K2 power output measurement accuracy?
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K2 power output measurement accuracy?
 
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My K2 and my watt meter do not agree. When I set the K2 power output at
5 watts I get almost 10 according to the external watt meter. Setting K2 power output at about 12 watts gives something between 15 and 20 out on the external meter. At settings above about 13 watts on the K2 knob, I get the high current warning. This is all driving a 1.2 : 1 or lower SWR, btw. It leads me to believe the K2's power output is fine but it's ability to measure and report it is off. How accurate is the power output control knob supposed to be? I don't recall doing any calibration steps or alignment steps that affect that part of the rig. I have not (yet) measured voltage into a 50 ohm dummy load but am seriously considering dragging the rig, PS, dummy load & cables into work to have access to a scope. - Keith KD1E - - K2 5411 - _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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I tried TWO good watt meters on the K2 and I found that the K2 is NOT accurate. The ONLY place I found it to be accurate is at exactly two watts. I also found that my K2/100 will go down to 100 Mw then jump to just over one watt, then to over to three and etc, it's not a smooth transition. I wish it would go from zero all the way up smoothly, but no way. My Icom is a lot smoother but will only go down to 1 1/2 watts. Working QRPP with my K2 requires 100 MW and thatâs all because it's too jumpy to set anywhere else. I don't have RF problems as far as I know but it sure is acting like it with the K2 but NOT on the Icom. That is my only beef with the K2 because my Icom acts more like a real QRP rig that the K2 does.
k3ey k2/100 s/n 5417 "Darwin, Keith" <[hidden email]> wrote: My K2 and my watt meter do not agree. When I set the K2 power output at 5 watts I get almost 10 according to the external watt meter. Setting K2 power output at about 12 watts gives something between 15 and 20 out on the external meter. At settings above about 13 watts on the K2 knob, I get the high current warning. This is all driving a 1.2 : 1 or lower SWR, btw. It leads me to believe the K2's power output is fine but it's ability to measure and report it is off. How accurate is the power output control knob supposed to be? I don't recall doing any calibration steps or alignment steps that affect that part of the rig. I have not (yet) measured voltage into a 50 ohm dummy load but am seriously considering dragging the rig, PS, dummy load & cables into work to have access to a scope. - Keith KD1E - - K2 5411 - _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: [hidden email] 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: K2 power output measurement accuracy?
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100 MW now that's what I call QRPP !
When is the next Elecraft QRO amp due ? :) 73 Stewart G3RXQ On Wed, 24 May 2006 07:45:19 -0700 (PDT), Curt wrote: > I tried TWO good watt meters on the K2 and I found that the K2 is NOT > accurate. The ONLY place I found it to be accurate is at exactly two watts. I > also found that my K2/100 will go down to 100 Mw then jump to just over one > watt, then to over to three and etc, it's not a smooth transition. I wish it > would go from zero all the way up smoothly, but no way. My Icom is a lot > smoother but will only go down to 1 1/2 watts. Working QRPP with my K2 > requires 100 MW and thatââ¢s all because it's too jumpy to set anywhere else. > I don't have RF problems as far as I know but it sure is acting like it with > the K2 but NOT on the Icom. That is my only beef with the K2 because my Icom > acts more like a real QRP rig that the K2 does. > > > k3ey > > k2/100 s/n 5417 > > "Darwin, Keith" wrote: My K2 and my watt meter do > not agree. When I set the K2 power output at > 5 watts I get almost 10 according to the external watt meter. Setting > K2 power output at about 12 watts gives something between 15 and 20 out > on the external meter. At settings above about 13 watts on the K2 knob, > I get the high current warning. > > This is all driving a 1.2 : 1 or lower SWR, btw. > > It leads me to believe the K2's power output is fine but it's ability to > measure and report it is off. > > How accurate is the power output control knob supposed to be? I don't > recall doing any calibration steps or alignment steps that affect that > part of the rig. > > I have not (yet) measured voltage into a 50 ohm dummy load but am > seriously considering dragging the rig, PS, dummy load & cables into > work to have access to a scope. > > - Keith KD1E - > - K2 5411 - > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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: [hidden email] > 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: [hidden email] 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: K2 power output measurement accuracy?
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In reply to this post by Darwin, Keith
The basic K2 power ouput indication is very accurate when operating into a
50 ohm non-reactive load. If it is driving anything other than that load, the indication will be inaccurate - he basic K2 does not have a wattmeter, t does have an RF Probe type detector which reports the RF Voltage to the microprocessor and the 'power' is computed based on the assumption that the load is 50 ohms. If the KAT2, KAT100 or KPA100 is intalled, the RF Probe type detector is not used, but the real wattmeter in these options is used instead (the firmware knows which to use with no user input), and the power readings on the K2 will be asaccurate as your calibration allowed. Be aware that wattmeters are notorious for inaccuracies, many staqte their accuracy based on a percentage of full scale - even the Bird does this, so with a recently calibrated Bird with a 100 watt slug, the error can be as great as 5 watts anywhere on the scale. How many hams have properly calibrated wattmeters? Youn can actually calibrate your wattmeter with the RF Probe in the basic K2 - all it takes is a known non-reactive 50 ohm load. I use 1% precision thick film power resistors, so I know my dummy loads are good to 50 MHz or more, and with these loads, I know the base K2 power indication to be accurate. If you have the basic K2, the power control circuits will adjust the power to make the RF voltage at the power detector probe equal to that required to produce the requested power into a 50 ohm load -- but if the load is different than 50 ohms (as it will be with a 1.2 SWR), then the power indication will not be correct - tosay how far off it will be requires knowledge of the resistive and reactive components of the 1.2 SWR (all 1.2 SWRs are not equal, the range of possibilities form a circle on the Smith Chart). 73, Don W3FPR -----Original Message----- My K2 and my watt meter do not agree. When I set the K2 power output at 5 watts I get almost 10 according to the external watt meter. Setting K2 power output at about 12 watts gives something between 15 and 20 out on the external meter. At settings above about 13 watts on the K2 knob, I get the high current warning. This is all driving a 1.2 : 1 or lower SWR, btw. It leads me to believe the K2's power output is fine but it's ability to measure and report it is off. How accurate is the power output control knob supposed to be? I don't recall doing any calibration steps or alignment steps that affect that part of the rig. I have not (yet) measured voltage into a 50 ohm dummy load but am seriously considering dragging the rig, PS, dummy load & cables into work to have access to a scope. - Keith KD1E - - K2 5411 - -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.7.0/346 - Release Date: 5/23/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: K2 power output measurement accuracy?
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In reply to this post by Curt-17
Curt,
The base K2 power reading is quite accurate if (and only if) the load is 50 ohms pure resistance. See my other post on the subject. Since you have a K2/100, the included wattmeter should be as accurate as your calibration of it. Prhaps you should re-do the calibration - or possibly both your external wattmeters are not properly calibrated (see my other post for more info) 73, Don W3FPR -----Original Message----- I tried TWO good watt meters on the K2 and I found that the K2 is NOT accurate. The ONLY place I found it to be accurate is at exactly two watts. I also found that my K2/100 will go down to 100 Mw then jump to just over one watt, then to over to three and etc, it's not a smooth transition. I wish it would go from zero all the way up smoothly, but no way. My Icom is a lot smoother but will only go down to 1 1/2 watts. Working QRPP with my K2 requires 100 MW and thatâs all because it's too jumpy to set anywhere else. I don't have RF problems as far as I know but it sure is acting like it with the K2 but NOT on the Icom. That is my only beef with the K2 because my Icom acts more like a real QRP rig that the K2 does. k3ey k2/100 s/n 5417 "Darwin, Keith" <[hidden email]> wrote: My K2 and my watt meter do not agree. When I set the K2 power output at 5 watts I get almost 10 according to the external watt meter. Setting K2 power output at about 12 watts gives something between 15 and 20 out on the external meter. At settings above about 13 watts on the K2 knob, I get the high current warning. This is all driving a 1.2 : 1 or lower SWR, btw. It leads me to believe the K2's power output is fine but it's ability to measure and report it is off. How accurate is the power output control knob supposed to be? I don't recall doing any calibration steps or alignment steps that affect that part of the rig. I have not (yet) measured voltage into a 50 ohm dummy load but am seriously considering dragging the rig, PS, dummy load & cables into work to have access to a scope. - Keith KD1E - - K2 5411 - _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: [hidden email] 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 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.7.0/346 - Release Date: 5/23/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.7.0/346 - Release Date: 5/23/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: K2 power output measurement accuracy?
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In reply to this post by Darwin, Keith
Thanks Don,
So with my basic K2, I should get agreement between the K2's setting and its output when driving my 50 ohm dummy load. I'll check it that way and report back. I never completed the RF probe with the K2 (didn't need it). I assume it simply converts RF AC voltage into DC voltage (probably RMS) so you can measure it with a DVM, right? So at 10 watts into a dummy load, I should see 22.4 volts? Does the diode drop some voltage so I'll actually see 21.7? There is so much I don't know about this stuff since rig since it went together with no problems and worked fine the first time. It didn't give much opportunity to do any trouble shooting. Gee Darn :-) - Keith KD1E - -----Original Message----- From: Don Wilhelm [mailto:[hidden email]] The basic K2 power ouput indication is very accurate when operating into a 50 ohm non-reactive load. If it is driving anything other than that load, the indication will be inaccurate - the basic K2 does not have a wattmeter, it does have an RF Probe type detector which reports the RF Voltage to the microprocessor and the 'power' is computed based on the assumption that the load is 50 ohms. _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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It's a standard diode peak detector I believe, so it would indicate 31.7 VDC (minus the drop) at 10 W for a 50 ohm load. I expect the drop is about 0.3 V. Larry N8LP Darwin, Keith wrote: > Thanks Don, > > So with my basic K2, I should get agreement between the K2's setting and > its output when driving my 50 ohm dummy load. I'll check it that way > and report back. > > I never completed the RF probe with the K2 (didn't need it). I assume > it simply converts RF AC voltage into DC voltage (probably RMS) so you > can measure it with a DVM, right? So at 10 watts into a dummy load, I > should see 22.4 volts? Does the diode drop some voltage so I'll > actually see 21.7? > > There is so much I don't know about this stuff since rig since it went > together with no problems and worked fine the first time. It didn't > give much opportunity to do any trouble shooting. Gee Darn :-) > > - Keith KD1E - > > -----Original Message----- > From: Don Wilhelm [mailto:[hidden email]] > > The basic K2 power ouput indication is very accurate when operating into > a 50 ohm non-reactive load. If it is driving anything other than that > load, the indication will be inaccurate - the basic K2 does not have a > wattmeter, it does have an RF Probe type detector which reports the RF > Voltage to the microprocessor and the 'power' is computed based on the > assumption that the load is 50 ohms. > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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: [hidden email] 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: K2 power output measurement accuracy?
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In reply to this post by Darwin, Keith
Ya lost me there Larry. P = E^^2 / R. R is 50 ohms, P is 10 watts, E
works out to sqrt(500) or 22.36 volts. But are we talking RMS, peak, or peak-to-peak? Let's see, if my number is an RMS and you're number is peak, then 22.36 is about 22.4. Multiply by 1.41 and I get 31.6 Pretty close to your number. Or am I way off base? - Keith - -----Original Message----- From: Larry Phipps [mailto:[hidden email]] It's a standard diode peak detector I believe, so it would indicate 31.7 VDC (minus the drop) at 10 W for a 50 ohm load. I expect the drop is about 0.3 V. Darwin, Keith wrote: > I never completed the RF probe with the K2 (didn't need it). I assume > it simply converts RF AC voltage into DC voltage (probably RMS) so you > can measure it with a DVM, right? So at 10 watts into a dummy load, I > should see 22.4 volts? Does the diode drop some voltage so I'll > actually see 21.7? _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: K2 power output measurement accuracy?
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In reply to this post by Don Wilhelm-3
----- Original Message ----- From: "Don Wilhelm" <[hidden email]> To: "Darwin, Keith" <[hidden email]>; <[hidden email]> Sent: Wednesday, May 24, 2006 9:29 AM Subject: RE: [Elecraft] K2 power output measurement accuracy? > K2 - all it takes is a known non-reactive 50 ohm load. I use 1% precision > thick film power resistors, so I know my dummy loads are good to 50 MHz or > more, and with these loads, I know the base K2 power indication to be > accurate. > > If you have the basic K2, the power control circuits will adjust the power > to make the RF voltage at the power detector probe equal to that required to > produce the requested power into a 50 ohm load -- but if the load is > different than 50 ohms (as it will be with a 1.2 SWR), then the power > indication will not be correct - tosay how far off it will be requires > knowledge of the resistive and reactive components of the 1.2 SWR (all 1.2 > SWRs are not equal, the range of possibilities form a circle on the Smith > Chart). > > 73, > Don W3FPR ----------------------------------------------------------------------- With my K2 into a DL1, my WM-2 meter shows up to 20 % higher power than my DMM and slide rule indicates. Is the DL1 likely more accurate than my WM-2 meter. If so, I will recalibrate my K2 with the DL1 and DDM. Than I will have a stronger QRP signal and be able to work 300 new countries. I could also recalibrate my WM-2. Also, I wonder if the K2 maximum output power is increased if the voltage goes up. Just in case I need to cheat a little with QRO power (15watts or so). But I promise not to get an amplifyer. 73 (72) Rick Dettinger K7MW _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: K2 power output measurement accuracy?
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Rick, K7MW asked:
With my K2 into a DL1, my WM-2 meter shows up to 20 % higher power than my DMM and slide rule indicates. Is the DL1 likely more accurate than my WM-2 meter. If so, I will recalibrate my K2 with the DL1 and DDM. Than I will have a stronger QRP signal and be able to work 300 new countries. I could also recalibrate my WM-2. Also, I wonder if the K2 maximum output power is increased if the voltage goes up. Just in case I need to cheat a little with QRO power (15watts or so). But I promise not to get an amplifyer.. ---------------------------------- At decent power levels (several watts), diode detector with a capacitor across the output to the DMM (to charge up and show peak voltage) is the most accurate wattmeter most hams can get. The accuracy is limited solely by the accuracy of the DMM and accuracy of the value of the resistive load on the RF source. Notice "resistive" in that statement. It's absolutely essential the AC (or RF) signal be looking into a non-reactive load. So go for it, and rack up those new countries!! All QRPers know that milliwatts are important. But you make an excellent point. A few milliwatts (or even watts) makes very little difference on the air in a given contact. The real thing to look at in comparing on-air performance is dB. We can hear a 6 dB difference pretty clearly, if we're listening for it. That's about 1 S-unit on most receivers. Although 1 dB is defined as that minimum change just perceptible in human hearing, most communications engineers consider 3 dB to be about the minimum discernable change in radio communications in the most ideal conditions. That's why twice that - 6 dB - is commonly consider an "S-Unit". It's just enough change to say the signal got stronger or weaker in most situations. I consider 6 dB to be about the minimum amount of change worth pursuing if I'm thinking of changing my power levels. Going from 15 watts with a QRP K2 to 100 watts with my K2/100 increased my signal by just over 8 dB. That's enough to be noticed. Going from 100 watts to 800 watts adds another 9 dB again. Again enough to be noticed. But I'd never spend a moment worrying about whether anyone can hear the difference between, say, 15 watts and 10 watts or between 100 watts and 50 watts. It just isn't going to happen. It's worth chasing milliwatts when we're trying to assemble the most efficient station. They add up. But in practice, doubling or even tripling the power (or reducing it that much) simply isn't going to be noticed. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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At 15W the DL-1 is by far more accurate. It is probably within a few percent, based on a normal random distribution of resistor values, and 5% worst case if they're all off in the same direction. Keep in mind though that the resistance changes as temperature rises... so it's best to take a quick reading before the resistors heat up. Larry N8LP Ron D'Eau Claire wrote: > Rick, K7MW asked: > With my K2 into a DL1, my WM-2 meter shows up to 20 % higher power than my > DMM and slide rule indicates. Is the DL1 likely more accurate than my WM-2 > meter. If so, I will recalibrate my K2 with the DL1 and DDM. Than I will > have a stronger QRP signal and be able to work 300 new countries. I could > also recalibrate my WM-2. Also, I wonder if the K2 maximum output power is > increased if the voltage goes up. Just in case I need to cheat a little > with QRO power (15watts or so). But I promise not to get an amplifyer.. > > ---------------------------------- > > At decent power levels (several watts), diode detector with a capacitor > across the output to the DMM (to charge up and show peak voltage) is the > most accurate wattmeter most hams can get. The accuracy is limited solely by > the accuracy of the DMM and accuracy of the value of the resistive load on > the RF source. Notice "resistive" in that statement. It's absolutely > essential the AC (or RF) signal be looking into a non-reactive load. > > So go for it, and rack up those new countries!! > > All QRPers know that milliwatts are important. But you make an excellent > point. A few milliwatts (or even watts) makes very little difference on the > air in a given contact. The real thing to look at in comparing on-air > performance is dB. We can hear a 6 dB difference pretty clearly, if we're > listening for it. That's about 1 S-unit on most receivers. Although 1 dB is > defined as that minimum change just perceptible in human hearing, most > communications engineers consider 3 dB to be about the minimum discernable > change in radio communications in the most ideal conditions. That's why > twice that - 6 dB - is commonly consider an "S-Unit". It's just enough > change to say the signal got stronger or weaker in most situations. > > I consider 6 dB to be about the minimum amount of change worth pursuing if > I'm thinking of changing my power levels. Going from 15 watts with a QRP K2 > to 100 watts with my K2/100 increased my signal by just over 8 dB. That's > enough to be noticed. Going from 100 watts to 800 watts adds another 9 dB > again. Again enough to be noticed. But I'd never spend a moment worrying > about whether anyone can hear the difference between, say, 15 watts and 10 > watts or between 100 watts and 50 watts. It just isn't going to happen. > > It's worth chasing milliwatts when we're trying to assemble the most > efficient station. They add up. But in practice, doubling or even tripling > the power (or reducing it that much) simply isn't going to be noticed. > > Ron AC7AC > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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: [hidden email] 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 |
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