I built a 40M EFHW with a home brew 30M LC trap wound on some PVC and
using a doorknob cap off of Ebay to form a "dual bander"
It's oriented almost vertically, with the feed point 4' off the ground
with the 2x 2.4" type 43 toroids. mounted in a vented plastic box
using the popular drawings downloaded from the web and a small cap.
The far end is held up by cord over a tall maple branch. It's
probably 80-85 deg to vertical.
SWR on the low end of 40 is almost unity and a bit higher ~ 1.2:1 on
30M... not worth me mucking around to potentially improve. It's
mounted to a chain link fence rail . There's an extensive rats nest of
wires on the forest floor also as radials and it's hooked to the
tower's ground field as well (six 8' ground rods / #4 copper wire)
It is 2 or more S units better on 30M than a 1/4 wave WARC trap
vertical mounted on the same fence rail on most signals
It's generally down an S unit compared to the Alpha Delta 160/80/40
sloper fed at 40' on 40M. It is much quieter than the AfD sloper
though.
I just rebuilt the Cushcraft WARC dipole element and will be able to
compare 30M performance to the 30M EFHW trapped section, but I'm
pretty sure the dipole will be better when aimed correctly. ( It's
claim to fame is that I worked Bouvet last time on 30 with 200W from
NC ) :-)
No chokes used at the feedpoint . No heating noted through the vented
Chinesium grey plastic box when fed 800W of CW with normal QSO duty
cycle. I should take the cover off, send a long CQ at power and
measure the core temps with the IR temp gun.
I would not expect a traditional center fed vertical 1/2 w dipole to
perform any differently , but I've been wrong before and all I know
about NEC is that they used to make a lot of uP chips.
John K5MO
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|