Re: [Elecraft] K3 SWR Accuracy - reprise
Will the revision be generic to the extent that it will also improve the readings for radios without the KAT3? My variations are not as great as Jack's, I suspect due to not having the KAT3, but my readings are consistently lower than Jack's, ie. 1.6 on most bands with a 2.0 load. Not a big deal, but as long as you're in there tweaking the code, can you verify that it works with non-KAT3 radios as well? 73, Larry N8LP wayne burdick wrote: Great data, Jack. We've been testing this, too, and we know why the K3's readings differ. A firmware change will be made to improve the accuracy in general. But part of the difference on the higher bands is due to strays in the KAT3 module. These strays can be tuned out by the KAT3 itself, thus presenting the correct load to the K3 internally. But an external instrument is on the other side of the KAT3 and thus sees a slightly different match. We'll post additional details soon. Meanwhile, no one need worry about this apparent discrepancy. The ATU is cancelling its own strays, and the SWR bridge is correctly reporting the load presented to the transceiver internally, which is the important thing when matching the rig to its load. 73, Wayne N6KR http://www.elecraft.com On Nov 8, 2009, at 7:18 PM, Edward Dickinson, III softb...@windstream.net wrote: _ From: Jack Smith [mailto:jack.sm...@cliftonlaboratories.com] Sent: Sunday, November 08, 2009 10:00 PM To: Edward Dickinson, III Subject: Re: [Elecraft] K3 SWR Accuracy - reprise Dick: http://www.cliftonlaboratories.com/swr_accuracy.htm I posted a message to the Elecraft reflector about the page being available but it has not shown up after an hour and a half. Jack K8ZOA Edward Dickinson, III wrote: Hi Jack. I extend invitation to apply your expertise regarding the matter being addressed in above referenced discussion. Best regards, Dick - KA5KKT __ 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 -- View this message in context: http://n2.nabble.com/FW-K3-SWR-Accuracy-reprise-tp3970987p3973505.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 SWR Accuracy - reprise
Speaking of the KAT3, Jack's report doesn't state whether or not his K3 contains the KAT3 module or not, and what state it's in. Bob NW8L On Sun, Nov 8, 2009 at 9:07 PM, Wayne Burdick n...@elecraft.com wrote: Great data, Jack. We've been testing this, too, and we know why the K3's readings differ. A firmware change will be made to improve the accuracy in general. But part of the difference on the higher bands is due to strays in the KAT3 module. These strays can be tuned out by the KAT3 itself, thus presenting the correct load to the K3 internally. But an external instrument is on the other side of the KAT3 and thus sees a slightly different match. We'll post additional details soon. Meanwhile, no one need worry about this apparent discrepancy. The ATU is cancelling its own strays, and the SWR bridge is correctly reporting the load presented to the transceiver internally, which is the important thing when matching the rig to its load. 73, Wayne N6KR http://www.elecraft.com On Nov 8, 2009, at 7:18 PM, Edward Dickinson, III softb...@windstream.net wrote: _ From: Jack Smith [mailto:jack.sm...@cliftonlaboratories.com] Sent: Sunday, November 08, 2009 10:00 PM To: Edward Dickinson, III Subject: Re: [Elecraft] K3 SWR Accuracy - reprise Dick: http://www.cliftonlaboratories.com/swr_accuracy.htm I posted a message to the Elecraft reflector about the page being available but it has not shown up after an hour and a half. Jack K8ZOA Edward Dickinson, III wrote: Hi Jack. I extend invitation to apply your expertise regarding the matter being addressed in above referenced discussion. Best regards, Dick - KA5KKT __ 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 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 SWR Accuracy - reprise
consistently lower than Jack's, ie. 1.6 on most bands with a 2.0 load. Not a big deal, but as long as you're in there tweaking the code, can you verify that it works with non-KAT3 radios as well? I'm curious -- are those who see a smaller indicated VSWR reading on the K3 meter with a 25-ohm load seeing the same discrepancy with a 100-ohm load? This may partially explain why some owners are seeing varying results under a 2:1 VSWR since that ratio can be comprised of those two resistance loads or an infinite set of resistive + reactive conditions -- any of which can form a load impedance of 25 or 100 ohms. Paul, W9AC __ 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 SWR Accuracy - reprise
He does have the KAT3, and it was in bypass for the tests. Larry N8LP Bob Cunnings wrote: Speaking of the KAT3, Jack's report doesn't state whether or not his K3 contains the KAT3 module or not, and what state it's in. Bob NW8L On Sun, Nov 8, 2009 at 9:07 PM, Wayne Burdick n...@elecraft.com wrote: Great data, Jack. We've been testing this, too, and we know why the K3's readings differ. A firmware change will be made to improve the accuracy in general. But part of the difference on the higher bands is due to strays in the KAT3 module. These strays can be tuned out by the KAT3 itself, thus presenting the correct load to the K3 internally. But an external instrument is on the other side of the KAT3 and thus sees a slightly different match. We'll post additional details soon. Meanwhile, no one need worry about this apparent discrepancy. The ATU is cancelling its own strays, and the SWR bridge is correctly reporting the load presented to the transceiver internally, which is the important thing when matching the rig to its load. 73, Wayne N6KR http://www.elecraft.com On Nov 8, 2009, at 7:18 PM, Edward Dickinson, III softb...@windstream.net wrote: _ From: Jack Smith [mailto:jack.sm...@cliftonlaboratories.com] Sent: Sunday, November 08, 2009 10:00 PM To: Edward Dickinson, III Subject: Re: [Elecraft] K3 SWR Accuracy - reprise Dick: http://www.cliftonlaboratories.com/swr_accuracy.htm I posted a message to the Elecraft reflector about the page being available but it has not shown up after an hour and a half. Jack K8ZOA Edward Dickinson, III wrote: Hi Jack. I extend invitation to apply your expertise regarding the matter being addressed in above referenced discussion. Best regards, Dick - KA5KKT __ 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 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 -- View this message in context: http://n2.nabble.com/FW-K3-SWR-Accuracy-reprise-tp3970987p3973584.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 SWR Accuracy - reprise
That's a good question, Paul. I have a medium power, 150 ohm load laying around that I made up a couple years ago for testing purposes. I just checked it with my VNA and it has an SWR of 2.92, pure resistive. I did a quick test with the K3 at 25W, and it measured between 2.4 and 2.7 depending on band. That's about the same percentage error as the 25 ohm load, but it's impossible to know if the error is in the same direction. I would think that you could calculate the direction using the tuned L-network values of a KAT3, but I don't have one installed. Larry N8LP P.B. Christensen wrote: consistently lower than Jack's, ie. 1.6 on most bands with a 2.0 load. Not a big deal, but as long as you're in there tweaking the code, can you verify that it works with non-KAT3 radios as well? I'm curious -- are those who see a smaller indicated VSWR reading on the K3 meter with a 25-ohm load seeing the same discrepancy with a 100-ohm load? This may partially explain why some owners are seeing varying results under a 2:1 VSWR since that ratio can be comprised of those two resistance loads or an infinite set of resistive + reactive conditions -- any of which can form a load impedance of 25 or 100 ohms. Paul, W9AC __ 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 -- View this message in context: http://n2.nabble.com/FW-K3-SWR-Accuracy-reprise-tp3970987p3973977.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 SWR Accuracy - reprise
__ 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 SWR Accuracy - reprise
I'm running tests today with the 25 ohm load connected to the K3/LP-100 with varying lengths of RG-142B/U coaxial cable, in 24 inch increments out to 120 or 144 inches. The result should be a constant SWR, neglecting the padding effect of coaxial cable loss, but with the impedance varying along the constant SWR circle if we think in Smith chart terms. I will also measure the R+jX of the load under the same conditions, with both the LP-100 and a VNA. I may have the data analyzed this evening, but more likely tomorrow. Also added a note confirming that my K3 has the KAT3 tuner, set to BYPASS for the tests. Jack N8LP wrote: That's a good question, Paul. I have a medium power, 150 ohm load laying around that I made up a couple years ago for testing purposes. I just checked it with my VNA and it has an SWR of 2.92, pure resistive. I did a quick test with the K3 at 25W, and it measured between 2.4 and 2.7 depending on band. That's about the same percentage error as the 25 ohm load, but it's impossible to know if the error is in the same direction. I would think that you could calculate the direction using the tuned L-network values of a KAT3, but I don't have one installed. Larry N8LP P.B. Christensen wrote: consistently lower than Jack's, ie. 1.6 on most bands with a 2.0 load. Not a big deal, but as long as you're in there tweaking the code, can you verify that it works with non-KAT3 radios as well? I'm curious -- are those who see a smaller indicated VSWR reading on the K3 meter with a 25-ohm load seeing the same discrepancy with a 100-ohm load? This may partially explain why some owners are seeing varying results under a 2:1 VSWR since that ratio can be comprised of those two resistance loads or an infinite set of resistive + reactive conditions -- any of which can form a load impedance of 25 or 100 ohms. Paul, W9AC __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Great data, Jack. We've been testing this, too, and we know why the K3's readings differ. A firmware change will be made to improve the accuracy in general. But part of the difference on the higher bands is due to strays in the KAT3 module. These strays can be tuned out by the KAT3 itself, thus presenting the correct load to the K3 internally. But an external instrument is on the other side of the KAT3 and thus sees a slightly different match. We'll post additional details soon. Meanwhile, no one need worry about this apparent discrepancy. The ATU is cancelling its own strays, and the SWR bridge is correctly reporting the load presented to the transceiver internally, which is the important thing when matching the rig to its load. 73, Wayne N6KR http://www.elecraft.com On Nov 8, 2009, at 7:18 PM, Edward Dickinson, III softb...@windstream.net wrote: _ From: Jack Smith [mailto:jack.sm...@cliftonlaboratories.com] Sent: Sunday, November 08, 2009 10:00 PM To: Edward Dickinson, III Subject: Re: [Elecraft] K3 SWR Accuracy - reprise Dick: http://www.cliftonlaboratories.com/swr_accuracy.htm I posted a message to the Elecraft reflector about the page being available but it has not shown up after an hour and a half. Jack K8ZOA Edward Dickinson, III wrote: Hi Jack. I extend invitation to apply your expertise regarding the matter being addressed in above referenced discussion. Best regards, Dick - KA5KKT __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Wayne (and Jack) I and at least one other user, have noted the K3 with ATU sometimes appears to leave a residual C or L in circuit on 10m when in bypass giving lower than expected power into a 50 Ohm load and may give incorrect TX power calibration as a result. Using the ATU to give a good SWR fixed the problem. The residual issue isn't always there, the typical false SWR is 1.5:1 or 1.6:1. 73 Dave, G4AON K3/100 #80 -- We'll post additional details soon. Meanwhile, no one need worry about this apparent discrepancy. The ATU is cancelling its own strays, and the SWR bridge is correctly reporting the load presented to the transceiver internally, which is the important thing when matching the rig to its load. 73, Wayne __ 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 SWR Accuracy - reprise
Just curious how you know that the LP100 is accurate? -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Stewart Sent: Wednesday, November 04, 2009 2:45 AM To: Elecraft Reflector Subject: [Elecraft] K3 SWR Accuracy - reprise Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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 SWR Accuracy - reprise
After reading your table and comments again, I'm also curious why you are using the antenna tuner in these measurements? Shouldn't the internal ATU be OFF in order to evaluate the SWR meter? With the tuner on, the K3's SWR meter is showing the results of the tuner doing it's job - no? I would hope that the K3 SWR meter would read different in this case. -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Stewart Sent: Wednesday, November 04, 2009 2:45 AM To: Elecraft Reflector Subject: [Elecraft] K3 SWR Accuracy - reprise Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Of course Robert, the ATU was OFF. My typing error. Any measurements made with it ON would be meaningless. 73 Stewart G3RXQ On Wed, 4 Nov 2009 07:14:43 -0600, Robert Naumann wrote: After reading your table and comments again, I'm also curious why you are using the antenna tuner in these measurements? Shouldn't the internal ATU be OFF in order to evaluate the SWR meter? With the tuner on, the K3's SWR meter is showing the results of the tuner doing it's job - no? I would hope that the K3 SWR meter would read different in this case. -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Stewart Sent: Wednesday, November 04, 2009 2:45 AM To: Elecraft Reflector Subject: [Elecraft] K3 SWR Accuracy - reprise Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
I suggest a reading of Larry's original paper on the design of the LP-100 to understand the heroic efforts needed to make these measurements with any accuracy. see: http://www.telepostinc.com/Files/phipps-1.pdf It should come as no surprise that the K3's built-in directional coupler lacks the directivity of the ones in Larry's LP-100, and directivity is extremely important in this application. For an example left to the reader to work out, measure a load with 20 dB return loss using a coupler with 20 dB directivity and see what the uncertainty is. Wes Stewart N7WS --- On Wed, 11/4/09, Stewart stew...@baker.nildram.co.uk wrote: From: Stewart stew...@baker.nildram.co.uk Subject: [Elecraft] K3 SWR Accuracy - reprise To: Elecraft Reflector elecraft@mailman.qth.net Date: Wednesday, November 4, 2009, 1:44 AM Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.99 1.8 80 1.99 1.8 60 1.99 1.8 40 1.95 1.8 30 1.97 1.6 20 1.97 1.4 17 1.97 1.3 15 1.96 1.2 12 1.96 1.5 10 1.96 1.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Wes and all, It is not unreasonable to expect some frequency dependency in the detection diodes as well. The tuner will function properly in any case - it tunes for the lowest SWR no matter what the exact value of that SWR may be. Now, if the SWR = 1.0 point was not correct, that would say there may be a problem with the tuning. Those wanting a more accurate SWR indication of the antenna side may want to consider the new Elecraft W2 as well. 73, Don W3FPR Wes Stewart wrote: I suggest a reading of Larry's original paper on the design of the LP-100 to understand the heroic efforts needed to make these measurements with any accuracy. see: http://www.telepostinc.com/Files/phipps-1.pdf It should come as no surprise that the K3's built-in directional coupler lacks the directivity of the ones in Larry's LP-100, and directivity is extremely important in this application. For an example left to the reader to work out, measure a load with 20 dB return loss using a coupler with 20 dB directivity and see what the uncertainty is. Wes Stewart N7WS __ 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 SWR Accuracy - reprise
Hi Stewart, The KAT3, like all wide-range ATUs, has significant stray reactance, especially on the higher bands. When you tuned it into 50 ohms, you created an L-network on each band that tunes out this reactance--at that one impedance. In your test, the KAT3 is between the K3's SWR bridge and the LP100, so the two bridges are looking at different points in the network. So changing the load Z to 25 ohms affects the two readings differently. The disproportionate error on 20-15 m reflects the nature of the KAT3's strays. On these bands, the stray-cancellation values that it automatically finds results in an L-network. On still higher bands, it may look more like a Pi network, which could explain why your SWR error delta is lower on 6 meters. On the lower bands, the strays are less significant, so the readings match. If you removed the KAT3, the readings would be in closer agreement. 73, Wayne N6KR http://www.elecraft.com On Nov 4, 2009, at 8:44 AM, Stewart stew...@baker.nildram.co.uk wrote: Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
The KAT3 cannot be completely removed from the circuit. When it is in BYPASS it uses very small L/C values to attempt to compensate for its own strays. There is not an actual bypass relay. 73, Wayne N6KR On Nov 4, 2009, at 6:10 AM, Stewart wrote: Of course Robert, the ATU was OFF. My typing error. Any measurements made with it ON would be meaningless. 73 Stewart G3RXQ On Wed, 4 Nov 2009 07:14:43 -0600, Robert Naumann wrote: After reading your table and comments again, I'm also curious why you are using the antenna tuner in these measurements? Shouldn't the internal ATU be OFF in order to evaluate the SWR meter? With the tuner on, the K3's SWR meter is showing the results of the tuner doing it's job - no? I would hope that the K3 SWR meter would read different in this case. -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Stewart Sent: Wednesday, November 04, 2009 2:45 AM To: Elecraft Reflector Subject: [Elecraft] K3 SWR Accuracy - reprise Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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 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 SWR Accuracy - reprise
I don't have the KAT3, i use an external homemade tuner and a cheap swr-meter between it and the K3. Don't know how accurate the swr-meter is, but i notice that the K3 shows 1.1:1 while the external meter still reads worse. Fiddling with the controls of the tuner settles the needle on the external meter, while the readout on the K3's display stays unchanged. I posted this to the list some weeks ago, but nobody noticed. -- 73, DM4iM __ 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 SWR Accuracy - reprise
What power level were you using? And what type of external bridge? The K3's SWR bridge has two sensitivity ranges. If you have power set to 12 W or lower, the higher-sensitivity range is used. If you have power set above 12 W, the lower-sensitivity range is used. This is necessary to prevent heating of the transformers in the bridge. SWR accuracy will be best when you're in the upper part of each range. So, for example, it'll be more accurate at 12 W than 1 W, and more accurate at 100 W than at 13 W. But accuracy should still be reasonable even in the lower end of the range. Your external bridge may have better sensitivity at the particular power range you were using. 73, Wayne N6KR On Nov 4, 2009, at 9:13 AM, DM4iM wrote: I don't have the KAT3, i use an external homemade tuner and a cheap swr-meter between it and the K3. Don't know how accurate the swr-meter is, but i notice that the K3 shows 1.1:1 while the external meter still reads worse. Fiddling with the controls of the tuner settles the needle on the external meter, while the readout on the K3's display stays unchanged. I posted this to the list some weeks ago, but nobody noticed. -- 73, DM4iM __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Hi Wayne, Thank you for your prompt and informative replies. When I first ran my experiment the results I got rather surprised me. Now you have explained the fact that the KAT3 is never really out of circuit even in BYPASS mode, and is seeing strays which the LP-100 does not, clarifies the situation. Most of the time, because of my antenna setup I use a fully balanced external tuner, and the exact SWR presented to the K3 is shown on the LP-100. Of course, as others have pointed out the value of SWR measured is immaterial, as the KAT3 will try and adjust to 1:1 when it is selected. 73 Stewart G3RXQ On Wed, 4 Nov 2009 07:50:35 -0800, Wayne Burdick wrote: Hi Stewart, The KAT3, like all wide-range ATUs, has significant stray reactance, especially on the higher bands. When you tuned it into 50 ohms, you created an L-network on each band that tunes out this reactance--at that one impedance. In your test, the KAT3 is between the K3's SWR bridge and the LP100, so the two bridges are looking at different points in the network. So changing the load Z to 25 ohms affects the two readings differently. The disproportionate error on 20-15 m reflects the nature of the KAT3's strays. On these bands, the stray-cancellation values that it automatically finds results in an L-network. On still higher bands, it may look more like a Pi network, which could explain why your SWR error delta is lower on 6 meters. On the lower bands, the strays are less significant, so the readings match. If you removed the KAT3, the readings would be in closer agreement. 73, Wayne N6KR __ 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 SWR Accuracy - reprise
Slight clarification. I said: The K3's SWR bridge has two sensitivity ranges. If you have power set to 12 W or lower, the higher-sensitivity range is used. If you have power set above 12 W, the lower-sensitivity range is used. This is necessary to prevent heating of the transformers in the bridge. The transformers in the bridge use the largest coupling ratio possible, consistent with not overheating when used at max power output (100-110 W). SWR measurement accuracy is better at higher power, in general, because it overcomes forward-bias voltage variation across the detector diodes. The sensitivity scaling occurs at *DC*, after the op-amps that amplify the forward and reflected voltages. The higher-sensitivity range, used at 12 W and below, has better noise immunity and better granularity feeding the A-to-D converter. There are two additional factors contributing to SWR measurement accuracy. (1) Some interpolation is done in firmware. (2) There's a small pre-bias (DC) on the bridge to compensate it at lower power levels. Wayne N6KR __ 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 SWR Accuracy - reprise
How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. 73, Eric Stewart wrote: Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.991.8 80 1.991.8 60 1.991.8 40 1.951.8 30 1.971.6 20 1.971.4 17 1.971.3 15 1.961.2 12 1.961.5 10 1.961.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
'bout 2 feet. 73 Stewart On Wed, 04 Nov 2009 09:53:25 -0800, Eric Swartz - WA6HHQ, Elecraft wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. 73, Eric __ 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 SWR Accuracy - reprise
I've noticed that too, but never though much of it since the external meter and the K3 agree at 1:1. Above 1:1, the K3's SWR indication reads lower than the external meter at 100 watts on the lower frequency bands (80, 160) but agrees well with the external meter on the higher frequency bands. The K3 and external meters agree well at 10 watts on all bands. For example, I set up my external tuner for an SWR of 1.6:1 on the external meter and transmit 10 watts on 80 M and the K3 agrees with the external meter just fine, but if I crank up the POWER while in tune I'll see the SWR indicated on the K3 drop to 1.0:1 when the KPA100 kicks in. At 100 watts out, the K3 indicates 1.1:1 while the external meter indicates 1.6:1 at all times. Adjusting the tuner for minimum SWR brings its meter and the K3 down to an indicated 1:1. I have about 18 inches of cable between the tuner and the K3. If it was going to have a significant effect, I'd expect it to show up on the higher frequencies, not the lower frequencies. Besides, all is well at 10 watts on all bands. It's a non-issue to me since all I care about is knowing I have the antenna system well matched to the K3. Ron AC7AC -Original Message- What power level were you using? And what type of external bridge? The K3's SWR bridge has two sensitivity ranges. If you have power set to 12 W or lower, the higher-sensitivity range is used. If you have power set above 12 W, the lower-sensitivity range is used. This is necessary to prevent heating of the transformers in the bridge. SWR accuracy will be best when you're in the upper part of each range. So, for example, it'll be more accurate at 12 W than 1 W, and more accurate at 100 W than at 13 W. But accuracy should still be reasonable even in the lower end of the range. Your external bridge may have better sensitivity at the particular power range you were using. 73, Wayne N6KR On Nov 4, 2009, at 9:13 AM, DM4iM wrote: I don't have the KAT3, i use an external homemade tuner and a cheap swr-meter between it and the K3. Don't know how accurate the swr-meter is, but i notice that the K3 shows 1.1:1 while the external meter still reads worse. Fiddling with the controls of the tuner settles the needle on the external meter, while the readout on the K3's display stays unchanged. I posted this to the list some weeks ago, but nobody noticed. -- 73, DM4iM __ 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 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 SWR Accuracy - reprise
Try using a double male connector to put the two SWR sensors right next to each other and repeat the measurement. At the higher freq's, even 2 ft of coax can change the indicated SWR, especially when the actual SWR is 1.9:1 like yours. I regularly see this when driving an amplifier with a non 1:1 SWR with any of my rigs. 73, Eric Stewart wrote: 'bout 2 feet. 73 Stewart On Wed, 04 Nov 2009 09:53:25 -0800, Eric Swartz - WA6HHQ, Elecraft wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. __ 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 SWR Accuracy - reprise
But if you: 1. Connect the antenna directly to the K3, ANT1 say, with KAT3 in bypass and note the SWR reading on the K3, 2. Then disconnect the antenna from ANT 1 and instead connect the external SWR indicator to ANT 1 with a length of coax, 3. Then connect the antenna to the external SWR indicator, should you not get a reading on the external indicator that you can properly compare with the one you noted in step 1? If so, what do people find? 73 to all Geoff G3UCK - Original Message - From: Stewart stew...@baker.nildram.co.uk To: Eric Swartz - WA6HHQ, Elecraft e...@elecraft.com Cc: Elecraft Reflector elecraft@mailman.qth.net; Wayne Burdick wa...@elecraft.com Sent: Wednesday, November 04, 2009 6:10 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise 'bout 2 feet. 73 Stewart On Wed, 04 Nov 2009 09:53:25 -0800, Eric Swartz - WA6HHQ, Elecraft wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. 73, Eric __ 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 SWR Accuracy - reprise
--- On Wed, 11/4/09, Stewart stew...@baker.nildram.co.uk wrote: Of course, as others have pointed out the value of SWR measured is immaterial, as the KAT3 will try and adjust to 1:1 when it is selected. I don't think I would go so far as to say SWR is immaterial. __ 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 SWR Accuracy - reprise
I've been noticing some apparently anomalies in this area too, for example... I have two dummy loads - one is a 2kW rated PalStar, which doesn't appear to be exactly 50ohms (but close enough for usual purposes), and a Bird Termaline, which is mil-spec 50ohms (and shows as such on a sweep analyser), 150W rated. With 100W at 3520kHz, into the Bird, my LP-100A shows 1.00:1, and the K3 shows 1.0:1. Into the PalStar, the LP-100A shows 1.20:1, but the K3 still shows 1.0:1. I'm using the same feedline arrangement in both cases (i.e. I unplug the cable from one load and plug it into the other), and I do NOT have the KAT3 installed. I've tried different feedline arrangements too (including a short one between the K3 and the LP-100A coupler), and the results seem to be consistent. ~Iain / N6ML On Wed, Nov 4, 2009 at 9:53 AM, Eric Swartz - WA6HHQ, Elecraft e...@elecraft.com wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. 73, Eric Stewart wrote: Hi, Now traffic on the new K3 Macro functions has somewhat died down, I would like to raise again the issue of the K3's SWR measurement accuracy. I did some tests using dummy loads and a LP-100 meter as follows. The dummy load is a precision 100W one which I measured with a VNA and has a VSWR of 1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR I used another dummy load (not quite as good) in parallel. The K3 output was from ANT1 using the internal ATU. The ATU was automatically tuned to 1:1 on all bands. The results I got for 2:1 VSWR are as follows:- LP-100 K3 160 1.99 1.8 80 1.99 1.8 60 1.99 1.8 40 1.95 1.8 30 1.97 1.6 20 1.97 1.4 17 1.97 1.3 15 1.96 1.2 12 1.96 1.5 10 1.96 1.4 As can be seen my K3 SWR indication consistently under reads. However, it really gets bad on 20,17 15. From previous replies I understand that this under reading would be compensated for in the firmware, sometime in the future . Is this still on the list of problems to be addressed ? 73 Stewart G3RXQ __ 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 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 SWR Accuracy - reprise
On Nov 4, 2009, at 12:31 PM, Ron D'Eau Claire wrote: I It's a non-issue to me since all I care about is knowing I have the antenna system well matched to the K3. I have to parrot the non issue part of this. I have several SWR bridges/meters. They rarely agree about anything. Accuracy is probably no better than +/- 5% AT BEST on any of them, and there are many other factors that come into play. So you can easily be way off from one indicator to another. The only thing that matters is whether or not you can read close enough to tune to a match condition -- auto or otherwise. Beyond that, it hardly matters and likely isn't worth the bits being transmitted on the subject :-) Grant/NQ5T __ 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 SWR Accuracy - reprise
I don't have a KAT3. I often use an external remote matching unit. I cannot directly control the lowest SWR found. My linear is somewhat sensitive to SWR. At times I have observed a more than satisfactory apparent SWR indication on my K3 and found my amplifier was less than satisfied. That's not a non-issue for me. Thanks for the tip regarding the 12 Watt power setting. It seems that will help some. Best regards, Dick - KA5KKT __ 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 SWR Accuracy - reprise
Hi all, This thread is getting rather long but I want to put my 2 cents worth in. The huge discrepancy between the K3 indicated SWR and the LP-100 shown in Stewarts original post is *not* normal or expected. Either there is something wrong with the data or the K3. I am finding that the K3 readings tend to be a little on the kind side. I don't have a precision meter like the LP-100 but have come to find my MFJ tuner with its cross-needle analog meter reasonably trustworthy. My K3 readings are generally lower by 0.2 to 0.3, but no more. This is both at the 10W level and the 100W level, and both at nearly perfect match and SWR more in 2:1-3:1 range. AB2TC - Knut Iain MacDonnell - N6ML-2 wrote: I've been noticing some apparently anomalies in this area too, for example... I have two dummy loads - one is a 2kW rated PalStar, which doesn't appear to be exactly 50ohms (but close enough for usual purposes), and a Bird Termaline, which is mil-spec 50ohms (and shows as such on a sweep analyser), 150W rated. With 100W at 3520kHz, into the Bird, my LP-100A shows 1.00:1, and the K3 shows 1.0:1. snip -- View this message in context: http://n2.nabble.com/K3-SWR-Accuracy-reprise-tp3943810p3948632.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 SWR Accuracy - reprise
How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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 SWR Accuracy - reprise
That assumes there is no RF on the exterior of the coax and the SWR sensors are ideal. Neither is the case and from personal experience I can tell you that the swr meters will change readings based on coax length. 73, Eric Phil Debbie Salas wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Phil Debbie Salas wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X _ . Generally, simple swr indicators are much less sensitive to impedances on the low impedance side of the smith chart. For example, I compared my K3 with an elderly Drake W4 using my 30 meter short vertical dipole which has a feed point resistance of of about 33 ohms using a six foot piece of RG-213 and then adding an additional 16 feet of coax. Surprisingly, the K3 and the R4 agreed within 1 per cent on forward power and had the same variation in swr. The antenna feed point resistance was measured with an elderly General Radio model 1606A HF impedance bridge. Of course, with only six feet of cable, it's difficult to get excited about a little swr. The reason that the feed line is so short is that the feed point is inside the shack. I have permission from my hoa to have an outside antenna provided that it's unobtrusive and mine is almost stealth. http://vibrotek.com/w5dc/w5dcant.html I'm currently at 95 dxcc countries since summer, up 33 from a few weeks ago when I replaced my 1975 vintage, very modified, FT-101E with the K3. One problem that I do have is that the K3 output seems low on 30 meters, varying from 85 to 90 watts with both the antenna and with my Heath Cantenna. Other bands show 110 watts. One thing to keep in mind is that a lot of coax that's sold as 50 ohms is really more like 60 ohms. The typical 50 ohm foam coax actually has a characteristic impedance of about 59.5 ohms so that an expected 1.1 to 1 swr could really be 1.44 and vice versa. 73, Dunc, W5DC (sometimes professional antenna designer - read qrz.com bio) __ 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 SWR Accuracy - reprise
That assumes there is no RF on the exterior of the coax and the SWR sensors are ideal. Neither is the case and from personal experience I can tell you that the swr meters will change readings based on coax length. The SWR *reading* may change as a function of coax length when current is present on the outer conductor, but as Phil states, the actual line SWR does not change, neglecting any line loss. In a mismatched condition, the Z measured at the line input does change with line length and as F increases, it takes smaller changes in line length to see changes in input Z. To deal with the problem Eric describes, I use choking line isolators between the transceivers and amps, immediately after the amp, and depending on the antenna type, again at the antenna feed point for most antennas with a coaxial feed point. Paul, W9AC __ 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 SWR Accuracy - reprise
I can vouch for Eric's statement. I routinely calibrate KPA100 wattmeters for SWR using a precision 100 ohm dummy load (which should produce a 2.0 SWR). At 40 meters, I get 2.0 if I use a direct connection with a male to male adapter, with a 1 foot coax, it shows SWR=2.1 and with a 2 foot coax, it indicates SWR=2.2. The coax length is NOT negligible. BTW - my MFJ-259B shows the same thing with those same cable lengths. The Smith Chart constant SWR circle is for ideal (theoretical) conditions, and the real world conditions of cable loss and RF in places the Smith Chart does not consider must be factored in to explain phenomenon like this. Since most instrumentation is balanced/calibrated for 50 ohms, things agree when the impedance is 50 ohms resistive, but away from that point, other factors come into play. 73, Don W3FPR Eric Swartz -WA6HHQ, Elecraft wrote: That assumes there is no RF on the exterior of the coax and the SWR sensors are ideal. Neither is the case and from personal experience I can tell you that the swr meters will change readings based on coax length. 73, Eric Phil Debbie Salas wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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 SWR Accuracy - reprise
I was using 4 Watts, the external bridge is a taiwan-made AV-20, I forgot the brand name. There is a sticker, it says accuracy 10%. Today I tested again using 10 Watts, the K3's and the external meters readout match a lot closer. With 10 W i can bring the K3s readout to 1.0:1 , with 4 W it was never better than 1.1:1. At 100 Watts , both meters agree in the range from 1.0:1 up to about 3:1. That is good enough for me. I don't care much about a perfect swr, but the components in the tuner *do* care when the K3 drives the Alpha. It should not be too bad then. :-) Martin -- Wayne Burdick schrieb: What power level were you using? And what type of external bridge? The K3's SWR bridge has two sensitivity ranges. If you have power set to 12 W or lower, the higher-sensitivity range is used. If you have power set above 12 W, the lower-sensitivity range is used. This is necessary to prevent heating of the transformers in the bridge. SWR accuracy will be best when you're in the upper part of each range. So, for example, it'll be more accurate at 12 W than 1 W, and more accurate at 100 W than at 13 W. But accuracy should still be reasonable even in the lower end of the range. Your external bridge may have better sensitivity at the particular power range you were using. 73, Wayne N6KR -- 73, DM4iM __ 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 SWR Accuracy - reprise
The first statement is correct. Length of coax will transform impedance and cause SWR meters to read differently. I've seen this Smith Chart reference before and it makes no sense. You can certainly use your feeder to match your antenna. Of course, if SWR meters didn't care what the impedance is then yes, it wouldn't matter where you put it along the line but such is not the case. Steve N4LQ n...@carolina.rr.com - Original Message - From: Phil Debbie Salas dpsa...@tx.rr.com To: elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 5:53 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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 No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.698 / Virus Database: 270.14.50/2481 - Release Date: 11/04/09 14:51:00 __ 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 SWR Accuracy - reprise
The SWR definitely does not change with line length. However the SWR _READING_ often does because of the inaccuracy of inexpensive SWR meters. The SWR reading should depend only on the relative magnitudes of the forward and reflected power and not on the phase angle between them. But with inexpensive SWR meters that is often not the case. Al N1AL On Wed, 2009-11-04 at 18:33 -0500, Don Wilhelm wrote: I can vouch for Eric's statement. I routinely calibrate KPA100 wattmeters for SWR using a precision 100 ohm dummy load (which should produce a 2.0 SWR). At 40 meters, I get 2.0 if I use a direct connection with a male to male adapter, with a 1 foot coax, it shows SWR=2.1 and with a 2 foot coax, it indicates SWR=2.2. The coax length is NOT negligible. BTW - my MFJ-259B shows the same thing with those same cable lengths. The Smith Chart constant SWR circle is for ideal (theoretical) conditions, and the real world conditions of cable loss and RF in places the Smith Chart does not consider must be factored in to explain phenomenon like this. Since most instrumentation is balanced/calibrated for 50 ohms, things agree when the impedance is 50 ohms resistive, but away from that point, other factors come into play. 73, Don W3FPR Eric Swartz -WA6HHQ, Elecraft wrote: That assumes there is no RF on the exterior of the coax and the SWR sensors are ideal. Neither is the case and from personal experience I can tell you that the swr meters will change readings based on coax length. 73, Eric Phil Debbie Salas wrote: How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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
Re: [Elecraft] K3 SWR Accuracy - reprise
Transmission line theory (and therefore the Smith Chart info) IS correct. Transmission line length DOES transform the impedance, but not SWR. So you may be changing the impedance to something that your tuner can tune when you add coax length, but you are not changing the SWR by adding coax - other than the change due to coax loss which is negligable for short lengths. Now I do agree that different SWR meters probably read differently when the SWR is the same but the impedances presented to the two SWR meters are different. Phil - AD5X - Original Message - From: Steve Ellington n...@carolina.rr.com To: Phil Debbie Salas dpsa...@tx.rr.com; elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 5:59 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise The first statement is correct. Length of coax will transform impedance and cause SWR meters to read differently. I've seen this Smith Chart reference before and it makes no sense. You can certainly use your feeder to match your antenna. Of course, if SWR meters didn't care what the impedance is then yes, it wouldn't matter where you put it along the line but such is not the case. Steve N4LQ __ 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 SWR Accuracy - reprise
Steve, Just one clarification - a mismatched length of coax will transform the impedance, but a perfectly matched line will not. Since we calibrate things at 50 ohms, if the coax is exactly 50 ohms and the SWR is 1.0:1, no impedance transformation will exist. But real coax lines are nominally 50 ohms, so the conditions of a perfectly matched line may not exist even though the meters tell us it is at a particular point along the line. 73, Don W3FPR Steve Ellington wrote: The first statement is correct. Length of coax will transform impedance and cause SWR meters to read differently. I've seen this Smith Chart reference before and it makes no sense. You can certainly use your feeder to match your antenna. Of course, if SWR meters didn't care what the impedance is then yes, it wouldn't matter where you put it along the line but such is not the case. Steve N4LQ n...@carolina.rr.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 SWR Accuracy - reprise
You have something terribly wrong. Two feet of coax at 7 MHz is negligible (~8 electrical degrees for solid dielectrics), even if its impedance is wildly different from 50 ohm. Furthermore, any loss in the cable should reduce the SWR, not increase it. --- On Wed, 11/4/09, Don Wilhelm w3...@embarqmail.com wrote: From: Don Wilhelm w3...@embarqmail.com Subject: Re: [Elecraft] K3 SWR Accuracy - reprise To: elecraft@mailman.qth.net Cc: Phil Debbie Salas dpsa...@tx.rr.com Date: Wednesday, November 4, 2009, 4:33 PM I can vouch for Eric's statement. I routinely calibrate KPA100 wattmeters for SWR using a precision 100 ohm dummy load (which should produce a 2.0 SWR). At 40 meters, I get 2.0 if I use a direct connection with a male to male adapter, with a 1 foot coax, it shows SWR=2.1 and with a 2 foot coax, it indicates SWR=2.2. The coax length is NOT negligible. BTW - my MFJ-259B shows the same thing with those same cable lengths. The Smith Chart constant SWR circle is for ideal (theoretical) conditions, and the real world conditions of cable loss and RF in places the Smith Chart does not consider must be factored in to explain phenomenon like this. Since most instrumentation is balanced/calibrated for 50 ohms, things agree when the impedance is 50 ohms resistive, but away from that point, other factors come into play. 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 SWR Accuracy - reprise
So here is the bottom line: 1. SWR is the same anywhere along the transmission line per Mr. Smith and his Chart. 2. When the transmission line doesn't match the antenna we have an SWR other than 1:1. 3. The SWR meter will often read differently at the antenna vs. at transmitter. 4. Example: A full wave dipole center fed with 50 ohm coax. SWR reads infinite at the antenna but with 1/4 wavelenth of coax, SWR reads low! 5. Why? SWR meters are designed to work with a specific impedance and the impedance is obviously different in the example. 6. Putting that SWR meter along various points along the xmission line gives different readings. 7. You can fiddle with the xmission line length and fool an SWR meter into thinking the SWR is 1:1 when it is really quiet high. 8. SWR meters are good for making sure your transmitter sees 50 ohms unless you like climbing. 9. SWR meters are good for antenna matching if they are placed at the feedpoint of the antenna. Tower or tree climbing needed unless you have a ground mounted vertical. 10 SWR meters will read correctly if the xmission line is a multiple of 1/2 wavelenth ( A rare occurance). 11. If your line is not matched, you could hook 100 SWR meters in series and they would all read something different. Steve N4LQ n...@carolina.rr.com - Original Message - From: Phil Debbie Salas dpsa...@tx.rr.com To: Steve Ellington n...@carolina.rr.com; elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 7:18 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise Transmission line theory (and therefore the Smith Chart info) IS correct. Transmission line length DOES transform the impedance, but not SWR. So you may be changing the impedance to something that your tuner can tune when you add coax length, but you are not changing the SWR by adding coax - other than the change due to coax loss which is negligable for short lengths. Now I do agree that different SWR meters probably read differently when the SWR is the same but the impedances presented to the two SWR meters are different. Phil - AD5X - Original Message - From: Steve Ellington n...@carolina.rr.com To: Phil Debbie Salas dpsa...@tx.rr.com; elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 5:59 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise The first statement is correct. Length of coax will transform impedance and cause SWR meters to read differently. I've seen this Smith Chart reference before and it makes no sense. You can certainly use your feeder to match your antenna. Of course, if SWR meters didn't care what the impedance is then yes, it wouldn't matter where you put it along the line but such is not the case. Steve N4LQ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.698 / Virus Database: 270.14.50/2481 - Release Date: 11/04/09 14:51:00 __ 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 SWR Accuracy - reprise
--- On Wed, 11/4/09, Steve Ellington n...@carolina.rr.com wrote: The first statement is correct. Length of coax will transform impedance and cause SWR meters to read differently. Absent loss, if the cable Zo matches the SWR bridge design impedance (or vice versa), then the SWR reading should be unaffected by the cable length. I've seen this Smith Chart reference before and it makes no sense. Of course it does, it makes perfect sense. If the chart is normalized to the line Zo, and the load Z is mapped accordingly, then changing line length moves the load Z around the chart. Yes, the impedance changes, but the SWR does not. A properly designed instrument, matched to the line Zo should read the same SWR regardless of line length. These devices aren't impedance bridges, they are (supposedly) reflection coefficient measurement instruments. As such, they haven't a clue what the impedance is, nor should they. You can certainly use your feeder to match your antenna. Of course, if SWR meters didn't care what the impedance is then yes, it wouldn't matter where you put it along the line but such is not the case. Well, as I said above, it should be the case. Wes N7WS Steve N4LQ n...@carolina.rr.com - Original Message - From: Phil Debbie Salas dpsa...@tx.rr.com To: elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 5:53 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise How long is the coax between the LP100 sensor and the K3? This can have a significant impedance transformation impact as you go to higher frequencies, leading to a different indicated SWR at each end. The impedance changes, but not the SWR. Looking at this on a Smith Chart, you can see that you just rotate around a constant SWR circle. Minus coax losses of course, which are negligable when we're talking a few feet at HF. Phil - AD5X __ 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 SWR Accuracy - reprise
On Nov 4, 2009, at 4:41 PM, Steve Ellington wrote: 4. Example: A full wave dipole center fed with 50 ohm coax. SWR reads infinite at the antenna but with 1/4 wavelenth of coax, SWR reads low! Nope -- the *impedance* at the end of a 1/4 wave transmission line when it is looking at a very large impedance, is close to zero, therefore the SWR remains close to infinite. The SWR definitely won't read low unless there is something wrong with the instrument. 73 Chen, W7AY __ 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 SWR Accuracy - reprise
Nope: The 1/4 wave line transforms the high impedance to a low one and the SWR meter reads low. It's called a transmission line transformer and is very common. It's the reason everyone is having trouble understanding why SWR meters read differently. The ONLY way to compare them is to swap them with each other. Putting them in series fouls up the readings for both meters. Steve N4LQ n...@carolina.rr.com - Original Message - From: Kok Chen c...@mac.com To: Elecraft Reflector elecraft@mailman.qth.net Cc: Steve Ellington n...@carolina.rr.com Sent: Wednesday, November 04, 2009 7:55 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise On Nov 4, 2009, at 4:41 PM, Steve Ellington wrote: 4. Example: A full wave dipole center fed with 50 ohm coax. SWR reads infinite at the antenna but with 1/4 wavelenth of coax, SWR reads low! Nope -- the *impedance* at the end of a 1/4 wave transmission line when it is looking at a very large impedance, is close to zero, therefore the SWR remains close to infinite. The SWR definitely won't read low unless there is something wrong with the instrument. 73 Chen, W7AY No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.698 / Virus Database: 270.14.50/2481 - Release Date: 11/04/09 14:51:00 __ 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 SWR Accuracy - reprise
On Nov 4, 2009, at 5:05 PM, Steve Ellington wrote: It's called a transmission line transformer and is very common. Yes, we all know about them. Just walk 180 degrees on a constant SWR circle on the Smith Chart, with the transmission line impedance at the center of the Smith Chart (or use 1/4 wavelength in the Telegrapher's Equation). But this is what you'd stated (I am not changing a single word): 4. Example: A full wave dipole center fed with 50 ohm coax. You can use a 600 ohm transmission line to transform a high impedance to get a reasonably close match to 50 ohms because the impedance at the center of that dipole is *not* infinite but some large number (W8JI has good estimates in the Zepp article on his web site). But you cannot transform anything other than a 50 ohm feed point into a 50 ohm termination by using a 50 ohm transmission line. (Unless the line is infinitely lossy.) It should be obvious from the Smith Chart -- constant SWR circles won't hit 50+j0 unless the SWR circle itself has 0 radius (i.e., SWR = 1.0:1) 73 Chen, W7AY __ 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 SWR Accuracy - reprise
But you cannot transform anything other than a 50 ohm feed point into a 50 ohm termination by using a 50 ohm transmission line. (Unless the line is infinitely lossy.) Don't worryIt will be! Steve N4LQ n...@carolina.rr.com - Original Message - From: Kok Chen c...@mac.com To: Steve Ellington n...@carolina.rr.com Cc: Elecraft Reflector elecraft@mailman.qth.net Sent: Wednesday, November 04, 2009 8:51 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise On Nov 4, 2009, at 5:05 PM, Steve Ellington wrote: It's called a transmission line transformer and is very common. Yes, we all know about them. Just walk 180 degrees on a constant SWR circle on the Smith Chart, with the transmission line impedance at the center of the Smith Chart (or use 1/4 wavelength in the Telegrapher's Equation). But this is what you'd stated (I am not changing a single word): 4. Example: A full wave dipole center fed with 50 ohm coax. You can use a 600 ohm transmission line to transform a high impedance to get a reasonably close match to 50 ohms because the impedance at the center of that dipole is *not* infinite but some large number (W8JI has good estimates in the Zepp article on his web site). But you cannot transform anything other than a 50 ohm feed point into a 50 ohm termination by using a 50 ohm transmission line. (Unless the line is infinitely lossy.) It should be obvious from the Smith Chart -- constant SWR circles won't hit 50+j0 unless the SWR circle itself has 0 radius (i.e., SWR = 1.0:1) 73 Chen, W7AY No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.698 / Virus Database: 270.14.50/2481 - Release Date: 11/04/09 14:51:00 __ 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 SWR Accuracy - reprise
I believe Steve is onto something critical to this discussion - here is my 'take' on the differences -- Remember that we *are* talking about the resultant SWR indications on a mis-matched line. The way most wattmeters indicate SWR is to detect the forward power and the reflected power - then an SWR is computed from those values of associated detector output voltages. The result is an SWR indication based on the absolute values of those magnitudes. No consideration is provided for the phase angles (the actual forward and reflected values are complex numbers). The forward power is indicated accurately (it is proportional to the square of the forward voltage minus the square of the reflected voltage), but the computation of actual SWR is more involved. When the impedances are close to the design point (balance point) of the meter, the error is small, but the error grows as the actual impedance departs from that design impedance. Those meters that properly detect the phase as well as the magnitude of the forward and reflected powers can indicate that the SWR does not change as the meter position is moved along the line - but most do not have phase detection capability nor complex number computation capability, so for those meters, the SWR indicated will change with the meter position along the feedline. In other words, use a good VNA and you should see a constant SWR along the line, but common wattmeters are not VNAs, so some error in SWR indication is to be expected when the impedance is removed from the design point. Even the well-respected Tandem Match computes the SWR as Vf+Vr/Vf-Vr, which is the correct formula, but the detector reports only the magnitudes of Vf and Vr and does not consider the phase angle, so it is not entirely correct either - it will be entirely correct when the SWR = 1.0. 73, Don W3FPR Steve Ellington wrote: Nope: The 1/4 wave line transforms the high impedance to a low one and the SWR meter reads low. It's called a transmission line transformer and is very common. It's the reason everyone is having trouble understanding why SWR meters read differently. The ONLY way to compare them is to swap them with each other. Putting them in series fouls up the readings for both meters. Steve N4LQ n...@carolina.rr.com - Original Message - From: Kok Chen c...@mac.com To: Elecraft Reflector elecraft@mailman.qth.net Cc: Steve Ellington n...@carolina.rr.com Sent: Wednesday, November 04, 2009 7:55 PM Subject: Re: [Elecraft] K3 SWR Accuracy - reprise On Nov 4, 2009, at 4:41 PM, Steve Ellington wrote: 4. Example: A full wave dipole center fed with 50 ohm coax. SWR reads infinite at the antenna but with 1/4 wavelenth of coax, SWR reads low! Nope -- the *impedance* at the end of a 1/4 wave transmission line when it is looking at a very large impedance, is close to zero, therefore the SWR remains close to infinite. The SWR definitely won't read low unless there is something wrong with the instrument. 73 Chen, W7AY __ 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
