| LSB transceiver for 3699 kHz | ||||||||||||
| This project is real but at the same time a joke. In OH-land the rag-chewing channel on HF is 3699 kHz LSB. | ||||||||||||
| Many people meet there every day, sometimes all day. And more are just listening. | ||||||||||||
| In fact those hams would not need more radio than this single channel LSB transceiver for 3699.00kHz. | ||||||||||||
| This is a filter based SSB transceiver, but it is not heterodyne. It is direct conversion transceiver, where xtal filter is on the channel. | ||||||||||||
| There is no VFO, no mixer, no traditional LC filters in the receiver input. But you can use it only on 3699 kHz, no QSY! | ||||||||||||
| In this construction CMOS gates are used as carrier oscillator. Analog switches are used in balanced modulator, | ||||||||||||
| receiver demodulator and transmit-receive-switching. | ||||||||||||
| The xtal filter is with 6 xtals. Two frequencies are used, having 500Hz difference. | ||||||||||||
| Bandwidth of the filter is 1800Hz, giving audio response 300-2100Hz. This could be 300Hz wider... | ||||||||||||
| The coils are critical. Amidon 61 material works fine, after many trials. | ||||||||||||
| The only RF amplifier stage in the receiver is between xtal-filter and demodulator. | ||||||||||||
| Receiver AGC works on audio level and is integrated into audio PA. There is also mute gate. | ||||||||||||
| Audio PA is the standard LM386. Audio output level is controlled with resistor in series with the speaker. | ||||||||||||
| The mic amplifier is with dual TL082C. Balanced modulator is a push-pull type with 74HC4052. | ||||||||||||
| DSB from the modulator goes via T/R-switch to xtal filter without further amplification. | ||||||||||||
| Max TX output from the xtal filter is -3dBm or 0.5Vpp / 50ohm. | ||||||||||||
| Different RF amplifiers could be built, depending on operators needs. | ||||||||||||
| My PA is with high voltage MOSFET and two bipolar driver stages. With 70V DC it gives 40Wpep. Filtering is incorporated. | ||||||||||||
| The only variable thing at the front panel is receiver audio level. | ||||||||||||
| Sensitivity is good enough when using a half wave dipole. Band noise dominates always. | ||||||||||||
| As the transmitter has no ALC, one must be careful with modulation. Best way to monitor output is with oscilloscope | ||||||||||||
| in order to avoid PA clipping.. | ||||||||||||
| OH1TV | ||||||||||||
| 24.6.2008 | ||||||||||||
| updated | ||||||||||||
| Block diagram | 26.6.2008 | |||||||||||
| Modulator / demodulator | 28.6.2008 | |||||||||||
| Xtal filter | 29.6.2008 | |||||||||||
| AF power amplifier | 5.5.2011 | |||||||||||
| RF power amplifier 2W | 5.5.2011 | added | ||||||||||
| RF power amplifier 40W | 24.6.2008 | |||||||||||
| Exciter pictures | 28.6.2008 | |||||||||||
| Back to projects page | ||||||||||||