It is a 30W transmitter. Generator is based on transistor BC548. The device is also equipped with separators on BF245 and BF199, 1 grade – also BF199, then 2N2219, KT907a and KT909G. The transmitter should have a low pass filter.

The transmitter has a stereo encoder (with 50us pre-emphasis) based on BA1404 and quartz 38kHz, making the remote control stable. Adjustment of audio signal strength is carried out independently for left and right channel. There is also a MPX signal control at the output of the encoder. The transmitter has a mono/stereo switch – in mono mode it is possible to disable or enable the pre-emphasis.

Another part of the device is microphone amplifier with adjustable gain. The transmitter has a built-in mini mixer, which makes possible transmitting both audio signal and microphone, in proportions determined by the user.

Frequency is adjusted using three buttons on the front panel of the transmitter: UP, DOWN and STEP, and it is displayed on the 2x16 LCD display. Microprocessor PIC16F84 and synthesis on SAA1057 control the whole device. The frequency (88-108 or 72-92 depending on the software) is constant in time.

The transmitter is powered by stabilized power supply 12V 1,5A and 24V (or 18V) 3A.

Two last grades are powered by 18V or 24V, the rest of the transmitter – 12V.

Schematics:
Generator and 3 gain degrees, coder as modified application of BA1404, pre-emphasis (mono) and microphone amplifier were taken from: LINK, synthesis (schematic 1), last grade (schematic 2).

Pictures:










Link to original thread (useful attachment) – Nadajnik FM z koderem stereo, PLL+LCD, ok. 30W