[Elecraft] KX1 + Tuner + Norcal Doublet

[Steve Ellington]

That's a bad design for 40m because the input resistance is only about 3 
ohms. The designer was concerned about the radiation pattern resembling a 
dipole on higher frequencies with little regard to matching.

Using a 4:1 balun would do the opposite of what you want to accomplish. 5 
ohms is difficult for any tuner to match and can cause a lot of power loss 
in the circuit and with higher power, burn up a torroid coil! That balun 
would drop the impedance to an insane value.

Generally a multiband doublet should be 1/2 wavelength on the lowest band. 
That's about 65 feet for 40m cw. Also that feedline that the author used no 
doubt has a rather low impedance which further complicates things. I'de 
guess it is about 100 ohms. Using 300 tv twin lead would help raise the Z 
for your tuner to about 15 ohms on 40m even with the 44' flat top. Try that 
first.

If all else fails, tie the feeders together and feed it like a long wire 
against a counterpoise.

Steve
N4LQ
----- Original Message ----- 
From: "Burke Jones" <burkejones at gmail.com>
To: <Elecraft at mailman.qth.net>
Sent: Friday, June 03, 2011 2:44 PM
Subject: [Elecraft] KX1 + Tuner + Norcal Doublet


>I constructed a Norcal Doublet using some speaker wire.  It seems to
> tune up fine on 20 meters using the internal KX1 tuner - but on 40
> meters I could not get the SWR under 4.
>
> Would a 4:1 balun help with this?
>
> Any links on how to build a simple balun using an aircore and not a 
> torroid?
>
> Thanks a bunch!
>
> Burke Jones
> N0HYD
> Olathe, KS
> http://www.n0hyd.com
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