Small QRP-GO-BOX powered by Raspberry Pi4, KX2 and TH-D74

Small multifunctional, digital, very compact amateur radio station for the radio operation at home, on the way or in the emergency radio.

For the digital QRP operation a Raspberry Pi 4, an Elecraft KX2, a Kenwood TH-D74 and a USB GPS have proven themselves. Annoyed by the many connection cables, I quickly felt the need to install everything, including battery and screen, in the smallest possible suitcase.  The EXPLORER 10 with the external dimensions AxBxC = 305 x 270 x 144mm had exactly the right size for me. The Raspberry is operated with a removable mini wireless keyboard with touchpad.

The power supply in the case is provided by a built-in 12V 7.2A lead battery. In the KX2 the original Li-Io battery is additional. This allows several hours of QRP operation. The battery is charged with a simple lead battery charger with charge control. Works great. At home I plug in 12V from my station power supply to make stationary radio operation. I plug the charger into the blue socket. So radio operation and charging are possible at the same time. During this time, the built-in battery is disconnected from the internal circuit via a switch. I realize the power supply for the Raspi with a step-down converter which is set to 5.1V and can deliver 3A. It hardly gets warm.

 

The 12V monitor is attached with an ALU bracket to the bottom of the case lid with two stainless steel screws. These are the only two screws drilled through the case. The sealing was done with silicone. There is enough space between the top of the monitor and the case cover inside to operate the function keys of the monitor.

When operating outdoors, the devices hardly warm up. In summer or in a building, however, something must be done to prevent heat accumulation. The KX2 is mounted on an 2mm ALU plate which has side flaps and thus ensures a transfer of heat to the ALU base plate. The Raspi has cooling fins and a switchable fan. The temperature is monitored by software.

The transceiver control is done with the original CAT cable from Elecraft. I only use the USB 2.0 ports of the Raspi and have installed a USB hub under the KX2 where also the GPS is plugged in. This USB hub protrudes from the right side of the KX2 and allows the reception of the GPS satellites. I connected the TH-D74 with USB to the Raspi. Bluetooth would also work but a cable connection is easier and more reliable. So I can use the built-in TNC for Xastier APRS.

I don’t use the built-in GPS of the TH-D74 although that would probably be possible. For positioning I use an additional USB GPS. Much more important for me than the position is the time synchronization I need for modes like WSJT-X. The USB GPS is perfect for this.

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