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Table of Contents
Features.............................................................................................................1
Technical Specifications (Typical Unit): .............................................................3
Receiver: .................................................................................................3
Transmitter: .............................................................................................3
Simplified Technical Description: .......................................................................4
MFJ-8621A Technical Description: ....................................................................4
General: ..................................................................................................4
Receiver: .................................................................................................4
Transmitter: .............................................................................................4
T/R Switching: .........................................................................................4
TNC Data Carrier Detect Compatibility ..............................................................4
Connecting To Your MFJ-8621A:.......................................................................6
Power Supply: .........................................................................................6
Antenna:..................................................................................................7
TNC Connection:.....................................................................................7
Computer Connections:...........................................................................7
RFI: .........................................................................................................8
Selecting Baud Rate: .........................................................................................9
Receiver Filter: ........................................................................................9
Transmitting: ...........................................................................................9
Transmitter Deviation:........................................................................................10
Setting Deviation: ....................................................................................10
Sound Card Operations:..........................................................................10
Two-Way Deviation Monitoring: ..............................................................11
Confirming Deviation: ..............................................................................12
Ordering Crystals: ..............................................................................................13
Receiver Crystal:.....................................................................................13
Transmitter Crystal:.................................................................................13
Installing Crystals:..............................................................................................14
Crystal Oscillator Calibration:.............................................................................15
Transmit Oscillator: .................................................................................15
Receiver Oscillator: .................................................................................15
More About 9600-Baud FSK Packet Signals: ....................................................16
Sending And Receiving 9600-Baud Data:..........................................................16
In Case Of Difficulty: ..........................................................................................18
1. Unable To Copy Off-Air Signals: .........................................................18
2. Unable To Connect: ............................................................................18
3. Transmitter Erratic Or Inoperative: ......................................................18
Important Operator Notes: .................................................................................18
Appendix ............................................................................................................20
Technical Assistance...............................................................................20
Replacing The Fuse Link.........................................................................20
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Summary of Contents for MFJ MFJ-8621A
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Page 1: Table Of Contents
Table of Contents Features......................1 Technical Specifications (Typical Unit): .............3 Receiver: ....................3 Transmitter: .....................3 Simplified Technical Description: ...............4 MFJ-8621A Technical Description: ..............4 General: ....................4 Receiver: ....................4 Transmitter: .....................4 T/R Switching: ..................4 TNC Data Carrier Detect Compatibility ..............4 Connecting To Your MFJ-8621A:...............6 Power Supply: ..................6... -
Page 2: Features
AFSK or FSK--for a fraction of what you'd pay for a converted voice radio. Cool Running: The MFJ-8621A 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 MFJ-8621A. Running Dual Sound Card TNC’s. No problem with the MFJ- 8621A. The Right Tool For The Job: Your MFJ-8621A was designed from scratch for fast, clean packet communication and nothing else! Whether you are monitoring the local DX cluster or breaking new ground at 9600, you can look forward to...
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Page 4: 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-8621A Data Transceiver... -
Page 5: Simplified Technical Description
MFJ-8621A Data Radio SIMPLIFIED TECHNICAL DESCRIPTION: Your MFJ-8621A was especially designed for packet-only operation. MFJ has eliminated costly circuitry that you don't need: such as squelch, repeater offsets, PL tones, DTMF pad, PLL synthesis, memory, and the speaker-amplifier. At the... -
Page 6: T/R Switching
1200 baud. In order to process unsquelched data from the MFJ-8621A (or any high speed data radio), your TNC must have a data carrier detect (DCD) circuit built in. All MFJ model TNCs -- starting with the MFJ-1270B-- and virtually any other TNC that operates over 1200 baud should have one as well (PK-96, DPK-9600 for example). -
Page 7: Power Supply
(-) or black lead to the outer sleeve. Use a 2 amp fast-blow fuse with any power supply other than the MFJ-4110. Your MFJ-8621A features "crowbar" protection to prevent damage from incorrect power supply polarity. -
Page 8: Antenna
AFSK OUT (2.2 V pp into 600 Ohms) N.C. Computer Connections: Refer to the rear of the MFJ-8621A for connecting to your Computer. A single 9- Pin serial cable and a pair of 3.5 mm to 3.5mm stereo cables are all that are required. -
Page 9: Rfi
RFI protection, many veteran packet operators recommend installing ferrite RFI chokes on interconnect and power cables--and keeping the radio as far as possible from the TNC and computer. The MFJ-701 RFI kit provides 4 snap-on chokes for this purpose, along with instructions. Snap-on RFI chokes are also... -
Page 10: Selecting Baud Rate
See Figure 2 below for placement of the jumpers on the pc board. Transmitting: The MFJ-8621A 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 11: Transmitter Deviation
TRANSMITTER DEVIATION: Setting Deviation: The MFJ-8621A has no internal deviation control. Deviation is adjusted via the AFSK output level control on your TNC (consult your TNC manual for specifics). If you don't have access to a FM deviation meter, you can set deviation by... -
Page 12: Two-Way Deviation Monitoring
H-time base. To set TX deviation while 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-8621A transmitter via the CALIBRATE function on your TNC--and adjust TNC output (TX-AFSK) for a waveform of about the same height. - Page 13 MFJ-8621A Data Radio If a node in your area uses the X-1J2 version of theNET, you can take advantage of that station's built-in deviation meter to confirm the accuracy of your setting. Anytime you experience consistent difficulty connecting with local stations, you...
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Page 14: Ordering Crystals
When ordering from JAN, simply tell the sales person that you wish to order a pair of crystals for the MFJ-8621A Data Radio and give the operating frequency in MHz. JAN has complete MFJ-8621A crystal specifications on file in their ordering system and no additional information is required. -
Page 15: Installing Crystals
To install new crystals in your MFJ-8621A, refer to the diagram below: [ ] Remove the MFJ-8621A cabinet lid (one screw on each side of the cabinet). [ ] Locate and pull the existing transmit crystal (Y3) from its socket. -
Page 16: Crystal Oscillator Calibration
8 times at 145 MHz! Receiver Oscillator: Your MFJ-8621A has a unique built-in feature that allows you adjust the receiver oscillator by using the calibrated MFJ-8621A transmitter signal as a reference. You'll need an accurate DC voltmeter (or DVM) and an insulated tuning wand for this adjustment. -
Page 17: More About 9600-Baud Fsk Packet Signals
If you are selecting a remote site for your station, please remember the MFJ-8621A 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 18 MFJ-8621A Data Radio 8621A does not come equipped with a crystal oven to maintain its operating frequency over a wide temperature range. Finally, make certain your transmitter is not interfering with commercial services sharing the site. Setting up a node for 9600 takes a little more care, but once you are "up and running", you can sit back...
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Page 19: In Case Of Difficulty
[ ] Transmitter locked out because TNC is not equipped with DCD circuit. IMPORTANT OPERATOR NOTES: Your MFJ-8621A 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-8621A's unsquelched audio as an incoming signal and will not allow the data radio to transmit. - Page 20 MFJ-8621A Data Radio Finally, the MFJ-8621A 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...
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Page 21: Appendix
Replacing the Fuse Link The MFJ-8621A 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-8621A is subjected to a reversed polarity power). - Page 22 MFJ-8621A Data Radio To use the KPC-9612 at 9600 baud with the MFJ-8621A: 1. Enter the command CD SOFTWARE at the cmd: prompt. 2. Set the 9600 receive level jumper (J9) to "ON" (both pins shorted together). 3. Set the 9600 equalization header for "variable" (pin 2 shorted to center).
- Page 23 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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