I like Bill's proposal of a second SI4432 in the tracking generator, probably easier to get a flat response and good isolation than adding an attenuator/amplifier.? Of course then its almost another TinySA.
Assuming this will go with your homebrew ESP32 TinySA then there are some options to experiment with:
- Try your proposal and see how well it works.? Perhaps use a passive splitter/combiner (2 off 33R in parallel for each branch should be near enough) and fit a dummy load to the port when not in use. Requires one SI4432, mixer and assign an IO pin to select it.? With a suitable pull up on the tracking generator and pull down on the main board it should be simple to detect if the tracking generator is connected on power up and initialise it to output the correct frequency.? Tracking generator will need to be positioned close to the TinySA to keep the SPI bus short.? This is easy to do.? Another option would be to use an Arduino Nano, ESP32 or similar that just sets the SI4432 frequency on power up.? This is also easy to do but slightly more work.? Gives more flexibility in locating the tracking generator somewhere convenient on the bench.
- As above with attenuator/amplifier as Erik suggests
- Add another SI4432 to the tracking generator as Bill suggests.? Needs another IO pin assigning.? The TinySA code will then have to control the tracking generator LO as the sweep progresses.? This is also easy to do.
- Make the tracking generator completely independent with its own ESP32 and power source, synchronised to the main sweep via the ESP32 Wifi.? Allows the tracking generator to be positioned anywhere convenient, but a LOT more work to implement so if anyone needs that then its DIY.
If you want to try any of the easy ones let me know and I can create a version for you to try out.? Pins 32/33 (reserved for encoder but unlikely to be implemented) or perhaps better 16/17 should be available for use.
If it works out OK then would need to add ability to calibrate frequencies of the other SI4432 to the menus.
Dave M0WID
