I have been building an antenna to take on a DXpedition in July to the South
Cook Islands. I have received many requests for dimensions and construction
details since this design was first mentioned on the reflector.
This design evolved from a simple 160M inverted-L to its present four-band
form, as I realized we would likely have some restrictions placed on the
number of antennas we could erect at the Rarotongan Resort Hotel.
The first 160M version was a straight forward 234/f length antenna with 60'
vertical and the rest horizontal. It only had 5 ground radials, each 133'
spread out and laying on the ground. It was fed with a 28:50 ohm Un-Un
(W2FMI design).
As I added traps to get additional bands, the overall length decreased. I
think the single band antenna would probably perform slightly better than
the final version.
Bandwidth is adequate on the final version, but not generous, except for the
narrow 30M band.
Ground losses for this design haven't been measured.
The feed point resistances and SWR figures below were obtained at the feed
point using an MFJ-259 Antenna Analyzer. A real nifty piece of test
equipment!!! It has a calibration error on the bands tested as indicated in
the notes below. It does give reliable indications when this factor is taken
into account.
On the air comparisons have been made between this antenna on 160M and my
full size insulated base 25G vertical with 30K' of radials under it. The
DXpedition model seems to get within about 6 to 10 dB (here to the east
coast regulars on 1850) of the full size counterpart. Separation between
these two antennas is about 1000'.
I present the final dimensions here that others might save themselves a
couple of saturday mornings for GOLF or some other activity. Building this
one and getting it to work should be a snap. If I had known how easy and
simple it was to do this, I would have done it many years ago.
===============================================================================
Dimensions To Trap Centers Fo SWR Feedpoint R
-------------------------------------------------------------------------------
Feed point to KW-30 = 21' 4" 10.12 mHz. 1.10:1 50
KW-30 to KW-40 = 7' 8" 7.05 mHz. 1.15:1 44
KW-40 to KW-80CW = 23' 3.61 mHz. 1.20:1 36
KW-80 to end insulator = 39' 1" 1.83 mHz. 1.60:1/(1.0:1 w/28-50 unun) 28
MFJ-259 resistance calibration: 50 ohms = approx. 42 ohms actual @ 1.0:1 SWR.
Feed point 1' 6" above ground, mounted on short ground rod 2' in earth.
Radials: 5 @ 133'
5 @ 68'
10 @ 33'
Wire use for the radiator and radials is #14 MTW (600 V Insulation). Using
bare copper wire for the radiator will be require these dimensions to be
increased by about 2%.
################################################################################
# The "Ugly-as-L" 160/80/40/30M DXpedition Inverted-L Antenna #
# Designed and tested by AA8U
#
############################################################################
#### # Tall
Tall # # Tree HI-Q Insulator HI-Q Insulator
Tree #
# O----5/32" Dacron-----====..........39'1".........====------5/32"Dacron----O #
# [=] KW-80CW
#
# : #
# :
#
# : #
# : 23' #
# : #
# : #
# : #
# [=] KW-40
#
# : #
# : 7' 8" #
# : #
# [=] KW-30
#
# : #
# : #
# : 21' 4" #
# : #
# : #
# X feed point (w/28:50 Un-Un on 160M) #
# : 1' 6"
#
# _____________________radials________________________ #
# (on ground) #
################################################################################
If you build one, let me know how this design works in your environment.
73 to all,
Bruce (AA8Ugly ZK1AAU)
aa8u@voyager.net
President: Mad River Contest Club
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