An introduction

What is the uBITx?

The µBitx is a HF (3-30MHz) all-band SSB and CW transceiver kit.   It is supplied as a completely pre-populated and tested circuit board by the manufacturer (trading as HF Signals).   The purchaser needs to assemble the board into an enclosure and wire up sockets, encoder and potentiometer and provide a power supply in order to get the transceiver working.

Receiver

The receiver is a double conversion superhet design with a first IF and 15kHz roofing filter at 45MHz and a second IF and 6 pole Coen crystal filter at 12 MHz.  The receiver has excellent rejection of unwanted signals above 30MHz at the first IF as it also has a 0 – 30 MHz 3 stage bandpass filter.  However,  if you live close to high power AM Medium Wave broadcasters you may have issues with broadcast interference.

The receiver has no AGC, and no RF gain control,  which does present as an issue at times,  but is nice and clean, with few birdies and nice sounding audio unless the AF gain control is wound up high.

The transceiver can work on both side bands (LSB and USB) so is fine for use with digital modes.  Software is already available to provide CAT control and WSPR modes within the  transceiver.

Transmitter

The transmitter gives output of up to 10 watts PEP on SSB and 10w continuous output on CW at least on 40m.   Output varies by band.  Output on 80m will be greatest.

Performance falls off with frequency. You can expect around 4 watts on 20m and 2 watts on 10m.

The transmitter follows the same approach as the receiver, with the microphone amplifier feeding into a mixer at 12 MHz and then mixed up to 45MHz and then to the final transmit frequency.  The exception is on CW transmit where the 1st local oscillator is fed into an unbalanced mixer to directly excite the pre-amp stages.

The microphone amplifier may not always provide adequate gain, depending on your chosen microphone.  The drive control can be adjusted to increase SSB (and CW) drive, but be cautious that you do not overdrive the finals, causing IMD products and distortion, and potentially damaging the finals in the transmitter.

The kit contents

The kit contains:

• the main board (pre-assembled and tested)
• the raduino daughter board assembly
• a collection of small components

Main Board

The µBITX boards are hand-assembled by a collective of women. Each of the toroids is hand wound. This provides these women with a livelihood.

The assembled boards are then DC checked and a final RF check is performed to check the receiver’s sensitivity as well as the transmitter’s output prior to being shipped. Each board is individually numbered and initialled by final quality control.   Most will have a “U” on them.  If you sight an “F” you have one that went past Ashhar Farhan, the designer and co-owner of HF Signals.

Raduino

The raduino comprises a 5v regulator, an arduino nano and the si5351 PLL chip along with connectors to the main board and to the 16×2 line LCD display unit (which come attached).   A contrast control is installed on the back of the board.  You may need to adjust this if the display does not have adequate contrast or appears “blocked out”.

Other components

The full list of other parts is included on the HF Signals website, but is as follows: