I chose to use an ADF4351 based synthesizer module to generate the 2256MHz local oscillator (LO) needed for my QO-100 QRP transmit converter. This is controlled by an Arduino Nano. Having already used one of these modules for the 54 to 4400MHz synthesizer based signal generator. Once again I used an Arduino sketch written by F1CJN, this one being the single frequency option developed for QO-100 use.
Like many of my smaller projects, copper-strip board formed the base for securing the modules and providing the inter-connections, level-shifters and so on. A tin box was used to house and screen the LO with the supply voltage fed via a feed-through capacitor. These steps being done to try to ensure the desired output was as clean as possible.
The photo above is a screen capture from my Rigol DSA815-TG Spectrum Analyser (SA). As standard this model has a maximum frequency of 1500MHz. To check the output of the LO synthesizer running at 2256MHz, I used a passive RF mixer plus my second ADF4351 signal generator running at 2000MHz to produce an input to the SA at 256MHz (2256MHz minus 2000MHz) Whilst the actual dynamic range of this solution has not been measured and calibrated against better equipment it is sufficient to enable me to get an idea of what is going on.