the system....and most marine electronics dealers will not test for this, 'cuz they don't know how or don't have the time....which is where you Mathias seem to be even better at this than most professionals are!}


2) I'm not clear about your (and the other boat's) antennas, so can you clarify the "antenna" situation?

You write that you both have the same antennas and the same AIS antenna sitting next to them? This means there are TWO VHF transmit / receive antennas at the masthead, and they are only inches away from each other? (this is not good....and, might be the proximate cause of your observed issue!)

So, to clarify things, can you tell me:
a) what antenna you have for your primary VHF, and where is it mounted?
b) what antenna you have for your AIS, and where is it mounted?
c) how far away are these antennas from each other?
d) what type, and length, of coaxial cable connects each of these antennas down to their equipment (radio and AIS)? And, is there a cable-connection at the base of the mast, for each of these cables?

...AND...

e) what antenna does the other boat have for their primary VHF, and where is it mounted?
f) what antenna does the other boat have for their AIS, and where is it mounted?
g) how far away are these antennas from each other?
h) what type, and length, of coaxial cable connects each of these antennas down to their equipment (radio and AIS)? And, is there a cable-connection at the base of the mast, for each of these cables?


3) RFI effecting VHF freqs used to be almost unheard of....but, unfortunately now-a-days it does happen....(just last week a gentleman here on Cruiser's Forum, mentioned his solar chargers' RFI wipes out his VHF aviation band reception).

So, this is good guess of what might be effecting the other boat's inability to hear you, when at 16.5nm, but you are still able to hear him.


4) Of course, there could be other possible causes (other than the antenna issues I asked for clarification of, and other than receive RFI on the other boat)

a) Is the other boat's radio adjusted properly? Is his squelch set too high?

b) Is your radio's output correct? 25 watts? (+/-)

c) Is your audio too low? Are you not speaking loudly enough? Or opposite, are you shouting and over-deviating?

d) Are you sure there isn't a radio problem on the other boat? (new radios CAN have problems right out-of-the-box, you know?)

e) Are you certain that the cable/connector assembly was done correctly? And, that you are, in fact, getting decent transmit power up to your antenna? You wrote that you didn't want to go up the mast to check it...but did the professional that installed it, actually test it? (this is part of the proof-of-performance testing, and should be written in your ship's log and/or radio log)

f) Are you certain that there are no obstructions (other than this other "AIS" antenna), either something else on the masthead (masthead tri-color light, etc.)....or a land-mass, etc. that can be effecting one vessel's transmit signal?


5) Notwithstanding what I wrote up top, regarding radiowaves being reciprocal, please be aware that even on VHF, even if you are line-of-sight, there are rare times when atmospheric conditions CAN enhance (or degrade) a radiowave path where you'd be able to notice, i.e. your signal isn't getting thru and someone else's is....(again this is rare, but it does happen)



I think if I can get a bit of clarification and some more details, we should be able to figure this out.

Fair winds.

John

Thanks so much for this detailed feedback, John!

I need to go through this one by one before I can reply in full.

As to my current position: In the southern part of Sea of Cortez, on the Baha side, sailing north. My sister ship is ahead of me.

I did notice some extraordinary long AIS reaches here. Other sailing vessels like mine (at least with a class B transceiver and less than 20 m long), I have spotted on the chart plotter more than 60 nm away. So, clearly much more than line of sight between the antennas.

I will answer in more detail when I have reached the anchor position.

Thanks again

Cheers, Mathias

[ka4wja]

Mathias,
No worries, take your time....
But...

But, you'd do well if you read these threads here....especially this first one!
(these are the ones I recommended earlier)

'Cuz you will quickly learn about VHF Radiowave propagation (hint: there is a LOT more than "line-of-sight"!), and some about coaxial cable losses, etc.

https://www.cruisersforum.com/forums...ge-149499.html


And, this one highlights details of AIS, as well as dealing a bit with coaxial cable losses, etc.

https://www.cruisersforum.com/forums...ld-130803.html


Fair winds.

John

[Stewie12]

Could be that your sister vessel has the squelch too high.

[S/V Illusion]

While guessing games may be fun and some have way too much free time writing lengthy diatribes, you need to measure power and SWR both at the output and at the antenna to define if/where the problem is.

[Cadence]

Check your coax shield connections.
Just a WAG!

[waterman46]

Originally Posted by Stewie12

Could be that your sister vessel has the squelch too high.

Great thinking! I recommend repeating the test with squelch set to zero (counterclockwise usually) on both boats. You could record how the received signal sounds - you can use a cellphone app to do this, or just place a call to the other station and have him hold his phone up to his VHF while you talk on yours and listen to your own voice. When you get together again, compare the quality of the received transmission of both of you. Is it "full quieting" (no noise, just the voice), scratchy with noise, or just noise.

Too bad VHF radios don't have a S/N meter or received signal strength "S" meter like SSB radios. That would answer a lot of questions. But comparing the actual sound of transmissions audibly is a good way to answer your question.

I think this would save you a lot of time and effort. If you get unsatisfactory results, then you can delve into the many mysteries discussed in great detail in other posts.

[ka4wja]

Mathias,
1) I'm sure you'll find what the "issue" is (perhaps there isn't one, perhaps it was just operator error and/or mother nature?). I wish you good luck, and hope my detailed post gives you both directions to look and info to help you figure things out...out there away from instant tech support... LOL

Especially as you're out cruising and at sea, etc., I understand both:
a) your internet connections may be spotty.... and
b) you may need some extra info that isn't easy to come by when out there!

So, if my too detailed post is overwhelming, just take it one step at a time....always going back to the original configuration / set-up, so that you can determine which of the "solutions" solve a particular problem or issue.




2) S/V Illusion....
Huh?

Originally Posted by S/V Illusion

While guessing games may be fun and some have way too much free time writing lengthy diatribes, you need to measure power and SWR both at the output and at the antenna to define if/where the problem is.

S/V Illusion, I reread this thread, and I cannot find anyone nor any words that even come close to even a generous definition of "diatribe"? (and, just to be sure....this physics major, went and checked on-line for the definition: "a forceful and bitter verbal attack against someone or something")

So, if you'd like to contribute to the discussion, helping a fellow sailor who is out cruising, who is trying to determine if his newly-installed VHF radio, antenna, and cable are in fact working properly or not.....well, pull up a chair and lend him all the assistance you can.

And, I do agree that endless guessing games usually lead to more confusion than needed, Mathias is out at sea and cruising (Sea of Cortez), and providing him with multiple thoughts / ideas / assistance, from multiple fellow sailors, seems like a good thing to me. Yes? I mean if I was having a problem with say....say my genoa roller furler, and I was looking for assistance trying to find a solution when out at sea or in a remote area, I'd gracefully accept any / all ideas or recommendations from those I'm asking help of....what sailor wouldn't?

So, to write that "some have way too much time writing lengthy diatribes", seems (in my personal opinion) to be both poor seamanship and generally rude to all here abouts. But, again, that is just my personal opinion, and I'm a smart guy who knows that I don't know everything and I ask questions when I need something.

Oh, and to be clear....I already asked Mathias if he (or the professional installer) verified the power output at the top of the mast...when he can get back to the internet he will see the thoughts, recommendations, and advice here, and I'm fairly certain we'll get some answers.



3) Waterman, I don't want to drift this discussion far afield, so I'm going to be brief...
Except for a few direct-sampling VHF SDR receivers and some software (and some old commercial gear from the 60's/70's??), FM receivers do not have actual S-meters (nor any actual signal strength indications), as they do not actually have AGC circuits (like AM, SSB, CW receivers do), rather they have limiter circuits....and the S-meter readings that we are used to, are generally derived from the receiver's AGC Voltage....
But, this is a good idea and I, too, wish that FM receivers had working S-meters (fyi, there are many FM receivers that do have s-meters, etc...but they show rather irrelevant info....as once the signal passes the limiter threshold, there is no other increase...)
Again, this will drift this discussion too far, but just thought you might be curious as to the "why" we don't have s-meters on our FM receivers.



Fair winds to all.

John

[thomm225]

Originally Posted by S/V Illusion

While guessing games may be fun and some have way too much free time writing lengthy diatribes, you need to measure power and SWR both at the output and at the antenna to define if/where the problem is.

Wow, I thought you had ruined this thread for a minute by giving some basic troubleshooting tips to correct a simple problem, but it looks like we are okay.

Let the entertainment can continue......

Most times these threads can go on for 50-100 posts for a problem that can usually be troubleshot in a couple minutes with the right checks.