I understand that about the HAGC1. Its purpose is to keep the level within the range of the A to D. If this signal is too big the A to D converter U23 will over range and the DSP is unable to perform the mathematical functions.
The HAGC1 is fixed and is not adjustable by the user. VIFGAIN1 on the other hand is adjustable and ultimately controlled by the DSP. The AGC loops are nested that is the HAGC1 is the main loop and the VIFGAIN1 is a sub loop. If you look at the IF schematic you will see that the two loops are summed at the same AGC buffer amplifier U3A. HAGC1 is routed to the DSP board and is actually an input to an A to D converter U8. It’s then processed by the DSP. Without knowing the DSP code, I suspect there’s a PID (Proportional Integral Derivative) function involved to maintain loop stability and data to calibrate the S meter. The RF gain control is a potentiometer connected an analog port of the PIC controller U1 (PIC18LF8722). It’s converted to a digital signal that’s also fed to the DSP to control the RF gain via VIFGAIN1. I guess where we differ is that you speak in terms of an analog signal and I like to speak in terms in the digital world. I was involved in a DSP project in the late 80’s and early 90’s called “The Hamblaster a DSP for Ham Radio”, where I wrote two articles in QEX. ----- Jack WA9FVP Willco Electronics -- View this message in context: http://elecraft.365791.n2.nabble.com/K-3-Roofing-filter-comment-tp6576237p6588698.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
