MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
31
WARNING
: ALWAYS CONNECT THE COMMON (ROTARY CONTACT) OF THE SWITCH TO THE
TUNER. THE SWITCH MUST CONNECT EITHER THE MFJ-269D OR THE STATION
EQUIPMENT TO THE TUNER.
TRANSMITTING EQUIPMENT MUST NEVER BE
CONNECTED TO THE MFJ-269D.
1.
Connect the MFJ-269D to the tuner input.
2.
Turn on the MFJ-269D and adjust it to the desired frequency.
3.
Adjust the tuner until the SWR becomes unity (1:1).
4.
Turn off the MFJ-269D and re-connect the transmitter.
7.5
Adjusting Amplifier Matching Networks
The MFJ-269D can be used to test and adjust RF amplifiers or other matching networks without applying
operating voltages. The tubes and other components should be left in position and connected so that stray
capacitance is unchanged.
To measure input circuits
, a non-inductive resistor equaling the approximate driving impedance of each
individual tube is installed between the cathode of each tube and chassis.
To measure tank circuits
, a resistor equaling the calculated tube operating impedance is connected from
the anode to the chassis with short leads.
The antenna relay (if internal) can be engaged with a small power supply. The amplifier’s external RF
input and output connectors are now connected to the amplifier’s RF matching networks.
The appropriate network can now be adjusted. When the analyzer shows 50 ohms and a 1:1 SWR at the
operating frequency with the proper amounts of capacitance to set the system Q, the networks are
working.
CAUTION
:
The driving impedance of most amplifiers changes as the drive level is varied. Do not
attempt to adjust the input network with the tube in an operating condition with the
low level of RF from the MFJ-269D.
7.6
Testing RF Transformers
RF transformers designed to operate with 10-1000 ohm termination on one of the windings can be tested
with the MFJ-269D.
The 10 to 1000 ohm winding is connected through very short (less than one electrical degree long) leads
to the
Antenna
connector on the MFJ-269D. The other winding(s) of the transformer is terminated with
a low inductance resistor equal to the desired load impedance. The MFJ-269D may then be swept
through the desired transformer frequency range. The impedance and bandwidth of the RF transformer
can be measured.
Transformer efficiency can be measured by comparing the source voltage from the MFJ-269D to the load
voltage, and using standard power level conversions. A second method is to NOT terminate the
transformer and measure the winding at it’s design operating impedance in
Advanced-2
Coax Loss
mode. Set the analyzer at the winding operating
Zo
value. Approximate loss can be measured using the
same method as measuring a transmission line.
7.7
Testing Baluns