Elecraft: Z Match tuner

[Martin.Evans]

Hi Guys, I have moved my shack to an upstairs bedroom and consequentially I
will need to feed my 130 feet wire at the end rather than at the centre (it
was a dipole fed with coax). I want to work 80/40/20m. I have made some
open wire feeder (about 15 feet) to get me from the chimney to the bedroom
and have left one end of the open wire feeder open circuit. I think I am
making a Zepp antenna.

Now to match this arrangement to my K1 on the above bands, I want to build
a tuner. I have just been looking at the design on this web site
(http://www4.tpgi.com.au/users/ldbutler/SingleCoilZMatch.htm) and it looks
just the ticket. It is suitable for balanced lines and would allow QRO up
to 100W in the future. Before I commence construction I just want to check
that it will match the very high Z of an end fed half wave wire.

Any thoughts.

Martin
M0KWV
K1 #1534


Why not take a look at our Web site?
http://www.simoncarves.com

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[Don Wilhelm-3]

Martin,

To be a Zepp antenna, the parallel feedline would have to be an odd multiple
of a quarter wavelength, and that quarter wave a;so serves in place of a
'counterpoise wire', so your 15 feet is a futile effort in that regard.
Just as well to use a single wire for the 15 feet to the end (and thaat
makes your end fed antenna 15 feet longer too).

You will also need something for a ground reference from your 2nd floor
shack location.  A ground (earthing)wire will have length to it and that
causes it to NOT be a good RF Ground.  You may have to resort to using a
counterpoise wire cut for each band.  Cut one insulated wire to 66 feet (80
meters), another to 33 ft (40 meters)  and another to 16 ft (20 meters).
Connect one end all of these wires to the ground point on your tuner, and
fan out the other ends as best you can.  Keep the far end of the wires
insulated and away from reach of people and pets because they will have high
RF voltage on those ends.  You may have to trim the wire length a bit to
make them resonant on each band, but doing so will eliminate RF in the
Shack.

73,
Don W3FPR

> -----Original Message-----
>
> Hi Guys, I have moved my shack to an upstairs bedroom and
> consequentially I
> will need to feed my 130 feet wire at the end rather than at the
> centre (it
> was a dipole fed with coax). I want to work 80/40/20m. I have made some
> open wire feeder (about 15 feet) to get me from the chimney to the bedroom
> and have left one end of the open wire feeder open circuit. I think I am
> making a Zepp antenna.
>
> Now to match this arrangement to my K1 on the above bands, I want to build
> a tuner. I have just been looking at the design on this web site
> (http://www4.tpgi.com.au/users/ldbutler/SingleCoilZMatch.htm) and it looks
> just the ticket. It is suitable for balanced lines and would allow QRO up
> to 100W in the future. Before I commence construction I just want to check
> that it will match the very high Z of an end fed half wave wire.
>
> Any thoughts.
>
> Martin
> M0KWV
> K1 #1534
>
>

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[Ron D'Eau Claire-2]

Don is right, about needing 1/4 wave of feedline (or an odd multiple
thereof) so it will act as a transmission line transformer to convert a high
impedance at the antenna to a low impedance at the rig. But that also
requires a high impedance feed at the antenna. That is, an antenna 1/2 wave
length or a multiple of 1/2 wavelength long. The true Zeppp is, in reality,
a single-band antenna!

His suggestion about just running a single wire is "spot on" in my book.
You'll want to arrange a counterpoise (either tunable for a 1/4 wave long
wire for each band). With a good, long wire like you have it won't be hugely
important as far as the efficiency of the antenna is concerned, but it will
serve to keep the rig at RF ground!  Indeed, the nearer your antenna is to a
multiple of a 1/2 wave on each band, the more efficient it will be.

Ron AC7AC

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