Mobile WSPR on 30m

A small WSPR transmitter built following the concept of the QRP-Labs U3S transmitter using several QRP-Labs kits and parts. This project uses a QRP-Labs firmware, Si5351A synth kit, and several parts from a LPF kit and a U3S case kit. The U3S BS-170 PA FET is further amplified to between 2 and 4 Watts of RF output (depending on supply voltage) with an IRF510N power FET. Everything is mounted on a piece of vero-board inside a small Eddystone/Hammond die-cast aluminium box similar to their 27134PSLA measuring 111 x 60 x 31 mm overall.

The antenna is a home made, 3-section, base loaded mobile whip which dismantles to fit inside my suitcase for other travel when the "mini-U3S" is not used on a car. See photos below.

The QRP-Labs firmware parameters are set to transmit 'extended WSPR' format to send the overseas prefix, my callsign and the 6-character Maidenhead locator ... e.g. VE6/ZL1RS DO02XU or M/ZL1RS IO93DQ

This project was used while driving across Canada in 2018, and also on a narrow boat while navigating the canals in Yorkshire, UK later that same year.



The finished 30m band "mini-U3S" transmitter




The "mini-U3S" transmitter internal layout at final assembly




The partially built "mini-U3S" ... still to add the IRF510 PA stage, BS170 driver stage and LPF




The "mini-U3S" transmitter internal layout before assembly




The home made 30m band mobile whip antenna - the complete 2m tall antenna




The home made 30m band mobile whip antenna - detail of the loading coil end of the antenna