Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
There are two 'gain calibration' procedures. One is for TRANSMIT gain which requires a dummy load. The other is for receiver RF gain and it can be done with a signal source or by loading the factory defaults without a signal source. It is on the Calibration page of the K3 Utility and is a button labeled 'Calibrate RF Gain'. On 10/27/2010 6:19 PM, Gary wrote: > I must have missed something. I don't see any requirement for a sig gen in > the rf gain calibration procedure instead, I read it as being an automatic > procedure in the K3 utility that only requires a suitable load or > termination. Where is the procedure that involves a sig gen other than the > S-meter calibration that follows the rf gain calibration in the owner's > manual (pg. 51)? > > I'm new to Elecraft, just built my K3 and P3 and am getting acquainted with > them. > 73, > Gary > N6LRV > > -Original Message- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Don Wilhelm > Sent: Tuesday, October 26, 2010 8:26 AM > To: Stan Gibbs > Cc: elecraft@mailman.qth.net > Subject: Re: [Elecraft] K3 Rf gain tracking (main vs. sub) > >Have you done as has been recommended several times during this > thread? - use the latest K3 Utility and run the RF Gain Calibration. > First do the "set to defaults", and then run the calibration with a > signal generator having a controlled output level. Follow the > instructions and be certain to tune the K3 exactly to the generators > frequency (use CWT if necessary). > > Several have commented that this step has corrected their problem. > > 73, > Don W3FPR -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
I must have missed something. I don't see any requirement for a sig gen in the rf gain calibration procedure instead, I read it as being an automatic procedure in the K3 utility that only requires a suitable load or termination. Where is the procedure that involves a sig gen other than the S-meter calibration that follows the rf gain calibration in the owner's manual (pg. 51)? I'm new to Elecraft, just built my K3 and P3 and am getting acquainted with them. 73, Gary N6LRV -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Don Wilhelm Sent: Tuesday, October 26, 2010 8:26 AM To: Stan Gibbs Cc: elecraft@mailman.qth.net Subject: Re: [Elecraft] K3 Rf gain tracking (main vs. sub) Have you done as has been recommended several times during this thread? - use the latest K3 Utility and run the RF Gain Calibration. First do the "set to defaults", and then run the calibration with a signal generator having a controlled output level. Follow the instructions and be certain to tune the K3 exactly to the generators frequency (use CWT if necessary). Several have commented that this step has corrected their problem. 73, Don W3FPR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Joe, Yes, I've been in touch with Lyle; he is trying to understand this issue and resolve it, for which I am very grateful. Perhaps the solution will illuminate why some observe this behavior and some do not. Where else but Elecraft can one find such truly outstanding support? - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5678456.html Sent from the [K3] mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Stan, > If I use my XG2, I get the Markus curve. My values are using the XG2 for calibration. > There is some unidentified cause for this behavior, since it > is both repeatable and reproducible, and I sure would like to > understand it. Lyle is apparently trying to duplicate and then find the cause for the behavior. It is neither repeatable nor reproducible for me (in two K3s - 622 and 1450 and two KRX3s) and I've tried most of the recent public beta FW/DSP releases as well. 73, ... Joe, W4TV On 10/26/2010 10:27 PM, Stan Gibbs wrote: > > Joe, > > I get essentially the same numbers as you show IFF I use the factory default > calibration values. If I use my XG2, I get the Markus curve. Maybe my XG2 > is defective? There is some unidentified cause for this behavior, since it > is both repeatable and reproducible, and I sure would like to understand it. > > > - > 73, Stan - KR7C __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Joe, I get essentially the same numbers as you show IFF I use the factory default calibration values. If I use my XG2, I get the Markus curve. Maybe my XG2 is defective? There is some unidentified cause for this behavior, since it is both repeatable and reproducible, and I sure would like to understand it. - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5677204.html Sent from the [K3] mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
> Contrary to my earlier statement my K3's main RX does show an RF gain > non-linearity. I certainly don't see any non-linearity here in either the K3 or KRX3. Using your "angle" references (RG/RG$ are the RF Gain values reported by the CAT protocol): --- MAIN -- KRX3 -- RG; ADC dBVRG$; ADC dBV CW250 239 0 250239 0 0228 210 - 0.5 231213 - 0.1 45182 164 - 4.2 181169 - 4.2 90130 114 -16 132124 -17 135 90 77 -34 91 86 -35 180 47 46 -51 50 49 -51 CCW 0 02 -85 0 02 -85 The compression at the "top end" is expected since the -73 dBm signal is well above the AGC threshold until the RF/IF gain is reduced to about the 12:00 (90 degree) position. K3 s/n 1450 firmware 4.14, DSP 2.60. Both receivers are calibrated using the XG-2 on 20 meters with K3 Utility 1.1.10.15. 73, ... Joe, W4TV On 10/26/2010 3:23 PM, hb9brj wrote: > > After reading all comments, I performed an RF calibration using a -73dBm > source and the K3 Utility 1.3.10.15. First run with factory defaults, second > run using my signal source. A picture tells more than a lot of numbers: > http://home.datacomm.ch/hb9brj/RFgain.jpg > > X axis = RF gain position angle in degrees: 0 = 3 o'clock, 90 = 12 o'clock, > 180 = 9 o'clock > Y_left = CONFIG:SW TEST SCN ADC readout of RF gain pot > Y_right = DISP AFV in dBV > > Contrary to my earlier statement my K3's main RX does show an RF gain > non-linearity. > > Markus > 1505 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Very nicely done, Markus! Exactly what I observe. - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5676326.html Sent from the [K3] mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
After reading all comments, I performed an RF calibration using a -73dBm source and the K3 Utility 1.3.10.15. First run with factory defaults, second run using my signal source. A picture tells more than a lot of numbers: http://home.datacomm.ch/hb9brj/RFgain.jpg X axis = RF gain position angle in degrees: 0 = 3 o'clock, 90 = 12 o'clock, 180 = 9 o'clock Y_left = CONFIG:SW TEST SCN ADC readout of RF gain pot Y_right = DISP AFV in dBV Contrary to my earlier statement my K3's main RX does show an RF gain non-linearity. Markus 1505 -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5676134.html Sent from the [K3] mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Don Wilhelm-4 wrote: > > Have you done as has been recommended several times during this > thread? - use the latest K3 Utility and run the RF Gain Calibration. > First do the "set to defaults", and then run the calibration with a > signal generator having a controlled output level. Follow the > instructions and be certain to tune the K3 exactly to the generators > frequency (use CWT if necessary). > Yes, I've repeated the calibration with my XG2 on 40 and 20 several times. Just to be sure there wasn't something up with the "do the defaults first", I followed your suggestion and repeated the calibration on 20m, first with factory defaults, then with my XG2. I'm using the 1.3.10.15 K3 Utility version. The non-linearity is still present as before. - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5675465.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Have you done as has been recommended several times during this thread? - use the latest K3 Utility and run the RF Gain Calibration. First do the "set to defaults", and then run the calibration with a signal generator having a controlled output level. Follow the instructions and be certain to tune the K3 exactly to the generators frequency (use CWT if necessary). Several have commented that this step has corrected their problem. 73, Don W3FPR On 10/26/2010 11:16 AM, Stan Gibbs wrote: > > paulb wrote: >> Interesting to note non-linear RF gain control. >> Same thing here on the main RX. >> > Nice to know that I'm not the only one seeing this! Thanks, Paul. > > Here's some more data. Perhaps someone can illuminate us on what it > indicates. > > With my XG2 on 20m, and adjusting the main RF gain knob from full CW to full > CCW, the AFV display goes from 2329 to about 18 at the 10 o'clock position, > jumps to 1233, then declines to about 80. The dbV display starts at +29.3 > and declines to -12.4, jumps to +23.6, and then declines to -0.1 at full > CCW. > > Remember that the "SCN ADC" results show us that the gain control is linear > in its output. > > What could cause the IF gain to behave this way? Anybody? > > > - > 73, Stan - KR7C __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
paulb wrote: > > Interesting to note non-linear RF gain control. > Same thing here on the main RX. > Nice to know that I'm not the only one seeing this! Thanks, Paul. Here's some more data. Perhaps someone can illuminate us on what it indicates. With my XG2 on 20m, and adjusting the main RF gain knob from full CW to full CCW, the AFV display goes from 2329 to about 18 at the 10 o'clock position, jumps to 1233, then declines to about 80. The dbV display starts at +29.3 and declines to -12.4, jumps to +23.6, and then declines to -0.1 at full CCW. Remember that the "SCN ADC" results show us that the gain control is linear in its output. What could cause the IF gain to behave this way? Anybody? - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5675065.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Stan, I dunno if it may be related, but I recently had a dead spot in the RF gain encoder. It was recommended that I do a recal (using 20M) with the XG2 and V1.3.10.15 of the utility. An earlier version had a bug where the settings were not saved. Cured my problem. GL & 73, Mike NF4L > Actually, the main RX is the one giving me trouble, not the Sub; that was > Mike's issue. I was trying to duplicate his when I discovered mine. :-) > The behavior of my main Rx is the same whether the Sub is enabled or not. > > I redid the RF gain calibration with my XG2 twice on 40 M and once on 20 M > with no change in the behavior. I would have to think that some circuit is > not properly aligned or calibrated, but I'm not enough of a receiver expert > enough to know which are the likely candidates. > > Thanks, > > - > 73, Stan - KR7C __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Hello folks Interesting to note non-linear RF gain control. Same thing here on the main RX. Scn Adc check is spot on. Approx 10o'clock position jumps to % 100. Sub RX is ok. cheers Paul b zl1ajy 3058 -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5673415.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
In the process of investigating this further, I tripped over a very nice diagnostic tool: the Config menu's "SW TEST" entry. This option can be set to "SCN ADC" to allow monitoring of the 4 potentiometer inputs to the PIC processor ADCs. This allows one to verify the range and linearity of the pots very easily. As expected, the ADC outputs produce a linear count ranging from 002 to 240 for the full travel of the pots (all 4 of them exhibit the same results). Those counts correspond to input voltages (from the pots) of 0.039V and 4.71V, respectively, which are essentially what I measured with my voltmeter. This method is MUCH easier, however, and eliminates any question as to what the ADC is actually seeing on its inputs. - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5673239.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
ab2tc wrote: > > Have you tried to redo the calibration on the erratic subreceiver? It's > now been a long time since I did this, but I had to do mine three times > before it came out right. > Hi Knut, Actually, the main RX is the one giving me trouble, not the Sub; that was Mike's issue. I was trying to duplicate his when I discovered mine. :-) The behavior of my main Rx is the same whether the Sub is enabled or not. I redid the RF gain calibration with my XG2 twice on 40 M and once on 20 M with no change in the behavior. I would have to think that some circuit is not properly aligned or calibrated, but I'm not enough of a receiver expert enough to know which are the likely candidates. Thanks, - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5672110.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Hi, Have you tried to redo the calibration on the erratic subreceiver? It's now been a long time since I did this, but I had to do mine three times before it came out right. The 2 first times I had a dead zone like you do. It's very important to make sure the frequency is spot on as the instructions call for a very narrow bandwidth to be used. AB2TC - Knut Stan Gibbs wrote: > > > Stan Gibbs wrote: >> >> Thanks, Mike, I'll do the same measurement and see what it tells me. >> Erratic behavior seems most likely due to a bad pot, but, as Sherlock >> would say, theorizing without data is a capital mistake. >> > Sherlock was right; it wasn't the pot. The behavior of the voltage on its > wiper is exactly what you would expect: a smooth transition from 0V to > 4.7V for the full travel of the knob from CCW to CW. > > So, the question remains, what could cause the very non-linear behavior > that I observe with the audio and S meter? > > This result also renews my curiosity about whether others have observed > any non-linearity around the 10 o'clock position of the RF gain when > listening to a test signal like an XG1? > -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5672038.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Stan Gibbs wrote: > > Thanks, Mike, I'll do the same measurement and see what it tells me. > Erratic behavior seems most likely due to a bad pot, but, as Sherlock > would say, theorizing without data is a capital mistake. > Sherlock was right; it wasn't the pot. The behavior of the voltage on its wiper is exactly what you would expect: a smooth transition from 0V to 4.7V for the full travel of the knob from CCW to CW. So, the question remains, what could cause the very non-linear behavior that I observe with the audio and S meter? This result also renews my curiosity about whether others have observed any non-linearity around the 10 o'clock position of the RF gain when listening to a test signal like an XG1? - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5671487.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
Mike Scott-7 wrote: > > To the person who has weird main receiver RF gain action the test I did > could help you determine if it is the Pot. > Thanks, Mike, I'll do the same measurement and see what it tells me. Erratic behavior seems most likely due to a bad pot, but, as Sherlock would say, theorizing without data is a capital mistake. - 73, Stan - KR7C -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Rf-gain-tracking-main-vs-sub-tp5668917p5669008.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Rf gain tracking (main vs. sub)
With no antenna attached do you see 0-3 volt range on the U3 side of R22 on the subRX board as you vary the RF gain from min to max? This would be the far end of the gain process. 73, Guy On Sun, Oct 24, 2010 at 7:48 PM, Mike Scott wrote: > Further to the issue that my K3 RF gain on the sub Rx won't cause the RF > gain to go very low (I can still hear band noise and signals on the sub Rx > at minimum gain). > > > > With the help of Guy I found the RF gain pots on the front panel schematic > and understand how they might work. > > The high end of each 10K RF pot is at +5 volts, the low end is ground. The > wiper is a voltage divider which goes to a PIC on the MCU board for decoding > through an A-D converter on the PIC. The decoded pot voltage is then used > later to compute RF (really IF) gain after some translation magic happens in > the PIC and later after all the magic an analog IF gain level is created in > a DAC to bias the RF IF amp stage. At least this is my understanding with a > lot missing in between. It looks to me that there are HAGC1 and HAGC2 test > points on the two RF boards. The HAGC is the hardware AGC which is derived > from either the RF gain position Pots or H/W AGC circuitry. If I could find > these test points and measure the 0 to 3 volts expected (0 = max gain and 3V > = minimum gain) in the respective IF amplifiers I might learn that the sub > RX never goes to 3V at minimum RF gain pot setting. The 0-3 volts is biasing > a J309 IF amplifier. > > > > Because it might have been possible that the ground end of the Sub Rx RF pot > was not at ground potential it was possible that the voltage signal on the > wiper was not correct and never going to zero. This might be caused by a > poor solder connection for example or just a faulty pot. > > > > The RF gain pots are accessible by removing the front bottom cover plate. > Each of the RF-gain pot connections can be seen by inspecting the location. > With a volt meter and tiny hook probes I measured the wiper voltage on the > main and sub RF-gain pots at three gain settings: full on (CW), full off > (CCW) and 12 o'clock. > > > > Pot full on full off 12 o'clock > > Main 4.682V .002V 2.36V > > Sub 4.682V .002V ` 2.40V > > > > It looks to me like both RF-gain pots are doing exactly the right thing. > > > > So, now I am down to one MCU PIC A/D port is not working properly, a bad > solder connection between the wiper arm and the PIC or Wayne is not decoding > the two pots the same way in my serial 506 K3 or the main and sub Rx are > treating the decoded RF gain positions differently or some other gain > calculation is going on to modify the gain requested by the RF gain pots. I > don't know how the variable RF gain setting is accomplished once the PIC > decodes the pot position. Since there is no real current draw through the > Pot I don't believe a bad solder joint is causing a partial voltage to > arrive at the MCU PIC, it should either work or not. > > > > To the person who has weird main receiver RF gain action the test I did > could help you determine if it is the Pot. As you are looking at the pot > with the bottom front cover off put a volt meter on the middle of the three > pot connections, the ones on the mic connector side of the pot, the other > side of the meter to a convenient ground. You should be working with the > most accessible or bottom-most pot. With K3 power on move the main Rx RF > gain and check to see that voltage moves from ~5v to 0v smoothly as you turn > the pot counter clockwise. I used mini hook grabbers to hook up the meter > before turning power on and verified that pot resistance to ground moved > properly when gain was moved. I didn't want to have a slip up and short > something, this verifies I was connected to the wiper arm of the pot. You > can't really test the full range of the pot in circuit with power off with > an ohm meter as the high side shows something like 900 ohms resistance to > ground with power off. > > > > AE6WA > > Mike Scott > > Tarzana, CA > > > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
[Elecraft] K3 Rf gain tracking (main vs. sub)
Further to the issue that my K3 RF gain on the sub Rx won't cause the RF gain to go very low (I can still hear band noise and signals on the sub Rx at minimum gain). With the help of Guy I found the RF gain pots on the front panel schematic and understand how they might work. The high end of each 10K RF pot is at +5 volts, the low end is ground. The wiper is a voltage divider which goes to a PIC on the MCU board for decoding through an A-D converter on the PIC. The decoded pot voltage is then used later to compute RF (really IF) gain after some translation magic happens in the PIC and later after all the magic an analog IF gain level is created in a DAC to bias the RF IF amp stage. At least this is my understanding with a lot missing in between. It looks to me that there are HAGC1 and HAGC2 test points on the two RF boards. The HAGC is the hardware AGC which is derived from either the RF gain position Pots or H/W AGC circuitry. If I could find these test points and measure the 0 to 3 volts expected (0 = max gain and 3V = minimum gain) in the respective IF amplifiers I might learn that the sub RX never goes to 3V at minimum RF gain pot setting. The 0-3 volts is biasing a J309 IF amplifier. Because it might have been possible that the ground end of the Sub Rx RF pot was not at ground potential it was possible that the voltage signal on the wiper was not correct and never going to zero. This might be caused by a poor solder connection for example or just a faulty pot. The RF gain pots are accessible by removing the front bottom cover plate. Each of the RF-gain pot connections can be seen by inspecting the location. With a volt meter and tiny hook probes I measured the wiper voltage on the main and sub RF-gain pots at three gain settings: full on (CW), full off (CCW) and 12 o'clock. Pot full on full off 12 o'clock Main 4.682V .002V2.36V Sub 4.682V .002V ` 2.40V It looks to me like both RF-gain pots are doing exactly the right thing. So, now I am down to one MCU PIC A/D port is not working properly, a bad solder connection between the wiper arm and the PIC or Wayne is not decoding the two pots the same way in my serial 506 K3 or the main and sub Rx are treating the decoded RF gain positions differently or some other gain calculation is going on to modify the gain requested by the RF gain pots. I don't know how the variable RF gain setting is accomplished once the PIC decodes the pot position. Since there is no real current draw through the Pot I don't believe a bad solder joint is causing a partial voltage to arrive at the MCU PIC, it should either work or not. To the person who has weird main receiver RF gain action the test I did could help you determine if it is the Pot. As you are looking at the pot with the bottom front cover off put a volt meter on the middle of the three pot connections, the ones on the mic connector side of the pot, the other side of the meter to a convenient ground. You should be working with the most accessible or bottom-most pot. With K3 power on move the main Rx RF gain and check to see that voltage moves from ~5v to 0v smoothly as you turn the pot counter clockwise. I used mini hook grabbers to hook up the meter before turning power on and verified that pot resistance to ground moved properly when gain was moved. I didn't want to have a slip up and short something, this verifies I was connected to the wiper arm of the pot. You can't really test the full range of the pot in circuit with power off with an ohm meter as the high side shows something like 900 ohms resistance to ground with power off. AE6WA Mike Scott Tarzana, CA __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
