µSDX Triband 7/14/21 MHz Handheld 5W QRP SDR Transceiver

Description

This transceiver can be used to make QRP SSB and CW contacts, or (in combination with a PC) can be used for digital modes such as PSK31, PSK64, FT8, JS8, FT4, RTTY, FSK, JT4, JT9, JT65, MFSK, SSTV, WSPR and so on. It can be fully continuously tuned on 7, 14, and 21 MHz bands in the LSB and USB modes. With a 2400 Hz bandwidth, it has up to 5 Watts PEP SSB output and features a software-based full Break-In VOX for fast RX/TX switching in voice and digital operations.

The SSB transmit stage is implemented entirely in a digital and software-based manner: at the heart, the ATMEGA328P is sampling the input audio and reconstructs an SSB signal by controlling the SI5351 PLL phase (through tiny frequency changes over 800 kbit/s I2C) and controlling the PA Power (through PWM on the key-shaping circuit). In this way a highly power-efficient class-E driven SSB signal can be realized; a PWM-driven class-E design keeps the SSB transceiver simple, tiny, cool, power-efficient, and low-cost (ie. no need for power-inefficient and complex linear amplifier with bulky heat-sink as often is seen in SSB transceivers). 

This has simplified the µSDX circuit a lot, and there are a number of advantages and features (compared to an analog approach): there is no longer a need for an I/Q alignment procedure due to the very accurate 90-degree Hilbert phase shifter, and there are now adjustable IF DSP filters for CW and SSB, and there is an AGC and there is a noise-reducing DSP signal conditioning function and there are three independent built-in attenuators in the analog front-end which helps to utilize the full dynamic range.

The speaker is directly connected and driven by the ATMEGA. A digital mixer with a narrow low-pass window (2 kHz), and steep roll-off (-45 dB/decade) combined with an oversampling and decimating ADC are responsible for a processing gain, dynamic range, and alias rejection sufficient to handle weak and strong signal conditions (e.g. contests or listening on 40 m just next to broadcasting band).

For the receiver, most parts are implemented in the digital manner (software): the ATMEGA328P is implementing a 90-degree phase shift circuit, the (CW/SSB) filter circuit, and the audio amplifier circuit (now a class-D amplifier).   The transceiver has been created to try out what can be achieved with minimal hardware while moving complexity towards the software; here the approach followed is to simplify the design where possible while keeping a reasonable performance. The result is a cheap, easy-to-use, versatile QRP SSB transceiver that actually is quite suitable for making QSOs (even in contest situations).

The µSDX triband handheld transceiver’s unique form factor allows you to operate from anywhere. Press the XMIT button to transmit and talk straight to the built-in microphone while holding the radio in your hand. For extreme portability, you can use the optional external wide-range ATU, 12V battery, CW keyer, or handheld microphone.

Transmit efficiency is also excellent, further improving battery life. Full-Featured, yet easy to use the µSDX triband handheld HF transceiver features a compact design with all controls optimized for convenient use.   You simply dig through simple menus to set the power level, adjust the keyer speed, or change filter settings. The radio has an LCD display, so all operating information is available at a glance. Free firmware upgrades are available via the internet.

The optional accessories allow this transceiver to be tailored to your needs, including the optional CW Keyer, Handheld Microphone, Data mode, CAT Control Interface, 100W Power Amplifier, Lithium Ion Battery, External ATU, light multiband HF portable antenna, Low Pass Filters Unit, micro PC unit. Please contact us if you need any of these.

Main Features and Specifications:

• LCD Display
• Built-in Speaker
• Built-in CW Decoder
• IRF MOSFET Power Transistors
• SMA Antenna Socket
• 13.8V Power Supply Provides up to 5 Watts PEP SSB Output Power
• Bands: 40, 20, and 15 m
• Modes: USB, LSB, CW, Digital
• DSP Filter: 4000, 2500, 1700, 500, 200, 100, 50 Hz
• Functions: Automatic Gain Control (AGC), Noise Reduction (NR), Voice Trigger, Voice Trigger Xmit (VOX), RX Attenuator (ATT), TX Noise Gate, TX Driver Control, Volume Control, dBm/S-meter
• SSB Reverse Sideband/Carrier Suppression Transmission: better than -45dBc, IMD3 (two tones) -33dBc, reception: better than -50dBc
• Open source firmware, built-in for Arduino IDE; allows experimentation, can add new functions, can share contributions through Github, software complexity: 2000 lines of code
• Software-based VOX that can be used as fast Full Break-In (QSK and semi-QSK operation) or assist in RX/TX switching for operating digital modes (no CAT or PTT interface required), external PTT output/PA control with TX-delay
• Fully digital and software-based SSB transmit-stage: samples microphone input and reconstruct an SSB signal by controlling the phase of the SI5351 PLL (through tiny frequency changes over 800kbits/s I2C) and the amplitude of the PA (through PWM of the PA key-shaping circuit)
• Three independent switchable analog front-end receiver attenuators (0dB, -13dB, -20dB, -33dB, -53dB, -60dB, -73dB)
• Receiver noise level MDS: -135 dBm (200Hz BW) at 28MHz
• Receiver front-end selectivity: steep tuning frequency -45dB / ten times roll-off +/- 2kHz
• Blocking dynamic range: 20kHz offset 123dB, 2kHz offset 78dB
• CW decoder, straight/Iambic-A/B keyer
• VFO A/B + RIT and Split, and switch the corresponding relay band filter through I2C
• CAT support (Kenwood TS-480 subset), you can stream audio, press keys, and display text through CAT
• Compact Size: 50 x 20 x 80 mm
• Weight: approx. 180 g

External Connectors: