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ContinuousWave: Small Boat Electrical
Marine VHF Radio Communications
|Author||Topic: Marine VHF Radio Communications|
posted 01-15-2005 09:54 AM ET (US)
Questions or comments on my article
Marine VHF Radio Communications
can be appended below. [This thread also accumulates several comments posted elsewhere.]
posted 01-09-2005 12:24 AM ET (US)
You did a great job on your article analyzing VHF Marine Communications that you recently added to the site. That is one complete and concise piece of work. Than you!
posted 01-09-2005 01:40 PM ET (US)
Great article. [Changed topic to discuss behavior of vertical monopole radiators when tilted with respect to the earth. This topic will be covered in a separate article.--jimh]
posted 01-09-2005 04:27 PM ET (US)
Excellent article, and as usual, very well written.
The angled back thing is something that happens by accident on our boat. It's possible to get it vertical, as it should be, but the antenna is on a ratchet rail mount, and one tooth off doesn't cut it. That's what happened this day, when we got in a hurry launching:
posted 01-14-2005 09:51 AM ET (US)
Many years ago I read, or someone said to me, that if you can't describe something in mathematical terms then you really don't understand it.
posted 01-15-2005 10:18 AM ET (US)
With regard to a vertical antenna which is tilted from the usual vertical orientation, the radiation pattern will be disturbed from the normal case. Vertical antennas tend to concentrate their radiation at the horizon. The "takeoff angle" would be 0-degrees, let's say. If the radiator is tilted to a 30-degree angle, the radiation pattern is not entirely tilted along with it. That is, the takeoff angle does not jump to 30-degrees. There will still be radiation along the horizon (at the 0-degree angle), but it may be reduced in intensity somewhat. Predicting exactly what effect occurs when the radiator is tilted is hard to say without a great deal of computation and modeling. There is some experience with antennas called "slopers" which are inclined at a 45-degree angle that seems to show an increase in the radiation in the direction in which the base of the antenna is pointed.
If a vertical antenna on a boat is tilted at a severe angle, in addition to possible lost power radiation in the desired direction, there will also be problems with polarization changes. VHF Marine radios are universally equipped with antennas that have vertical polarization, so as the antenna tilts it also begins to become cross-polarized with the receive antenna. In the case of two boats bobbing in waves, it is not farfetched to image that their antennas could become oriented at 90-degrees to one another. This would result in additional loss in the circuit path due to cross polarization.
posted 01-16-2005 12:58 PM ET (US)
You may not have noticed, but truckers tend to angle their CB antennas FORWARD, this means that when they are barrlling down the road at 100 miles per hour ( or so it seems),the resultant wind will push them back and they will then be as upright as possible. You do not have to go to such extremes on a boat, slower speeds hopefully, but it is something to take into account. I know it looks 'cool' to rake 'em back but at what cost? Lost range? Missed communication when needing help? Mmm!
My vhf on my sailingboat is upright and at the top of the highest mast. Gives me great range, but I lose it when she heels over or rolls in those waves. Just my 2cents.
posted 01-16-2005 02:40 PM ET (US)
The exteneded rage often seen on the VHF band is due to Troposheric ducting. It can't really be predicted with any accuracy. It is caused by weather, especially temperature inversions. Any boater interesed in safety should never ever rely on, or depend upon Tropo-ducting to get the range they may require. If you need extended range, you should be looking at marine supressed sideband (SSB)or get your ham radio ticket. BillS
posted 01-16-2005 06:58 PM ET (US)
Many boaters are unaware that services like the U.S. Coast Guard or the Canadian Coast Guard use trunked radio systems with many repeaters and auxiliary receive and transmit sites. We have been cruising along in northern Lake Huron and heard radio calls from Coast Guard Group Detroit, located about 250 miles away. It is not enhanced propagation that allows us to hear those transmissions, but rather an elaborately networked radio communication system. The naive boater may think he is hearing the transmission directly from the station announcing them, when more likely they are coming from a tall tower on the water's edge no more than about 30 miles away.
The Canadian Coast Guard recently shut down all of their local radio watch standers on Lake Huron, and they run their whole Lake Huron/Georgian Bay radio service by remote links from a post on western Lake Superior. I miss the Scottish accent of the guys from Wiarton, on the Bruce Peninsula, who used to keep watch on Georgian Bay and the eastern end of the North Channel and read the continuous marine broadcasts of notices to mariners and weather.
posted 01-16-2005 07:39 PM ET (US)
Very good article Jim For what it's worth I think Jim H is doing some super work keeping this forum going and those that have very little to offer can only criticize! Most of us find this forum to be of great benefit!
By the way Jim, what about a thread on the digitital selective calling and the Coast Guard install of the new use for emergency response??? I hear some of the west coast is up and running. When will the Great Lakes be able to use it??
posted 01-17-2005 10:52 AM ET (US)
Rescue 21, the CG's new comms system, was scheduled to go
online at the first two sites, Atlantic City and Chincoteague,
by Sept. 30, 2004. I found some stuff that said they got up,
but had found technical problems in the lab. Their Group
by Group schedule has disappeared since the last time I
looked, and the materials have gotten a lot glitzyier.
The most recent schedule I could find was
posted 01-19-2005 04:06 PM ET (US)
I think a saying that my preacher likes to use fit very well here Jimh:
I like what you did way better than what he didn't.
I learned quite a bit that I can use, and as an engineer, I can certainly appreciate the math behind anything.
posted 01-19-2005 07:02 PM ET (US)
What I remember hearing from my early days of cruising with my folks was the very precise cant in the radio operators dialect that operated WLC, in Rogers City, Michigan. The station was origionally "the" AM radio station for ship to shore contact in the upper Great Lakes. It was funded by US Steel. As FM overtook AM for (relatively) short distance communication in the region, WLC had a footprint on that band also.
They broadcast the MAFOR at 0730 and again at 1800hrs. At 1830 hrs channel 16 became quiet and the station would give out was my dad called the "Ship's traffic report". This report was for vessels that WLC needed to establish contact with and either relay a short message, or assign a particular marine channel for a phone call. You waited in "line" on the channel, waiting for the other call to terminate (and listened to the traffic, it was like a huge party line).
The operator always sounded like:
"THIS IS DOUBLE-U-LLL-SEE, RRRROGERS SIT-EEE........WITH THE FOLLOWING TRAFFIC..........."
posted 01-19-2005 07:27 PM ET (US)
Regarding the Canadian Coast Guard repeaters and antennae (I think we're talking anout the same thing!), we had a 50 foot tower with an 8" whip VHF antennae on top on Neptune Island, and using that hooked up to an old cheap vhf radio and a battery, we had our choice of calling Wiarton or Sault Ste. Marie Coast Guard to have them make a land line phone call connection so we could touch base with family back in the states, before cell phones. We'd get in line as Don said, monitor channel 16, and when they had a channel free they'd hail us and assign us a channel (seems like it was usually channel 24) and develop a phone connection for us. Cost $30 or $40 a pop though. As I remember, we would hail either "VBB The Soo" or "VBC Wiarton" to reach them. Sault Ste. Marie has to be 130 miles as the crow flies, and Wiarton must be more than that I think.
posted 01-20-2005 08:51 AM ET (US)
John--The Canadian Coast Guard has radio installations at several auxiliary sites in the North Channel region.
The site at Wiarton is very advantageously located. Just north of town there is a very large hill--anyone who has towed their boat trailer to Tobermory will remember it--and at the summit of the hill there is a very tall radio tower, some 500-feet or more. I am fairly certain that is where the CG radio at Wiarton is located, which gives it a very substantial elevation above lake level.
With an antenna at, say, 1000-feet, the radio horizon would be about 45 miles. With your antenna at 80-feet (here I am assuming your 50-foot tower was located above the water level by a about 20-feet knowing the terrain there at Neptune Island), you would have a radio horizon of about 13 miles. That would give a combined radius of about 58 miles. You may be farther from Wiarton than 58-miles as the crow flies, but not that much farther!
Here is a list of stations in the northern Lake Huron radio network of the Canadian CG, which are now controlled from Thunder Bay in Lake Superior:
Thunder Bay, Horn, Bald Head, Sault Ste Marie, Silver Water, Killarney*, Tobermory, Pointe au Baril, Wiarton, Meaford, Churchill, Fraserwood***, Jackhead***, Longpoint***
* The remotely controlled site at Killarney is shut down from January 1 to March 31.
Here is a coverage map:
posted 01-20-2005 11:18 AM ET (US)
My parents spent 40+ years cruising the Georgian Bay/North Channel area and I well remember that Scotsman's voice at VBC Wiarton. Back in those days there was much less traffic and chatter and more of a family feel to the voices as I recall. My Mother loved telling the story about the time I telephoned on my father's 65th and the Scotsman's comments to all listening congratulating him, over the air. He then did the same again when I called announcing my engagement.
posted 01-20-2005 11:27 AM ET (US)
I got carried away with the memories and forgot to add that your article is great and timely for me as I just registered to obtain my Operators Certificate and I'm purchasing a new VHF quite soon. Maybe even at the Toronto Boat if there's a deal on this weekend. The article, plus the subsequent posts, have helped to give me a better understanding of the technical issues to ask about.
posted 01-20-2005 01:22 PM ET (US)
By the way, we only made one marine radiotelephone call via that service from the North Channel. We were at anchor in Rattlesnake Harbour in Georgian Bay, and we got a good connection with Wiarton. Yes, those calls were expensive, but the funny part is that we don't recall ever getting the call on our telephone bill. We called one number and billed it to another, so somewhere the paperwork got mixed up.
I find it interesting that others also recall the distinctive voice of the Wiarton station. I wish I had recorded it. When were were up there cruising we always listened to those guys every morning to get the weather and any (maritime) news.
posted 01-20-2005 02:06 PM ET (US)
Way back when in my sailboat days here in the PNW, the land with no ski season this year, I remember using the Belligham marine operator to call home and work. I can not remember how much it cost. For entertainment we would listen to other phone calls on the channel. Most folks were unaware that anybody with a VHF radio could hear thier conversation. Very entertaining, then they blipped out one side of the conversation, I think it was the land line side. I wonder if this service is still around with everone and thier dog having a cell phone? John
posted 01-20-2005 02:48 PM ET (US)
If I remember correctly the term was making a "duplex" call. Despite the cellphone usage these days, the coverage is still very sporadic in a number of areas and the duplex call should be more reliable in those areas, assuming of course you want to pay the $30 to $40 for the first few minutes. I'm sure the cellphones have lessoned the usage of duplex calls but I'd like to think they are still available?
Aren't they? Anyone?
posted 01-20-2005 03:00 PM ET (US)
I must be one of those naive boaters. Two summers ago, about 1/4 mile outside the inlet at Ocean City Maryland, heard Coast Guard Baltimore communicating with a disabled boater somewhere off Bodkin Pointc in my home waters of the Chesapeake. Could not hear the disabled boater, but the Coast Guard came in loud and clear from a tower I thought was an impressive 95 miles away. Based on what's been stated above, it was part of the "elaborately networked radio communication system" and the I was virtually in the shadow of the actual transmission tower at CG OC MD.
posted 01-20-2005 06:05 PM ET (US)
VHF is ok in most locations as long as it is flat. I had a 3 way conversation last fall when I had lost power on main engine and called Bellingham, WA Coast Guard (which was 13-15 miles away & 2 islands between us)on Ch 16 to let them know and I was heading in on my kicker. I didn't get an answer from them, but Seattle, (100+ miles) came on and told me that Victoria Station, Canadain CG, (Vancouver Is B C)was attempting contact, I was not hearing them at all. Victoria was about 4 islands and 50+ miles away. I answered Seattle, but real scratchy and we finished up on cell phones and I got in ok on my kicker. So around here one never knows if someone is going to hear you.
I sometimes think my CB w/mouse boost reaches out farther, bit really don't use it much except w/friends.
JMARTIN, I haven't used the Bellingham Marine Operator in several years, I assume it is still operating.
Cell phone service in the islands is kind of patch works and depending on your location whether you have a signal.
posted 01-24-2006 09:44 PM ET (US)
Here is an on-line calculator with which you can calculate the path loss in a line-of-sight transmission path:
posted 02-22-2006 04:45 PM ET (US)
[Commented that the reason] why truckers angle the antenna forward is to avoid interference with their exhaust stacks.
posted 06-28-2009 01:45 PM ET (US)
While I find it some incongruous that this comment should follow one regarding how truck drivers orient the CB radio antennas on their exhaust pipes, nevertheless I will proceed:
For a long time it has bothered me that the derivation of the path loss equation for free space propagation loss in decibels for various common units, such as Megahertz and Miles or Megahertz and Kilometers, has never been shown. It was not entirely clear to me or immediately obvious how the relationship between the path loss equation in its power ratio form and its decibel loss form came to be derived. Therefore I have added an addendum to my article to demonstrate how the decibel form of the path loss equations are derived from the generic path loss.
Users of CB radio antennas may not find this particularly interesting. However, the implied topic of how tilting a vertical monopole radiator with respect to the earth affects its radiation pattern is another topic I intend to look into in the future for some better explanations. I will report on that in a separate follow-up when I have found a satisfactory explanation.
posted 06-29-2009 12:43 AM ET (US)
gss036: The USCG operates a lot of remote stations. As
near as I can tell, USCG Monterey does not have an antenna
on the roof. Bellingham may not have been able to hear you
from the remotes that they monitored, but Group Seattle was
probably monitoring them all. There are some coverage charts
posted 07-06-2009 06:41 AM ET (US)
Jim, this is the free software I use for modeling antennas:
I believe you will find it interesting that it works excellently with WINE under Ubuntu Linux (with Nvidia non-free drivers), as well as with Crossover/Mac, a commercial port of WINE for OS-X. That includes rotating the 3-D models.
posted 07-09-2009 10:22 PM ET (US)
ASIDE to Moe: A gentleman has ported the whole NEC antenna modeling application to the MacOS X using the Aqua display kit. It works beautifully. I just have not had the time to fiddle with it. It is more of a winter activity for me. Something to do in those long and dark December days.
When I found this beautiful port of the NEC code, I was delighted. However, I soon discovered that using it requires a lot of work in describing the antenna to be modeled. There is always something that needs to be done in the future. For me, this is one of those things.
posted 07-10-2009 03:14 PM ET (US)
I'd never read this artcile until now. I can see why. There's so much techno-jargon and mathmatical equations that I couldn't stay focused longer than the first paragraph. Chock it up to being part of the MTV generation, I guess.
But what strikes me is that, in an article about VHF communication, there's no mention of VHF protocol, etiquette, or the benefits of having a VHF radio on board. It seems that every time I go out, I hear some knucklehead misusing his radio. I have lots of friends with boats. But I'm the only one with a VHF. I'm sure there are MANY boaters who have no idea why they would ever even want one of those things when they "could just as easily use a cell phone."
I wish more people had radios, knew how to use them, and did so on a regular basis.
posted 07-13-2009 08:27 PM ET (US)
Except in the addendum, the "techno-jargon and mathmatical equations" are limited to arithmetic addition. I guess if addition is too much for you, you'd be better off on a bass boat website.
Radiotelephone procedure is quite a separate topic from the underlying principles of VHF radio range. However, I do read the mail on a lot of VHF Marine Band radio traffic, and I can agree that there certainly are some goofballs out there using their marine radios. Start a new thread and we can have a few hoots talking about it. Ten-four?
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