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[TowerTalk] Increasing Hygain Tribander BW

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Subject: [TowerTalk] Increasing Hygain Tribander BW
From: (Ed Jensen)
Date: Thu, 27 Mar 1997 10:11:50 -0600
The restricted SWR BW of single D.E. Hygain tribanders was mentioned in  the
thread on TH6's.  I also had a real problem with SWR BW (starting in 1978
when I bought my first solid state transceiver) and thought some might be
interested in the following.

I modified my Hygain tribander (an extended TH-3 built from combining parts
from a "TH-4" and TH-5) to increase the BW by eliminating the beta match and
off center feeding the D.E.  This technique might work for other Hygain

I off-center fed the D.E. by making one side longer and the other side
shorter while observing the swr. I was not able to center the swr on 10 and
15 due to limits on shortening the elements and interaction with 20m with
which I was mainly concerned.

I used a simple RF choke (35 turns on a 1" PVC form) between the center of
the D.E. to replacethe  DC ground between the elements that the beta match

The results were (measured with MFJ-259):

freq           swr spec       swr modified
14.0         1.8                    1.3
14.15       1.1                    1.0
14.25       2.0                    1.3
14.35       NA, >2              1.8

21.0         NA,>2                2.5
21.1         1.6                     1.8
21.2         1.3                     1.3
21.3         1.8                     1.2
21.45      NA, >2                2.0

28.0         1.5                     1.0
28.3         1.2                     1.0
28.6         1.7                     1.4
28.9        NA,  >2               1.9

I think this technique works because it eliminates the beta match
transformer which inserts another frequency sensitive element in the antenna

73, Ed

PS: Re the thread regarding SWR meters. I have both the Autek RF-1 and
MFJ259 and don't use the RF-1 anymore to tune antennas.  It's just too
unhandy to use.  The MFJ is very quick and easy to use.  The RF-1 is good
for measurements after the tuning process over though.

PPS: I don't like antenna tuners because they can have significant losses
and also slow down frequency changing.

PPPS: I also don't like traps because I think they have significant losses
when used in the resonant condition (every trap failure in which I know the
circumstances occurred when the trap was resonant, ie the 15m trap failed by
overheating (melting, charring, flaming) when the antenna was being used on
15m).  I plan to replace my TH3x this summer with a beam that uses full size
elements.  If anyone has first hand info on the little Tennadyne( LP5 I
think) or the C3S (I'm limited in the size of the antenna I can put on my
tower), I would like to hear it.
Ed Jensen, K5ED or

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