Heathkit THE TWOER - Page 52

Page 38
ANTENNA
FEED
OR MATCHING
SYSTEM
The antenna connector on your "Twoer" is de-
signed for an unbalanced transmission line of
50-75 ohms (coaxial cable). Frequently antenna
systems are designed to be fed with 300 S2 twin
lead or "ladder lines." A
simple balun system
shown in Figure 13
or Figure
13A,
will provide
the conversion from a 75 EZ unbalanced to
300 S2
balanced line and may be used at either end of
the transmission line.
For normally short runs of transmission line,
either coax or twin lead may be used. For long
runs, coax will have considerably more loss
than twin
lead or ladder line. If twin lead
transmission line is used to the antenna, the coil
type balun (Figure 13A)
will work well. If the
balun is used at the antenna (using coax as the
transmission line), the coaxial balun (Figure 13)
is preferred due to its exposure to outdoor con-
ditions.
Figure
13B
is a schematic view of a balun coil.
For experimental purposes only, certain types of
television antennas will work to a fair degree
at 144 mc. The notable one in this category is
a conical type in which case the coil balun
would be used to feed the 300 n TV twin lead to
the antenna. In general, most TV antennas will
NOT perform well on two meters.
1:4
UNBALANCED
INPUT
(COAX)
7511
1:1
UNBALANCED
INPUT
(COAX
7511_
300 n.
BALANCED
TO ANTENNA
TAPE
I -
TRANSMISSION
LINE TO
ANTENNA
4'1'1
Figure
13B
CONNECT
3 SHIELDS
(TAPE AND SEAL)
COAXIAL CABLE
LOOP, ELECTRICAL
ALF-WAVE LENGTH
(APPROXIMATELY
251"- LONG)
75 11
PLUG FOR ANTENNA
UNBALANCED
JACK ON TWOER - CENTER
COAX CONDUCTOR TO PIN,
OUTER COAX SHIELD TO
PLUG FRAME
Figure 13
Figure 13A
0
BALANCED
OUTPUT
PARALLEL
CONDUCTOR
LINE
3001E
0
BALANCED
4,-o OUTPUT
PARALLEL
CONDUCTOR
LINE
0 7511
PAIR OF TV
'ELEVATOR COILS
TO 300 0
TWIN LEAD