Posted by
Geoffrey Mackenzie-Kennedy on
Mar 16, 2009; 1:27pm
URL: http://elecraft.85.s1.nabble.com/43-Vertical-and-the-K2-tuner-tp2481408p2485984.html
Roy,
It is likely that a 40m 1/4 wave vertical and a 30m 1/4 wave vertical fed in
parallel, will exhibit about 3 - 4db less gain on 30m than if you used only
a 40m 1/4 wave on both bands. One reason for this is that when 40m and 30m
1/4 wave verticals are fed in parallel, the feedpoint impedance of the 40m
element is still low enough on 30m for the 40m element to absorb power and
affect the pattern of the 30m element.
This problem does not exist when feeding a 40m 1/4 wave in parallel with a
20m 1/4 wave, because on 20m virtually all of the RF power ends up in the
20m element.
Since you would have to use some form of matching network at the antenna in
any case, a 40m network and a 30m network would be required to match a 40m
1/4 wave vertical to a 50 ohm feeder on the two bands, unless you are
prepared to accept additional loss in the 50 ohm feeder by not using a
matching network at all. One option of course is to use relays to switch
networks when changing bands, another is to use "electronic switches" using
passive coils and capacitors instead of relays.
I have not looked at the actual feedpoint impedances to see if the matching
job could be done by using lengths of different types of coax in the main
feeder.
73,
Geoff
GM4ESD
Roy Davis <
[hidden email]> wrote on Monday, March 16, 2009 12:23 AM
>I am in the process of building a 40 meter 1/4 wave vertical. My hopes
>for
> this antenna is that when the conditions favor vertical antennas as
> opposed
> to a dipole, that it will help me to work in to the far East as my dipole
> does not. I understand that a dense radial field is necessary for good
> results and that the far field which I have no control is a factor. My
> plan
> is to use 64 insulated radials as close to resonant as possible, buried a
> few inches below soil. I thought of using ladder line as the radiator,
> cutting one side for 40 and the other for 30 meters supported by a
> catenary
> line. If that does not prove out, I have aluminum tubing which to make a
> 1/4 wave for 40. Anyone have any comments pro or con for my project? So
> far, I have the pipe in the ground, and the radials cut ready to attach to
> the DX Engineering radial plate.
>
> I have K3 #1366 and really like this radio. A lot to offer in such a
> small
> package.
>
> 73.
>
> Roy Davis - WK4Y
> Richmond VA
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