RE: [Elecraft] voltmeter offset and accuracy in K2
Jean-Francois, You certainly could do that - it should not alter any other function that I am aware of. The current display can be trimmed by changing Control Board R7. R10 and R7 are 1% resistors, and that provides repeaability from one K2 to another - one could hand-pick from 5% resistors just as well. I personally would be concerned about leaving a trimmeer in place because of the possibility of the setting being changed, but certainly using a trimmer to determine the exact value required would be an easy method. 73, Don W3FPR -Original Message- Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ == -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
Thanks, I will try and let you know my result !!! 73 Le 05-07-24 à 07:32, W3FPR - Don Wilhelm a écrit : Jean-Francois, You certainly could do that - it should not alter any other function that I am aware of. The current display can be trimmed by changing Control Board R7. R10 and R7 are 1% resistors, and that provides repeaability from one K2 to another - one could hand-pick from 5% resistors just as well. I personally would be concerned about leaving a trimmeer in place because of the possibility of the setting being changed, but certainly using a trimmer to determine the exact value required would be an easy method. 73, Don W3FPR -Original Message- Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ == -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 == Jean-François Ménard / VA2VYZ == ___ 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
RE: [Elecraft] voltmeter offset and accuracy in K2
Folks, After thinking about this voltmeter 'adjustment' a bit more, I discovered I had erred. The value of R10 should be INCREASED to make the reading higher. Sorry - I guess I had a 'senior moment' and got my head turned around wrong. 73, Don W3FPR -Original Message- Jean-Francois, You certainly could do that - it should not alter any other function that I am aware of. The current display can be trimmed by changing Control Board R7. R10 and R7 are 1% resistors, and that provides repeaability from one K2 to another - one could hand-pick from 5% resistors just as well. I personally would be concerned about leaving a trimmeer in place because of the possibility of the setting being changed, but certainly using a trimmer to determine the exact value required would be an easy method. 73, Don W3FPR -Original Message- Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
I'm planning to use a little higher value trimmer, so I would be able to be more or less in a second. I let you know wich one I use... I would like the really smaller one (in size) that it can take not much space as the actual resistor. Le 05-07-24 à 09:03, W3FPR - Don Wilhelm a écrit : Folks, After thinking about this voltmeter 'adjustment' a bit more, I discovered I had erred. The value of R10 should be INCREASED to make the reading higher. Sorry - I guess I had a 'senior moment' and got my head turned around wrong. 73, Don W3FPR -Original Message- Jean-Francois, You certainly could do that - it should not alter any other function that I am aware of. The current display can be trimmed by changing Control Board R7. R10 and R7 are 1% resistors, and that provides repeaability from one K2 to another - one could hand-pick from 5% resistors just as well. I personally would be concerned about leaving a trimmeer in place because of the possibility of the setting being changed, but certainly using a trimmer to determine the exact value required would be an easy method. 73, Don W3FPR -Original Message- Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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 == Jean-François Ménard / VA2VYZ == ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
Don, Do you think after the voltage will be adjust according to an external DC voltage and an accurate external volt meter, if we change later the DC source supply, like a battery with a little bit different voltage, instead of a standard power supply by example, do you think there will be or might be another voltage offset or it will be calibrate for any kind of DC supply in the range of, let say, 12V to 14V ??? Maybe an error offset will be anyway present, and by changing the DC source it could increase the offset error and indicate an improper value again Sorry for the clumsy question ;-) Le 05-07-24 à 09:13, JEAN-FRANCOIS MENARD a écrit : I'm planning to use a little higher value trimmer, so I would be able to be more or less in a second. I let you know wich one I use... I would like the really smaller one (in size) that it can take not much space as the actual resistor. Le 05-07-24 à 09:03, W3FPR - Don Wilhelm a écrit : Folks, After thinking about this voltmeter 'adjustment' a bit more, I discovered I had erred. The value of R10 should be INCREASED to make the reading higher. Sorry - I guess I had a 'senior moment' and got my head turned around wrong. 73, Don W3FPR -Original Message- Jean-Francois, You certainly could do that - it should not alter any other function that I am aware of. The current display can be trimmed by changing Control Board R7. R10 and R7 are 1% resistors, and that provides repeaability from one K2 to another - one could hand-pick from 5% resistors just as well. I personally would be concerned about leaving a trimmeer in place because of the possibility of the setting being changed, but certainly using a trimmer to determine the exact value required would be an easy method. 73, Don W3FPR -Original Message- Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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 == Jean-François Ménard / VA2VYZ == ___ 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 == Jean-François Ménard / VA2VYZ == ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
Please forgive me for putting on my physics teacher hat and doubly forgive the algebra which is to come :^)) I'd argue against trying to recalibrate the K2 internal voltmeter to compensate for the diode drop in series with the supply. How come? Because changing the resistor values in the voltage divider is a multiplier correction, while the problem is an additive offset. The algebra: if the supply voltage is Vs and the metered voltage is Vm then Vm = Vs - Vfwhere Vf is the forward drop of a diode if you fiddle with the voltage divider you can get Vm = k (Vs - Vf)where k is the factor for the new divider. Now, for any particular Vs, and knowing that Vf is pretty much constant, you can choose a k that will make the meter read perfectly, that is Vm = Vs if k = Vs/(Vs-Vf) But if Vs changes, you'll need a new k. Granted, since Vs will probably vary over only a small range, say 11 V to 15 V, the difference won't be large. But ... the diference now won't be known, whereas before there was a known, predictable offset. The k value will only need to change by 2% or so, but 2% of 14V is a couple of tenths. You went from *knowing* the reading was about a half volt too low, to having a reading that could be a couple of tenths high or low depending on where in the range you are. What you really needed to do was add Vf to both sides: Vm (new) = Vm + Vf = (Vs - Vf) +Vf And that you can't do by changing the divider ratio. Could it be done in the firmware? Sure, just add in the requisite counts to put back the diode offset. But I'll betcha Wayne and Eric figured it was better to know the actual voltage the rig is seeing (after the protection diode AND any voltage drop in the power cord). OK, physics teacher hat off, QRPer hat back on If it ain't broke 73 Jim N5IB ___ 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
RE: [Elecraft] voltmeter offset and accuracy in K2
Jim, You are exactly right - it will read a bit high for all voltages. I don't believe that would be a problem for most folks since they seldom use the voltmeter for anything other than monitoring the K2 voltage. If you use the K2 metering circuit in its EXT mode by changing the jumper and using a probe, you will find those readings a bit high after making the change. Proper compensation COULD be done in firmware - but the firmware would have to know exactly the diode drop and that varies from diode to diode, and it is not a good solution for those using the EXT voltmeter function either because there is no input to the firmware to indicate when the voltmeter is in the INT or the EXT position. I hope I did not give the wrong impression - I am not advocating nor recommending this as a change, I was simply responding to those folks who wanted to know how to do it. 73, Don W3FPR -Original Message- Please forgive me for putting on my physics teacher hat and doubly forgive the algebra which is to come :^)) I'd argue against trying to recalibrate the K2 internal voltmeter to compensate for the diode drop in series with the supply. How come? Because changing the resistor values in the voltage divider is a multiplier correction, while the problem is an additive offset. The algebra: if the supply voltage is Vs and the metered voltage is Vm then Vm = Vs - Vf where Vf is the forward drop of a diode if you fiddle with the voltage divider you can get Vm = k (Vs - Vf) where k is the factor for the new divider. Now, for any particular Vs, and knowing that Vf is pretty much constant, you can choose a k that will make the meter read perfectly, that is Vm = Vs if k = Vs/(Vs-Vf) But if Vs changes, you'll need a new k. Granted, since Vs will probably vary over only a small range, say 11 V to 15 V, the difference won't be large. But ... the diference now won't be known, whereas before there was a known, predictable offset. The k value will only need to change by 2% or so, but 2% of 14V is a couple of tenths. You went from *knowing* the reading was about a half volt too low, to having a reading that could be a couple of tenths high or low depending on where in the range you are. What you really needed to do was add Vf to both sides: Vm (new) = Vm + Vf = (Vs - Vf) +Vf And that you can't do by changing the divider ratio. Could it be done in the firmware? Sure, just add in the requisite counts to put back the diode offset. But I'll betcha Wayne and Eric figured it was better to know the actual voltage the rig is seeing (after the protection diode AND any voltage drop in the power cord). OK, physics teacher hat off, QRPer hat back on If it ain't broke 73 Jim N5IB -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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
RE: [Elecraft] voltmeter offset and accuracy in K2
If you want the K2 voltmeter to read the correct external voltage, why not connect directly from the input power jack to the external input of the voltmeter, and slide the switch/strap over to the EXT position? In this way you bypass the diode loss and there is no need for recalibration. Or are there some constraints in the original posting that I am missing with this rather simple solution? 73 Sverre LA3ZA http://www.qslnet.de/la3za/ ___ 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
RE: [Elecraft] voltmeter offset and accuracy in K2
Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). By process of elimination, the more 'critical' voltage regulator is the 8 volt low dropout regulator. The main thing the 5 volts drives is the front panel and control board digital stuff and as long as the voltage is within the tolerances for digital components, it will be close enough. The really critical circuit - the PLL is regulated by a secondary regulator down to 5 volts driven from the 8 volt line. The major parts of the K2 driven from the 8 volt regulator are the IF amp and product detector, the AGC, and the low level transmit stages - the devices used in those stages are not particularly sensitive to the voltage level. The only thing really sensitive to the exact voltage level is the AGC threshold since it is a resistive divider. I would think you could better 'improve' your K2 by carefully setting the AGC threshold level by changing the Control Board R1 value and leave the regulator as it is. As I recall, you may have optimized the AGC Threshold the last time you 'tweaked' your K2. 73, Don W3FPR -Original Message- NB: this posting is about an Elecraft radio ;-) * * * I was thinking about doing two things to my vereable K2 #0771, as I wait for new Elecraft toys: ... one is to re-jigger the divider resistors to offset the K2 voltmeter so it reads what my actual input-port voltage is, rather than the internal voltage and ...two was changing the TO-220 regulator(s) to some kind of precision type ... could not remember if it was the 8V LVDO or the plain-old 7805 type that set the reference voltage for other measurements. Wasn't obvious from the schematic, at first. On the matter of the offset, I suppose that the voltmeter's ultimate accuracy will be reduced a bit because a fixed offset won't compensate for the actual, varying drop through the polarity-protect diode, as that will vary over the IsubF ... however, I've switched mine to the newer Schottky type -- and aren't they V-drop-flatter over the current curve than the original? And on the second matter of the regulator precision, maybe I am mistaken about the availability of more-accurate TO-220 parts. What is the typical load that the 8V rail has? I'm guessing a 1 amp regulator will suffice. Which regulator was the critical voltage unit? It was the +5v, right? Steve KZ1X/4 -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ == ___ 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
Re: [Elecraft] voltmeter offset and accuracy in K2
Hi Don, You said : By lowering the value of R10 ... Could I just put a trimmer near that value instead of R10 and tune the trimmer so that the voltage displayed match more closer the real external voltage ??? And could I do limilar thing with the current display ??? I don't want to be more catholic than the Pope, but is it possible to do those mods ??? Best 73 from a junior ;-) Le 05-07-23 à 18:56, W3FPR - Don Wilhelm a écrit : Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit). == Jean-François Ménard / VA2VYZ == ___ 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
