During the February tech night we streamed some initial design discussion and work.

IF frequency selection was discussed including some common frequencies. They are good options since many components for these frequencies are available and inexpensive. High IFs are good at image rejection and low IFs are better for small bandwidth filters. A low IF of 455 kHz was chosen as the single IF since a tight filter is more important than image rejection. A more robust design would have 2 or 3 IFs to cover both requirements.

Component selection was discussed. Trevor (K8TRC) has some amplifier and mixer components in his junk drawer which are inexpensive and seemed adequate for the job so we chose those as a basis for the design. The SA612A Gilbert cell mixer will be used for IF and baseband conversion and the BGA2812 amplifier will be used in the IF. In order to get reasonable gain levels, 2 of these will amplify for a combined 60dB or so in the IF. The remaining gain will likely come from the audio stage but another BGA2812 in the RF stage is also a possibility. The WTL6R60427VH ceramic filter is an inexpensive monolithic device designed for 455 kHz filtering and has a bandwidth of about 2kHz. Ideally this would be a little wider but there was no 3 kHz device available.

The Si5351A is often used as an oscillator for DIY radios as it's inexpensive, easy to use, and provides multiple square wave outputs up to a few hundred MHz. Modules with support components are readily available. The module from QRP Labs allows for an inexpensive crystal reference or for a few dollars more, a TCXO for better stability.

We went over basic use of Digikey and similar suppliers and how to use parametric search to find components.

We then laid out a basic IF strip in KiCad 6.