MFJ-269 Instruction Manual HF/VHF/UHF SWR Analyzer
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1.) 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.
2.) To measure tank circuits, a resistor equaling the calculated tube operating impedance is connected from the
anode to the chassis with short leads.
3.) 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-269.
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-269.
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-269. The other winding(s) of the transformer is terminated with a low
inductance resistor equal to the desired load impedance. The MFJ-269 can 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-269 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’s 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
Baluns can be tested by connecting the 50 ohm unbalanced side to the MFJ-269 "ANTENNA" connector. The
balun must be terminated with two equal value load resistors in series. The resistor combination must have total
resistance equal to balun load impedance. For example, a pair of 100 ohm carbon resistors are required to
properly test the 200 ohm secondary of a 4:1 balun (50 ohm input).
Measure SWR while moving a jumper wire from point "A" through point "C".
Voltage and current balun test:
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