[Amps] 10dB and propagation

[Ian White G3SEK]

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