T-MATCH
Construction
The
T-Match with its balanced feed point is one method of feeding a
SCHEMATIC:
Spacing between Arms & Dipole can be anything convenient for construction
6m
***** 6m Antenna T - MATCH *****
FREQUENCY of the Antenna (Mhz) 50
LAMBDA 5995.85 mm or 236.057 ins
DIPOLE 2836.04 mm or 111.655 ins
DIPOLE DIAMETER 12.7 mm or 0.5 ins
ARM LENGTH 709 mm or 27 ins
ARM DIAMETER 6.3 mm or 0.25 ins
ELEMENT SPACING: make it convenient for construction
*****
4:1 COAXIAL CABLE BALUN *****
The frequency selected is:
50 Mhz
The coax you selected is:
RG-213/U
The velocity factor of the coax selected is: .66
The physical length of a half-wave coaxial (4:1)
Balun is: 1978 mm or 77
ins
2m
***** T - MATCH *****
FREQUENCY of the Antenna (Mhz) 144.300
LAMBDA 2077.56 mm or 81.794 ins
DIPOLE 982.69 mm or 38.688 ins
DIPOLE DIAMETER 4.765 mm or 0.187 ins
ARM LENGTH 245 mm or 9 ins
ARM DIAMETER 4.765 mm or 0.187 ins
ELEMENT SPACING: make it convenient for construction
***** 4:1 COAXIAL CABLE BALUN *****
The frequency selected is:
144.3 Mhz
The coax you selected is:
RG-213/U
The velocity factor of the coax selected is: .66
The physical length of a half-wave coaxial (4:1)
Balun
is: 685 mm
or 26 ins
(NOTE: The
PHYSICAL LENGTH is for the shield. Keep the center conductor as
short as possible. Keep the
insulation long enough for high power.
Example: for 432 Mhz use a 5 mm or .197 ins length of insulation.)
*****
BALUN CHECKING PROCEDURE *****
To make or check a 4:1 balun when the velocity may be unknown use a
.7 factor and cut the coax
longer than the formula indicates for the shield. Cut
the leads as short as possible but to a useable length, short them
together on one end.
On the other end connect the leads together to form a
small loop. Use a grid-dip oscillator (GDO) with minimum coupling to the
loop and tune for a sharp dip.
Adjust the GDO while listening for the GDO on
your receiver. Reduce the length of the coax in small increments until the
frequency on the receiver
approaches the desired frequency. With
each adjustment
keep the leads just long enough to make the connections.
70cm
*****
T - MATCH *****
FREQUENCY of the Antenna (Mhz) 431
LAMBDA 695.57 mm or 27.385 ins
DIPOLE 329.01 mm or 12.953 ins
DIPOLE DIAMETER 4.765 mm or 0.187 ins
ARM LENGTH 82 mm or 3 ins
ARM DIAMETER 3.175 mm or 0.187 ins
ELEMENT SPACING: make it convenient
for construction
*****
4:1 COAXIAL CABLE BALUN *****
The frequency selected is:
431 Mhz
The coax you selected is:
RG-213/U
The velocity factor of the coax selected is: .66
The physical length of a half-wave coaxial (4:1)
Balun is: 229
mm or 9 ins