rf - Free and Open Source Software

'0'
'"
'0.
Fig. 2. T he direct r ea ding swr in d ica t or
w h ic h gives more accurate results.
can be eq uipped with a dial ca librated in
SWR: i.e., the midpoint wo uld correspond to
SWR = 3.0. The dial ca n be calibrated by
usc of an oh mm eter as fo llows:
Resistance (from
_po u n~__ ~_~L_
-
SWR
--
1.0 0
1.2 909
1.5 2000
2 .0 3333
3.0 50 00
5.0 6667
10 .0 8 182
20.0 9048
00 10000
The meter used in my version is a I MA
movement wit h a transistor a mplifier similar
to that described in January 1966 issu e of
73. The meter amplifier was built on an
etched circuit board for mounting directly to
the meter terminals. The meter scale is arbitrarily
calibrated wit h zero in the center. A
resistor (82K) is used in series with the base
lead to prevent cha nges in the ze ro-set when
R I is varied. My bridge has a positive output.
If the one to he used has a negative output
, the meter sho uld, of course, be reversed .
The use of this device is ex tremely simple.
T he transmitter is first tuned up using the
dunmy load . The antenna matching unit is
then connected to the transmitter through
the SWR bridge. The meter is set to zero.
and the transmitter is the n energized. Adjusti
ng R I to bring the meter back to zero
will then enable t he SWR to be read from
R1's dial. After this, any adjustment of the
antenna matching unit which ca uses a more
positive meter reading o n the SWR indicator
is in the right direction. The amount of Increase
in meter reading is a relative matter.
dcpending not o nly o n the SWR but also o n
the transmitter power. If the operator dCM
sires to determine the ne w (i mprov ed) SWR.
he ne ed o nly adj ust R I to bring the meter
back to zero and read off the SWR from the
ca librated dial.
Of course . the
usc of the direct-reading
BTl LK·2000
LINEAR
AMPLIFIER
For SSB, (W, RTTY
Maximun legal input
Full loading BO·l0M
Rugged Eimac 3.10002
Dependable operation
Easy to load and tune
No flattopping with ALe
Distinguished console
Instant transmit
High efficiency circuit
Designed for safety
Fast band sw itch ing
Real signal impact
Price •••. $795 0 0
RE A D Y TO OPERAT£I
I TI AMATEUR DIVISION
Hafstrom Technical Products
4616 Santa Fe , San Diega, Ca. 92109
A look at the interior. Obviously a simple
device to build.
SWR indicator is not limited to tuning ant
enna matching networks. It can be used by
anyone who would prefer its simplified SWR
readout. If R I is se t to a higher SWR than
that actually existing, a positive meter reading
results, and the transmitter can be tuned
for maximum output by maximizing the
reading, just as in using the co nventio nal indicator
in the FWD position. ... K3WRW
M A Y 1969 6 1