On Sun, 11 Apr 1999 21:55:17 -0600, Gary McDuffie, Sr. wrote:
> Has anyone experimented with moving the TH-7 down band?
Well, I promised a digest, but now that I have had time to catch up on
the list, I see most of it has been posted by others. I won't duplicate
everything, but will say Roger Cox had recommended two "newer" settings
since the original book was printed. The DX settings move the VSWR
curves lower in all three bands, giving suitable performance from the
bottom of CW through the mid phone band. There are also a CW settings
that are lesser known according to respondents. Predicted curves
weren't given, but it may be worth playing with. I'll be trying them.
The lengths changed are only on the two driven elements, inside the
first trap. As of this morning's comments from Roger Cox, he cannot
recommend changing parasitic element lengths at this time, as the
performance has not been confirmed under those conditions.
Stating the obvious for the novice, these changes will sacrifice the
VSWR at the top of the bands. I get a nose bleed higher than 14.220
anyway. ;o)
DX settings (Hy-Gain):
FDE-2 = 42 inches (previously 40")
RDE-2 = 33 inches (previously 31")
Moves resonance to 14.140, 21.250, and 28.950 with the bottom of each
band at approximately 1.5:1.
Later quote from Roger:
VSWR at the bottom of each band are:
28.0 1.6
21.0 1.7
14.0 1.5
CW settings (Roger):
FDE-2 = 43 inches (previously 40 inches)
RDE-2 = 34 inches (previously 31 inches)
No VSWR predictions given
A notable quote from one of Roger's early messages when speaking of the
CW settings:
"RDE-2length is 36", so there is still 2" insertion. You could possibly
go another inch on each dimension, but I would replace RDE-2 first.
Recommended insertion minimum is (3 X DIA)."
In other words, if you play, pay attention to proper overlap at the
joints to maintain mechanical integrity.
Thanks again to all who responded, especially the calls listed below.
WA7MIG
WØUN (by way of quoted note from someone else)
W8IK
K8LN
WBØDGF
For those who asked, I'm sorry to say I won't be at Dayton this year.
73, Gary - AGØN
web: www.scottsbluff.net/~mcduffie
E-mail: mcduffie@scottsbluff.net
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