MFJ-8621 Data Radio
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IN CASE OF DIFFICULTY:
Many equipment problems can be traced to simple setup errors or minor
malfunctions that are easily corrected. Before contacting the MFJ factory for help,
please take a few minutes to read through the list of symptoms below and check out all
appropriate suggestions. If the problem persists, refer to the technical assistance
section in the Appendix.
1. Unable To Copy Off-Air Signals:
[ ] Improper TNC setup (consult TNC manual and double-check setup).
[ ] Defective antenna or interconnect cables (check for shorts, opens, etc.).
[ ] TNC or computer RFI (install cabinet covers, check cable shields).
[ ] Wrong crystal installed at Y2 (RX crystal should be in the 44-MHz range).
[ ] 1200-baud filter on, blocking 9600-baud reception (remove JMP-1).
2. Unable To Connect:
[ ] Transmitter or receiver off-frequency (see crystal-oscillator calibration).
[ ] Incorrect deviation (see FM-deviation adjustment).
[ ] Trying to copy 9600-baud data with AFSK filter on. (Remove JMP-1).
[ ] Using wrong modulator (consult manual, check JMP-2, JMP-3).
[ ] Insufficient signal strength (check antenna orientation).
[ ] Node overloaded with traffic (wait for things to quiet down).
3. Transmitter Erratic Or Inoperative:
[ ] Insufficient power source (check voltage of power supply under load).
[ ] Wrong crystal installed at Y3 (crystal should be in the 18-MHz range).
[ ] High-VSWR antenna (check antenna with bridge -- should be 2:1 or less).
[ ] Transmitter locked out because TNC is not equipped with DCD circuit.
IMPORTANT OPERATOR NOTES:
Your MFJ-8621 is specially designed to work with TNCs that are DCD equipped. If
your TNC does not have data carrier detect circuitry, it will read the MFJ-8621's
unsquelched audio as an incoming signal and will not allow the data radio to transmit.
Your MFJ-8621 is not VSWR protected and will not tolerate prolonged operation into
high-VSWR antennas. Most commercial antenna installations provide a VSWR or
1.5:1 or less, and this is a good rule of thumb to follow for VHF amateur installations.
Also, do not retune RF circuits in your MFJ-8621; this should only be done at the
factory by a trained technician with access to correct procedures and instrumentation.
MFJ cannot be held responsible for the on-air performance of radios subjected to
unapproved tampering.
Finally, the MFJ-8621 is not FCC type accepted for commercial radio service and is
intended solely for amateur use. Do not attempt to adapt this unit for commercial
applications, and always test for interference to other radio services when using the
MFJ-8621 in amateur service at a shared commercial site.
