Hi Gerard.
Apologies for not responding earlier but I have been extremely busy trying to achieve a deadline at work.? Just about made it.
Yes you do need to modify the SI4432 boards as shown by Erik.? It is quite tricky!? These parts are filters specified for the intended frequency range of the particular SI4432 board, but we want to be able to operate over a wide range of frequencies and often the filter parts fitted are not correct for the frequency range of the unit purchased anyway!
Be aware that there is a mistake in my schematic, which I really must fix.? The RF switch U9 needs to have a capacitor between the output RF2 on pin 3 and R36.? I used 100nF but its is not at all critical.
The question about SW1 is a good one!? SW1 was planned as a slide switch for on/off.??
I did not install these parts and just plug in 5V USB power to the ESP32 module.??
J5 was intended to connect to a switch mode power module to reduce 13.8V shack supply down to say 7V to reduce heat dissipated by the 7805.? If used a link would be placed between J8 and pin 2 of J6, and then from pin 1(or 3) of J6 to pin 3 of J7.? It would also be possible to replace the 7805 with a 3V3 regulator and then use pin 2 of J7 instead.? This was thought to be useful if a 3V7 LiPo or similar battery is used as power source, though some other changes would also be needed if that was the plan.
DNF means Do Not Fit by the way.? As previously noted you would need to short the inductors.
As Erik points out it is difficult to get the actual built filter to perform as the simulations, so your idea of a sub board to test and optimise is not bad.? I think if I were to do my board again I would not have a ground or power plane beneath the filters, or at least not on the middle layers.? Interesting idea to have the inductors made as part of the PCB.? I have no experience of that so let us know if it works!
Another point.? This software as is will not work with software on the PC intended for the TinySA.? It could be done perhaps but the idea behind using the ESP32 in the first place was a)? I had one, b) Low cost and c) It has built in WiFi and capability of including a web server.? So the software as is is web enabled - you cannect to the simpleSA via WiFi and a web browser.? You can see the trace and control most things from the web page.? The sweep speed is a bit slower, but still pretty good.? Other settings which are less frequently used can be set either via the touch screen or text commands from a terminal via the USB.? It would be possible without too much effort to make all of these available via a web page.? The web page allows some things to be done easier than via the screen, and you can have many more data points in the sweep.? Having said that I very rarely use this and just use the built in display together with the encoder.? I find it a very useful tool, especially with the tracking generator.
Good luck and keep us updated on progress.
73
Dave M0WID
