MFJ MFJ-8704 User Manual

MFJ-8704

Micro ATV Transmitter

High Performance, SAW stabilized

Micro Video Amateur ATV Transmitter

This products is only to be used by a licensed radio amateur

Specifications:

Video
Video Input:	NTSC or PAL composite video (1 V P-P) SMPTE STANDARD
	NTSC 625 Line 60 Hz
	PAL 625 Line 50 Hz

RF
Center frequency without modulation		433.97 MHz +/- 50Khz
Output level:		+19dBmclean carrier
		+16.5dBm modulated
Modulation type:		High level amplitude modulation
Spurious output:		2nd harmonic better than 40dB down
VCC
Supply Voltage	9V DC (+/- 300mV)
Current draw	35 - 40 mA

The MFJ-8704 is a high quality, high performance SAW stabilized video transmitter, using surface mount technology.

A SAW oscillator is used in the fundamental operating mode to transmit at 433.97 MHz (Cable channel 59). The power output stage uses the latest in MMIC technology.

The MFJ-8704's range can vary any where from 1/4 mile to 8 miles depending on the antenna used. A high gain yagi antenna usually provides the best gain. If you plan to build your own antenna, an experimental antenna plan is included; however, commercially available high gain antennas provide the best performance. Use the highest gain antenna possible for both the transmitter and receiver with the shortest possible transmission line.

Operation and Setup

Video Input

The block diagram above shows the how the MFJ-8704 needs to be connected to a video source. Make sure that you have SMPTE standard video at 1 V P-P. Most consumer and commercial cameras and camcorders deliver SMPTE standard video, at the “video out” connector. If for any reason you are not sure if the video device is delivering SMPTE standard video, you can confirm this by looking at the video signal on an oscilloscope.

VCC Input

Due to size limitations there is no regulation provided inside the MFJ-8704. It operates on a 9V supply. While the MFJ-8704 may tolerate about +/- 2V of VCC error, higher supply voltages may reduce the power output. A power supply could be substituted in place of a battery. Use caution in providing the proper polarity. For battery operation, best results are obtained while using nickel hydride or lithium 9V batteries. For extended operational time, you can parallel two 9V batteries. Caution: The MFJ-8704 does not include reverse polarity protection. Therefore be careful to not reverse polarity. The red power lead is (+) positive and the black power lead is (-) negative.

Antenna

The transmitting and receiving antenna are probably the most critical items for attaining best range. A small piece of 1/4 wave wire as a transmitting antenna in combination with a high gain receiving antenna will work for short-range video transmission. Best results are obtained while using both high gain transmitting and receiving antennas.

Range testing was performed using the following antennas. The transmit antenna was a 14 element yagi, the receiving antenna was an 8 element yagi . At an approximate distant of 3/4 of a mile excellent picture quality was received. The receiver was a consumer grade Sony TV tuned to Cable CH 59. Please remember, that while a cable ready television would suffice as a good receiver, a sensitive ATV down-converter will far outperform any cable ready television.

Using a 1/4 wave ground plane (shown below) as a transmitting antenna and using a 14-element yagi antenna for the receiving antenna, excellent picture quality at 1/2 mile is possible.

Experimental transmit / receive antenna

Some antenna performance characteristics

While some transmit-receive antennas combinations perform differently, the following chart depicts the theoretical system performance of the MFJ-8704 using various combinations of antennas and an ATV down-converter.