MFJ MFJ-762 User Manual
MFJ-762 Instruction Manual Step Attenuator
MFJ-762 STEP ATTENUATOR
Introduction
The MFJ-762 Step Attenuator is ideal for any application requiring a low power
50 ohm attenuator that operates from dc to lower UHF.
The MFJ-762 Step Attenuator can be used to prevent front end overload or as an
"isolation pad" to p roperly terminate filters and/or preselectors. Common uses
include receive signal reduction for tr ansmitter hunting, a standard dB refer ence
for S meter scale calibration, a dB change reference for antenna comparisons,
and many other low-power signal level attenuation applications.
The MFJ-762 Step Attenuator provides attenuation values to 81dB in one dB
steps. The maximum power rating is 125 milliwatts (1/8 watt) and the usable
frequency range extends into the UHF range. T he input and output c onnectors
are standard 50 ohm BNC females.
Specifications
Connectors........................................ BNC female
VSWR..............................................<1.25:1 from dc to 170 MHz
(worse case for all values of attenuation)
Bypass Loss...................................... <0.65 dB at 170 MHz
<2 at 500 MHz
Power Rating.................................... 125 milliwatts continuous
Attenuation Steps ............................. 1dB, 2dB, 3dB, 5dB, 10dB,
and (3) 20dB steps.
Attenuation Accuracy....................... 0.2 dB or 5% of total attenuation,
whichever is greate r
<1.6:1 from 170 to 500 MHz
(typically <1.1:1)
(typically <1.1:1)
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MFJ-762 Instruction Manual Step Attenuator
Operation
The MFJ-762, like all constant impedance "pi" or "T" attenuators, is a bidirectional device. It simply connects in series with the signal path, the direction
is not important.
Be sure to never exceed 125 milliwatts of applied power, especially with higher
attenuation values.
Like all 50 ohm attenuators, the attenuation is most accurate when the attenuator
is correct ly terminated. If the loa d impedance is unknown or the impedance is
not perfectly matched, use at least 10 dB of attenuation before depending on
accurate level changes. If this advice is not followed, the first several dB of
attenuation might produce more or less attenuation than expected. In other
words, if you have a receiver with unknown input impedance and you want to
accurately check the S-meter, start the reference with a 10 dB (or larger)
attenuator in-line before making any changes. This simple step ensures any
additional attenuation will provide very close to the marked signal level change,
even if the receiver input impedance is other than 50 ohms pure resistance.
WARNING: Never transmit through the MFJ-762.
Technical Assistance
If you have any problem with this unit first check the appropriate section of this
manual. If the manual does not reference your problem or your problem is not
solved by reading the manual you may call MFJ Technical Service at 601-323-
0549 or the MFJ Factory at 601-323-5869. You will be best helped if you have
your unit, manual and all information on your statio n handy so you can answer
any questions the technicians may ask.
You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial
Park Road, Starkville, MS 39759; by Facsimile to 601-323-6551; or by email to
techinfo@mfjenterprises.com. Send a complete description of your problem, an
explanation of exactly how you are using your unit, and a complete description
of your station.
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