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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