[TowerTalk] Beta match adds capacitive reactance on 2 el Hy-gain 40m ?

[Steve Hunt]

To transform 22-j25 close to 50 Ohms you need a shunt reactance of +j44
To transform 17-j24 close to 50 Ohms you need a shunt reactance of +j36

Hope that helps

73,
Steve G3TXQ


On 24/10/2012 10:21, DX Supply AB wrote:
> Hello!!
>
> Has anyone an answer to this Beta Match behavior on a 2 el linear loaded
> Hy-gain DIS 7-2?
>
> I have assembled the antenna again after some years in the garage. I
> designed it for SWR min at 7040 kHz and measured up the
>
> Feed point impedance at 30 feet to Z=17 --j24 after having shortened the
> driver a little more ( about 1 ½ ") than what is said in the manual. In line
> with theory for a linear loaded design. Increasing height to 60 feet I
> assume change (according to Cebik) the Z to about 22 --j25 or so. Not much
> change.
>
> According to theory (and W4RNL Cebiks excellent paper on web) the only thing
> now needed to tune out the capacitive reactance of --j24 is to add an
> inductance of about 33 ohms. This can be done with a Beta match and I
> started using the Hy.gain Beta match supplied with the antenna (1/4" x 72 "
> rods spaced 2,4 " from the boom). This way final impedance ens up close to
> 50 ohms which is good. However, inserting the Beta match worsened the Z to
> 32,5-42 that is adding both resistance and capacitive reactance to the feed
> point impedance. How an earth can the reactance be more capacitive with an
> inductive Beta match over the feed point?
>
> Is the best thing to throw the beta match over board an build a small
> inductor coil of 33 ohms?
>
> Thanking in advance,
>
> Kari SM0HRP
>
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