NIKI2 - multiband HF QRP DIGI transceiver

NIKI2 is a continuation of the popular PSK NIKI80 mini transceiver.

The main difference is the use of frequency conversion, a quartz filter and the ability to work with any digital mode, including SSTV mode. Also new is the use of frequency synthesis instead of a quartz resonator and the ability to work in all bands in the range from 1.8MHz to 30MHz.

The transceiver system is a classic frequency conversion system. The signal after the BPF bandpass filter is directed to the mixer on the SA612A system, then the quartz filter and the product detector also based on the SA612A system.

The quartz filter used in the set has a bandwidth of 3.0kHz/-6dB and an I/O impedance of 1kHz. The signal after the detector is amplified by a low-frequency amplifier on the BC847C transistor, then it is fed to the output socket for connection to the computer's sound card.

The receiver has a sensitivity of 0.18uV s/n -12dB. This is the sensitivity determined by the stable visibility of the signal on the waterfall.

The transmitting part uses the conversion path of the receiver circuit. The mixer of the receiver is used as a modulator and the product detector as a mixer of the transmitter. After the mixer, the RF signal is directed to the BPF filters, which work both on receiving and transmitting. Band selectivity rx/tx is ensured by the appropriate combination of BPF and LPF filters.

The signal selected from the BPF bandpass filters is amplified in the preamplifier on the transistor BFR106, then through the transformer T1 to the transistor BFQ19 and through the matching transformer T2 to the push-pull amplifier on the transistors BFQ19.

This arrangement ensures stable operation and low distortion. The push-pull circuit is matched to the LPF output filters by means of a T3 transformer. The quiescent currents of the BFQ19 transistors are about 30mA.

The output power of the amplifier is 1W in the 1.8 - 30MHz bands.

The VFO/BFO frequency generator is made on the Si5351 chip.

The VFO/BFO outputs are switched by software during transmit/receive.

The software provides an Atmega 328P with an 8x2 display.

The transceiver does not require additional control from the computer for proper switching of transmit/receive.

Switching is carried out using the vox m.f. system. directly from the sound card.

In the system, this is done by the amplifying and separating circuit based on the LM358 with adjustable gain level. Switching to transmit mode is signaled by a red LED.

The DIY (do it yourself) kit includes a board with soldered elements in SMD technology, elements for through-hole assembly and sockets.

Assembly instructions in English - download here