Don, W3FPR wrote: For anyone contemplating connecting an analog S-meter to the K2, A better connection point for the takeoff AGC voltage is Control Board U2 pin 1. That point should have a voltage relating to the signal strength whereas the AGC input into the MC1350 is a current based rather than voltage - the only difference between the two points is a resistor (R4), but still using U2 pin 1 will not have potentila adverse effects on the normal K2 AGC operation.
-------------------------- Quite right. It's been several years since I last used that I.C. in a receiver I.F. design. While Motorola specifies a control voltage range 5 VDC to almost 7 VDC, they specify that the voltage must be applied to the pin through a recommended 5.6K resistor. Elecraft used a 5.1k resistor for that purpose, R4. So the metering circuit should be connected to the output of U2A rather than directly to the MC1350. Getting back to Keith's original comments, that receiver I designed - a single-conversion superhet using the MC1350 for an I.F. - was where much of my attitude toward AGC systems was probably created. I was playing with a variety of AGC systems including some "hang" AGC circuits, but the range of AGC gain control using a single MC1350 wasn't great enough to keep me happy. I was playing around with using PIN diodes controlled by the AGC to switch in fixed attenuators in the front end for greater range. One day, while I was sitting there looking at the schematic for an AGC system whose complexity rivaled the rest of the receiver, it occurred to me that I was doing all of that only to make an S-meter needle wiggle about! I think Wayne came up with an excellent design that balances complexity with effectiveness. That's the difference between one who tinkers and an engineer <G>. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
