Hi The last K2 I built had strange AGC and S-meter operation that sounds like the one you are working on. The problem was I had skipped installing the toroid RFC11 on the bottom of the board. It is amazing the K2 worked at all but it received fairly well. I could even hear the 1 uV signal from the XG2. Anyway installing the RFC solved the problem. May be worth a look to see if you have the same problem
Don Brown KD5NDB ----- Original Message ----- From: "Gerhard Schwanz" <[EMAIL PROTECTED]> To: <[email protected]> Cc: <[EMAIL PROTECTED]> Sent: Friday, November 11, 2005 2:23 AM Subject: [Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI > Hi list, > hi all those who answered my first question. > > I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to > 3.65, > 3.72 and 3.8V. It got better for sure. The difference between AGC on and > off > is in all cases noticable, but slightly. But I think it's significant, > because... > > When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start > lighting. So I guess AGC sets in. And this should not be the case, I > guess? > Any idea? > > Have a nice day, > > Gerhard > > > ----- Original Message ----- > From: "Don Wilhelm" <[EMAIL PROTECTED]> > To: "GS" <[EMAIL PROTECTED]> > Sent: Wednesday, November 09, 2005 3:35 PM > Subject: RE: RE: [Elecraft] K2 receiver problem > > > > Gerhard, > > > > If you have a K2 with serial number greater than 3000, the AGC > > adjustment > > pot is on the Control Board near the right end - the designation is R1. > > > > For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor. > > Same procedure applies - change the value of R1 to set the AGC > > threshold. > > It is easy to substitute a temporary pot (50K will do fine) to make the > > adjustment - once the right value is found, solder in the closest value > > fixed resistor. > > > > In my experience, the fixed resistor that one would end up with will > > vary > > between 33K at the low end and 47k at the high end. > > > > BTW, if this receiver has worked properly before and suddenly developed > this > > problem, look more closely for a failed component - it will likely be in > the > > AGC area - see the control board schematic in the lower left corner. > > > > 73, > > Don W3FPR > > > > > -----Original Message----- > > > From: GS [mailto:[EMAIL PROTECTED] > > > Sent: Wednesday, November 09, 2005 9:48 AM > > > To: [EMAIL PROTECTED] > > > Subject: Ant: RE: [Elecraft] K2 receiver problem > > > > > > > > > Hi Don, > > > > > > I can't find how to set the AGC threshold for optimum > > > receiver sensitivity, neither in the manual nor is > > > there any hint in the circuit. At least not for me ;-) > > > > > > Only threshold mentioned in the manual is for the > > > NB... > > > > > > WHAT do I have to adjust to achieve max. voltage at U2 > > > pin 5, ctrl board? > > > > > > Thanks!!! > > > > > > Gerhard > > > > > > > > > --- Don Wilhelm <[EMAIL PROTECTED]> schrieb: > > > > > > > Gerhardt, > > > > > > > > It sounds like the AGC Threshold is not set > > > > properly. > > > > > > > > I would proceed by first checking the alignment of > > > > the bandpass filters in > > > > Transmit mode (at 2 watts) and then set the AGC > > > > Threshold for optimum > > > > receiver sensitivity - with no antenna connected and > > > > AF and RF Gains set to > > > > max, adjust for the highest voltage at Control Board > > > > U2 pin 5 which yields > > > > no change in the audio noise when switching the AGC > > > > between OFF and ON. > > > > That will usually result in a voltage in the range > > > > of 3.65 to 3.8 volts at > > > > U2 pin 5. Set the S-meter end points (CAL S Hi and > > > > CAL S-Lo) after setting > > > > the threshold. > > > > > > > > If that does not cure the problem, then look for a > > > > problem in the IF receive > > > > chain - that will be where the signal tracing is > > > > required, follow the > > > > p[rocedure for receiver signal tracing in the > > > > Troubleshooting appendix of > > > > the K2 manual. > > > > > > > > > > > > 73, > > > > Don W3FPR > > > > > > > > > -----Original Message----- > > > > > > > > > > got a K2 from another OM on my workbench. It's got > > > > a > > > > > receiver problem and I just want to make sure I do > > > > the > > > > > checks in the correct order and I'm looking for > > > > hints, > > > > > if available! > > > > > > > > > > Thanks in advance! > > > > > > > > > > So here's the problem and what I want to do. It > > > > seems > > > > > the receiver runs with "handbrake on". So the > > > > s-meter > > > > > shows 3 bars without an antenna but the rf gain is > > > > > fully clockwise. I can reduce signals to zero > > > > (using > > > > > RF gain) with this K2 which I can't using my own > > > > K2. > > > > > So mine has a higher sensitivity. > > > > > > > > > > Any idea what's wrong? > > > > > > > > > > What I want to do: > > > > > - s-meter alignment > > > > > - I.F. amplifier alignment > > > > > - (maybe band pass alignment) > > > > > - signal tracing receiver and synthesizer > > > > > > > > > > Kind regards > > > > > > > > > > Gerhard > > > > > DH3FAW > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ___________________________________________________________ > > > Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - > > > Hier anmelden: http://mail.yahoo.de > > > > > > > > > -- > > > No virus found in this incoming message. > > > Checked by AVG Free Edition. > > > Version: 7.1.362 / Virus Database: 267.12.8/163 - Release Date: > 11/8/2005 > > > > > > > > > > > > > > > ___________________________________________________________ > Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - Hier > anmelden: http://mail.yahoo.de > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > _______________________________________________ Elecraft mailing list Post to: [email protected] 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
