MFJ-1205 DigiLINK USB Radio Interface Instruction Manual

: June 5, 2024
: MFJ

Table of Contents

MFJ-1205 DigiLINK USB Radio Interface
DISCLAIMER
INTRODUCTION
FEATURES
CONTROLS & CONNECTIONS
SYSTEM SETUP & OPERATION
- INSTALLATION
TECHNICAL ASSISTANCE
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MFJ-1205 DigiLINK USB Radio Interface

MFJ-1205-DigiLINk-USB-Radio-Interface

DISCLAIMER

The information in this manual is for user purposes only and is not intended to supersede information contained in customer regulations, technical manuals or documents, positional handbooks, or other oﬃcial publications. The copy of this manual provided to the customer will not be updated to reﬂect current data. Customers using this manual should report errors or omissions, recommendations for improvements, or other comments to MFJ Enterprises, 300 Industrial Park Road, Starkville, MS 39759.
Phone: 662-323-5869
Fax: 662-323-6551
Business hours: M-F 8:00 AM – 4:30 PM CST.

INTRODUCTION

The MFJ-1205 USB Radio Interface enlists you in Ham Radio’s ongoing Digital Revolution. Now easier than ever to use, the MFJ-1205 simpliﬁes setup with a single, detatchable USB cable. Two front-mounted LEDs give you the device’s status instantly, and auxiliary input and output jacks let you monitor your audio, even if you have to use your headphone port for a connection. Building on the success of its predecessor, the MFJ-1204, the MFJ-1205 retains the convenient form factor, yet removes the permanently-attached USB cable. Now the unit can easily be stored for transport. MFJ-1205-DigiLINk-USB-Radio-
Interface-1

FEATURES

The MFJ-1205 is a signiﬁcant leap forward for MFJ’s digital products. Some of the features include

USB 2.0 audio and power
On-board audio device
Plug-and-play connectivity
Internal PTT

Perhaps of greatest importance, the MFJ-1205 has the exact same audio response characteristics as the popular SignaLink USB. The MFJ-1205 outputs PSK (Figure 2a), RTTY (Figure 2b),
CONTESTIA (Figure 2c), and even military-standard M110A waveforms (Figure 2d) identically to the SignaLink, meaning you do not have to choose between quality and aﬀordability! MFJ-1205-DigiLINk-USB-Radio-
Interface-2

CONTROLS & CONNECTIONS

MFJ-1205-DigiLINk-USB-Radio-
Interface-4

PTT: Illuminates when the PTT circuit goes active
STATUS: Indicates the status of the audio chip
RECEIVE: Adjust receive audio
TRANSMIT: Adjust transmit audio
IN: Auxiliary audio input
OUT: Auxiliary audio output
RADIO: Connect to radio
USB: Connect to computer

SYSTEM SETUP & OPERATION

INSTALLATION

Connecting the MFJ-1205 is incredibly simple. First, plug the unit into any free USB port on your computer. Second, plug the audio cable into the appropriate radio ports. Make sure that your computer has properly mounted the interface, and you’re good to go! One of the beneﬁts to using the MFJ-1204 is that if you ever upgrade your radio, you don’t have to purchase an entirely new unit. Simply order a new cable and jumper board, swap them out with the old ones, and reconnect!Table 1 lists all of the current jumper board and cable combinations available for the MFJ-1205.
Once connected to your computer, the MFJ-1205 will be recognized and mounted as an audio device. The exact details of this will vary depending on your operating system. Look for “USB Audio Device.” During this process the green LED may ﬂash about once per second depending on the OS, but will glow steadily once ready. At this point the MFJ-1205 is ready to be used by your favorite software.

Table 1: Jumper Boards and Cables

Board	Cable	Termination	Radios
PA	MFJ-5704P	4-pin Round	Any 4-pin round microphone jack
G	MFJ-5706G	6-pin MiniDIN	Xiegu G-90 & X5105
MD6	MFJ-5706MD	Yaesu & ICOM 6-pin MiniDIN	FT-100, 687, 817, 897, 950, 991

IC-706, 746, 7000, 7400

P8| MFJ-5708P| 8-pin Round| IC-728, 735, 738, 746Pro, 751,

756Pro, 761, 765, 775, 781

VII

7410, 9100

D13K1| MFJ-5713DK1| Kenwood 13-pin DIN| TS-140, 450S, 570D, 590S, 66,

850, 870, 950, 2000

DIGITAL-MODE AUDIO ADJUSTMENT

Operating digital modes is very diﬀerent than operating traditional phone or CW modes. For starters, not every mode works well at all power levels. PSK31, for example, is an excellent low-power mode (<20 W); however, driving PSK31 at 100 W not only can damage most radios (they typically are not built for 100% duty cycle), but it can distort your signal into something undecipherable, create spurious harmonics, and increase your bandwidth to the point where you are wiping out everyone else around you. This is the epitome of bad operating, but fortunately it is fairly easy to avoid with a basic understanding of how your radio is generating its signal.
Most analogue HF radios simply inject audio from a digital interface somewhere along the audio input circuit. Radios built before the rise of digital modes often require the audio to be injected at the microphone port, while newer radios typically have an auxiliary input that bypasses some of the initial audio conditioning at the mic for a more stable signal. Regardless of the exact method, the audio is injected onto the same line, and therefore must pass through the ALC circuit on the way to the ﬁnals.

Most of us are used to simply adjusting the power control to where we want to be, speaking into the mic, and then adjusting the mic gain to minimize distortion. For digital modes, you want to do something a little diﬀerent. For less-complex analogue radios (i.e. the ones for which you need an external digital interface) you actually want to open up your power control all of the way and use the audio controls on your interface to adjust transmit power.∗ The reason for this is to keep the ALC from turning on and distorting your signal. The drawback is that it is easy to undermodulate your signal, increasing your signal-to-noise ratio. Another common method is to set the power to the desired level, then slowly increase the audio volume until the ALC “just barely ﬂickers.” This method makes full use of your dynamic range and will produce the best signal-to-noise ratio; however, it does involve using the ALC as the upper limit, runs the risk of overmodulating your signal, and requires constant ﬁne tuning as you move around the band. Both of these techniques are valid, and the best one to use will depend on your radio and your operating style.

In order to make the audio adjustments easier, the MFJ-1205 has two sets of audio controls. The ﬁrst is the direct control of the audio chip’s output level through the computer. the second is the pair of potentiometers on the front of the unit. As discussed earlier, we do not want to overdrive the digital audio; however, interfaces such as the MFJ-1205 require a certain audio threshold to engage the PTT circuit. This threshold is met by increasing the volume using the Pi until the PTT LED is solidly on. It is quite likely that this will be too much audio drive for the desired power output; therefore, a 10 kΩ potentiometer has been placed in the output audio circuit. Adjusting this pot will lower the audio drive while still maintainin the level required to activate the PTT circuit.
Note: Remember that the power of an AM or sideband signal is directly proportional to the volume of the input. This is why shouting at the mic on AM or sideband will get you more power.

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 reading the manual does not solve your problem, you may call MFJ Technical Service at 662-323-0549 or the MFJ Factory at 662-323-5869. 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 Facsimile (FAX) to 662-323-6551; or by email to techinfo@mfjenterprises.com. Send a complete description of your problem, an explanation of exactly how you are using your unit, and a complete description of your station.