MFJ MFJ-8709 User Manual

MFJ-8709 Instruction Manual

MFJ-8709 ATV Transmitter Module

Introduction

The MFJ-8709 is a very high performance amateur radio ATV transmitter module. The
MFJ-8709 design is based on a custom mixed signal ASIC (Application specific
Integrated circuit) solution, minimizing size without compromising performance. The
MFJ-8709 is designed as a module, that can be integrated as a standalone or sub-circuit
for various amateur radio projects. The transmitter is mounted on an aluminum plate.
This plate serves as a heat sink for low power operation (Output less than 0.5W). For
high power operation (output >0.5W) the MFJ-8709 needs additional heat sinking,
therefore the MFJ-8709 will have to be mounted on an external heat sink.

Frequency control is provided by means of a digital integer-N, phase locked loop. Dual
PLL’s provide a frequency locked video carrier and an audio sub-carrier. Based on
customer requirements, the MFJ-8709 can be programmed for operation outside the US,
for PAL and SECAM video standards. The transmit frequency is selected via a four
position dip switch. Four standard US ATV frequencies are provided.

Video modulation is accomplished via a 12 bit digitally controlled DAC-digital to analog
controller. A specially embedded software algorithm controls the modulation depth and
pre-distortion level to deliver an ultra clean video signal to the final RF amplifier. The
result is a near broadcast quality signal with minimum distortion and Sync signal
interference with the audio carrier. A built in video and audio test signal generator is
provided for testing purposes.

RF power output is controlled via an analog potentiometer. The RF power output can be
controlled from near zero RF output, to about 4.5W maximum output. The current draw
varies with the power level selected. The MFJ-8709 is set at 1W output at the factory.
The user may change this to the desired level.

MFJ recommends that the MFJ-8709 be mounted to an external heat sink. If transmitting
without an external heat sink, limit the power to no more than 0.5W output, and avoid
long key down periods. When provided with an external heat sink, the MFJ-8709 can be
used for extended key down operation. To avoid damage to the MFJ-8709, do not operate
the MFJ-8709 without proper heat sinking. The MFJ-8709 should be only warm to the
touch.

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MFJ-8709 Instruction Manual

Application Diagram

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MFJ-8709

70CM Video-Audio Transmitter

ONLY FOR AMATUER RADIO USE

F req Channel SW1 SW2 SW3 SW4

426.25MHz

427.25MHz 58 0 0 1 0

434.00MHz 59 0 1 0 1

439.25MHz 60 1 0 0 0
Inverse settings select test signal on same

channel frequencies

0 0 0 1

3
4

5
6
7

8

9

Fig. 1

1. Mounting hole – Hole diameter 0.125 Use the six holes to mount the MFJ-8709

to an external heat sink.

2. Antenna connector – SMA antenna connector, 50 ohm impedance. Connect this to

an external matched antenna or 50 ohm dummy load before powering unit.

3. External 12-13.5V in – Positive Solder terminal

4. External 12-13.5V in – Negative Solder terminal

5. Audio In, Solder terminal – Line level audio in. Connect an audio signal ( line

level, 200 – 250mV RMS)

6. Ground Solder terminal – Audio / Video Ground terminal

7. Video In, Solder terminal– Composite NTSC video in ( 1V P-P)

8. RF output control – Full CCW for minimum RF output – Full CW for maximum

RF output

9. Dip switch frequency select. See chart on next page for settings.

Video Connection

Supply a composite video signal between this terminal and GND. See Fig.2 on how to
build a video cable with a female RCA connector.

Fig.2

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