VHF and AIS Radiowave Propagation and VHF and AIS Radio Range

[StuM]

Originally Posted by ka4wja

The troposphere extends from approx. 1000' - 3000' above sea level up to approx 35,000' above sea level....

I've never seen that definition before. (And I've read a lot of meteorogical and scientific material about the troposhere). What do you call the layer below the troposphere?

[ka4wja]

Okay, Okay, Stu...
I'm sure you just chiding me!

Originally Posted by StuM

I've never seen that definition before. (And I've read a lot of meteorogical and scientific material about the troposhere). What do you call the layer below the troposphere?

But, fyi, for those interested in the details....

--- I'm an amateur meteorologist, not a professional... (but, I majored in Physics), and I am of course not speaking in meteorological terms here at all!

--- This refers to the area of the Troposphere that is actually responsible for the bending and/or scattering of the VHF (and UHF, and lower microwave) signals....

--- The part of the troposphere that is closer to the ground than a couple thousand feet, is generally not responsible for "VHF Tropo" comms, as the area where signals would appear is typically covered by "direct wave" (line-of-sight), etc.....except in the case of actual "tropo ducting", where the "duct" can have a rather narrow vertical section (but, this doesn't really appear much in our daily lives, and is rather well described above)


I hope this clears things up?

Fair winds

John

[Cadence]

Stu,
I believe was John was saying is the troposphere is not necessarily at one altitude thus skip distances change. I would not bet VHF marine radios rely on any skip being FM line of sight. A B class AIS will only be good from 25-40 miles, probably dependent on both antenna heights, however the sats will catch them since its line of sight to them. No earth curvature in the way. Now I expect someone to tell me I'm full of the brown stuff.

[ka4wja]

Hello to all,

With much of the recent discussion regarding "VHF radio horizon" / communications range, filled with misunderstandings and some wild misinformation, I thought maybe some here might actually enjoy the facts (and the hows / whys) surrounding VHF radiowave propagation...

So, I'm posting this message to bump up this thread, where you'll find a great deal more info on VHF radiowave propagation and VHF (and AIS) range, than you're ever likely to need....but, it should help all of you...

Also, please remember that coastal, and over-the-sea, VHF communications are much more effected by the tropospheric weather conditions than those over land....and there are many times that we benefit from these effects to such a continuous / long-lasting effect (days. weeks, months?) that some assume these conditions are always there....fyi, except for tropo-scatter, they are not...



FYI, for those purists out there, yes I do use some commonly-accepted terms rather than all of the scientific / engineering terms....mainly 'cuz outside of PhD thesis, etc. few use the term tropo-refraction / super-refraction (rather using the term tropo-enhancement, or local tropo-enhancement....or even just "tropo")...

And, while beyond line-of-sight diffraction (from sea waves, etc.) can effect VHF radiowave propagation, it is almost always a fairly minor effect, especially compared to the "always there" and reliable tropo-scatter....as well as, compared to the atmospheric-weather enhanced tropo-refraction (i.e. "tropo-enhancement")....and always has issues with fading, etc., so I simply dismiss this as a viable topic to delve into for my fellow sailors...

Also, while our actual line-of-sight path losses are slightly higher than the calculated free-space losses (due to multipath reflections, and other refractions in our atmosphere) the differences are small, and the variations in antenna patterns due to vessel heeling, pitching, etc. as well as the wind whipping the antenna around, are typically much more significant....so, I just used free-space loss figures and add additional "fudge-factors" to compensate for all the variations....(again, not good enough for a IEEE paper, but plenty good enough for us here...



I do hope this helps all of you....but, please remember that while I started studying radiowave propagation in the early 1970's, almost 50 years ago....and have been teaching radiowave propagation, antenna system design, etc., now for over 40 years, I also learn something new once-in-a-while....so, understand that nobody expects my fellow sailors to know all of this....so..

So, read over the details and you'll learn a lot....and, for those whose eyes glaze-over when math / science, etc. comes up, please just take the gist of the discussion:

With masthead-mounted antennas, most sailboat-to-sailboat VHF communications is within the typical line-of-sight range of 15nm - 20nm....and once beyond that, the typical "normal communications range" will be approx. 30nm - 35nm (depending on radios, antennas, cable, microphones, operator, etc.) and a typical MAXIMUM range (without any special atmospheric enhancement) is going to be approx. 50nm...

And understand that these "normal ranges" are commonly exceeded because of certain atmospheric conditions...

Sailboat-to-sailboat VHF Marine communications beyond 50nm (and typically much beyond the 30nm - 35nm range) ALWAYS uses some form of "enhanced" propagation....almost all times this is "tropo" or "tropo-enhancement" [tropo-refraction/super-refraction] (which can propagate signals hundreds of nautical miles, over quite large geographic areas / regions, typically along the edge of a hi-pressure area, and coastal areas, especially in summertime...)Except in certain specific geographical areas, actual "tropo-ducting" is rare, and is typically restricted to specific narrow paths, and most times the distant signals (from as much as 1000 - 1500nm away or more) are as stronger as those 200 - 300nm away...

Fair winds.

John

[ronje]

Hello all

I'm from Australia and spent many years working for Aus's equivalent of the US FCC.

Not as an admin but as a field enforcement officer. We investigated problems and/or offences without assistance from Aus equivalet of the "US Marshall Service" in the cases of search warrants and apprehensions.

Marine radio issues were part of our job along with maritime search and rescue activities.

Aus's maritime S&R system was very basic and until the introduction of VHF marine in mid 80s. It existed before then in a very limited capacity with very few VHF base stations along the coast of my state (Queensland) with its 2,000 miles of coastline.

The govt philosophy was that they weren't going to put in long range base stations 'cos few mariners had VHF.

Few mariners had VHF because there were no long range base stations.

Inadequate distance of VHF marine was why we all ended up with a "busted" search and rescue system in Aus.

Nobody wanted "to make a move to fix it".

I stepped away from my work committments and set about "fixing it" in a volunteer capacity in my private time. I still carried out work committments but my focus was on search and rescue failings.

I had to hold engineering qualifications in communications and electronics for my job to enable my testomony in court matters to be accepted as a "expert witness" whose opinions are accepted by the court, the prosecution and the defence. I gained those qualifications in 1972 and gained the expert witness role about 15 years later.

I was also held (privately) "ham radio" qualifications VK4KJ. Stopped that activity when I became involved in more serious S&R work.

My thought were:
. i know how the existing S&R system works and why it doesn't;

. i know chatacteristics of radio propagation over water at hi-band VHF frequencies;

. i had built up many contacts within radiocom sites all over Queensland particularly along the coastline where the majority of the population lives;

. i had plenty of private time to devote to "fixing it";

. i had contact with many equipment suppliers to act as free equipment providers for VHF marine industry;

. I was prepared to "take the government on" over their dismal record in maritime communications in Aus especially in S&R and VHF marine.

I set out to fill that vacuum via the use of VHF marine talk-through-repeaters.

I set up 2 such repeaters (TTR) operating on the VHF marine band utilising unused ship/shore 2 fequency simplex channels.

In Brisbane area (large boating population- for Aus anyway) and another in my home Town 500 miles to the north.

I chose Ch 81 VHF IMM for each site. Transmit 161.675 tx and 157.075 receive.

With 4.6 mhz frequency split, antenna arrangements for isolation were simple. I used a two antenna installation (1 up and 1 down immediatley underneath it. More than sufficient r/f isolation to avoid de-sensitisation of the receiver).

I had to soak test the coverage areas obtained and spent many weeks doing so in the reefs and islands of the southern Great Barrier Reef doing so. It must confess that it was hard to take.

Should these first two repeaters prove successful then I had to design and allocate channeling for a string of repeaters along the Queensland coast. I had 4 more unused channels in mind making 5 available.

What I did find was that the coverage area obtained was nothing like all of the predictors about line-of-sight, radio horizons etc were telling me it should be.

So I had to make up my own predicion calculator which turned out very acceptable for future installations.

The reason I came onto this forum was after seeing all that was written, all the technical explanations and jargon used and with the subject of VHF marine no further advanced.

I'm happy to share what happened here as a result (there are currently 40 or so VHF marine talk-thru-repeaters in Qld all working very well and which have saved the lives of many boaties) with you guys and mariners in general if you want.

If you're happy not to hear what I've got to contribute just tell me to go away and chase crocodiles, wombats or kangaroos or something and I will.

Cheers

[S/V Illusion]

Originally Posted by ronje

Hello all

I'm from Australia and spent many years working for Aus's equivalent of the US FCC.

Not as an admin but as a field enforcement officer. We investigated problems and/or offences without assistance from Aus equivalet of the "US Marshall Service" in the cases of search warrants and apprehensions.

Marine radio issues were part of our job along with maritime search and rescue activities.

Aus's maritime S&R system was very basic and until the introduction of VHF marine in mid 80s. It existed before then in a very limited capacity with very few VHF base stations along the coast of my state (Queensland) with its 2,000 miles of coastline.

The govt philosophy was that they weren't going to put in long range base stations 'cos few mariners had VHF.

Few mariners had VHF because there were no long range base stations.

Inadequate distance of VHF marine was why we all ended up with a "busted" search and rescue system in Aus.

Nobody wanted "to make a move to fix it".

I stepped away from my work committments and set about "fixing it" in a volunteer capacity in my private time. I still carried out work committments but my focus was on search and rescue failings.

I had to hold engineering qualifications in communications and electronics for my job to enable my testomony in court matters to be accepted as a "expert witness" whose opinions are accepted by the court, the prosecution and the defence. I gained those qualifications in 1972 and gained the expert witness role about 15 years later.

I was also held (privately) "ham radio" qualifications VK4KJ. Stopped that activity when I became involved in more serious S&R work.

My thought were:
. i know how the existing S&R system works and why it doesn't;

. i know chatacteristics of radio propagation over water at hi-band VHF frequencies;

. i had built up many contacts within radiocom sites all over Queensland particularly along the coastline where the majority of the population lives;

. i had plenty of private time to devote to "fixing it";

. i had contact with many equipment suppliers to act as free equipment providers for VHF marine industry;

. I was prepared to "take the government on" over their dismal record in maritime communications in Aus especially in S&R and VHF marine.

I set out to fill that vacuum via the use of VHF marine talk-through-repeaters.

I set up 2 such repeaters (TTR) operating on the VHF marine band utilising unused ship/shore 2 fequency simplex channels.

In Brisbane area (large boating population- for Aus anyway) and another in my home Town 500 miles to the north.

I chose Ch 81 VHF IMM for each site. Transmit 161.675 tx and 157.075 receive.

With 4.6 mhz frequency split, antenna arrangements for isolation were simple. I used a two antenna installation (1 up and 1 down immediatley underneath it. More than sufficient r/f isolation to avoid de-sensitisation of the receiver).

I had to soak test the coverage areas obtained and spent many weeks doing so in the reefs and islands of the southern Great Barrier Reef doing so. It must confess that it was hard to take.

Should these first two repeaters prove successful then I had to design and allocate channeling for a string of repeaters along the Queensland coast. I had 4 more unused channels in mind making 5 available.

What I did find was that the coverage area obtained was nothing like all of the predictors about line-of-sight, radio horizons etc were telling me it should be.

So I had to make up my own predicion calculator which turned out very acceptable for future installations.

The reason I came onto this forum was after seeing all that was written, all the technical explanations and jargon used and with the subject of VHF marine no further advanced.

I'm happy to share what happened here as a result (there are currently 40 or so VHF marine talk-thru-repeaters in Qld all working very well and which have saved the lives of many boaties) with you guys and mariners in general if you want.

If you're happy not to hear what I've got to contribute just tell me to go away and chase crocodiles, wombats or kangaroos or something and I will.

Cheers

Any ham radio op with any experience in VHF could have saved you a lot of time. Regardless, it’s common today to link repeaters which cover thousands of square miles. The only limitation with boats is the lack of land on which to site repeaters.

[ronje]

Any ham radio op with VHF experience?


I think you misunderstand.

I was one of the Govt guys who examined these ham radio guys for their licences and qualifications to operate and enforced activities within the radio frequency spectrum.

I KNEW about that sort of stuff already. They would have saved me a lot of time?

How?


THEY used to come to ME for advice on maritime matters including radio (even visiting US yachties with their broadband HF transceivers).

These days there are broadband links joining many eventual Govt networks together.
Those govt networks on VHF marine accommodate single frequency simplex or two frequency simplex but NOT repeater configuration and they appeared 15 years after the repeaters. The govt VHF stuff is linked by microwave.

However, there are NO VHF IMM repeaters here linked together. They are all standalone for safety reasons.

We didn't want a problem on one repeater taking out a nearby linked repeater depriving users of both.

They are simple stand-alone separate installations which can be easily temporarily fixed by normal S&R personell who have been trained on how to do first-in diagnosis on a replace basis. Permanent technical fix can come after any temporary fix.

There are a couple of ham radio guys been on here already.

Has the conversation topic been further advanced?

[S/V Illusion]

Originally Posted by ronje

Any ham radio op with VHF experience?

There are a couple of ham radio guys been on here already.

Has the conversation topic been further advanced?

Far be it from me to explain it to someone who clearly thinks he knows it all.

[ronje]

I do know quite a lot about communications my friend.

This may come as a surprise to you but the US isn't considered to be the font of all knowledge by the rest of the world.

The font of arrogance and social discourtesy? US has the market cornered there on this forum.

Sure but not knowledge.

It seems that the role of a few contributers on here is to impress each other with their Walmart standard of academic and certificated knowledge.

Its a pity that these guys didn't concentrate on helping others who aren't so knowlegeable but would like some information to help them out about something(that's why they try to use these sorts of forums).

But that's amateur radio for you, I guess. Brings out the "not-so-good" competitive side in some.

For many years I was paid by the Aus govt to tolerate "dickheads" but I retired and don't have to tolerate them anymore.

I can hear some crocodiles, wombats and kangaroos etc that need chasing.

At least they're not arrogant my friend.

I'll see mysef out.

[S/V Illusion]

Originally Posted by ronje

I do know quite a lot about communications my friend.

This may come as a surprise to you but the US isn't considered to be the font of all knowledge by the rest of the world.

The font of arrogance and social discourtesy? US has the market cornered there on this forum.

Sure but not knowledge.

It seems that the role of a few contributers on here is to impress each other with their Walmart standard of academic and certificated knowledge.

Its a pity that these guys didn't concentrate on helping others who aren't so knowlegeable but would like some information to help them out about something(that's why they try to use these sorts of forums).

But that's amateur radio for you, I guess. Brings out the "not-so-good" competitive side in some.

For many years I was paid by the Aus govt to tolerate "dickheads" but I retired and don't have to tolerate them anymore.

I can hear some crocodiles, wombats and kangaroos etc that need chasing.

At least they're not arrogant my friend.

I'll see mysef out.

Just broke the irony meter

[Jim Cate]

MODERATOR HAT ON:

guys, this had degenerated into personal slurs. Abandon that approach or the thread will be closed.

for the mod team,

Jim

[Wotname]

Hi ronje, welcome aboard CF and thanks for being willing to bring your hard won professional knowledge to the discussion. I for one am most interested how the Aussie SAR system developed its VHF network.

As I started cruising in QLD long before VHF was common on sailboats and having spent an entire working life in radio comms, I think you will have good info to share. Apportion your available time between us and the crocodiles, wombats and kangaroos please. Perhaps start a new thread to pertains to the history of the Aussie's VHF development for small boats.

I also endorse Jim's admonishment to everybody to keep all posts respectful and thoughtful; one of CF's hallmarks is the absence of personal attacks.

[continuouswave]

Regarding practical examples of VHF distress monitoring systems, the United States government has invested about $1-billion into the U.S. Coast Guard RESCUE21 radio system. The stated system requirement is to ""receive, at minimum, a one second transmission from a one watt power source with an antenna two meters above sea level up to 20 nautical miles from shore."

To comply with that burden, the contractor has created coastal sites that are separated by about 25 to 30-miles, using direction-finding antenna arrays mounted at elevations of up to 300-feet or higher, and often located on hills giving even greater elevation above the water.

I am located in Michigan, which, because of the enormously long shorelines of Lake Superior, Lake Michigan, Lake Huron, and Lake Erie, has MORE Rescue21 installations than any other state. I have visited many of these installations. They are impression constructions.

For a look at what it takes to provide reliable communications out to seaward for 20-nautical miles, you can see several of these installation in my article at

Rescue 21 Radio Installations
https://continuouswave.com/whaler/re...1Stations.html

Disclaimer: I played no part in the design or construction of this system. My only role was to pay my federal taxes so the government could build this system.

I have never been qualified as an expert witness in any subject. But I was employed for over 40-years as a broadcast engineer.

[GreenWave]

Originally Posted by Jim Cate

MODERATOR HAT ON:

guys, this had degenerated into personal slurs. Abandon that approach or the thread will be closed.

for the mod team,

Jim

Since the thread is a good one, how about you just delete the last 4-5 posts.

[AKA-None]

Originally Posted by GreenWave

Since the thread is a good one, how about you just delete the last 4-5 posts.

Or we just play nice
I can see some good stuff coming out of this thread