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Old 25 August 2004, 06:36   #61
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Quote:
Originally Posted by gingercoastie
Actually it is ducting.
What's that??
Des
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Old 25 August 2004, 06:57   #62
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Here goes,

High pressure keeps the radio signal trapped near to the Earths surface. As it still needs to go somewhere its range is increased. Imagine squashing a soft ball, its radious will increase.
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Old 25 August 2004, 07:15   #63
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Quote:
Originally Posted by gingercoastie
High pressure keeps the radio signal trapped near to the Earths surface. As it still needs to go somewhere its range is increased. Imagine squashing a soft ball, its radious will increase.
Fascinating - I'd always rationalised the high pressure improvements as due to there being less interference from water particles in clouds mist etc with a high pressure .

Thanks for that Mr Coastie
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Old 25 August 2004, 07:20   #64
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Hi Brendan,

If you look at Jon Broks later post you'll see where I was coming from with my 2 to 3 watts. Real output as opposed to nominal out put based on all the variables that Jon describes...connections, length of cable run, corrosion , type of antennae etc.

In my other career I'm a Signals Officer in the Army and so would have quite a lot of experience with hand held and fixed VHF both marine and otherwise.

Regularly when you test older kit you can find actual radiated output power from the antenna to be down on 50% of what you expect.

While endorsing all of what Jon has said I would tend to be more cautious on the miles and would "generally" say 3 to 5 miles for hand held and 15 miles for a RIB mounted Fixed VHF in good condition. The ranges quoted in RYA manuals are often based on sailing yachts with a much higher mast !! Again as Jon rightly says there are so many variables !!!

Not scientific ............but I did a test a few years ago .Me with a hand held swimming in the middle of one of the large Shannon Lakes at night with a one metre short chop had good Stength 5 comms with a fixed unit in one of the Boat Squad RIBs 3 miles away.

We have a saying in my unit which is " Promise less - Deliver more !!" or err on the side of caution !



Kind regards,

Stuart
Quote:
Originally Posted by BrendanS
Not worried about the "."

Most people can surely work out that fixed is 25W. What concerned me is that you thought handhelds worked at 1-2W? Yes, as you say, handhelds work at 1W at times, but either you have to select a channel where that kicks in automatically, or select it yourself. The rest of the time it's typically 5W.

Anyway, I'm with you on having a fixed set with hand held for backup, but a hand held is far better than none at all. The next issue is taking the exam, and understanding these issues?
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Old 25 August 2004, 22:25   #65
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Originally Posted by Rogue Wave
where are the masts in the Solent other than at Lee.
That got me interested. I thought Needles had masts, but not sure? Do they have aerials at St Cats as well?
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Old 25 August 2004, 22:35   #66
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Quote:
Originally Posted by Powerboat
Hi Brendan,

If you look at Jon Broks later post you'll see where I was coming from with my 2 to 3 watts. Real output as opposed to nominal out put based on all the variables that Jon describes...connections, length of cable run, corrosion , type of antennae etc.


Stuart
Err! but you actually said 1-2 watts, and we were talking handhelds, so no probs with length of cable run, connections etc. A good handheld rated for 5W will put out pretty much that
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Old 25 August 2004, 22:40   #67
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Quote:
Originally Posted by Scary Des
Ive got to take the boat out later
My boat is Lymington too. Want to give this a crack? I've got cabin fever. I'll wear furry mid layer under drysuit this time, it got bleedin cold last time. If we can't get three boats out, I'll hang off a line from my boat while you do distance work. Serious!
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Old 26 August 2004, 04:03   #68
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The other thing with any hand held is that is standard antenna is not very efficient.

We try to make them as good as we can but its all about the "laws of physics Jim"

You are taking a 1/4 wave whip and turning it into a compressed spring.
So you have approx 450mm of wire wound into a length of 160-180mm.

The 5w is what comes out of the top of the unit not the top of the antenna.

So if it is a very poor helicoil you could end up with an ERP (effective radiated power) of a fair bit less.
It would be an average of 3db loss (so half power) I have seen tested (not ours!) that have massive loss.
So you end up with a watt or less being radiated.

Some more helpful stuff for you to chew over!!

Regards
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Old 26 August 2004, 04:47   #69
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Hi GingerCoastie & Des
Glad you got the Ducting bit done was going to mention that.
Best example I know was a shipping pilot in the persion gulf talking to a oil rig in N Sea and he had a hand held ( probbably throught a repeater I guess).
Now thats what you call a lift !! (Ham talk) only lasted 2-3 minutes.
Jelly
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Old 26 August 2004, 04:57   #70
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Quote:
Originally Posted by BrendanS
My boat is Lymington too. Want to give this a crack? I've got cabin fever. I'll wear furry mid layer under drysuit this time, it got bleedin cold last time. If we can't get three boats out, I'll hang off a line from my boat while you do distance work. Serious!
Its a plan , but we need the weather for 1 mtr waves, so any time during the summer I suppose.

Des
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