+++++++++++++++++++++++++++++++ Date: Wed, 11 Apr 2001 18:26:31 -0700 From: "Ron D'Eau Claire" Subject: RE: [Elecraft] K2 S-Meter Display Tom KB9SIZ wrote: "I turn AGC off and the S-Meter changes as signal strength changes. About 3 bars on the S-Meter normally between weak and strong signals with RF Gain set 90% clockwise. When I turn AGC on, the S-Meter remains at the same level for all signals. This makes sense to me, but seems to be opposite of what was said. I am still confused a bit..." The S-Meter is not measuring how loud the signal is in your speaker or phones, but rather how much the receiver gain has to be turned down to keep the audio level relatively constant. To say it another way, when the AGC is on, a voltage is generated that corresponds to the strength of the signal. This voltage is used to turn down the gain of the receiver as needed to keep the audio output pretty much the same. The RF Gain control adjusts this voltage manually. So when the AGC is OFF, there is no AGC voltage generated and your S-Meter should not show any change. With AGC on, your meter should vary in accordance with the level of the AGC voltage. Hope that helps! Ron AC7AC K2 # 1289 ++++++++++++++++++++++++++++++++++++ From: "Ron D'Eau Claire" To: "Andreas Hofmann" , Subject: Re: [Elecraft] AGC OFF --> S-meter gone? Date: Tue, 30 Apr 2002 09:56:14 -0700 > I found a strange thing on my K2 (#2555). A S9 + 20db CW station with > AGC ON does not make the S-meter move when I turn off the AGC. The > signal itself stays just as loud in the speaker. > Any ideas? > Andreas, DL6UST/W7 That' is normal, Andreas. Here's why. The AGC helps maintain a relatively constant output at the speaker or phones by creating a voltage that REDUCES the gain as needed. In the K2 it works just like the "RF Gain" control except that it adjusts the gain automatically. (In the K2 the "RF Gain" control is actually an i-f gain control, adjusting the gain of the intermediate amplifier). That's why you must have the RF Gain control full UP for the AGC to work properly. The AGC circuit will then take over and reduce the gain as needed, depending upon the signal strength. All the "S" meter does is to measure the gain control voltage that the AGC or the "RF Gain" controls use to adjust the i-f gain. The greater the control voltage (meaning the more the gain is REDUCED), the HIGHER the S-Meter indicates. That way a very strong signal requires a big reduction in the gain, so S-Meter reads very high. If you turn the AGC Off, the i-f gain is now set by the "RF Gain" control alone. Normally you have this full up. With the AGC Off, try turning the RF Gain control DOWN, and you will see the S-meter display move UP the scale. Now you are controlling the i-f amplifier gain manually, and the "S Meter" is showing you how much you have reduced the i-f gain, just like it does when the AGC is on. The K2 has excellent 'dynamic range' meaining that it is hard to overload the receiver. So when you turned off the AGC, the change was not really apparent. Actually, you should have had heard the volume increase. If the signal was strong enough, it would begin to sound distorted. It is ALWAYS a good idea to keep the "RF Gain" at the lowest level needed to avoid having strong signals overload the receiver. Overload can cause noise that sounds like QRN or splatter that spreads across the band as well as causing the strong signals to sound distorted. That's why Elecraft included the Attenuator as well. Have that ON any time you have adequate signal strengths coming in, and keep the RF Gain turned down (or the AGC On) to avoid overloading the receiver. If you don't use the AGC, it is a good idea to set the Audio Gain just below the point where you can hear noise in the speaker or phones with a dummy load on the receiver and leave it there. Then use the RF Gain control to adjust the volume. I prefer to operate with AGC off because it makes the bands sound more natural and a LOT quieter! When you use AGC, it turns up the gain to full between signals so the background noise between stations is nearly as loud as the strongest signal. Ron AC7AC K2 # 1289 ++++++++++++++++++ From: "Ferguson, Kevin" To: "'elecraft at mailman.qth.net'" Subject: Re: [Elecraft] AGC OFF --> S-meter gone? Date: Thu, 2 May 2002 11:07:53 -0600 The logarithmic response of most S-meters (the K2's included)is achieved via the non-linear (multiplication) negative feedback inherant of any AGC loop. If the loop is opened so that AGC is disabled, yet the detected signal strength (which would be the AGC voltage were it still active) is still used to drive an S-meter, then the logarithmic response of the meter is becomes nearly linear instead. This will make the meter nearly useless except on very weak signals. To achieve logarithmic response, the AGC must be active so that the detected signal strength is allowed to "fight" the incoming signal. Best to learn to judge signal strength "by ear" in any case...that always works, and the calibration doesn't even shift between various rig manufacturers, etc. +++++++++++++++++++++ Date: Thu, 02 May 2002 13:00:39 -0700 From: lhlousek To: elecraft at mailman.qth.net, jamesd1 at flash.net Subject: [Elecraft] Re: S meter operationg Dear Dr MC, You wrote: "In general, there is no reason why the S-meter should not work when the AGC is turned off. One can disconnect the AGC control point and leave the meter still connected to measure the AGC voltage. You only need to disconnect the control line, not the line to the S-meter. This way, the S-meter still works but the AGC does not." As you point out this works in some designs but in the K2 and other designs I am familiar with the S meter is in the AGC control loop so that its response is calibrated when the loop gain is taken into consideration. If you open the loop after the meter the meter will be overly sensitive. Lou W7DZN +++++++++++++++ Date: Thu, 02 May 2002 15:06:09 -0700 From: Eric Swartz WA6HHQ - Elecraft Organization: Elecraft To: elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: S meter operationg As several pointed out earlier, the S Meter voltage is derived from the AGC loop voltage when the loop is closed (AGC on). When AGC is off there is no S meter as a result. This is how just about all current ham rigs are currently designed. Jesse suggested just taking the linear, open loop, voltage and correcting it in a software table to derive the s meter display. This will not work because the open loop linear signal level voltage will quickly reach its upper limit, well in advance of the maximum s meter display, preventing an accurate software based display. There are definitely many other ways to approach S meter design. We won't be changing the K2 design in this respect since it is more than adequate for most uses, be we will certainly look at alternatives in the future. 73, Eric WA6HHQ ++++++++++++++++ Reply-To: "Ron D'Eau Claire" From: "Ron D'Eau Claire" To: "Helmut Usbeck" , Subject: Re: [Elecraft] AGC Date: Thu, 2 May 2002 16:44:54 -0700 > In looking over the schematic of the K2 I noticed that the AGC is > derived by converting to a lower IF and then producing the necessary > AGC voltages. Interesting design. Any immediate advantages to doing > it in this fashion? No big deal, just curious. > -- > Helmut Usbeck, WB2ADT Yes, there is a significant advantage. Using a signal at an i-f is common of most "high performance" AGC systems. One of the major things it does is to provide a very fast "attack" or response to turn down the gain when a very strong signal arrives .The AGC can do this in a few cycles of signal, which when using an i-f signal as several Megacycles is very fast indeed. The common alternative for a less expensive system is what is used in the K1 - audio-derived AGC. That also responds in a few cycles, but now it is looking at audio frequencies instead of the much higher i-f, so the speed with which it can turn down the gain is much, much slower. So slow, in fact, that it produces the characteristic "pop" ops have report that the K1 makes on strong signals. That is common with virtually all audio-derived AGC systems. Of course, the AGC system could use the same i-f as the main signal path, but that means that great care must be taken to keep the BFO out of the agc circuit! Otherwise, the AGC will respond to it instead of the on-air signals coming through. That's why AGC's were not commonly used on older receivers and if you do turn it on with the BFO on, the receiver normally desenses. The AGC thinks the BFO is a very strong signal and reacts accordingly. The easiest way to keep the BFO out of the AGC is to put the AGC detector on a whole different frequency from the BFO, as they did in the K2. Ron AC7AC K2 # 1289 +++++++++++++++ Date: Thu, 02 May 2002 22:29:49 -0700 From: Eric Swartz WA6HHQ - Elecraft Organization: Elecraft To: Larry East Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: S meter operationg ... Hi Larry, Actually there are a couple of very good reasons for turning off the RX AGC on occasion. Many operators prefer to use the manual RF (IF) gain control with AGC off when listening to weak signals. This prevents larger signals within a few 100 hz from pumping the AGC and masking the weak signal. The filter between our ears does wonders for pulling out the weak ones this way. Also, when local noise (thunder crashes, pc harmonics etc.) is masking a weak signal, turning off the AGC can mean the difference between solid copy and nothing. Of course, its up to the operator and their lightening fast reflexes to protect their ears from overload with the RF gain control! (Or they will certainly suffer the rock and roll symptom you alluded to..) 73, Eric WA6HHQ ======== Larry East wrote: > > I fail to understand all the whoo-pa about the S-meter not working with the > AGC off. WHY turn the AGC off in the first place? ++++++++++++++++++ Date: Fri, 03 May 2002 10:54:05 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: Eric Swartz WA6HHQ - Elecraft Cc: Larry East , elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: S meter operationg ... Not necessarily recommended as a "mod" but in olden times before CW and AGC co-existed, it was not uncommon to place back to back parallel diodes across the audio output line to the headphones to limit the sound level. Surely there are more elegant and modern ways to do this now. 73/72/oo, George W5YR - the Yellow Rose of Texas ++++++++++++++++++ Date: Sat, 04 May 2002 09:17:26 -0600 From: "James R. Duffey" To: Cc: Subject: [Elecraft] AGC Larry - I agree with you, this thread may have take more significance that it deserves. But perhaps it is more relevant to the list than G5RV baluns? As to your question of why turn the AGC off? I find the operation of a receiver much more pleasant without AGC. For cruising the bands I use AGC when strong signals are present to preserve my ears, but other than that I seldom use it. I find a "AGCless" receiver to sound better. It has more audio dynamic range, a quieter noise floor, less spurious thumps and clicks, and gives a true indication of the strength of signals. Weak signals are weak, strong signals are strong. The ear is presented with an accurate representation of the signals with respect to the noise. With reasonably strong signals and the AGC turned off, one can adjust the AF and RF gain (attenuation) controls to achieve a nice sounding CW signal with little if any background noise. It is almost like listening to a code practice oscillator. This makes for a more pleasant listening experience. The AGC is introducing nonlinearity into the receiver. There are circumstances when the introduced nonlinearity is unpleasant, or at least not as pleasant as a receiver without AGC. I run my K-1 with the AGC turned off all the time. I find that the receiver is much more palatable this way. Despite your request not to, I am posting this to the list, as I hope that some others may find experimenting with turning off the AGC useful. ALso, my mailer has trouble recognizing the unusual e-mail address you gave, "bogus at stuffit.nul" as valid. Is there an error in that address? Sorry if I mucked it up onmy end. As to rock and roll - recall that famous line from American Graffiti - Rock and Roll has been going down hill ever since Buddy Holly died. And it has nothing to do with having one's eardrum's pounded by something. Keep in touch. - Dr, Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 ++++++++++++++++++ Reply-To: giantbug at earthlink.net From: "Mychael Morohovich / AA3WF" To: "kb1dxc" Cc: Elecraft at mailman.qth.net Subject: Re: [Elecraft] More AGC Date: Mon, 6 May 2002 8:0:25 -0400 Hi, Mike- Simultaneously depressing PRE/ATT and AGC toggles the AGC on and off. 73, Mychael AA3WF K2#1025 > [Original Message] > From: kb1dxc > To: > Date: 5/6/2002 7:52:19 AM > Subject: Re: [Elecraft] More AGC > > My AGC only seems to have SLO and fast. Is there something wrong with > my rig? I have version 2.01 of the firmware. > > Mike, > kb1dxc > k2 s/n 02097 +++++++++++++++++ Date: Thu, 09 May 2002 15:38:30 -0700 From: Wayne Burdick Organization: Elecraft To: Bill Coleman Cc: giantbug at earthlink.net, kb1dxc , Elecraft at mailman.qth.net Subject: Re: [Elecraft] More AGC Bill, We considered adding OFF to the AGC switch rotation, but this causes one major problem: if there are strong signals present, you can get slammed by very loud audio during the interval (even brief) where it's set to OFF. It's a jarring experience for those who don't have any idea that AGC can or should ever be turned off. Therefore, we took the safer route and made AGC OFF an "advanced "(2-button) function. Few operators use it, so this was, we felt, a good compromise. The same applies to other things you have to do with two buttons. The K2 would have to be substantially larger to accomodate all the buttons *everyone* would like to have on the front panel ;) 73, Wayne N6KR Bill Coleman wrote: > > On 5/6/02 8:00, Mychael Morohovich / AA3WF at giantbug at earthlink.net > wrote: > > > > >Simultaneously depressing PRE/ATT and AGC toggles the AGC on and off. > > It really would be nice to have OFF as one of the AGC toggles (eg cycle > through FAST/SLOW/OFF) ++++++++++++++++ Date: Sun, 24 Nov 2002 12:42:36 -0800 From: Vic Rosenthal Organization: Transparent Software To: Elecraft Subject: Re: [Elecraft] Funny AGC switch behavior -- SOLVED Vic Rosenthal wrote: > Recently I've noticed that the AGC speed on my K2 seems to switch itself to FAST > without being asked. It was happening when I was recalling a stored frequency from memory. I hadn't realized that the AGC characteristic is saved along with the frequency, mode, etc., and it had been set to FAST when I saved it. Vic K2VCO ++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'R. Torsten Clay'" , Subject: RE: [Elecraft] K2 AGC problem Date: Sat, 4 Jan 2003 19:38:31 -0800 Hi, Torsten: Dig out the troubleshooting data in the back of the K2 manual and make sure that the crystal oscillator in the AGC I-F system is working. My K2 had a bad xtal, so no signal going down the i-f strip for the agc. The result was something much like you are experiencing. There are a couple of suggestions in the troubleshooting for things to check and even a resistor to add that might get the oscillator started if it's not working. Once you confirm that, there are a number of voltage checks in the chart. Ron AC7AC K2 # 1289 I'm having a problem with my K2's (#3134) AGC. I've got everything built up through the 40m rx tests. The problem is that the AGC is very weak. ...I have set the AGC voltage to spec and calibrated the S-meter, but somehow don't get enough AGC action. Any suggestions on how to troubleshoot? Torsten N4OGW ++++++++++++++++ Date: Mon, 20 Jan 2003 09:34:48 +0000 From: "Julian (G4ILO)" Subject: Re: [Elecraft] K2 & PSK-31 To: Hank Kohl K8DD , "Elecraft List" Thanks Hank, and everyone else who pointed out how turn the K2's AGC off. I wish this function was on the AGC button. Is there a knack to doing this? I did see the word OFF appear once on the display, but mostly I just toggled the preamp, attenuator and AGC time-constant! 73, -- Julian, G4ILO. (RSGB, ARRL, G-QRP, K2 #392) G4ILO's Shack: http://www.qsl.net/g4ilo ==== Original message ==== To disable, or turn off, the AGC simultaneously press AGC and > PRE/ATT +++++++++++++++ To: elecraft at mailman.qth.net Date: Thu, 3 Apr 2003 17:07:04 -0800 From: k6se at juno.com Subject: [Elecraft] K2 AGC A question for the experts on the K2: The S-meter on my K2 (#2622) has always been very stingy. Long ago I was told by Gary Surrency of Elecraft that if I reduced R1 on the control board to 33k, it would increase the S-meter sensitivity. I left it unchanged until today (although I did change the diode he mentioned to a more "sensitive" one, which helped the S-meter slightly). On 2 December 2002, Wayne, N6KR wrote: "The vast majority of K2 revision A owners will NOT have to make any change to R1. To see a change is warranted, listen to background noise on a very quiet band, then turn off the AGC (by holding PRE/ATTN and AGC together). If the background noise comes up significantly in volume, R1 is probably slightly too large." With the original value of R1 (51k), I had a slight increase in background noise when I turned off the AGC. I then changed R1 to 47k and that indeed made the S-meter a tad more sensitive (I had to recalibrate the LO and HI settings), the the noise increase when turning off the AGC was a bit more pronouced. I then changed R1 to 33k to see what the effect would be. The S-meter was much more sensitive, and the increase in noise with the AGC off was noticeably greater. 10 MHz WWV, which previously would be about S9 on the meter, is now S9 +40 dB. This is with the preamp on and is about the same reading as on my FT-1000MP. My 8V regulator output is about 8.2 volts, BTW. I understand that K2s after #3000 have a pot at R1 and that it should be adjusted for an "AGC threshhold" of 3.9VDC. I haven't measured the AGC voltage, but my main concern is that past posts say that if the value of R1 is decreased, there should be less change in background noise when switching the AGC on and off. My K2 has a larger change in noise with the lower value of R1. What gives??? 73, de Earl +++++++++++++++++++ Subject: Re: [Elecraft] K2 AGC Date: Fri, 11 Apr 2003 00:07:52 -0400 From: Bill Coleman To: , On 4/3/03 8:07 PM, k6se at juno.com at k6se at juno.com wrote: >A question for the experts on the K2: > >The S-meter on my K2 (#2622) has always been very stingy. Long ago I was >told by Gary Surrency of Elecraft that if I reduced R1 on the control >board to 33k, it would increase the S-meter sensitivity. I left it >unchanged until today (although I did change the diode he mentioned to a >more "sensitive" one, which helped the S-meter slightly). I had a problem with the AGC that eventually turned out that Q12 was bad. I replaced it with a 2n2222A that I had in the junkbox. I had R1 at 33 K at Gary's suggestion, largely because of the stinginess and the earlier trouble I had. After the A->B mods I tried a pot at R1. I never could make the background change when AGC switched off entirely go away, but 30 K was the point it was the most subtle. My R1 is 30.1K, and a carefully selected diode with maximum Vf. I think my AGC action is near perfect, not nearly as stingy as earlier. Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 ++++++++++++++++++ To: elecraft at mailman.qth.net Date: Fri, 25 Apr 2003 16:25:45 -0700 From: k6se at juno.com Subject: [Elecraft] K2 AGC Threshold Back to the AGC threshold discussion on the K2. I have a K2, #2622. It has a fixed 51k resistor at R1 on the control board. Starting with #3000, that resistor was replaced with a 51k pot. The following has been noted: 1) The Rev C manual (S/Ns less than 3000) shows 7.3 VDC on U2 pin 5 in the voltage chart on page 15 of Appendix E. This measurement is taken with the front panel removed, otherwise U2 pin 5 would be about half of that with the RF gain controlset to max. 2) The Rev E manual (S/Ns 3000 and up) on page 46 says to adjust R1 for 3.8 VDC on U2 pin 5. This is measured with the front panel connected and the RF gain control set to max. 3) The Rev E manual also says on page 6 of Appendix E that R1 should be adjusted for 3.9 VDC on U2 pin 5 (0.1 VDC higher than the procedure on page 47). 4) Page 6, Appendix E, Rev E manual goes on to say, "You can set R1 for a slightly higher voltage at U5 pin 5 (obvious typo - should be U2 pin 5) to increase the no-signal I.F. gain." (However, setting U2 pin 5 to a lower voltage would increase the S-meter sensitivity.) 5) It has been implied by others on this list that R1 should be set so there there is little or no difference in the no-signal noise level when turning the AGC on and off. It seems to me that this would result in poor S-meter sensitivity. 6) Once, someone stated on the list that if the regulated +8.0 VDC is a bit high (mine is about +8.2 VDC) that R1 should be adjusted for some other level as measured on U2 pin 5 (forget what voltage would be right). It appears from the above that decreasing the value of R1 will increase the AGC voltage thereby increasing the S-meter sensitivity, however it will decrease the no-signal I.F. gain of the receiver. I've decreased the value of R1 in my K2 to 33k and that indeed has increased the sensitivity of the S-meter. However it has decreased the gain of the receiver, noticeable when trying to receive weak signals with the AGC turned on. This has been a dilemma with me since my K2 was born. Has anyone delved into this problem more deeply? I know the S-meter reading is only relative, but it would be nice to have it not be as stingy as mine is without sacrificing receiver I.F. gain. 73, de Earl, K6SE ++++++++++++++++ Date: Tue, 29 Apr 2003 18:04:25 -0700 From: Wayne Burdick Organization: Elecraft To: k6se at juno.com Cc: belsley at bc.edu, elecraft at mailman.qth.net Subject: [Elecraft] AGC adjustment k6se at juno.com wrote: > ... the procedure for adjusting R1 on the control board should > be so that no AGC is developed with the AGC turned on and the antenna > disconnected. Hi Earl, You're absolutely correct on this point. I just reviewed the manual and I can see that it is lacking in clarity regarding final AGC threshold adjustment. I'll clarify the instructions in the next manual revision. (Note: If the AGC threshold is adjusted, the operator must also re-adjust S HI and S LO using the CAL menu.) The meter should not be "stingy" when adjusted correctly. Gary and I will test a few K2s and see if we can reproduce what you've described. 73, Wayne N6KR +++++++++++++++ Date: Tue, 29 Apr 2003 20:18:36 -0700 From: Wayne Burdick Organization: Elecraft To: David Gropper Cc: k6se at juno.com, elecraft at mailman.qth.net Subject: [Elecraft] Re: AGC adjustment David Gropper wrote: > > Wayne, Earl, > > I would sure appreciate a short email explaining what to do! Hi Dave, In practice, the setting of the AGC threshold pot is a compromise. Setting it to a higher voltage results in the AGC coming on sooner, i.e. with lower-amplitude on-air signals. Setting it to lower voltages prevents the AGC from reducing the audio output level of the K2. The 3.8 volt setting, which is the one recommended in the K2 manual (revision E, page 46), is a good choice for most operators. As the manual explains, you can optimize this setting later if desired. The approach I take is: 1. With an antenna connected, switch to a "quiet" band (one with light atmospheric background noise, e.g. 15 m at night). Tune to a place with no incoming signal. 2. Turn AGC OFF (using PRE/AGC + AGC as explained on page 97 of the manual). If the background noise level increases dramatically with AGC off, the AGC threshold is probably set too aggressively. A lower voltage setting, as measured at pin 5 of U2 on the Control board, might be more appropriate. I'd try 3.5 or 3.6 V for starters. (Note: when adjusting the AGC threshold, disconnect the antenna. Otherwise incoming signals could make it harder to adjust.) 3. After selecting a different threshold setting, test the AGC on strong signals to make sure you haven't set the threshold voltage too low. 4. Finally, adjust CAL S HI and CAL S LO as explained on page 46. 73, Wayne ++++++++++++++ To: dmg at bossig.com, elecraft at mailman.qth.net Date: Tue, 29 Apr 2003 20:29:19 -0700 Subject: Re: [Elecraft] AGC adjustment From: k6se at juno.com Dave, KK7SS wrote: "Are you saying 3.8v with no antenna and the AGC OFF? or, No antenna, AGC ON, adjust for no difference in noise floor when switching the AGC ON/OFF??" ========== No antenna, AGC ON, and adjust for no difference in the noise level when switching the AGC ON/OFF sounds to me like the way to do it. My K2 is before #3000 and R1 is a fixed resistor, so until I change it to a pot, "adjusting" it means replacing it with a different fixed value. When I do change R1 to a pot, I plan to use a 100k pot because the 51k (original), 42k and 33k values I have tried have all successively resulted in more S-meter sensitivity, but with successively greater noise change between AGC ON/OFF (with more noise when the AGC is OFF). It appears that R1 in my K2 will have to be greater than 51k to have the no-signal receiver gain at full tilt with the AGC ON (no noise change between AGC ON/OFF). Wayne is the expert, and I'm anxious to see what his new adjustment procedure for R1 will be. 73, de Earl, K6SE +++++++++++++++ Date: Tue, 29 Apr 2003 22:01:52 -0700 From: Wayne Burdick Organization: Elecraft To: k6se at juno.com Cc: elecraft at mailman.qth.net Subject: [Elecraft] Re: AGC adjustment This is a darn good question, Earl. As the voltage at U2-5 goes down, the voltage at pin 1 should also go down. This in turn should increase the gain of the IF amp (MC1350 on the RF board). At some point the IF amp will be at maximum gain; this should occur when the voltage at U2-1 is around 3.5-3.7 V. Lower voltages then would have no effect. All that AGC OFF does is cut the gain of the AGC mixer (U1, NE602) to nearly zero. Assuming you installed a resistor value at R1 that resulted in a low voltage at pin 5 of U2, turning AGC OFF should have no effect on background noise *unless* there was an unexpected signal present at the AGC mixer's output that is affected by pulling the bias low at U1 pin 2. (I suppose U2B could also be in saturation at the voltage you have selected, but this should't happen.) Gary and I will do some measurements tomorrow and see if we can duplicate what you're seeing. Wayne k6se at juno.com wrote: > > Wayne, N6KR wrote: > > "If the background noise level increases dramatically with AGC off, the > AGC threshold is probably set too aggressively. A lower voltage setting, > as measured at pin 5 of U2 on the Control board, might be more > appropriate." > ========== > When I decrease the value of R1 (thereby decreasing the voltage at U2 pin > 5), the change in background noise becomes even greater when switching > between AGC ON/OFF. Why is my K2 working vice-versa? > > 73, de Earl, K6SE > K2 #2622 ++++++++++++ From: "Eddy Avila" To: n6kr at elecraft.com, elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: AGC adjustment Date: Wed, 30 Apr 2003 14:27:09 +0000 Wayne...thanks much for explaining in more detail the adjustment and action of the K2 AGC....based on this I've landed mine at 3.75v and really like what I'm hearing now....tons of audio when needed, good S-meter sensitivity and kool AGC action! This convinces me I'm not having any problems with the receiver and all is working great! Some of my replys about AGC action I posted hinted I had a receiver problem but hey....I knew better! Ya right.... By-the-way, I do retract my comments regarding the K2 having puny audio....now with AGC on at the new, improved setting I can still turn it up enough to blast me outa the shack and also to "mask" my wife's hollering at me to turn the DAMN THING DOWN!! ....what did you say dear? It has been kinda fun getting my hands "dirty" tweaking on the K2...I can't image ever trying this on a $3000+ import rig? E G A D S!!! May be this is what its all about! Good job guys....73 ed +++++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: Cc: Subject: RE: [Elecraft] Re: AGC adjustment Date: Wed, 30 Apr 2003 22:48:03 +0200 I am completely happy with both my AGC-action and S-meter after I did the following: 1. Adjust AGC threshold so that AGC on/off does not change perceived level on noise in a quiet band. I have installed a pot for R1 - and it really helped increase audio gain. Of all the rev A to B mods, this was the one that really made a difference. 2. Follow Don Brown's setup for setting S-meter sensitivity, after you are happy with the AGC-setting (http://www.qsl.net/ve3mcf/elecraft_reflect/K2_S-Meter_Sensitivity.txt) 2a. First set CAL S LO as per the manual (page 84 in my rev C April, 2000 version). 2b. Then adjust CAL S HI by setting RF GAIN to the 9 o'clock position (instead of fully CCW) and set parameter so that right-most bargraph is barely turned on. I have played with various other setting such a 10, 11 o'clock, but found the 9 o'clock position to be fine. It also agrees reasonably well with 50 uV from my generator to give S 9. If the AGC-setting is changed, the S-meter calibration has to be redone. I use the S-meter all the time to give signal reports. Being a new ham, I have yet to develop the proper ears for this, so I want it to work properly. Also, I can understand the discontent one feels if the rig is perfectly set up, except for a useless S-meter. If it is there, it should work! In my view it will only make things difficult if yet another variable is introduced (R5), so for me R1 and CAL S HI is enough to get both an AGC and an S-meter to work properly. 73, Sverre ------------------ Sverre Holm, LA3ZA www.qsl.net/la3za +++++++++++++ To: k6sdw at hotmail.com Cc: elecraft at mailman.qth.net Date: Sat, 3 May 2003 06:41:47 -0700 Subject: Re: [Elecraft] New K2 Options From: k6se at juno.com Hi, Ed, Ed, K6SDW wrote: "I'm more curious about ur AGC findings then I am about the new products!!!" ========== Eric agreed with me that the voltage on U2-5 is still too high, causing the AGC voltage at the output of U2-1 to be too high, even with no antenna connected. The remedy is to decrease the value of R1 even more than I already have (originally 51k, now ~33k) so that the voltage at U2-1 is close to what it is when the AGC is turned off when the antenna is disconnected. My K2's 8-volt regulator outputs 8.35 volts thereby requiring the decrease in value of R1 to be even more drastic to achieve the desired result. Therefore I have chosen to replace the 8-volt regulator with a new one (hoping that the new one outputs closer to 8.0 volts) so that the change in the value of R1 need not be so drastic. When I replace the regulator and adjust R1 so that I get the desired output from U2-1, I'll post the results on the Elecraft reflector. 73, de Earl, K6SE +++++++++++++++++ From: "Lyle Johnson" To: Subject: RE: [Elecraft] K2 Voltage Regulators Date: Sun, 4 May 2003 16:34:50 -0700 > 8-volt regulator was putting out more than 8 volts (8.35 Volts, he > reported). >... might be affecting his > AGC circuit, and presumably numbing the receiver a bit. You can reduce the AGC threshold voltage by changing the resistor. It is simply a voltage divider biasing a pin on an amplifier. Earl was apparently uncomfortasble going to less than 33K ohms in his radio's divider and opted to try and change the regulator. But there is no reason that I can see that you can't go to less. In my radio, a value around 27K is right. YMMV, mine certainly does! 73, Lyle KK7P +++++++++++++++++ To: elecraft at mailman.qth.net, n6kr at elecraft.com, eric at elecraft.com, gary at elecraft.com Date: Mon, 5 May 2003 15:18:19 -0700 From: k6se at juno.com Subject: [Elecraft] AGC adjustment I just replaced R1 on my K2's control board with a 22k resistor. The original 8-volt regulator is still in place, outputting 8.35 VDC. With no antenna connected, no signal and RF gain fully CW, I measured the following: U2-5 = 3.74 volts U2-1 (AGC on) = 3.73 volts U2-1 (AGC off) = 3.23 volts Previously, with the original 51k in parallel with a 100k (~33k), I measured the following: U2-5 = 3.87 volts U2-1 (AGC on) = 3.80 volts U2-1 (AGC off) = 3.44 volts Notice that the AGC output at U2-1 when switching the AGC on/off previously (with R1 ~ 33k) had a delta of 0.36 volts. After replacing R1 with 22k, the delta is 0.50 volts. The greater delta apparently is why the AGC on/off background noise difference is greater as I decrease the value of R1. As the value of R1 decreases, the AGC OFF output at U2-1 decreases faster than the AGC ON output at U2-1. The S-meter gets hotter each time I reduce the value of R1, as it should. My goal is to have the U2-1 difference between AGC ON and AGC OFF be only slight, so as to have the receiver operating at maximum gain with the AGC ON and no signal received. Each time I reduce the value of R1, the gain of the receiver increases, but it increases faster with the AGC OFF than with the AGC ON. How now, brown cow? 73, de Earl, K6SE +++++++++++++++ Date: Fri, 9 May 2003 10:24:08 -0700 (PDT) From: Daniel Reynolds Subject: RE: [Elecraft] AGC/S-meter To: elecraft at mailman.qth.net I found that out at lunch when I put the K2 on the bench at work. Running 50uV into the K2 on 7040 yielded S9 (after I readjusted my S-meter last night... more about that adjustment process below). BUT - when I dropped from 50uV (-73dBm) to -53dBm (+20dB gain), the meter went from S9 to Full Scale... and when I backed it off to -85dbm (approx 2 S-units) it actually dropped to S-5... So the lesson is that the meter is very relative (and not very precise)! ----- I adjusted my meter last night using the following procedure... - AGC Voltage set at 3.80. - Set S Lo with max RF gain - Set S Hi with RF gain at 9 o'clock (instead of min RF gain). It resulted in what I felt was significantly improved meter action compared to what my meter was doing before (it was very stingy). ----- Is it accurate? Is the K2 designed to be exactly 12-dB between each LED between S-5 and S-9 and 10-dB between each LED from S-9 to +40 dB? Who knows... I just know that I 'feel' better seeing the meter travel more than S-1 or S-2 on signals that seem pretty clear and 'strong' to my ears. I also know that a strong signal (50uV) will now give me a strong reading of S-9. BTW - 50uV on 7040 was S9, and 50uV on 21060 was S7 - so the gain varies from band to band. - Daniel/AA0NI +++++++++++++++