Dear Group,
Rik and Jean Pierre were asking about the new aerial here.
Jean-Pierre sent yesterday a series of captures from 2208-0730
showing much variation in the signal levels on 477.7 kHz.
They were quite strong between 0330 and 0500 though there
were other peaks and complete fades during the night.
Many thanks Jean-Pierre.
Here are the details about the "Rotated L" now on the air on 477.7 kHz.
Comments and critiques are most welcome.
The current was read with a clamp-on ammeter which was then
calibrated by measuring current through a 50 ohm load. The
wattmeter power was 70 watts but the scope was showing 200V p/p
which is 100 watts. Perhaps the wattmeter is reading low.
It had a nasty accident with a Decca, was repaired but not properly
recalibrated. Assuming the scope is the more accurate, the current
was I=P/V=100/71=1.4 A. Scaling the aerial current accordingly
yields 1.6 amps.
The RL extends from the feedpoint up 27 metres and slopes down to
12 metres over a 100m span. The mean height is about 18 metres.
It is fed with ~50 uH of tuning; no R matching was needed.
A 30m vertical has Rrad~1 ohm on 630 metres. The ON7YD page gives
an expression for Rrad for a horizontal top load, but the RL is
sloping this will reduce Rrad. Let's guess that it's 2 ohms
So... ERP=I^2R= 2.6 R or about 5 watts.
I'd best crank the variac down a few notches to keep it legal!
73
Joe VO1NA
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