++++++++++++++++++ From: "Don Brown" To: "H. L. Stephenson" , Subject: Re: [Elecraft] K2 low AGC threhold Date: Sat, 15 Mar 2003 11:30:10 -0600 Hi If the 8 volt regulator is on the high side of the tolerance (8.3-8.5) then the AGC threshold will adjust up to 3.9 volts without any problem. But if the regulator is 8.1 volts or a little less then the adjustment will not reach 3.9 volts. The several K2's I have seen with this problem will only reach 3.82-3.87. This should not be a problem as it is probably close enough but if you want it right on 3.90 volts you can connect a 47K resistor from pin 8 to pin 5 of U2 on the back of the control board. This will bring up the voltage so the 3.9 volt point will be in the center of the range on the pot. Then adjust for exactly 3.9 volts and redo the S-meter calibration. Don Brown KD5NDB ----- Original Message ----- From: "H. L. Stephenson" To: Sent: Saturday, March 15, 2003 10:49 AM Subject: [Elecraft] K2 low AGC threhold > Has anyone completed a K2 with the low AGC threshold > voltage? Was it a problem? I have 3.84 with R1 full > counter-clock wise. > When I did bargraph current test the current "jumped" > between .22 and .24. It would not "lock in". > Is this normal? > > Howard Stephenson > KG6WP ++++++++++++++++++++ From: "John Huffman" To: "H. L. Stephenson" , Subject: Re: [Elecraft] K2 low AGC threhold Date: Sat, 15 Mar 2003 12:54:18 -0500 Howard - > Has anyone completed a K2 with the low AGC threshold > voltage? Was it a problem? I have 3.84 with R1 full > counter-clock wise. I built my K2 sn3000+ and got 3.83 volts. I called and the boys said, "no problem." After using it a while, I saw the AGC was too strong. The test is to turn AGC on and off while listening to an empty band. Turning the AGC on made the noise quieter, thus the AGC was kicking in too soon. I adjusted R1 until the noise was just the same in and out, but verified that with AGC in, strong stations were suppressed. The correct setting for me was with R1 at less than half the maximum. This shows that 3.83 volts, or whatever, is much too much AGC and there's nothing to worry about. You will end up turning R1 down anyway. > When I did bargraph current test the current "jumped" > between .22 and .24. It would not "lock in". > Is this normal? Page 46, step 6 I got E13.1 i 0.06 Page 46, step 7 I got E12.7 i 0.22 If by not locking you mean the last digit fluctuates by one number, that's normal. My guess is that all is well. 73 de NA8M John ++++++++++++++++++ From: "Dave. Interaccess.com" To: Subject: Re: [Elecraft] K2 low AGC threhold Date: Sun, 16 Mar 2003 05:31:37 -0500 John Posted: I adjusted R1 until the noise was just the same in and out, but verified that with AGC in, strong stations were suppressed. The correct setting for me was with R1 at less than half the maximum. Say John Out of curiosity (BTW I got 3.84 volts as well) what voltage did you end up with after you redid the threshold setting? Dave WB9SOG (SN #3231) ++++++++++++++++++++ From: "John Huffman" To: "Dave. Interaccess.com" , Subject: Re: [Elecraft] K2 low AGC threhold Date: Sun, 16 Mar 2003 08:27:17 -0500 > John Posted: > > I adjusted R1 until the noise was just the same in and out, but verified > that with AGC in, strong stations were suppressed. The correct setting > for > me was with R1 at less than half the maximum. > > > Say John Out of curiosity (BTW I got 3.84 volts as well) what voltage > did you end up with after you redid the threshold setting? > > Dave WB9SOG (SN #3231) Dave - I get 3.458V with this setting of R1. 73 de NA8M John +++++++++++++++++++ From: "Dave. Interaccess.com" To: Subject: Re: [Elecraft] K2 low AGC threhold Date: Sun, 16 Mar 2003 11:16:57 -0500 Would you believe 3.48volts? Thanks for the confirmation, John. I was thinking that my K2 was a little "hard of hearing" before I reset mine, but not now! I just re-checked my setting and I ended up down where you had yours set. So I guess I must be real close 8-) 73 de Dave WB9SOG ++++++++++++++++++++ Date: Mon, 17 Mar 2003 12:52:54 +1200 From: Ron Willcocks To: Elecraft Reflector Subject: [Elecraft] pre series "B" AGC adjustment. Hi folk, I have been reading the mail about setting the AGC levels in the latest "B" series K2's and noted the comments therin about tuning to a quiet part of a band and switching the AGC ON/OFF and noting the whether the background noise has a marked change in level. If it does change quite a bit then apparently the AGC is acting too soon. I tried it on my K2 (pre "B" series no. 2204) and I had a very marked difference in level when the AGC was turned ON/OFF, so I had a look through my saved items of interest from the Elecraft team, and found the article put out by Gary Surrency AB7MY back in Dec 2001, relating to "Poor S-Meter action". The main content of the article is about changing a diode to improve the S-Meter action, but as a related alteration, Gary wrote:- "If you notice a fairely large drop in RX hiss when you turn off the AGC, then you may want to decrease the value of R1 (also on the control board) from 51k to 33k. This has the same effect as if you could turn the RF gain a little further clockwise, and RX sensitivity will be better than before on weak signals." Anyway, I did change R1 to 33k and it has made a very noticeable difference in the sensitivity of my K2. There is now only a very small change in "hiss" when the AGC is turned ON/OFF, and it sure beats turning the AGC off when copying weak signals as I had been doing. I did have to alter the "S LO" and "S HI" setting a wee bit, but the overall AGC action is unchanged. Cheers.....Ron ZL1TW +++++++++++++++++++