MFJ MFJ-852 User Manual
MFJ-852 Instruction Manual AC Line Noise Meter
INTRODUCTION
Congratulations on purchasing the MFJ-852 AC Line Noise Meter. Like
professional RFI trackers used by utility companies, your MFJ-852 leads you to
trouble spots fast. Here are some important features:
VHF Design: The MFJ-852 operates at 135 MHz where antenna length is short,
on-air interference is minimal, and RFI is localized easily for accurate tracking.
Wideband IF: 100 kHz IF bandwidth provides optimized noise sampling.
1 uV Sensitivity: Picks up all noise signatures, weak or strong.
Semi-Log Metering: Semi-log metering system covers a wide signal range
without the need for add-on step attenuators.
Balanced Antenna: Built-in collapsible dipole is decoupled from case
electronics and headphone leads to deliver a clearly-defined null. Locates RFI
sources easily.
Audio Jack: Plug in stereo or mono type headphones for audible monitoring, or
connect a portable cassette recorder to make sound recordings for later analysis.
Many powerline faults have identifiable noise signatures that experienced
powerline technicians can identify easily--even over the phone!
Battery Indicator: LED power indicator also monitors battery status--let's you
know when it's time to replace the battery before the meter stops working
properly.
Tracks Many Types o f RFI: In addition to transmission line noises, the MFJ852 also ferrets out residential and industrial noise sources such as electric fence
arcs, sparking power equipment, poorly suppressed specialty lighting, and much
more. Give your claims added credibility by showing the owners of defective
equipment where the problem is being generated--and letting them hear what it
actually sounds like!
Fully Portable: Compact hand-held size and built-in battery power let you to
explore freely in search of trouble spots.
Always Available: Many power-related noise problems are intermittent and
rarely occur when power company engineers are in the neighborhood with the
RFI truck. With the MFJ-852, you can capture the data you need instantly-when its happening!
Be a detective and put the fun back into Ham Radio! In addition to solving
problems in your own neighborhood, this is a great way to lend assistance to
friends or fellow club members who are having problems of their own. When
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MFJ-852 Instruction Manual AC Line Noise Meter
power companies get a concise description of the noise and a specific pole
number, you get much faster service!
SPECIFICATIONS
Operating Frequency: 135 MHz (internally tunable)
Receiver Sensitivity: .3 uV for audible detection
Meter Sensitivity: <2 uV for usable deflection
Meter Range: 50 dB, semi-log response
Receiver IF Bandpass: 100 kHz
Audio Output: Fixed, headphone level (line level for record)
Power Source: Self-contained, 9 volt flatpack battery
Current Drain: 30 mA
Antenna: Choke-balun-decoupled collapsible dipole
CONTROLS AND LOCATIONS
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MFJ-852
AC Power-Line
Monitor
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3
1. Collapsible Antenna: Extend full length for maximum sensitivity and best
directivity. Best pick-up sensitivity is obtained when dipole is broadside to
the source. A pronounced null is obtained when dipole is 90-degrees to the
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Power
MFJ-852 Instruction Manual AC Line Noise Meter
source. Length may be shortened to reduce sensitivity for extremely strong
RFI sources.
2. Headphone Jack: Connect standard stereo or monaural type headphones
using a 3.5 mm plug. Also, the headphone jack may be used to feed a
portable cassette recorder (line-level input)--or even a portable oscilloscope
for complex waveform analysis.
3. Power Switch: Press in to apply power to unit.
4. Pow er/Battery LED: Illuminates when po wer is ap p lie d , e xtingui shes when
battery voltage drops to a marginal level.
5. Meter: Semi-log metering system displays wide signal range with more
resolution at the low end of the scale.
HUNTING DOWN NOISE ON THE POWER LINES
Most utility-line noises comes from arcing or corona. Arcing (or sparking)
happens when 60 Hz AC swings to its e xtreme plus or minus value. This can
induce voltage in associated wiring and hardware that arcs across an imperfect
insulating medium. The resulting RFI often appears as a 120 Hz AM modulated
buzz or hum. Corona happens when a discharge occurs in ionized air rather than
through a d ischa r ge p ath to gr ound . Co ro na may pr od uc e a more co nsta nt no ise ,
frying, or even a hi gh-pitched whine.
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Arc
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Energy on
AC line
Arc
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Off-Air RFI60-Hz
120 Hz Buzz
The distance powerline RFI propagates usually drops rapidly as monitoring
frequency increases. A noise that's received for a mile or more in the AM
broadcast band may only be detectable for a hundred feet or so at 130 MHz.
That's why utility companies use handheld VHF-AM receivers instead of HF
radios to zero in on line noise problems.
RFI
Strength
10 MHz130 MHz
Distance from Fault
1 MHz
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