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Old 26 August 2004, 08:03   #71
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For those really interested in "Ducting" I have found you a website.


http://home.cogeco.ca/~dxinfo/tropo_nwe.html
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Old 26 August 2004, 13:33   #72
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Attenuation

Hi Brendan,

I refer you to Jon's post below.

As someone who deals with hand helds and field VHF equipment daily for the last 20 years, I would instinctively think of 1 or 2 watts when thinking hand helds. Hence my mention earlier (Like Jon) of effective "radiated Power" or what makes it out of the antenna.

As we all seem to have said, there are a lot of variables once you introduce weather and people to an exact science ! So always I guess, err on the side of caution on your equipments capabilities!

Kind regards,

Stuart




QUOTE=Jon Brooks] 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 [/QUOTE]
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Old 26 August 2004, 13:46   #73
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Do I get an award for starting this massive thread? It has helped though as my new handheld arrives on Tuesday and the fixed vhs will be purchased at the boat show and installed shortly after. Will go away now and try to think of another topic to get you all going.....

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Old 26 August 2004, 13:58   #74
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Happy Ending !!

Nice to know that there was a happy ending Ollie !!

Stuart
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Old 26 August 2004, 17:50   #75
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Originally Posted by qcamel
Will go away now and try to think of another topic to get you all going.....

Ollie
Excellent, this one was great fun!
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Old 26 August 2004, 17:55   #76
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Quote:
Originally Posted by Powerboat
I would instinctively think of 1 or 2 watts when thinking hand helds.
Stuart, That's very reasonable in the context you quote, though most people are going to assume that low power has been selected, as that is what handhelds are rated in, 5W high power, 1W low power .....though as stated, power from aerial is somewhat different. I've always assumed handheld aerials to be pretty inefficient, but never seen any numbers around it before now.

Great informative thread, and look forward to meeting up with Des to try some experiments.
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Old 26 August 2004, 17:58   #77
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Cheers, Brendan and Des for having the guts to give it a try. Rather you than me!!! Let us know when it's happening - maybe we could all come and watch. It could be the start of a whole new section - Put To The Test By Real Ribsters! You could test something every month, say.
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Old 26 August 2004, 18:00   #78
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Hi Des - can't remember off hand. Will get Richard to post when he gets home - he usually has a better memory for these things than I do!
Louise, we won't accept anything other than the result of a real test.

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Old 26 August 2004, 18:02   #79
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Old 26 August 2004, 18:09   #80
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Quote:
Originally Posted by Jon Brooks
So if it is a very poor helicoil you could end up with an ERP (effective radiated power) of a fair bit less.
My experiment was with an M1 Euro V which I know gives better transmit and reception than many handhelds, so the figures I came up with (miles) had better be revised down for many sets! What does the Euro V transmit at the aerial?

If Des and I do the rough water test, we'd better accumulate a good selection of different sets to make it worthwhile (and all of them had better be waterproof, cos they are going in the water with me! )
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