Re: RD16HHF1 in the uBITX #ubitx
OK, stupid question time.
Let me preface this by saying that although I'm a EE, I've only recently gotten my Technician's license, and I've done nothing but digital design since taking my solid-state amplifier course 30 years ago. So I don't know a lot about RF design, and what I did know I've likely forgotten...
That being said, I ran across this web page earlier today: https://www.sv1afn.com/rfattenuator.html . This design uses a 6-bit, 50 ohm, 1-4000 MHz digital RF attenuator chip from Peregrine Semiconductor to vary RF attenuation from 0dB to 31.5dB in 0.5dB steps via an SPI serial interface. Could we place something like this in between two of the earlier uBitX TX gain stages and use this to control our TX drive level digitally rather than using RV1 alone? The newer PE4312 chip (the replacement for the obsolete PE4306 used in the design above) goes for less than $5 in small quantities (less than 100 units).
Please note from the PE4312 datasheet (http://www.psemi.com/pdf/datasheets/pe4312ds.pdf) that the maximum allowed input RF power is much lower for HF frequencies, going from roughly 11.5db @ 1MHz to about 23.5dB @ 50MHz (see Figure 4). The PE4312 also allows control via a parallel interface for those that would rather control it that way, perhaps using an I2C digital I/O expander chip to control the attenuation rather than using SPI to save pins on the Raduino.