MFJ-224 Instruction Manual
2-Meter FM Analyzer
12
Limitations
The MFJ-224 is a highly-affordable handheld tester that will help you perform many
functions that would otherwise require a sophisticated FM service monitor. However,
please keep in mind that it is not a direct replacement for a $5000 commercial instrument!
Here are some of the unit's natural limitations--and some useful tips to help you work
around them:
1. The VFO is LC-tuned (not synthesized). Because of this the receiver may be subject to
minor frequency drift when exposed to temperature changes or when first turned on.
Use the discriminator meter function to ensure accurate tuning before taking readings.
2. The receiver 1st-IF filter at 10.7 MHz is fairly broad. When tuning
extremely strong
signals
, the band of "quieting" on either side of center-signal may be wide--making
tuning by ear alone somewhat difficult. In this case, use the discriminator meter to
locate the exact center of the signal.
3. The MFJ-224 receiver is, by design, approximately 20 dB less sensitive than a typical
VHF-FM transceiver (this is done to accommodate bench measurements involving
strong transmitter signals). If you must copy extremely weak off-air signals for
diagnostic purposes, you may install an external in-line 2-Meter preamplifier to boost
sensitivity. Be sure to incorporate preamp gain into your measurements. For example,
if your preamp has a measured gain of 20 dB, be sure to subtract this gain from your
meter reading. For example, a -90 dBm reading made with a 20dB preamp in-line
would indicate an actual input signal strength of -110 dBm (-90dB [-]+20 dBm = -
110 dBm).
These limitations should not significantly detract from the unit's many overall
capabilities.
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 station 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 FAX to 601-323-6551; or by email to [email protected].
Send a complete description of your problem, an explanation of exactly how you are
using your unit, and a complete description of your station.