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MFJ -8621 User Manual

2-meter packet only data radio
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Features......................................................................................................................................................... 1
Technical Specifications (Typical Unit):.............................................................................................. 2
Receiver: ......................................................................................................................................... 2
Transmitter: .................................................................................................................................. 2
Simplified Technical Description: ......................................................................................................... 3
MFJ-8621 Technical Description: ...................................................................................................... 3
General: ........................................................................................................................................... 3
Receiver: ......................................................................................................................................... 3
Transmitter: .................................................................................................................................. 3
T/R Switching: ............................................................................................................................. 3
TNC Data Carrier Detect Compatibility ............................................................................................ 4
Connecting To Your MFJ-8621:.......................................................................................................... 4
Power Supply: ............................................................................................................................... 4
Antenna:.......................................................................................................................................... 5
TNC Connection:.......................................................................................................................... 5
RFI:..................................................................................................................................................... 5
Selecting Baud Rate: ................................................................................................................................ 6
Receiver Filter:.............................................................................................................................. 6
Transmitting:................................................................................................................................. 6
Transmitter Deviation: ............................................................................................................................. 6
Setting Deviation: ........................................................................................................................ 6
Two-Way Deviation Monitoring: ............................................................................................ 7
Confirming Deviation: ................................................................................................................ 7
Ordering Crystals: ...................................................................................................................................... 8
Receiver Crystal:.......................................................................................................................... 8
Transmitter Crystal:................................................................................................................... 8
Installing Crystals: ...................................................................................................................................... 9
Crystal Oscillator Calibration:................................................................................................................ 10
Transmit Oscillator:.................................................................................................................... 10
Receiver Oscillator:..................................................................................................................... 10
More About 9600-Baud FSK Packet Signals: ............................................................................... 11
Sending And Receiving 9600-Baud Data: ....................................................................................... 11
In Case Of Difficulty:................................................................................................................................... 12
1. Unable To Copy Off-Air Signals: ........................................................................................ 12
2. Unable To Connect:............................................................................................................... 12
3. Transmitter Erratic Or Inoperative: ............................................................................... 12
Important Operator Notes:.................................................................................................................... 12
Appendix......................................................................................................................................................... 13
Technical Assistance................................................................................................................. 13
Replacing The Fuse Link........................................................................................................... 13

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Summary of Contents for MFJ MFJ-8621

  • Page 1: Table Of Contents

    Features................................. 1 Technical Specifications (Typical Unit):....................2 Receiver: ............................2 Transmitter: ..........................2 Simplified Technical Description: ......................3 MFJ-8621 Technical Description: ...................... 3 General: ............................3 Receiver: ............................3 Transmitter: ..........................3 T/R Switching: ..........................3 TNC Data Carrier Detect Compatibility .................... 4 Connecting To Your MFJ-8621:......................

  • Page 2: Features

    Cool Running: The MFJ-8621 draws only 25 mA on receive, and less than 1 A on transmit. Run it 24 hours a day 365 days a year, or pack it with your lap-top and take it on the road.

  • Page 3: Technical Specifications (Typical Unit)

    150 mV p-p @ 1200 baud, .8 V p-p @ 9600 Deviation........0-5 KHz, adjustable at TNC RF Power Output....... 4.0 - 5.0 Watts into 50 Ohms VSWR Tolerance....... 3:1 Max. Current Drain......1.0 Amp @ 13.8 Volts Figure 1 Block Diagram of MFJ-8621 Data Transceiver...

  • Page 4: Simplified Technical Description

    AFSK, PIN-diode switching, data-passband IF filtering, and a tailored 0-Vu DC-coupled line driver to ensure top-notch performance. There are no user-adjustable controls to set incorrectly, and the MFJ-8621 works with most popular TNCs. MFJ-8621 TECHNICAL DESCRIPTION: General: The MFJ-8621 is a dedicated-channel 2-Meter FM-AFSK transceiver designed for use with DCD equipped TNC-2 style modems at data-rates through 9600 baud.

  • Page 5: Tnc Data Carrier Detect Compatibility

    MFJ-8621 Data Radio As a "packet-only" radio, the MFJ-8621 is specially designed to transmit and receive all data rates through 9600 baud. However, to accomplish this, the MFJ-8621 must deliver unsquelched AFSK or FSK data to the TNC. The MFJ-8621 does not provide squelched AFSK because conventional squelch circuits are far too slow to be useful above 1200 baud.

  • Page 6: Antenna

    Use a 5-pin DIN-to-5-pin DIN cable, MFJ-5100, for connection to MFJ TNCs or the PK-96. Caution: Not All TNCs have DCD (Data Carrier Detect) circuitry, and your MFJ-8621 -- which has an unsquelched output---will not work with those TNCs.

  • Page 7: Selecting Baud Rate

    See Figure 3 on page 9 for placement of the jumpers on the pc board. Transmitting: The MFJ-8621 has two FM modulators selected by jumpers, JMP2 and JMP3. One is a sensitive reactance modulator designed for mic-level AFSK signals. Since most TNC's output mic-level signals at 1200 baud, the reactance modulator should be used at 1200 baud.

  • Page 8: Two-Way Deviation Monitoring

    RX-AFSK, first note the waveform height of average off-air signals (2.2 V p-p is typical for 3-KHz deviation). Next, key the MFJ-8621 transmitter via the CALIBRATE function on your TNC--and adjust TNC output (TX-AFSK) for a waveform of about the same height.

  • Page 9: Ordering Crystals

    When ordering from JAN, simply tell the sales person that you wish to order a pair of crystals for the MFJ-8621 Data Radio and give the operating frequency in MHz. JAN has complete MFJ-8621 crystal specifications on file in their ordering system and no additional information is required.

  • Page 10: Installing Crystals

    To install new crystals in your MFJ-8621, refer to the diagram below: [ ] Remove the MFJ-8621 cabinet lid (one screw on each side of the cabinet). [ ] Locate and pull the existing transmit crystal (Y3) from its socket.

  • Page 11: Crystal Oscillator Calibration

    RF output signal with a digital frequency counter. To obtain a usable signal sample, place the counter's pickup antenna near the MFJ-8621 PA section--or install a sampling tap in the coax line leading to your dummy load. Use the CALIBRATE function on your TNC or short pin-3 of the data jack (PTT Line) to ground to key your transmitter's PTT line.

  • Page 12: More About 9600-Baud Fsk Packet Signals

    If you are selecting a remote site for your station, please remember the MFJ-8621 is a $120 amateur radio product and not a $5000 commercial repeater! Avoid high-IMD locations if you can, or be prepared to provide additional filtering to reduce the effects of intermod and desensing from nearby transmitters.

  • Page 13: In Case Of Difficulty

    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.

  • Page 14: Appendix

    Replacing the Fuse Link The MFJ-8621 has a thin foil trace on the pc board that acts as a line fuse. This trace connects power to the rest of the circuitry and may "burn out" under certain conditions (such as when the MFJ-8621 is subjected to a reversed polarity power).
  • Page 15 Data Radio FULL 12 MONTH WARRANTY MFJ Enterprises, Inc. warrants to the original owner of this product, if manufactured by MFJ Enterprises, Inc. and purchased from an authorized dealer or directly from MFJ Enterprises, Inc. to be free from defects in material and workmanship for a period of 12 months from date of purchase provided the following terms of this warranty are satisfied.

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