K3 SWR Accuracy - reprise
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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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Stewart Baker
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Iain MacDonnell - N6ML-2
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
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In reply to this post by Eric Swartz - WA6HHQ
"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:[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
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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:[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 |
Re: K3 SWR Accuracy - reprise
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In reply to this post by Phil Salas
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:[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
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In reply to this post by Eric Swartz - WA6HHQ
> 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Eric Swartz - WA6HHQ
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
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:[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
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In reply to this post by Phil Salas
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 [hidden email] ----- Original Message ----- From: "Phil & Debbie Salas" <[hidden email]> To: <[hidden email]> 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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
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:[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 |
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In reply to this post by Steve Ellington
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" <[hidden email]> To: "Phil & Debbie Salas" <[hidden email]>; <[hidden email]> 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Steve Ellington
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 > [hidden email] > > 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 |
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In reply to this post by Steve Ellington
Hello,
Please, please, does anybody remember the original poster's problem anymore? Quote: 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 I am repeating. This makes no sense given that he is using a parallel combination of two dummy loads which results in a 2:1 SWR. I am repeating: Either there is something wrong with the data or the K3 is faulty. Errors this large should not occur with properly functioning equipment. AB2TC - Knut
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In reply to this post by Don Wilhelm-4
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 <[hidden email]> wrote: From: Don Wilhelm <[hidden email]> Subject: Re: [Elecraft] K3 SWR Accuracy - reprise To: [hidden email] Cc: "Phil & Debbie Salas" <[hidden email]> 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:[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
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In reply to this post by Phil Salas
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 [hidden email] ----- Original Message ----- From: "Phil & Debbie Salas" <[hidden email]> To: "Steve Ellington" <[hidden email]>; <[hidden email]> 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" <[hidden email]> > To: "Phil & Debbie Salas" <[hidden email]>; <[hidden email]> > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Steve Ellington
--- On Wed, 11/4/09, Steve Ellington <[hidden email]> 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 [hidden email] ----- Original Message ----- From: "Phil & Debbie Salas" <[hidden email]> To: <[hidden email]> 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Steve Ellington
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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by n7ws
I give up. Please somebody end this thread. There is no useful information in this thread to the OP. I can't really help him because I don't experience his problems. I have decent agreement between all instruments in my feed line about the antenna SWR.
Knut - AB2TC
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In reply to this post by ab2tc
The KAT3 is between the two bridges. The two will see different
impedences on some bands as a result of stray L and C. This probably accounts for some or most of the reading error. 73, Wayne N6KR ---- http://www.elecraft.com On Nov 4, 2009, at 4:23 PM, ab2tc <[hidden email]> wrote: > > Hello, > > Please, please, does anybody remember the original poster's problem > anymore? > > Quote: > > 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 > > > I am repeating. This makes no sense given that he is using a parallel > combination of two dummy loads which results in a 2:1 SWR. I am > repeating: > Either there is something wrong with the data or the K3 is faulty. > Errors > this large should not occur with properly functioning equipment. > > AB2TC - Knut > > > Steve Ellington wrote: >> >> The first statement is correct. Length of coax will transform >> impedance >> and >> cause SWR meters to read differently. >> <dsnip> >> > > -- > View this message in context: http://n2.nabble.com/K3-SWR-Accuracy-reprise-tp3943810p3949304.html > Sent from the [K3] mailing list archive at Nabble.com. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[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 |
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