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ohm coaxial cable off ce nte r will offe r a
fairly close impedance match between the
feedline and the slo t. The theoretical distance
fro m either en . of the slot is 1/20
wave lengt h, but the exact point must be
found experimentally for each installation as
surrounding structu res offer so me change to
the impeda nce characteristics. The " Ruleof-t
humb" is to start at the I/ 20 wavelength
point and work both ways until an optimum
match is achieved.
The aluminum foil "Slot" antenna is the
ultimate of simplicity in construction as ca n
to be seen fro m Fig. 4.
The figures in Columns A & B were
c o m p u t e d from Length (Inches) ­
5905f1'req (M llz) and will work as is, but
the figu re in Column C must be found t hru
trial and error. I found that the distance
from the end computed for 1/ 20 wavelength
worked better from the middle.
For the best operatio n so me method of
-
~
Al+ ' .. l • •
,
. I
~
. ~
o
bonding the coax to the sheet is necessary . I
found that transparent tape can be used with
little or no loss of power transfer if the tape
is tight over the coax cond uc tor and shield
whe re it comes in contact with the sheet.
After co nstructio n of the slot antenna
you should have so mething that looks like
(Fig. 5).
'S' X6 "
4 LU'" " UM FO'L
S..EE T iol/ ' T" S LOT - i-
CO ol, x CH H E" ''..-_
CO NO UC TOA:"
t'Tll'
FLOOR
Fig. 5 . Complete slot antenna. If moun ted
o n a door it ca n be rotated to cover all directions.
T he two major lo bes of this ante nna will
be through the slot, pe rpendicular to the
plane of the sheet. As seen from the top of
the antenna (see arrow in Fig. 5) you ca n
expect a pattern similar to that shown in
Fig. 6.
If this antenna ca n be mounted o n a door
, .~ ,~
( , ~ J Fe:E 0 eo,"T
I
i FAO"' E, r ..ER E" D)
.---
I -
Fig. 4 . The VH F Vacation S p ecial. 65"
sh ee t o f 18" w ide aluminum foil {e} . ( b)
using c h ar t 1 for measu r em en ts, and a single
edge razor blade, c u t out cen t er piece and
d iscard .
Distance
I:req A B C from cnd
Mll z Inches In ches In ches I used .
144.0 12.30 41.00 4. I 0 17.40
144.5 12.26 40.88 4.09 17.41
14 5.0 12.23 40.75 4.08 17.42
145.5 I 2. 18 40.60 4.06 17.43
146.0 I 2. 14 40.45 4.0 5 17.45
147.5 12.08 40.2 9 4.03 17.47
147.0 12.04 40. 13 4.01 17.49
147.5 I 1.99 39. 98 3.99 I 7.5 I 144. 0 M C
148.0 I I.95 39.83 3.98 17.5 2 tton.
slot antenna, hori zont al p clariaa-
MAY 1969 11