Pro's & Con's of fixed vs handheld dfc/vhf radio's

[Andy Stevens]

Rich and Lousie,

I hope you don't fall over board!

With all that weight round your necks you'll never be seen again!

[Louise]

(to Stu & Andy)

To Stu - re. footstraps: Got them too. And flares, and spare lifejackets, and throwing line, and MOB ladder (when we remember it's there ) and fire extinguishers and enough other stuff to sink the boat!!!

[Rogue Wave]

Have you got a Fkkn big knife?

[Scary Des]

Originally Posted by BrendanS

as I said to Louise. 2 - 4 mile MAX! and it depends on sea conditions! If you are in rough conditions, you'd be well advised to make the most of the time you are on top of the waves, not down in the trough

Yes I know you said 2 to 4 miles max but I’m still not convinced, my reasoning is that in waves 75% of the time you are either in the trough or going up or down one of the sides, great in Atlantic rollers but in the ‘Solent chop’ where the wave frequency is 12’ I think you would be lucky to get ½ a mile. It would be an interesting thing to test, anyone interested? Des

[BrendanS]

Yes, have done it, which is why I can give figures. We were bored one day and had a similar conversation, so went and tried it. Went in water in dry suit, and another boat with a fixed set set off. Sea conditions were about 1' swell and got good comms at 3 miles, and understandable with repetition at 4 miles (they could hear me, I couldn't hear them, but the boat standing by me with a fixed set relayed that I was being received or I'd have given up at that point)

If you want to try it in rougher conditions I'm up for it

[Rogue Wave]

I'll try it out the next time I am on the boat without customers. cos I think you are right Des. where are the masts in the Solent other than at Lee.

[Jon Brooks]

Although all the books say VHF is line of sight this is one of those rule of thumbs things.

In practice its tends to be line of sight + a 1/3.

Radio signal theory is not a exact art, so many factors can effect you signal path.

But we suggest as a guide and only a guide:-
for a 5w hand held 7-10 miles,
for a 25w fixed 25-30 miles,

Some have suggested an external antenna on an hand held to in prove range.
Things to consider here is cable loss and conector loss which you WILL get.

On a rib this will not be a major issue as no real huge runs of coax but a yacht up the mast you will.

Again as a rule of thumb and not an exact thing, you will get 1db loss for every connector/adaptor and 1db loss for every 10m of RG58 coax.
This is based on good quality conectors and coax.
Cheep stuff will give you even more loss.
If you get 3db loss you have halved your power output.

So 5w can very quickly become 2.5w or less.

This will mean your RX will be much improved but a minor change on your TX range.

Hope that helps a bit.

Regards

[Scary Des]

Originally Posted by BrendanS

Yes, have done it, which is why I can give figures. We were bored one day and had a similar conversation, so went and tried it. Went in water in dry suit, and another boat with a fixed set set off. Sea conditions were about 1' swell and got good comms at 3 miles, and understandable with repetition at 4 miles (they could hear me, I couldn't hear them, but the boat standing by me with a fixed set relayed that I was being received or I'd have given up at that point)

If you want to try it in rougher conditions I'm up for it

Interesting just what I had in mind , was the swell 1’ or 1mtr (3’)? Des

[Scary Des]

Originally Posted by Jon Brooks

Although all the books say VHF is line of sight this is one of those rule of thumbs things.

In practice its tends to be line of sight + a 1/3.

So Jon are you saying that at the bottom of a 1 mtr height 4mtr frequency wave trough the range should be 5.3 mtr?
Des

[Jon Brooks]

Originally Posted by Scary Des

So Jon are you saying that at the bottom of a 1 mtr height 4mtr frequency wave trough the range should be 5.3 mtr?
Des

The rule of thumb is based on ideal condition not rough sea.
Brendan's test would be a more acurate way of getting the answer you need.

We have access to lots of computer simulators and programms for working out path loss but the only real way to get a right answer is a practical test.

When I have set up radio system I always do a live test, as I said only way you will get the right answer.

On different days you will get different results too.
As I said so many things can and will effect VHF comms.

Regards

[Jon Brooks]

Originally Posted by Louise

(to Stu & Andy)

To Stu - re. footstraps: Got them too. And flares, and spare lifejackets, and throwing line, and MOB ladder (when we remember it's there ) and fire extinguishers and enough other stuff to sink the boat!!!

Blimey Louise thats one hell of a belt kit you have!!!
Batman would be green with envy!
or is it all in your hand bag?


Regards

[Scary Des]

Originally Posted by Jon Brooks

The rule of thumb is based on ideal condition not rough sea.
Brendan's test would be a more acurate way of getting the answer you need.

We have access to lots of computer simulators and programms for working out path loss but the only real way to get a right answer is a practical test.

When I have set up radio system I always do a live test, as I said only way you will get the right answer.

On different days you will get different results too.
As I said so many things can and will effect VHF comms.

Regards

Is that a yes? Range 5.3mtrs Des

[Jon Brooks]

Originally Posted by Scary Des

Is that a yes? Range 5.3mtrs Des

Its a - I would need to test before answering that as I would not want you to think it is ir is not without.

That vague enough for you?

Sorry but I would want to test the theory before giving a deff answer.

Jon for politic? no I don't think so!!!

Brendan's test is a good idea of what you can expect.

Regards

[BrendanS]

It was a short sharp nasty 1 foot chop, though as is ever the way with these things, some were larger some were smaller.

- after 20 minutes in the water, they start looking a lot bigger!

[Scary Des]

Originally Posted by Jon Brooks

Brendan's test is a good idea of what you can expect.

Regards

Brendan’s test was conducted in 1' swell (unless he made a typo), in my book that is smooth, I am taking about rough weather, the type of weather that makes you fall out of boats. Still I agree we should test it I think the results will be very interesting.
Des

[Jon Brooks]

Originally Posted by Scary Des

Brendan’s test was conducted in 1' swell (unless he made a typo), in my book that is smooth, I am taking about rough weather, the type of weather that makes you fall out of boats. Still I agree we should test it I think the results will be very interesting.
Des

So a minging day out in the Sloent is on the cards then!!

[gingercoastie]

Just to add to the range debate,


In a high pressure weather system the range of Vhf is dramatically increased. We can listen to Liverpool and Dover coastguard sometimes.

[Scary Des]

Originally Posted by Jon Brooks

So a minging day out in the Sloent is on the cards then!!

I‘ve got to take the boat out later, should be a bit lumpy. I’ll have to see if the wife is up for a bit of testing, She’ll probably think it is an elaborate ruse to get her life insurance money. Des

[Scary Des]

Originally Posted by gingercoastie

Just to add to the range debate,


In a high pressure weather system the range of Vhf is dramatically increased. We can listen to Liverpool and Dover coastguard sometimes.

Given the relative heights of your aerials I guess that is almost (+1/3) line of sight. Or is it stratosphere bounce ? Des

[gingercoastie]

Originally Posted by Scary Des

Given the relative heights of your aerials I guess that is almost (+1/3) line of sight. Or is it stratosphere bounce ? Des

Actually it is ducting.