MPX96 APPLICATIONS

The MPX96 will be useful anywhere a short range low power FM audio link is needed. It is far superior to free running FM transmitters and will not drift off channel, and is perfectly compatible with digitally tuned FM receivers. It is also useful as a teaching aid. Unlike low end units using a BA1404 or other black box IC, the MPX96 allows access to all multiplex signal waveforms and the observation of the signal generation process. The circuit is adjustable for optimum performance, and works well with default settings if no test equipment is available. Anyone can get satisfactory performance with only a VOM or a DVM for alignment. In the USA and certain other countries, signal radiation must be kept to a level low enough so as not to exceed specific field strength levels and not to interfere with other stations using the FM broadcast band. Check with the applicable laws in your nation, such as the FCC or DOT rules and regulations. In the USA Part 15 of the FCC rules and regulations applies. Having no easy way to measure field strength, keep the power as low as you can and use only a simple antenna, as short as possible. The MPX96 will provide a +10 dBm signal (10 milliwatts) into 50 ohms, running 5 volts on the output amplifier. This is more than adequate for covering an average property and only a 12 inch antenna is needed for this. It is recommended to terminate the output of the transmitter in a 56 ohm resistor, connecting the antenna to the hot side of the termination. This will give a useable range of 50 to 200 feet with a typical pocket stereo receiver.

For best results a relatively clear channel is necessary. The PLL helps tremendously by keeping the signal on frequency. In large metropolitan areas it may be difficult or impossible to find a clear channel. In this case try using an in between channel ie. even 100 KHz in the USA, odd 100 KHz in areas using even channel allocations. Also, you might try to get between two weak stations if possible. However, this can be impossible for digitally tuned receivers, but analog (continuously tuned) receivers will have no problem. Many lower end pocket stereos are still analog. It is best to operate between 88 and 92 MHz as this part of the band is used by lower powered stations.

The circuit uses a LM1458 dual op amp for audio matrixing, LM1496 balanced modulator two CD4000 series IC devices for MPX 19 and 38 KHz generation (crystal controlled), a Motorola 145150 series PLL synthesizer, a 74F160 prescaler, CA3420 buffer, LM340T-5 regulator, a FET VCO, and several discrete RF transistors for buffer and interfacing functions. All necessary test points are available for testing and observation of signals for educational purposes.

The MPX96 may be mounted in our NC1550 Plastic case. This is recommended in order to provide mechanical protection . It is mechanically the same size as our AM88 AM transmitter and operates from the same power source and audio interfaces

1. Home audio systems. Listen to your CD player, tape deck, etc on a pocket stereo receiver while not in same room as audio equipment, or outside the house, garage, deck, etc
2. Other applications such as private or in-house broadcast systems for schools, real estate, health clubs, stores, offices, museums, etc.
3. Use as a short range FM station in remote areas where no other FM reception is possible, or no suitable stations can be received.
4. For entertainment of groups where a foreign language is spoken. Two languages can be carried, one on each channel, for a bilingual PA system, using small pocket stereo receivers. Useful for churches, shows, etc. The AM88 can also be used along with the MPX96 for additional channel capability
5. The MPX96 can be used with our Voice Messenger and Identifier to make a "talking sign" for sales purposes, such as real estate, entertainment, flea markets, etc. A sign can be posted instructing one to tune their radio to an FM channel that the MPX96 is set to, and hear the message.

MPX96 FEATURES

• PLL Synthesized for accuracy (0.1 kHz or better, adjustable) with digital receivers
• Easy construction and setup, with VOM and audio source
• RF output filter for clean RF and low harmonic output less than -50 dBc
• No obsolete, drift prone, unstable BA1404 used
• Excellent audio quality and separation, noise and spurs -60 dBc or better, separation 30 dB
• Audio response 20 to 15000 Hz, 75 usec. preemphasis built in, takes standard line level audio
• Operates from 12-14V DC supply at 125 mA
• Small size 4" X 4", rugged epoxy fiberglass G-10 PC board used
• Fits into our NC1550 Plastic case
• All signals accessible for educational and service purposes
• Covers 88 to 108 MHz and 76-88 MHz (used in some nations), 100 KHz steps
• For export use only, can cover a village or community with our 1 Watt amplifier
• 19 and 38 KHz MPX signals crystal controlled
• On -board audio generator (1187 Hz) crystal controlled, for testing
• Fully compatible in mechanical and electrical interfaces with our AM88 AM Transmitter
• Excellent learning tool
• Low cost

For export use, where regulations permit (NOT IN USA) more output is possible but this amount is not guaranteed in any way. In this case a matched antenna should be used. This may allow up to a mile or more range, depending on local terrain, if a properly matched antenna is used. However, the MPX96 is strictly an entertainment device and is not meant for commercial broadcasting, therefore no guarantees of any kind can be offered nor technical assistance be given for export use, details of which must be worked out by the user.

For export applications only a 1 Watt amplifier  is available for boosting the power output of the MPX96. This enables coverage of a village or community and is useful where regulations permit as a low cost alternative to a commercial FM transmitter. This is not legal in the USA

For applications requiring an AM broadcast band transmitter similar in design, function and size to the MPX96, see our   AM88 PLL synthesized Low Power AM Transmitter