It’s not every day that you get the opportunity to test out a new radio, even less frequently the opportunity to test one that you assembled yourself. Richard VK2ARH was fortunate to be given the opportunity to trial the 40m Pebble QRP radio last week during the regular Friday morning portable activation activity that several Club members participated in.

Following early morning signal tests receiving 5/9 into Brisbane and then last-minute checks with Brian VK2AXC and Carmel VK2NO at their home stations who reported good signal strength and voice quality, Richard decided to use the radio and join the HADARC 9:00am Net on 7.106MHz using the Pebble with great success. Although band conditions were not ideal, the

40m Pebble performed admirably and a tribute to the designer Barb WB2CBA. 5/9 Signal reports were also received from Adelaide via a short wave listener. The experience confirmed the decision to use the Radio as the basis for our ‘Lunch Box ‘equipment challenge’ being developed by the Portable Special Interest Group, supported by the Builders and 3D printing groups within the Club. The idea being to make a recommendation and design a low-cost equipment setup that can fit into a ‘lunch box’, and enable anyone to easily join our regular portable activities.

The 40m ‘Pebble’ is being built by several club members, as an opensource project and a variant of the original 20m kit. The ‘Pebble’ project is the brainchild of Mike N4FFF and Becky N4BKY the HamRadioDuo on YouTube, in collaboration with Barb WB2CBA as a way to give back to the Amateur Radio Community. Barb designed the hardware leveraging from his earlier projects and an existing firmware design by Guido PE1NNZ.

The Pebble takes about one hour to assemble and requires a small number of THD components to be soldered to the preassembled main board populated by SMD components. A solid 5w out with 12.8v DC input, harmonic suppression >46dB, and with a crystal stabilized Si5351 on board there was no need for any frequency calibration. The radio can operate on USB/LSB, and CW using the built in CW key or plugging in a straight key or iambic paddle. The radio has a digital display, built in CW decoder and CW practice mode, twin VFO’s, RIT, NR, ATT. Although you can connect an external microphone, the built in Microphone produces good quality audio.

This little Pebble made a big splash on its first field activation and generated a lot of interest.

Here’s a picture of the setup used by Richard, The speaker mic is only being used for its amplified speaker and power was supplied by a 3 x 18650 (nominally 12v) battery pack.

Richard VK2ARH has produced an Assembly and Operations Manual for the MWRS 40m Pebble project which can be downloaded from his GitHub site: https://github.com/VK2ARH/40m-Pebble-HF-Radio.

Screenshot

The full open-source project can be found at Barb’s GitHub Site : https://github.com/WB2CBA/PEBBLEHF-MONOBAND-SDR-HF-TRANSCEIVER