K3 SWR Accuracy - reprise
Locked
123
123
 
|
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 SWR Accuracy - reprise
|
|
Just curious how you know that the LP100 is accurate? -----Original Message----- From: [hidden email] [mailto:[hidden email]] 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 1.99 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
LP100 is calibrated with NIST traceable reference.
I have no question about the accuracy with LP100. I caliberate my W1 by using LP100. 73 Johnny Siu VR2XMC ________________________________ 寄件人﹕ Robert Naumann <[hidden email]> 收件人﹕ Stewart <[hidden email]>; Elecraft Reflector <[hidden email]> 傳送日期﹕ 2009/11月/4 (三) 8:19:57 PM 主題： Re: [Elecraft] K3 SWR Accuracy - reprise Just curious how you know that the LP100 is accurate? -----Original Message----- From: [hidden email] [mailto:[hidden email]] 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 1.99 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Yahoo!香港提供網上安全攻略，教你如何防範黑客! 請前往 http://hk.promo.yahoo.com/security/ 了解更多! ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 SWR Accuracy - reprise
|
|
In reply to this post by Stewart Baker
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: [hidden email] [mailto:[hidden email]] 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 1.99 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:[hidden email] 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
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: [hidden email] > [mailto:[hidden email]] 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 > 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:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
In reply to this post by Stewart Baker
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 <[hidden email]> wrote: From: Stewart <[hidden email]> Subject: [Elecraft] K3 SWR Accuracy - reprise To: "Elecraft Reflector" <[hidden email]> 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:[hidden email] 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
Administrator
|
In reply to this post by Stewart Baker
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 <[hidden email]> 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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
Administrator
|
In reply to this post by Stewart Baker
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: [hidden email] >> [mailto:[hidden email]] 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 1.99 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:[hidden email] >> >> 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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
In reply to this post by Stewart Baker
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
Administrator
|
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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
In reply to this post by wayne burdick
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
Administrator
|
In reply to this post by wayne burdick
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 SWR Accuracy - reprise
|
Administrator
|
In reply to this post by Stewart Baker
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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
'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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
In reply to this post by wayne burdick
CONTENTS DELETED
The author has deleted this message.
|
Re: K3 SWR Accuracy - reprise
|
Administrator
|
In reply to this post by Stewart Baker
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 SWR Accuracy - reprise
|
|
In reply to this post by Stewart Baker
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" <[hidden email]> To: "Eric Swartz - WA6HHQ, Elecraft" <[hidden email]> Cc: "Elecraft Reflector" <[hidden email]>; "Wayne Burdick" <[hidden email]> 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
|
|
In reply to this post by Stewart Baker
--- On Wed, 11/4/09, Stewart <[hidden email]> 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 SWR Accuracy - reprise
|
|
In reply to this post by Eric Swartz - WA6HHQ
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 <[hidden email]> 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:[hidden email] >> >> 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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
«
Return to [K3]
|
1 view|%1 views
| Free forum by Nabble | Edit this page |