The range of VHF radios

[Hudson Force]

I hear thoughts of installing a "second" VHF at the helm. I figure, unless your running some megayacht with a radio officer, you'd best have your primary radio at the helm,- where else do you plan to be? Nav. station? get real,- if you're underway, then the helmsman needs radio communication! 'take care and joy, Aythya crew

[btrayfors]

Originally Posted by Jim Cate

A related query:

Does anyone know what the actual vertical beam width is for the various commercial higher gain (6,9, 12 dB, etc) VHF antennas ?
We are admonished to not use such equipment on our oh-so-tippy monohulls, while our brethren on motor yachts (many of which roll like pigs in bigger seas) seem happy with the high gain devices. Personally, I seldom want to use myVHF when I'm sailing at big heeling angles, and so wonder how big an issue it really is.

Cheers,

Jim and Ann s/vInsatiable II

It's not negligible nor is it irrelevant. See, e.g.,
continuousWave: Whaler: Reference: VHF Marine Band Antennas

Scroll down to see the vertical radiation patterns.

Bill

[Jim Cate]

Originally Posted by btrayfors

It's not negligible nor is it irrelevant. See, e.g.,
continuousWave: Whaler: Reference: VHF Marine Band Antennas

Scroll down to see the vertical radiation patterns.

Bill

Bill,

Thank you very much for the reference. This seems to completely justify the use of only unity gain antennas on anything but very stable vessels.

My query was driven by having my VHF antenna mounted on my radar arch, only some 3+ meters above the water. Seemed like it was worth investigating the higher gain. Not currently interested in a masthead mount, hoping for a bit better range... ain't no free lunch here!

Thanks again

Jim

[s/v Jedi]

Originally Posted by fairbank56

Nick,

Your entire post is nonsense in my professional opinion. Anyway, my first reply was to dispute your claim that the GMDSS requires your VHF to have a range of 50nm between you and shorestations and other ships. It is simply not the case.

Eric

Well, you did it now Eric; first you call my post nonsense and now absurd. You must know that using terms like that heats up the discussion and urges me to reply instead of just letting go. It also makes you look... well, less smart, if you use those words and it turns out that I am right.

So, here you go, round 3:

First, I am gonna assume that you are a US citizen and that you do not have your General GMDSS Operators Certificate (for all areas), nor a Restricted GMDSS Operators Certificate (area A1 only). These assumptions are based on your loud choice of words and my general observation that not many US cruisers have their GMDSS certificate. Also, if you would have it, they would have told you in class that the A1 area can extend up to 50 nm from shore, like they told me when I was in that class.

If nothing changed lately, the US is about the last of the developed nations NOT to have even a single A1 area established. They are still busy implementing some project for that.

The United States presently has no A1 Sea Areas. Establishment of an A1 Sea Area in the U.S. is expected to depend upon approval and funding of the National Distress System Modernization Project.

(source: USCG GMDSS Areas of Operation - USCG Navigation Center)

and

Sea Area 1 will not be declared until Rescue 21 has reached Full Operational Capability.

Source: USCG: Rescue 21

This means that you can press the Distress button on the VHF until your finger falls off, there's no guaranty the USCG will receive that, although a handful of shore stations are supposed to receive it.

However, Western Europe has full A1 and A2 coverage in addition to the A3/A4 areas. I would advise you not to go sailing there because the A1 area outer limit ranges from 30 to 50 nm from shore, just like I wrote before. You need proof. You will find it in this PDF, incl. a very nice chart with each area colored: http://www.ofcom.org.uk/static/archi...y4075final.pdf I quote from page 30:

Sea area A1 extends 30-50 nautical miles from the coast

(Ofcom is the UK version of FCC)

More? The ITU (International club this time, defines technical requirements for IMO) states:

Area A1 lies within range of shore-based VHF coast stations (up to about 50 nautical miles)

Source: http://www.itu.int/ITU-R/conferences.../00-18_pp7.ppt

More? The International Hydrographic Organization (IHO) states:

A1: Within range of shore-based VHF stations [...] about 20-50n miles

Source: http://www.iho-ohi.net/mtg_docs/rhc/...o_to_GMDSS.pdf

One more for fun: BoatUS takes it a step further:

Area A1. This is for boats that are sailing within shore-based VHF radio range. Typically, that distance is in the range of 20 to 60 nautical miles (nm).

Source: BoatUS.com Articles and Tips from DIY Magazine

So, there you have it. Now, you post some links that say A1 is maximum 20 nm or 30 nm or whatever you claim. I wrote before that I agree that those ranges are typical, but not maximum.

cheers,
Nick.

[GordMay]

According to the USCG:
Sea Area 1 (USA) will not be declared until Rescue 21 has reached Full Operational Capability.
The Rescue 21 system is standing the watch and answering the call of duty across 24,758 miles of coastline.
Rescue 21 is operational in the following Regions:
o Sector Mobile
o Sector St. Petersburg
o Sector Seattle
o Group/Air Station Port Angeles
o Sector New Orleans
o Sector Delaware Bay
o Sector Long Island Sound
o Sector New York
o Sector Jacksonville
o Sector Hampton Roads
o Sector Miami
o Group/Air Station Astoria, OR
o Sector Baltimore
o Group/Air Station North Bend
o Sector Portland
o Sector Key West
o Sector Houston/Galveston
Goto: USCG: Rescue 21

[MidLandOne]

Originally Posted by s/v Jedi

...First, I am gonna assume that you are a US citizen and that you do not have your General GMDSS Operators Certificate (for all areas), nor a Restricted GMDSS Operators Certificate (area A1 only). These assumptions are based on your loud choice of words and my general observation that not many US cruisers have their GMDSS certificate. Also, if you would have it, they would have told you in class that the A1 area can extend up to 50 nm from shore, like they told me when I was in that class...

I am sure you will find that some of us here regard the operators' certificates you refer to as being very basic qualifications giving no knowledge at all apart from how to operate some basic items of radio equipment.

Originally Posted by s/v Jedi

...If nothing changed lately, the US is about the last of the developed nations NOT to have even a single A1 area established. They are still busy implementing some project for that...

In fact a number of developed nations have stated that they are never going to declare Sea Areas A1 and that for very good reasons, so the USA is in very good company. Those decisions do not compromise safety.

Originally Posted by s/v Jedi

...However, Western Europe has full A1 and A2 coverage in addition to the A3/A4 areas. I would advise you not to go sailing there because the A1 area outer limit ranges from 30 to 50 nm from shore, just like I wrote before. You need proof. You will find it in this PDF, incl. a very nice chart with each area colored: http://www.ofcom.org.uk/static/archi...y4075final.pdf I quote from page 30:

(Ofcom is the UK version of FCC)

More? The ITU (International club this time, defines technical requirements for IMO) states:

Source: http://www.itu.int/ITU-R/conferences.../00-18_pp7.ppt

More? The International Hydrographic Organization (IHO) states:

Source: http://www.iho-ohi.net/mtg_docs/rhc/...o_to_GMDSS.pdf

One more for fun: BoatUS takes it a step further:

Source: BoatUS.com Articles and Tips from DIY Magazine

So, there you have it. Now, you post some links that say A1 is maximum 20 nm or 30 nm or whatever you claim. I wrote before that I agree that those ranges are typical, but not maximum....

You clearly did not understand my previous post.

It is IMO that sets the criteria for the establishment of Sea Areas not any of the organisations you mention. Governments establish Sea Areas within those criteria. ITU, IHO, etc have nothing to do with the criteria or establishment of Sea Areas. The IMO Resolution setting the criteria makes no mention whatsoever of 50nm nor of any other maximum limit on the radius of a Sea Area A1 from a shore station.

Whether the Sea Area is established at 20 miles or 50 miles or any other miles is of no effect whatsoever on what is required of the boat's radio as the outer limit of the Sea Area is established using a simple line of sight path and the only variable used in that is the height of the receiving antenna of the shore station.

So if the boat's mounted radio installation is capable of operating from the outer limit of a 20nm Sea Area A1 it is then automatically capable of operating from the outer limit of a 50nm one. This may be hard for a person with little exposure to radio physics to understand but it is so for simple VHF line of sight paths and I am sure any person with the required knowledge will assure you it is so. It is irrelevant as to what the radius of the Sea Area is.

The problem here is that you are leading people astray on a serious matter of safety (VHF DSC, together with EPIRB's, being the prime alerters for Sea Area A1). You are also contradicting people, including myself, who I know work in the maritime industry either directly in radio or on wider related safety management matters. The original poster's question was if a basic radio installation would suffice - the answer is yes and it will suffice no matter what the size of the Sea Area A1 is (assuming it is DSC capable if in a declared Sea Area A1).

I am sure it is not worth perservering any more on this as I am sure that those with an open mind or with some knowledge of radio beyond a simple operators' certificate will have taken the correct message on board. So I am off out of this stupidity.

[Talbot]

Originally Posted by MidLandOne

I am sure it is not worth perservering any more on this as I am sure that those with an open mind or with some knowledge of radio beyond a simple operators' certificate will have taken the correct message on board. So I am off out of this stupidity.

Good answer
(based on decades of seagoing experience)

There are none so deaf as those that dont want to hear!

[MidLandOne]

.

One could end up wondering if all this CE palaver you EU types have to put up with is to ensure that your radios have that important little secret gizmo in them that enables them to work out to 50nm .

[fairbank56]

Nick,

Once again, you miss the entire point of my first reply to your post. I never said that the A1 area cannot extend to 50nm, I merely stated that it was typically 20nm. I was disputing your claim that "Your radio is supposed to have 50 nm range between you and shorestations and other ships"..."These are the GMDSS requirements as implemented by coastguards/SAR services worldwide". Please show me the official regulation that says this. The shore station must have an antenna of sufficient height/gain to reach to the extent of the designated area, whether it be 20nm or 50nm. Ships are not required to be able to communicate with each other over a 50nm range. Thats just ridiculous.

Yes, I'm a U.S. citizen, I have an FCC GROL, GMDSS Operator/Maintainer with radar endorsement license, am a Certified Electronics Technician and have 34 years experience as a marine electronics technician with the federal government.

Eric

[Talbot]

Originally Posted by MidLandOne

.One could end up wondering if all this CE palaver you EU types have to put up with is to ensure that your radios have that important little secret gizmo in them that enables them to work out to 50nm .

Did you not get the inter-office memo, we (Europe) have put lots of money into an electronics device that artifically creates localised anaprop conditions within 50nm of the shore, thus ensuring that not only does our vhf work to that range, but also our ship's radar. It was the invention of this device that allowed us to artificially create the 50nm limit.



The "true" answer of course is that the politicians thought that the maritime types meant 50km, and whilst this was the outside of their limits, they accepted it. It was not until the act was passed that somebody realised that nm had been substituted for km without doing any change to the actual number.

[GordMay]

Originally Posted by Talbot

Did you not get the inter-office memo, we (Europe) have put lots of money into an electronics device that artifically creates localised anaprop conditions within 50nm of the shore ...

Anomalous Propagation (anaprop) is not just a joke.

See the story “Longer Legs for VHF” about the Northrop Grumman subsidiary, Park Air Systems commercial anaprop system:

Avionics Magazine :: Longer Legs for VHF

"A drawback to standard VHF radio communication is that it is limited in range to little more than line of sight. Unlike HF and lower frequencies, VHF's transmitted waves propagate minimally around the Earth's surface. When, on occasion, VHF transmissions do reach well beyond the horizon, they often are regarded as anomalous and a nuisance.

A number of systems, however, have capitalized on anomalous propagation modes and made them the basis for viable over-the-horizon (OTH) VHF communication. Such extended-range systems can be a useful adjunct to normal air traffic control (ATC) ground/air communications, particularly in locations having high levels of air traffic, where early contact with aircraft before they enter a core region would be useful.

One such location is in the People's Republic of China, where the country's Air Traffic Management Bureau (ATMB) has implemented over-the-horizon VHF communications for earlier contact with traffic over the South China Sea...

More: Avionics Magazine :: Longer Legs for VHF

[hellosailor]

Jim-
If you look at Marc's Technical Pages: Antenna Gain Explained or similar pages, there are antenna gain diagrams. In case they are not clear....pretend you are looking "down the wire" into one end of a horizontal wire. The polar chart is showing you the radiation lobes that extend out from your "wire", your antenna.
For a vertical antenna, the actual radiation spred is more like a donut, with the antenna extending up through the middle. But if you slice the donut at any point--it will look very much like the patterns shown on that page. Some donuts are nice and plump, like the rounded one at the top. Others (the hi-gain donuts) resemble pancakes.
The plump donut at the top has main lobes that spread a good 45 degrees off axis (a combined 90 degree spread) before they show a 3db loss, which is half of the signal strength. The fourth donut on the page (the 9db flattish one) shows the beam spread is down to more like 10 degrees--so at a five degree heel, you'd be transmitting "into" the water and sky.

Reality isn't that simple, since you may also hits flukes of signal bounce/skip with VHF, but those are flyers that give rise to people saying things like "Well but we contacted...and they're way over in..." once in a while.

So 3db, maybe 6db...but once you start pushing it, you're going to want to keep the boat upright during radio sessions. Considering that many boats really should be heeling 10 degrees or less to make best speed, a 20-degree beamspread might sound like enough. But once you add in the greater need for radio in rough weather, when you might be getting tossed around, rocked, pitched...the 3dB gain number becomes more common, and a convenient point of antenna design, as well.

[btrayfors]

Wow, Gord, that's what I've been dreaming about for years....

A 24-element stacked yagi array antenna atop my mast, a 250 watt FM transmitter, and an effective radiated power of more than 10 kilowatts!

Of course I'd need some means of pointing it in the right direction.

Whoopee! Can you spell, "tropo backscatter"???

Oh, heck, I'd have to trim those 24 elements back a bit to move resonance from 126 mHz up to the marine band at 156 mHz. What a pain! Think I'll just stick with my 3' 3db whip.

:-)

Bill

[btrayfors]

Hellosailor,

So, you want both gain AND vertical bandwidth?

A stacked yagi array is the way to go. Those 24-element, 6-stacked antennas put up by Northrup Grumman have 60-degrees of it!

We'll leave it up to others to figure how to mount it, and point it, atop the average cruising boat :-)

Bill

[Jim Cate]

Hello sailor,

Roger that... actually didn't have any difficulty in understanding the plots, and they were exactly what I was looking for.

Cheers and 73

Jim N9GFT/VK4GFT