Hi Joe the sloping top would reduce thr Rrad a little so <1ohm ....crank the
Variac back upagain :-))
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, January 29, 2015 1:09 AM
Subject: LF: RL aerial
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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