VHF - can hear but not be heard at a distance

[Opie91]

Do you have a large solar array? Victron solar controllers are known to cause interference with VHF. Receive and transmit.

If you do try shutting it off and see what you get.

[MoodyS]

Which channel was used for the test? It's possible that one set up was using US simplex channel while the other was on INTL and possibly duplex?

[MathiasW]

So, very sorry for this cliff hanger, it took a bit longer to come back to this excellent set of questions. Anchoring is one thing, but anchoring with internet access is an entirely different mater here in the Sea of Cortez...

I am trying to answer this set of questions without having looked at any new comments that may have come in. I will look at them after this one.

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 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. ]

ok, I do understand this reciprocity theorem, having studied physics ages ago... And this is why all this is puzzling me. I would rule out all effects that do not violate the reciprocity. And there are not many effects that I can think of that would. For instance, yes, I agree, the type of antenna, its mounting, its neighbours will all affect the quality of the setup, but even then I would argue that all these variables apply equally well for tx and rx. A complicated wave pattern around the antenna caused by a conflicting antenna would affect tx and rx equally, would it not?

Originally Posted by ka4wja

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.

This last test I did whilst sailing in 15-20 kn of wind with waves between 1 and perhaps 2 metres and about 2-4 miles offshore. The bearing of the sister vessel was about 45 degrees to port side. But being a trimaran, my heeling was small. The sister vessel was at anchor in a calm bay, open in my direction. Judging from the main wind direction, its bearing of me was likely to be about 135 degree starboard side. In other words, the wind was coming directly from where my destination was.

Originally Posted by ka4wja

What weather conditions, etc.?

No rain, only few clouds, a typical day with moderate northerly winds in the Sea of Cortez at this time of the year.

Originally Posted by ka4wja

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

I have noticed this behaviour in the past already a few times, and also very recently with another cat (which has a very old installation I believe). In total perhaps 3-4 times over two years.

Originally Posted by ka4wja

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.?

I do not recall the exact make of the antennas, but they are standard 1 or 1.5 metre off-the-mill 3db antennas and exactly the same as my sister ship has. My sister vessel and I have different mast heads: We both have the VHF and AIS antenna (same make), a stereo radio antenna, but I have on top of this an active Ecomax antenna (not in use), and a little prod with a ball of spikes at its top that is supposed to reduce the number of ions in the air and thus reduce the risk of lightning strikes. Called Forespar.

When looking from the top, and up being forward, the arrangement is roughly as follows (I am afraid I do not manage to get the lines aligned... ):

. |-------| Forespar
. |........ |
. |........ | Stereo Radio
. |........ |
. VHF |........ |AIS
. |-------|

And yes, I am aware of such a crowded arrangement where antennas are only 20 cm apart negatively affecting performance. But I would have thought it is affecting tx and rx equally.

Our masts are roughly 20 metres tall from the deck.

Originally Posted by ka4wja

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

I am using a number of ferrit rings slid over my cabling at the foot of the mast and in front of the radio.

Originally Posted by ka4wja

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.

Very true, but what factors are actually violating the reciprocity of tx and rx.

Originally Posted by ka4wja

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.

Yes, I understand that. It is in parts my normal habit to strive for perfection, which is taking control, but then again, I would think that it does matter if the other antenna is placed at a very high position, like for a costal station, or a commercial vessel. In such a case line of sight is still given and transmission power at the antenna starts to matter. If only for sound quality.

Originally Posted by ka4wja

{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!}

Yes, that is absolutely true. My sister vessel's installation is some 30 months older than mine, which is now about 15 months old after my last recabling. And yes, I could have screwed up with doing the connectors. Not likely the one at the mast foot, since I was able to measure it, but the one at the mast top was difficult to install in situ and impossible to test. But then again, if I had a poor connector up there, it would affect tx and rx equally well, I would have thought.

Ah, and I just realise - my connector at the mast head is new and does not exist on why sister vessel. Originally, there was a long cable directly attached to the antenna and going down the mast, but because of my newly installed Ecoflex cable, I had to introduce a connector up there.

Originally Posted by ka4wja

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?

see diagram above. With some effort, I may be able to find out the exact make of my VHF and AIS antennas, but this will not be trivial.

Originally Posted by ka4wja

b) what antenna you have for your AIS, and where is it mounted?

see above. Exact same make as the VHF antenna.

Originally Posted by ka4wja

c) how far away are these antennas from each other?

Only about 20 cm, I would say.

Originally Posted by ka4wja

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?

I had changed my cabling to highly flexible low-loss Ecoflex 15 Plus cable with a diameter of some 15 mm. Before that I had a standard RG58 cable running from the radio to the mast foot, and from there an unidentifiable cable of slightly larger diameter up into the mast top. Yes, there is a connector at the mast foot, which used to this simple standard VHF connector and now is one compatible with the Ecoflex cable. At the top of the mast I had to introduce a new connector to switch from the Ecoflex cable to the cable that comes out of the antenna. The original installation had a couple of spare metres cable run back and forth with very tight corners at the ends of these legs, which I removed. This is still the installation on my sister vessel. The AIS I upgraded only the cable from the unit at the nav table to the mast foot. Here I took, I believe, an Ecoflex 10 cable. It also has a connector there and it had also spare cable running back and forth.

Very roughly, my cable from radio to mast foot is 6 metres long, and from there to top of mast 25 metres.

I did note this asymmetry in rx and tx already before I had changed this cabling.

Originally Posted by ka4wja

...AND...

e) what antenna does the other boat have for their primary VHF, and where is it mounted?

See diagram above. It is the same antenna as mine.

Originally Posted by ka4wja

f) what antenna does the other boat have for their AIS, and where is it mounted?

See above. It is the same as mine and also mounted on the mast head, but I am not sure about its position relative to the VHF antenna.

Originally Posted by ka4wja

g) how far away are these antennas from each other?

about 20 cm...

Originally Posted by ka4wja

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?

see above. The mast is about 20 metres tall, mine being a metre or so taller than that of the sister vessel. The cable from radio to mast foot is perhaps 6 metres, after cutting out most of the slack that the original installer had added. Thus, for my sister vessel this cable between radio and mast foot is perhaps 9 metres long.

Originally Posted by ka4wja

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.

I do have a lot of solar on vessel, more so than the sister vessel. We both use high-end Mastervolt regulators.

Originally Posted by ka4wja

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?

Could be, of course, I do not know. I am regularly double checking my squelch.

Originally Posted by ka4wja

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

Yep, measured that. Bang on 25 W.

Originally Posted by ka4wja

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

Could be, of course, but I usually speak with normal voice, I do not shout. My buddy on the sister vessel has a bit deeper and louder voice than mine. Perhaps it is worth noting here that all these tests have been done using the wireless remote handheld that comes with this radio. The sister vessel is likely to have used the radio mic directly, being at anchor.

Originally Posted by ka4wja

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?)

No information about that.

Originally Posted by ka4wja

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)

Well, this ship was built in France and there were no such tests performed and such a log was not handed down to me either. So, it could be that the connector at the top of the mast is poor on my vessel after I redid the installation at the top of the mast, or the connector at the foot of the mast of my sister vessel (I did measure mine). But all this I would have thought would not introduce an asymmetry in tx and rx, or would it?

Originally Posted by ka4wja

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?

Ah, yes, I have a tri-colour light, but so has my sister vessel. For other possible obstructions see above.

Originally Posted by ka4wja

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)

Yep, and I am likely to have seen this a few times over the past days. I am about 200 nm away from Mazatlan, which is just across the Sea of Cortez, but more than once I could at night hear some commercial vessels communicating with Mazatlan Pilot Control on VHF 16, and I could even hear Mazatlan's response. I could not believe my ears, actually. Likewise, I was able to see more than one fellow cruisers some 60+ nm away on AIS during the day. Normally I stop seeing them if they are more than 15 nm away, depending on the other vessel's mast height and quality of AIS installation.

Originally Posted by ka4wja

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

Thank you so much John for this detailed questionnaire and any subsequent help.

I am not claiming I am an expert on radio stuff, not at all. I took my licenses some years back and I have a decent background in theoretical physics, but I am not a specialist on this matter. But still, I would have thought that the majority of items in the list above would affect tx and rx equally well, for the better or the worse. Just to pick an example, if the VHF and AIS antennas are too close to each other - which they are - and this is the same for me and my sister vessel, I cannot see how this would violate the reciprocity of the tx and rx signals, even if I have a few more items on the top of my mast compared to my sister vessel. Admittedly, this is not a confirmed knowledge of mine but rather a hunch based on my general knowledge of the matter, but this is what is puzzling me...

Cheers, Mathias

[MathiasW]

Originally Posted by Stewie12

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

Possibly, but unlikely, as he is a very experienced chap...

[MathiasW]

Originally Posted by Cadence

Check your coax shield connections.
Just a WAG!

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...

[MathiasW]

Originally Posted by waterman46

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.

Thanks for this! I will try this out next time I am apart from my sister vessel. Currently, we are just under 200 metres away at anchor...

[MathiasW]

Originally Posted by Opie91

Do you have a large solar array? Victron solar controllers are known to cause interference with VHF. Receive and transmit.

If you do try shutting it off and see what you get.

I did not know, but thanks for this tip. I have Mastervolt MPPT regulators, and so has my sister ship, but I think I have more than he does.

I have added quite a few extra ferrits to the VHF power input as well as antenna.

[MathiasW]

Originally Posted by MoodyS

Which channel was used for the test? It's possible that one set up was using US simplex channel while the other was on INTL and possibly duplex?

Oh yes, I had to learn a hard lesson or two here in Mexico when realising that my international VHF is different to US VHF - for instance on the most often used channel 22 at anchorages here...

But we used channel 16 for hailing, and so we should be ok on this one. But thanks!

[S/V Illusion]

Originally Posted by thomm225

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.

Some people have waaaaay too much free time on their hands and apparently cannot succinctly answer a question without over-complicating a simple thing. Quantity vs quality in the advice department, rationalized by the familiar - trying to help - theme song.

[MathiasW]

Originally Posted by 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

Thank you for these links, John!

Whilst reading the first I thought perhaps this little item can help shedding some light onto the matter:

In one reply it was said that some engine LEDs in the mast caused interference with the VHF. My sister ship did notice some months back some negative interference of their LED deck light (or engine light, I forgot) with their AIS rx signal. I then gave them some of my ferrit clip ons and they said it improved the matter. But perhaps their is still some residual effect there? 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 did not shield my LEDs and perhaps should do so, but I do have quite a few ferrit clip ons on my antenna as well as the power input of my VHF radio.

So, possibly, because of these ferrits, I could set the squelch to a lower value than my sister vessel can? I guess they can check that if they switch off these lights and then see whether they can lower the squelch...

Just speculation, I know...

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...

You can use a piece of coat hanger to receive not so transmitting you need to do the best with a SWR a bad coax connection screw that up.

[thomm225]

Originally Posted by S/V Illusion

Some people have waaaaay too much free time on their hands and apparently cannot succinctly answer a question without over-complicating a simple thing. Quantity vs quality in the advice department, rationalized by the familiar - trying to help - theme song.

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?

[MathiasW]

Need to correct myself - it is Ecoflex 10 Plus, not 15 Plus...

[MathiasW]

Originally Posted by Cadence

You can use a piece of coat hanger to receive not so transmitting you need to do the best with a SWR a bad coax connection screw that up.

Hmm, sorry, I do not understand what you want me to do...

[Cadence]

Originally Posted by MathiasW

Hmm, sorry, I do not understand what you want me to do...

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.