MFJ MFJ-213 - Accuracy Limit; SWR Measurements and Local Interference; Checking for Local Interference

MF/J-213 HF/VHF/UHF Antenna Analyzer Instruction Manual
Before moving on to the next section, take time to review the MFJ-213’s
basic set-up procedures. Operation becomes second nature quickly, but
should you need it, there’s a supplemental "quick guide" in the back for
reference (Section 8.0). The remainder of the manual will focus on general
instructions and helpful tips for making accurate measurements.
5.0 ACCURACY LIMITS
The MFJ-213 will serve as your “eyes and ears” when working with RF
systems, and it can deliver results that rival units costing thousands of
dollars. However, all handheld analyzers share certain limitations, and being
aware of them will help you to achieve more meaningful results.
5.1 SWR Measurements and Local Interference
The MFJ-213 (and other hand-helds) uses a broadband diode detector that is
open to receiving signals across the entire radio spectrum. Most of the time,
the unit's built-in stimulus generator is powerful enough to overcome any
lack of front-end selectivity and override stray pickup. However, a powerful
transmitter located nearby could inject enough RF energy into the detector to
disrupt readings. If this condition occurs, performance will become erratic
and SWR readings may appear higher than they really are.
5.2 Checking for Local Interference
Unlike many analyzers, the MFJ-213 has an onboard function for identifying
local interference. In the 1.Antenna function simply switch to the third mode
and note the readings you obtain with the antenna connected. If a strong
signal (>100) registers on the display, then suspect interference. If the
interfering source can't be turned off or your antenna can't be moved to a
different location, you may need to use a station transceiver and a thru-line
directional Wattmeter to complete the adjustments.
Stimulus Frequency
Noise
level
Noise
indicator
5.3
Detector
Linearity
and
Accuracy
Diode detectors typically become non-linear at very low voltages. Because
of diode non-linearity, it's not uncommon for two identical analyzers to show
slightly different readings when checking a load with very low SWR (or low
RF-return voltage). For example, one analyzer may read 1.2:1 while another
reads 1.1:1 when checking the same antenna. The MFJ-213 is electronically
compensated to minimize detector error, but be aware of the potential for
minor differences.
Version | 6 © 2012 MFI Enterprises, Inc