[TowerTalk] Beta match adjustment

[Tim Duffy K3LR]

Hello Scott,

You can easily match 26 ohms (with no reactance) to 50 ohms with a one
quarter wavelength piece of RG-83 coax (35 ohms) in series. Simply attach
the proper length of RG-83 (246/F x VF = length in feet - about 23 ft) in
series with the antenna feedpoint and 26 ohms will become very close to 50
ohms - connect your 50 ohm coax and you are done!

Easy and no adjustments needed.

Consult with Davis RF for the RG-83.

73,
Tim K3LR

http://www.k3lr.com




-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Scott Yost
Sent: Saturday, July 17, 2010 3:27 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Beta match adjustment

Are there any beta match experts onboard who could give me some guidance in
adjusting a beta match on a 40m beam?



I built a 40m 2 element Yagi.  Physical detail on the antenna can be shared
if pertinent.  It plays well, but I would like to utilize a DXE beta match
to see if I could improve the match.



I have an antenna analyzer thus can measure a variety of antenna parameters.
At my frequency of interest, R=Z @ 26 ohms, and an angle of 0 degrees.  This
is without the Beta in place.  Beta in place has yielded no worthwhile
results, regardless of setting.



The antenna is on a tilt over/crank down tower so I can access it at ground
level to work, but would like to minimize the number of times my XYL has to
crank the tower up and down.  (That was a joke.  She actually does help me,
though.)



So how does one configure a beta match?



The info that came with the beta match suggests experimenting with the match
and driven element length to tune it at ground level, but the info with it
is vague as to the process.  And, I can't uncover a correlation that would
permit me to pre-tune it at ground level that translates to being tuned when
raised on the tower at 65 feet.



I have searched the Tower Talk archives and while I uncovered a lot of good
information, the key to tuning the beta match still eludes me.



Many thanks.



Scott

NM8R
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