Earl-K6SE wrote:
...SNIP...
> An EZNEC model shows that if the inverted L is 100' vertical and 57'
> horizontal, at 1830 kHz the impedance at the base will be 50 + j174.1
> ohms over a good ground system. A series capacitor at the base of about
> 498 pF will cancel the inductive reactance, giving a perfect match to
> 50-ohm coax.
I just helped install an "L" at a friend's station a couple of weeks ago.
>From the ground system, a 500pF capacitor, up ~ 45', and straight out about
125' gave the same results.
We just cut the top section quite long, trimmed until the reactive component
matched the capacitive reactance of the door knob cap at 1840. Poof!
Success. The SWR was about 1.5 at 1.8MHz and then dropped to about 1.25 at
1840, then up to 2:1 at 1.9MHz. Very manageable. If my memory serves me
right, the "R" value was just below 50 ohms.
I used the same technique on my tower inverted L and only spent about 20
minutes messing with the length of the top hat. Very easy to tune with my
Autek VA1.
Ford-N0FP
ford@cmgate.com
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