Radio Signal Horizons

[Guest]

Just been doing my pre-read for the VHF course, I found the following may be of interest to some :-

If you wish to calculate the distance of the radio horizon of your vessel or indeed any other antenna, you need to apply this formula :-

Distance in Nautical miles = 2.25 of sq route of height of the antenna in metres

Example 1
Your antenna is 16m above sea level =
distance in nautical miles = 2.25 square route of 16
= 2.25 x 4 = 9 miles

Example 2
If you are speaking to another boat with antenna of 9mtrs also, radio range is 18 miles

Example 3
Suppose you are speaking to coast station whose antenna is 225 mtrs above sea level, his radio horizon is :-
Distance in nautical miles = 2.25 square route of 225
= 2.25 x 15 = 34 miles
Add to this your radio horizon of 9 miles
Total = 43 miles

Clear as mud, good luck calculating, and don't forget the tape measure /forums/images/icons/laugh.gif

Some pre calculated :-

2 mtrs high = 3 miles
4 mtrs high = 4.5 miles
6 mtrs high = 5.5 miles
8 mtrs high = 6.5 miles
10 mtrs high = 7 miles
12 mtrs high = 8 miles
14 mtrs high = 8.5 miles

Moral of the story is :- Get it up as high as you can

 

[BarryH]

Ok questioin, when does all this theory go out of the window and your VHF can have a range in the 100's of miles. Hint something to do with the weather and atmosphere.

 

[BrendanS]

Thank god you didn't post this on PBO, or we'd be in for weeks of propagation, refraction, reflection, free-space waves, ionospheric waves, tropospheric waves, ground waves, scatter, ionospheric and geomagnetic storms and a load of other reasons why your formula won't work in the real world

 

[BarryH]

Bah! you told him the answer!

 

[Guest]

I SAID I was doing my pre-read, I haven't done the course yet, but believe me by tomorrow night I will have the answer for you, and don't warn the instructor [laugh[

 

[BrendanS]

Oops, looks like we were thinking along similar lines!

 

[BrendanS]

If this course is for the standard marine radio VHF licence, you'll be sorely disappointed. Most of it is about the different types of radio transmitter (VHF, DSC, Epirb etc) how they operate in very basic terms, and a whole load about how you give a mayday or pan pan call.

They'll want you to be able to recite a mayday call format, and I doubt most instructors have the slightest idea about anything much beyond this, unless they have a personal interest. If you push some of them, they'll recollect that someone told them that the aerial should be high up, and vertical (laying it at a nice racing angle reduces it's efficiency)

 

[Guest]

So what exactly am I paying all this money to learn for, if it's all 'up in the air'. I have read the book that cost £9.95, it tells me everything I need to know (apart from Barry & Brendons hard questions), I then have to hear the same from an instructor for £80, then pay £19 for a licence (these all three of us, each). Is there a scam going on.

 

[hlb]

So. Like I said. Hand held is about as much good as a fart in a bottlle. You need Hight and power. So add to your wanted list. An extention ladder and A frame to hold it. I've gora see this boat when ot comes out................/forums/images/icons/laugh.gif

<font color=blue> Haydn

 

[BarryH]

Most of the instructors know nothing about the "mechanics" of radio. I had and argument with mine over the amount of gain that could be had from using a Yazi array and a stacked array. He gave up after we got onto half wave and 5/8th wave di poles and the harmonics. He took me to one side at the tea break and told me to stop making him look like he knew nothing about it. He passed me though!

 

[BrendanS]

The licence, training and exam are all about correct use of the radio, not the theory behind it. It's a safety thing.

Don't want lots of people exchanging messages about where to meet on Ch16, when some poor sod is sinking.
You'll learn which channels to use for what purpose, 16 for contact and distress, 77 for 'appropriate' chat such as conversing between boats on a club trip, 80 for marinas
How to use DSC etc etc

When you listen to some of the idiots who use VHF, you'll soon learn, a little like driving exams, that few have taken it in. Emphasis is on correct usage and understanding the big picture, and on what frequencies things like epirbs work, and how the coastguard coordinate all this, and how a mayday or epirb sets off a chain of events

Not a rip off, and not a waste of time. If you want to know a great deal more about theory and propagation and other radio effects, you'll want to go on a SSB or ham course and speak to people who really understand these things. That is not what the marine VHF course is about

 

[Guest]

Yes this is for the VHF DSC course, we did however buy all books we could find relating to this subject. I have memorised most formulas and common calculations, but am struggling to learn all the International Maritime VHF Bandplan charts. There are 88 channels to memorise, with single & dual frequency, ship transmition bands, Coast receive bands, Coast transmit bands, ship receive bands, distress calling, Intership, Port Ops ship MVMT and Coast radio st for each of the 88 channels. It is doing my brain in. I bet I won't even need to use many of them in the River Medway. I am OK on all the UK coast radio stations, their working channels, broadcast channels and dual frequency, and memorised their locations, but there again not much use outside the river medway!! Tired now anyway, may just get some sleep.

 

[Guest]

I have studied and digested the Reeds VHF DSC Handbook by Sue Fletcher, it is well layed out and makes it pretty simple, its just the memorising of all the info that is time consuming. Should be a good day, I still have alot of questions to raise on the VHF course about safety e.t.c I also think I may have worked out some easier formulae for them, we will see tomorrow.

 

[BrendanS]

Give up! You don't need all that stuff

Just need to know basic channels for exam, which the instructor will tell you/give you big hints about.Locations and the rest of it are useless.

You've just got a Reeds. When you go somewhere like portsmouth, you look up the frequencies the QHM use and write them down, or more likely like 99% of boaters don't even know they exist and don't bother, and just stay out of the way of the ferries and big boats.. You're making life difficult for yourself.

 

[Guest]

That's all a bit in depth for me Barry and isn't in the book, I am aware of some of what you are on about but not to a good technical knowledge level anywhere as good as you. I will stick to what I have at the moment, but I am certainly going to get that 10mtr whip aerial, I should get a good signal with that running at 25 watts.

 

[hlb]

Scam. Maybe. I sent Tutts to liverpool. A long time ago. She has qualifications for radio. But we dont let her use it. No No No. Cept maybe talk to marina.Cos I'm upstairs and out of ear shot. But still have to say. Make sure it's on chanel 80. Please dont blast out on 16 that you want to talk to fred!!! So I use the radio in anger. No Licence but ok cos she is normaly aboard. o what happens is. If I use the radio. No Problem. But no licence. If Tutts uses radio. She sticks mouth piece to ear and..........................??!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! /forums/images/icons/laugh.gif

<font color=blue> Haydn

 

[BrendanS]

If you've read Sue's book, and understood, you'll pass with flying colours. I read and digested, and the instructor/examiner said I was best prepared candidate he'd encountered (and I'd read it a year before hand and forgotten 90% of it!!) It's a really simple exam, designed for people who have never used radio equipment before - complete beginners - you've got military training, it's a different ball game. Like I said ,stop, you're trying to learn at a level the course was never designed for

PS, Sue is my instructor on the yachtmaster course I'm doing/forums/images/icons/smile.gif

 

[crazyhorse]

Hi grumpy its crazy how ya doing

Ya cheeky monkey

 

[BrendanS]

I can well believe it, and all I can say is that you were lucky to find an instructor who understood it to that level...probably a raggie who had cruised?. It's not really what the course is about.

I did ham radio with Air Training Corp as a kid, and got ham licence, where you had to know incredible amounts of detail, but forgotten it all now.

 

[Guest]

Hi Crazy, I'm going bloody crazy, can't move in my house for maritime books, and won't be able to move in the boat for safety gear !!!!!!!!!! Anyway I'm getting there, Nice to see you over from the 'other channel' it is brilliant here with great people and a lot of experience. I reckon you could build a boat, and learn everything there is to know, just about on here. Enjoy it.