Lime Microsystems are just about to begin shipping the LimeRFE. This is a software-controlled multi-band and wideband PA and preamp, specifically designed to work with the LimeSDR. The initial specification is on the CrowdSupply website, but essentially it is capable of a DVB modulated half to one watt output on all amateur bands from 1.8 MHz to 2.4 GHz and about 200 mW on 3.4 GHz. The receive preamps are matched to the requirements of the LimeSDR, but crucially, like the transmit stages, all have bandpass filtering.
Using an early (pre-production) prototype model I have added LimeRFE support to the Portsdown 2020 Digital ATV Transmitter (which uses a Raspberry Pi 3). The LimeRFE is controlled through a USB connection to the Portsdown, and is band-switched and PTT switched automatically. Control is currently very simple with the LimeRFE either enabled or disabled in the Lime Configuration Menu.
Using this configuration, I was able to generate half a watt of very clean DVB-S2 on 70cm (437 MHz). The shoulders were over 40 dB down at this power level. CW power obtainable was almost 2 watts. Results were similar on 146 MHz. Tests on other bands, and on the performance of the receive preamps, are ongoing.
Dave Crump is chair of the British Amateur Television Club (BATC).