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Re: [Amps] 10dB and propagation

To: amps@contesting.com
Subject: Re: [Amps] 10dB and propagation
From: Ian White G3SEK <G3SEK@ifwtech.co.uk>
Reply-to: Ian White G3SEK <g3sek@ifwtech.co.uk>
Date: Mon, 7 Feb 2005 17:14:55 +0000
List-post: <mailto:amps@contesting.com>
Yuri wrote:
A non-linear medium would have to mean that your signal was directly
affecting the ionization density or the refractive index of the
troposphere. As I already said, that's wishful thinking at amateur
power levels.


OK, do some calculating:
During the contest, like CQ WW you would have on average about 600 stations
CQing their heads off with 1.5 kW into about 10 dB antennas. Some running
"plywood boxes" so err on the plus side. What do we get? Wishfull thinking?

Yes, wishful thinking still. Just try to put in some numbers.


The only information I've been able to find easily about non-linearity in ionized media, where they have done the work in a lab under controled conditions, refers to non-linearity observed at RF power input levels of "less than milliwatts per cm3."

Now if they had really meant that non-linearity was observed at power levels of only microwatts/cm3, they would surely have said so (because that would have been a much more interesting result); so it's pretty safe to take that statement of "mW" at face value. In handier units, 1 milliwatt per cm3 is one kilowatt per litre.

You, individually, have only 1.5kW of RF power available, which would only be enough power to drive a few litres of ionized gas into non-linearity, if you had it right there in a jar. But you are trying to zap a refraction volume that must total billions to trillions of litres, at a distance of hundreds to thousands of kilometres, so it's the Inverse Square Law that gets you.

Also, nobody else is heating up the ionosphere for you during CQWW. Even if you were using a refraction point right over Kilowatt Alley, all those QRO users have invested large amounts in achieving low-angle radiation themselves. That means they are in the same situation as your - contributing trivial amounts of energy to the ionosphere a long, long way away.

(I also feel extremely suspicious about the "Luxembourg effect", the claimed cross-modulation of the ionosphere by super-power BC stations. The first and most obvious question is: how much of the reported cross-mod effects are actually occurring in receiver front-ends?)


-- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps

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