MFJ-852 Instruction Manual
AC Line Noise Meter
4
Due to standing waves, RFI varies in intensity along the powerline. This makes
precise tracking at HF nearly impossible. However, near the fault, HF peaks
occur progressively closer together and amplitude becomes more constant,
signaling a "ballpark" location.
Use car's AM radio to find general area. Use MFJ-852 to find the exact source.
RFI Intensity
A good way to track residential RFI is to tune your car's AM radio to an open
channel near the high end of the band. Drive around the affected area looking
for a location where the RFI seems to peak up and hold relatively constant.
When you find a "getting-warm" zone, get out of the car and use the MFJ-852 to
look for a source (usually a specific pole). You should see (or hear) a null in the
RFI noise when the antenna tip is pointed at the source. If possible, get out from
under overhead wires and well off to one side to pinpoint source. When you
think you've isolated the source, write down the pole number.
Occasionally, the RFI source may be visible from the ground (a branch on wire,
etc), or audible (a buzzing or frying sound). At night, corona or sparking may be
visible, as well.
A null occurs when
the end of the antenna
points at the RFI source.
Occassionally, the cause of the RFI
will be obvious. Usually, however, it isn't!
Power lines are made up from a large inventory of hardware and individual
components, any one of which may eventually loosen or fail. Cracked
insulators, loose bonding wires, corroded hardware, unbonded switches, open
ground wires, damaged lightning arrestors, and defective line fuses are just a few
causes! Also, weather (especially wind and humidity) may be an important
contributing factor. For example, corona more likely occurs in damp weather,
while arcing is more common in dry or windy conditions. Many utility-company
