Changes to the Fms2 Assembly

1

2 WATT FM TRANSMITTER MANUAL (100Khz spacing)

NOTE: PLEASE READ ALL THE INFORMATION IN THIS MANUAL BEFORE OPERATING.

Introduction

The FM-2WM transmitter is a high performance wideband broadcast transmitter board that can be programmed in 100 KHz steps to transmit on any commercial FM frequency in the 87.5-108 MHz band.

The output power of this unit can be adjusted from around 0-2 watts buy adjusting the RV1 control pot and the unit can be power from a standard 12 to 15 volt regulated power supply. Using a 15-volt power supply will produce slightly more output power. Almost any audio source can be used to modulate the transmitter from 2 volts P-P up to 20 volts P-P since the board has a modulation control pot to adjust for 100 % modulation. Modulation can be calibrated by comparing your stations level to that of other stations.

The input audio connections to the board are soldered on to the pad labeled AUDIO and the DC power input is labeled DC. The only other connection to the board is the RF OUT. A mini 50-ohm cable is soldered to these pads. The other end of the mini coax cable must be connected to a antenna or 50 ohm non inductive power resistor to provide a proper match to the output transistor. If the unit is powered up without correctly terminating the output damage could occur to the output transistor! Always make sure the unit is correctly set up before applying power.

Fast lock up circuitry has been used to enable the transmitter to lock on frequency almost instantly. The lock indicator led will indicate if the transmitter is locked when it is lit. If the unit is not locked the transmitter will not generate an output signal. This could occur if the transmitter is incorrectly programmed to a frequency out of the oscillator tuning range. If this occurs it is a good idea to double-check the dip switch codes.

Frequency Selection

To change the frequency of operation, the dip switch settings must be changed. The switches control the amount that U14 divides the incoming frequency from U10. By changing the switch setting we change the division factor and ultimately the frequency of operation. To set the frequency follow the format listed below:

Example: Suppose you want to operate on 87.5 MHz.

• Shift the decimal one place to the right-----we now have 875
• Using the chart below, subtract the highest number that is equal to or less than 875. The chart indicates the highest number is 512-----we now have 363
• Continue until there is nothing left to subtract.

Note: Switch 12 is always in the on position.

The final result should look like this:

1 2 3 4 5 6 7 8 9 10 11 12

Frequency codes for transmitter (Logic 0 means switch is on)

Parts list for 2-watt mono transmitter with 100Khz

Resistors

R43 is installed under the board. R29 should be 150 to 180 ohms if using the Stanford Micro device amplifier (RF2334) for U4. If using the MAR-6/SM for U4 then change R29 to 220 ohms. If using a Hittite 481 chip for U4 then use 68 ohms for R29

Resistors parts count using the Hittite 481 for U4

Capacitors

C46 should be changed to 18 pf for 50 uS European units. If an external stereo generator is used then omit C46 and change R39 to 100K or even lower in some cases.

Capacitors parts count

Inductors

Most inductors are hand wound. The 3 resistors in the inductor table above are already accounted for in the Resistor parts count table.

Diodes

Semiconductors

Misc.

1

320 Dixon Rd #302-Toronto-ON-Canada-M9R 1S8 #(416) 243-2260
web: email: