VHF Range

[Simon B]

Originally Posted by Jon Brooks

Also is this with a unity gain antenna or a 3dB type?

Regards

Originally Posted by ashbypower

Looks a great formula apparently you don't need any

power!!!

Not a clue but a clue can be gained, will look into this, I believe stable antenna height is more of a factor than power. Not that any of this will do any good when you are out there!

[Nick Thompson]

David,

Thanks for that

Originally Posted by David Hickman

Nick,
...When Brixham receive a call. they look at the Computer screen and see which mast is receiving the highest signal strength and then that is the mast they will use to reply.

Presumably that is why they asked me to wait for their call back on 67.

Regards

Nick

[wavelength]

Presumably that is why they asked me to wait for their call back on 67.

it is easy to forget that whilst you cannot hear anything else going on on 16 and 67 or whatever other channel they are using it doesnt mean they are not busy with radio traffic on another aerial you cannot hear. And that could be why you are on standby til they are free. Of course the other thing with multiple aerials is a fix can be made on a casualty by crossing the bearings from a couple of aerials.
High pressure weather here the other week and suddenly we were hearing lots of radio traffic from the aerials at Isle of Man and Wales which normally we wouldnt hear.

[Nick Thompson]

Originally Posted by wavelength

it is easy to forget that whilst you cannot hear anything else going on on 16 and 67 or whatever other channel they are using it doesnt mean they are not busy with radio traffic on another aerial you cannot hear.

Especially when you don't realise they use so many masts

[wavelength]

Especially when you don't realise they use so many masts

All part of the service - good in'it!

[Rogue Wave]

Originally Posted by Nick Thompson

David,

Thanks for that

Presumably that is why they asked me to wait for their call back on 67

Regards

Nick

I think the reason for the channel change is that it keeps the hailing channel (16) open. The idea being that you can do your routine chat on the back channel and leave 16 open for distress and datstress and stuff like dat

[wavelength]

of course for routine traffic you have to go to a working channel such as 67 (or unfortunately ch86 around here)-ch16 cannot be used to pass routine stuff. I think the question was about the "go to ch 16 and await my call" type of instruction.

[Nick Thompson]

Originally Posted by Rogue Wave

I think the reason for the channel change is that it keeps the hailing channel (16) open.

Yes, normally the CG ask you to go to 67 & continue the 'conversation', but this time they said go to 67 & wait.

[Doug Stormforce]

Originally Posted by Simon B

Not a clue but a clue can be gained, will look into this, I believe stable antenna height is more of a factor than power. Not that any of this will do any good when you are out there!

Popular misconception that power effects range. With VHF it does not make a blind bit of difference. It does not matter how strong a signal you send out, if the top of your antenna is line of sight with the top of the receivers antenna then the signal will get there. All that higher power does is make your signal drown out everyone elses.

If of course we were talkng about MF then an increase in power would increase range but with VHF and HF not so.

I have always worked on the formulae being 2.12 sq route height, however it does not make much difference so lets call it 2.2 etc.

Jon The formulae works for either sort of aerial. The difference is effectivly the angles that the signal leaves the antenna from. I can explain easily by diagram so will show you when I next see you if you are still interested.

Now to put the formuae into practice. If I have an antenna height of 16m and a CG has an antenna height of 100m- how far apart could we communicate?

Well sq route of 16 is 4, times by 2.2 equals 8.8. My radio horizon is therfore 8.8 miles. Sq route of 100 is 10, multiply this by 2.2 and the CG has a radio horixon of 22 miles. OUr range from/to each other is therfore the sum of the two=30 miles. I expect that if you have a look at the rising/dipping distance table in the almanack it will give you much the same result.

In reality of course the CG generally has a higher mast than that and most RIBS dont have a 16m A frame.

Now there are of course various conditions that can increase or decrease this range. Sea State, atmospheric pressure, temperature differences, sun spot activity to name but a few. Yacht sof Gibralter have been known to pick up Dover Coastaguard but when it happens it does not happen for long.

[Matt]

I can't believe that 3 pages in you lot are still arguing about this.

[Rogue Wave]

Vix is letting you stay up late!

[Shaggy]

Originally Posted by Doug Stormforce

Popular misconception that power effects range. With VHF it does not make a blind bit of difference. It does not matter how strong a signal you send out, if the top of your antenna is line of sight with the top of the receivers antenna then the signal will get there. All that higher power does is make your signal drown out everyone elses.

If of course we were talkng about MF then an increase in power would increase range but with VHF and HF not so.

I have always worked on the formulae being 2.12 sq route height, however it does not make much difference so lets call it 2.2 etc.

Jon The formulae works for either sort of aerial. The difference is effectivly the angles that the signal leaves the antenna from. I can explain easily by diagram so will show you when I next see you if you are still interested.

Now to put the formuae into practice. If I have an antenna height of 16m and a CG has an antenna height of 100m- how far apart could we communicate?

Well sq route of 16 is 4, times by 2.2 equals 8.8. My radio horizon is therfore 8.8 miles. Sq route of 100 is 10, multiply this by 2.2 and the CG has a radio horixon of 22 miles. OUr range from/to each other is therfore the sum of the two=30 miles. I expect that if you have a look at the rising/dipping distance table in the almanack it will give you much the same result.

In reality of course the CG generally has a higher mast than that and most RIBS dont have a 16m A frame.

Now there are of course various conditions that can increase or decrease this range. Sea State, atmospheric pressure, temperature differences, sun spot activity to name but a few. Yacht sof Gibralter have been known to pick up Dover Coastaguard but when it happens it does not happen for long.

Hi Doug
I’m afraid you are not correct in stating that RF power in line of sight propagation has no bearing on the ability of the signal to be received at the far end.

You have failed to consider Free Space loss.

As a radio signal propagates through the air, it experiences a loss in amplitude. If the range between the sender and receiver increases, the signal amplitude declines exponentially. In an open environment, one clear of obstacles, the RF signals experience what engineers call free-space loss, which is a form of attenuation. The atmosphere causes the modulated signal to attenuate exponentially as the signal propagates farther away from the antenna. Therefore, the signal must have enough power to reach the desired distance at a signal level acceptable that the receiver needs.

Free space loss. Geometric spreading happens because the wavefront radiated signal
energy expands like a big column as a function of the distance from the transmitter.
When the distance from the transmitter is measured in units of the signal wavelength

Shaggy

[Mollers]

Blimey Shaggy!! So you are the man next time me' wireless is playin' up.

[Jono]

Yeah!... what Shaggy says.....!

[Doug Stormforce]

Originally Posted by Shaggy

Hi Doug
I’m afraid you are not correct in stating that RF power in line of sight propagation has no bearing on the ability of the signal to be received at the far end.

You have failed to consider Free Space loss.

As a radio signal propagates through the air, it experiences a loss in amplitude. If the range between the sender and receiver increases, the signal amplitude declines exponentially. In an open environment, one clear of obstacles, the RF signals experience what engineers call free-space loss, which is a form of attenuation. The atmosphere causes the modulated signal to attenuate exponentially as the signal propagates farther away from the antenna. Therefore, the signal must have enough power to reach the desired distance at a signal level acceptable that the receiver needs.

Free space loss. Geometric spreading happens because the wavefront radiated signal
energy expands like a big column as a function of the distance from the transmitter.
When the distance from the transmitter is measured in units of the signal wavelength

Shaggy

Shaggy, Thank you and you are of course quite correct if we were trying to transmit to the moon, however 1Watt of RF power from a VHF on board a RIB will quite happily reach the radio horizon (line of sight), it will in fact reach the line of sight horixzon if transmitted from a taller antenna height (say a container ship).

Let me clarify my badly worded earlier statment. Using high or low power from a marine VHF on board a RIB will not make a blind bit of difference to the range if you are trying to communicate with another station also on earth.