> ...Lyle would have to comment on whether the DSP > AGC is developed before or after the IF gain is applied...
Assuming ATT and PRE are OFF, hardware AGC voltage begins to have an effect on IF amplifier gain with a signal at the antenna in the region of -60 dBm, plus or minus a few dB. The hardware AGC voltage is developed at the final IF of 15 kHz and applied to the 8.215 MHz IF stage. Its purpose is to prevent the 15 kHz A to D converter at the DSP from being driven beyond its input limits (called over-ranging). The "onset of hardware AGC" level is influenced by PRE (which increases gain ab out 10 dB, decreasing the signal required at the antenna by the same 10 dB), ATT (which reduces signals by 10 dB, thus increasing the required signal at the antenna), and RF Gain when backed off sufficiently. What is "sufficiently"? The DSP outputs a voltage to control the IF gain of the radio. This voltage is compared with the hardware AGC voltage, and the higher voltage is applied to reduce the IF gain. If the RF Gain is backed off enough so that the resulting gain control voltage is grater than the hardware AGC voltage derived from the 15 kHz IF signal, then the criterion for "sufficiently" has been met. The DSP reads the hardware AGC voltage, regardless of the source, and uses the value as part of the S Meter calculation. The DSP AGC algorithm is computed based on the 15 kHz IF signal applied to the DSP's A to D converter. Thus it is after the IF gain is applied. Enjoy! 73, Lyle KK7P ______________________________________________________________ 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
