Posted by
W8JI on
Jun 06, 2010; 1:00am
URL: http://elecraft.85.s1.nabble.com/K2-ATU-and-43-ft-Vertical-tp5144100p5144389.html
> Does anyone have any experience with trying to match one
> of these 43-ft
> verticals, that are being offered by several
> manufacturers, using the K2s
> internal ATU? Is it able to find a match on 80-meter CW?
> Are there any
> particular brands of 43-ft verticals that you like or
> don't like? Most of these
> verticals that I have seen are in the mid to upper $300
> range, except for the
> fiberglass one from S9 Antennas. Any opinions on that
> particular antenna?
Paul,
I know power limits are not the problem with the K2
barefoot, but consider on 80 meters the base impedance of a
fat 43 foot vertical with a modest radial system is about
12 - J 290 ohms. It would be worse with a thin wire. You
would have to supply almost 1200 volts peak at almost 3
amperes to the antenna base to apply 100 watts on 80 meters.
Since the 50 ohm SWR is over 100:1 on 80, it would be very
difficult to get a significant percentage of your
transmitter power into it on 80 (and impossible on 160)
unless you put a real matching system right at the antenna.
(and no, an unun is not a matching system and won't fix 80.)
On 60 and 40 meters things are OK. SWR is under 6:1 so
feedline efficiency would be OK without the unun.
On 30 and 20 things are tough again, but far more workable
than 80 and the unun at the base would help. Without the
unun SWR is about 30:1. With the 4:1 unun maybe 8:1 SWR.
Personally the only way I would have an antenna like that is
if I remoted a good tuner right at the base. Otherwise I'd
buy a trap vertical like a 6BTV or that Butternut vertical
that actually has things that act like traps but that are
not called traps by name. Overall, unless you put a tuner
very close to the antenna, a trap vertical would work a
whole lot better.
For 80 you could base load the thing, and a 43 foot vertical
with a good ground would be decent. Just make sure the
antenna has a good base insulator, because at 100 watts
you'd have over 1000 volts at the antenna base. DX
Engineering has the best mechanical construction and a very
good base insulator.
73 Tom
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