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

Case open

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.

The monitor has two loudspeakers which can be controlled with HDMI. Unfortunately the support by Raspbian OS is not perfect so it is necessary to connect an analog headphone or loudspeaker to the 3.5mm jack plug, e.g. for GQRX (SDR). To make this possible I have built in a socket in the switch area and connected it to the Raspi. Extended upwards I also have the network connection.

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. 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. So that the USB GPS has a good reception I mounted it on the battery with an second USB hub. This has the advantage that I can easily connect other devices like the DX-Patrol SDR (for QO-100 etc.). For the SDR there was unfortunately no more space in the Go-Box 😉 During operation it turned out that I do not always have optimal GPS satellite reception (In the forest, in buildings etc.). So that an exact time is available I mounted an additional RTC DS3231 Real Time Clock. GPS and hardware clock works great together. Checkout my article about setup raspi for ham radio for more information.

The simple Sabrent sound card works great with all digital modes I use. Over all cable connections that go to the Raspi I have inserted ferrite cores to reduce the irradiation of high frequency.

Admittedly, with a total weight of 5 kg, the case is not particularly light, but everything is included and immediately ready for use after opening the lid. Grab and go is the motto. I use an AlexLoop on a tripod for shortwave, a logarithmic-periodic dipole antenna for 2m and 70cm and a small satellite dish, currently only for QO-100 reception. In the future I will deal with the transmission technology.

And yes, you’ve certainly noticed it in my wallpaper. I am a trekkie. “V” live long and prosper… vy 73 Karl-Heinz – DL1GKK

For the software I used I wrote my own article. Have a look here:

Below is the hardware I used:

EXPLORER 10 (2712) Case

Elecraft KX2

Kenwood TH-D74

IPS Monitor, 10.1 Zoll Full HD 12V Screen

Diymall Vk-172 Usb Gps Dongle

Hardware Precision Real Time Clock DS3231ÅMÅŽÕÑ&keywords=DS3231&qid=1574585133&s=ce-de&sr=1-6

Sabrent USB Soundcard AU-EMAC

GeneralKeys mini keyboard MFT-240

Panasonic LC R127R2PG Blei Akku

5V Step-Down-Converterärtswandler-Hocheffizienter-Einstellbares/dp/B07F38DJLS/ref=sr_1_3?keywords=step-down-converter&qid=1572591425&sr=8-3

DX-Patrol SDR – QO-100 Hardware


Log-Periodic Antenna