KXAT1 with dipole
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I was out in the woods of Oregon today (up by the coast range town of
Jewell) with my KX 1 and a few different antennas. I used a long wire for a while, but then for the heck of it I set up a 40M inverted vee with my portable mast. The KXAT1 had no trouble with the long wire (and counterpoises) bringing it right down to 1:1, but no such luck with the dipole ( cut to resonate on 40, and fed w/RG 174).I've used this antenna a bunch w/ the K2 and it's pretty much a 1:1, but when using the KX1 atu I got around 9:5 SWR! So, I promptly forgot how to bypass the tuner (until I got home and re-read the manual;set it to 'CAL':).But,also in the manual it states that it'll match most coax type dipoles, etc.Elsewhere it's stated that it won't match a half wave length,but I wasn't clear if that's only for a half wave end fed.I'll bet it's the same for a resonant dipole as it's a ground independent half wave, but maybe someone who has come up against this before can clarify as far as the tuner is concerned. I usually bring a separate antenna 'dipper' just to check the antenna in case there's a short or bad coax,etc., but that got left behind. Just for reference, I use the lightweight dipole kit from N2CX with a nice sealed center insulator and RG 174 (I know it's not the most efficient, but for a short run it's fine and very lightweight). I'm still trying to find more of the type of wire he used in there-it's springy yet has a great slick and tough coating which holds up well in trees, etc, It's also a light yellow in color so it blends nicely.N2CX quit making these kits a while back and ran out of that wire.The 'Wireman' sells some similar stuff,(524?) but it's still not the same. Any thought appreciated on the tuner-I'm trying to get as much outdoor radio time in before summer ends:) -- Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Dan, FWIW, at home I run my KX1 into a trapped 40 meter dipole (only 38ft. long) that is resonate around 7.040. I have a HI-Q 1:1 balun installed and have 75ft of feedline. The dipole is a flattop running NE to SW up about 40 ft. I have worked Alaska and NM and AZ and Southern California to mention just a few of my QRP contacts. I also run 13.8 watts into the unit at home. On the KX1 it shows a .5 Volt drop to 13.5. I have the internal tuner for the KX1 installed and I set it for CAL mode and I get 4+ watts and 1.0 SWR out of it. I can work up to 7.058 and down some with switching to Tun mode. I also run the unit outdoors into long wires (usuually 28 ft with counterpoises) and use the TUN mode and get very low SWR readings and perhaps a half watt less power. The reduction in power might be attributted to the lower power into the unit. I use a small 2800AH 12 volt batter that charges to about 13.5 and delivers at least 12 volts by the time I use it in the field. Jack Regan, AE6GC -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Dan Presley Sent: Tuesday, August 22, 2006 12:13 AM To: [hidden email] Subject: [Elecraft] KXAT1 with dipole I was out in the woods of Oregon today (up by the coast range town of Jewell) with my KX 1 and a few different antennas. I used a long wire for a while, but then for the heck of it I set up a 40M inverted vee with my portable mast. The KXAT1 had no trouble with the long wire (and counterpoises) bringing it right down to 1:1, but no such luck with the dipole ( cut to resonate on 40, and fed w/RG 174).I've used this antenna a bunch w/ the K2 and it's pretty much a 1:1, but when using the KX1 atu I got around 9:5 SWR! So, I promptly forgot how to bypass the tuner (until I got home and re-read the manual;set it to 'CAL':).But,also in the manual it states that it'll match most coax type dipoles, etc.Elsewhere it's stated that it won't match a half wave length,but I wasn't clear if that's only for a half wave end fed.I'll bet it's the same for a resonant dipole as it's a ground independent half wave, but maybe someone who has come up against this before can clarify as far as the tuner is concerned. I usually bring a separate antenna 'dipper' just to check the antenna in case there's a short or bad coax,etc., but that got left behind. Just for reference, I use the lightweight dipole kit from N2CX with a nice sealed center insulator and RG 174 (I know it's not the most efficient, but for a short run it's fine and very lightweight). I'm still trying to find more of the type of wire he used in there-it's springy yet has a great slick and tough coating which holds up well in trees, etc, It's also a light yellow in color so it blends nicely.N2CX quit making these kits a while back and ran out of that wire.The 'Wireman' sells some similar stuff,(524?) but it's still not the same. Any thought appreciated on the tuner-I'm trying to get as much outdoor radio time in before summer ends:) -- Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Dan Presley-2
You don't mention on what band you were trying to get a match... 40 meters?
If so, I can relate that once in a while, my KXAT1 seems to get "stuck" in the sense that I can't get a match even when it's a easy scenario - such as resonant antenna fed with 50 ohm coax. I've learned that by using TUNE at some point of the band considerably removed from my initial freq, the KXAT1 will "snap out of it", and get a nice match. Returning to the original freq and using TUNE again results in a good match, and all is well. It happened just this past weekend... I went into the field and put up my nice portable 20 m ground plane vertical, which presents a nearly perfect match to coax, but couldn't get a match with the KXAT1 at 14.060... odd. After checking connections, etc. I simply moved to 14.200 and got the usual good match in just a few clicks of the relays. Returned to 14.060 and all was well, I could re-tune at will without trouble. It happens rarely, and I've always been able to recover by shifting freq temporarily - or once, by tuning into a dummy load. I've checked by KXATI construction and alignment several times, seems to be ok.My suspicions center on the SWR bridge and nulling, but usually it works just fine. Maybe I'll find a cold solder joint some day if I keep looking. RC On 8/22/06, Dan Presley <[hidden email]> wrote: > I was out in the woods of Oregon today (up by the coast range town of > Jewell) with my KX 1 and a few different antennas. I used a long wire > for a while, but then for the heck of it I set up a 40M inverted vee > with my portable mast. The KXAT1 had no trouble with the long wire > (and counterpoises) bringing it right down to 1:1, but no such luck > with the dipole ( cut to resonate on 40, and fed w/RG 174).I've used > this antenna a bunch w/ the K2 and it's pretty much a 1:1, but when > using the KX1 atu I got around 9:5 SWR! So, I promptly forgot how to > bypass the tuner (until I got home and re-read the manual;set it to > 'CAL':).But,also in the manual it states that it'll match most coax > type dipoles, etc.Elsewhere it's stated that it won't match a half > wave length,but I wasn't clear if that's only for a half wave end > fed.I'll bet it's the same for a resonant dipole as it's a ground > independent half wave, but maybe someone who has come up against this > before can clarify as far as the tuner is concerned. I usually bring > a separate antenna 'dipper' just to check the antenna in case there's > a short or bad coax,etc., but that got left behind. Just for > reference, I use the lightweight dipole kit from N2CX with a nice > sealed center insulator and RG 174 (I know it's not the most > efficient, but for a short run it's fine and very lightweight). I'm > still trying to find more of the type of wire he used in there-it's > springy yet has a great slick and tough coating which holds up well > in trees, etc, It's also a light yellow in color so it blends > nicely.N2CX quit making these kits a while back and ran out of that > wire.The 'Wireman' sells some similar stuff,(524?) but it's still not > the same. > Any thought appreciated on the tuner-I'm trying to get as much > outdoor radio time in before summer ends:) > -- > Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 > [hidden email] > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Dan Presley-2
Dan wrote:
I was out in the woods of Oregon today (up by the coast range town of Jewell) with my KX 1 and a few different antennas. I used a long wire for a while, but then for the heck of it I set up a 40M inverted vee with my portable mast. The KXAT1 had no trouble with the long wire (and counterpoises) bringing it right down to 1:1, but no such luck with the dipole ( cut to resonate on 40, and fed w/RG 174).I've used this antenna a bunch w/ the K2 and it's pretty much a 1:1, but when using the KX1 atu I got around 9:5 SWR! ------------------------------------------------------- You should not have had any trouble with a center fed dipole, Dan. The issue with the KX1 ATU, as with any ATU, is impedance extremes. Because of the limited number of inductors and capacitors that could be fitted into the tiny space available in the KX1, it has a more limited tuning range than any of the other Elecraft tuners. The end of a dipole presents a very high impedance, possibly in the thousands of ohms. At the other extreme, a very short antenna will present a very low impedance, often less than an ohm. Actually, end-fed short antennas often tune up more easily because they are working against ground and typically Hams have lousy RF grounds <G>. Even with several "radials" the ground impedance will likely be in the tens or, more likely, the hundreds of ohms. That's in series with the antenna so what the tuner is matching is a total impedance of perhaps a hundred ohms or more. The fraction of an ohm that the antenna represents is just part of the total. It's also why such antennas have a very, very low efficiency: often less than a few percent. In your case, I'd suspect you had an unlucky length of feed line. Unless the SWR is truly 1:1 on that feeder, something that is almost never achieved in practice, the feed line acts like a random impedance transformer. I suspect you got unlucky and the combination of the effect of surrounding objects, antenna length, feeder impedance and feeder length all added up to an impedance the KX1 ATU couldn't handle. Adding a few feet of feed line will usually fix that. Another possibility is a short or open, as you suggested. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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>
Thanks,Ron and all of those who replied for the good advice. I'm
>------------------------------------------------------- > >You should not have had any trouble with a center fed dipole, Dan. The issue >with the KX1 ATU, as with any ATU, is impedance extremes. Because of the >limited number of inductors and capacitors that could be fitted into the >tiny space available in the KX1, it has a more limited tuning range than any >of the other Elecraft tuners. > >The end of a dipole presents a very high impedance, possibly in the >thousands of ohms. At the other extreme, a very short antenna will present a >very low impedance, often less than an ohm. Actually, end-fed short antennas >often tune up more easily because they are working against ground and >typically Hams have lousy RF grounds <G>. Even with several "radials" the >ground impedance will likely be in the tens or, more likely, the hundreds of >ohms. That's in series with the antenna so what the tuner is matching is a >total impedance of perhaps a hundred ohms or more. The fraction of an ohm >that the antenna represents is just part of the total. It's also why such >antennas have a very, very low efficiency: often less than a few percent. > >In your case, I'd suspect you had an unlucky length of feed line. Unless the >SWR is truly 1:1 on that feeder, something that is almost never achieved in >practice, the feed line acts like a random impedance transformer. I suspect >you got unlucky and the combination of the effect of surrounding objects, >antenna length, feeder impedance and feeder length all added up to an >impedance the KX1 ATU couldn't handle. Adding a few feet of feed line will >usually fix that. > >Another possibility is a short or open, as you suggested. > >Ron AC7AC > betting you're right on the money as far as feedline length. I'll put the antenna back up and check it with my dipper to see how it reads, and also with the rig in 'cal' (tuner bypass) mode. That'll tell me also if there's a short somewhere too. I tend to forget about the feedline length as I often just use an endfed wire from the KX1, or at home I use ladder line. I know this can still happen with ladder line, but perhaps less of an issue than coax.Besides, the ol' Johnson matchbox is pretty forgiving:) -- Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Guys, my money is on the connector on the feedline. It must have a
short developed since the last time you used it. Or the short might be at the antenna feed point. The feed line length is just not a factor even when there is RF on the shield, and there is some. The MFJ Antenna Analyser will find the problem. I love mine. 73 Karl K5DI Dan Presley wrote: >> >> ------------------------------------------------------- >> >> You should not have had any trouble with a center fed dipole, Dan. >> The issue >> with the KX1 ATU, as with any ATU, is impedance extremes. Because of the >> limited number of inductors and capacitors that could be fitted into the >> tiny space available in the KX1, it has a more limited tuning range >> than any >> of the other Elecraft tuners. >> >> The end of a dipole presents a very high impedance, possibly in the >> thousands of ohms. At the other extreme, a very short antenna will >> present a >> very low impedance, often less than an ohm. Actually, end-fed short >> antennas >> often tune up more easily because they are working against ground and >> typically Hams have lousy RF grounds <G>. Even with several "radials" >> the >> ground impedance will likely be in the tens or, more likely, the >> hundreds of >> ohms. That's in series with the antenna so what the tuner is matching >> is a >> total impedance of perhaps a hundred ohms or more. The fraction of an >> ohm >> that the antenna represents is just part of the total. It's also why >> such >> antennas have a very, very low efficiency: often less than a few >> percent. >> >> In your case, I'd suspect you had an unlucky length of feed line. >> Unless the >> SWR is truly 1:1 on that feeder, something that is almost never >> achieved in >> practice, the feed line acts like a random impedance transformer. I >> suspect >> you got unlucky and the combination of the effect of surrounding >> objects, >> antenna length, feeder impedance and feeder length all added up to an >> impedance the KX1 ATU couldn't handle. Adding a few feet of feed line >> will >> usually fix that. >> >> Another possibility is a short or open, as you suggested. >> >> Ron AC7AC >> > Thanks,Ron and all of those who replied for the good advice. I'm > betting you're right on the money as far as feedline length. I'll put > the antenna back up and check it with my dipper to see how it reads, > and also with the rig in 'cal' (tuner bypass) mode. That'll tell me > also if there's a short somewhere too. I tend to forget about the > feedline length as I often just use an endfed wire from the KX1, or at > home I use ladder line. I know this can still happen with ladder line, > but perhaps less of an issue than coax.Besides, the ol' Johnson > matchbox is pretty forgiving:) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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> Guys, my money is on the connector on the feedline. It must have
>a short developed since the last time you used it. Or the short >might be at the antenna feed point. > > The feed line length is just not a factor even when there is RF >on the shield, and there is some. > > Sorry Karl-Ron had it exactly right.Feedline length is always a potential factor; I've run into it before and just forgot.Both with coax and ladder line sometimes you have to add or subtract a bit for impedance mismatch. You can look it up in the ARRL handbook In fact, you can even do a fair matching job with ladder line bypassing a tuner with the correct lengths.I added two feet of feedline and it loaded right up sweet as pie. I also should have realized it wasn't a shorted feedline as it still took some power and signal strengths were not hugely different as when there's nothing connected. -- Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Dan Presley wrote:
>> Guys, my money is on the connector on the feedline. It must have a >> short developed since the last time you used it. Or the short might >> be at the antenna feed point. >> >> The feed line length is just not a factor even when there is RF on >> the shield, and there is some. >> >> > Sorry Karl-Ron had it exactly right.Feedline length is always a > potential factor; I've run into it before and just forgot. But to say you changed the feed line and then it tuned up fine is not to me correct. I am an Electrical Engineer and I studied feed lines and antenna design. I do things with a Smith Chart. If your dipole has an impedance of 72 ohms, which it really does at it's resonance frequency, then that impedance is what your feed line is seeing and it's characteristic impedance (RG-217) is 50 ohms. I plot both on my Smith Chart and look for a feed line length that will give a really bad low or high impedance at the transmitter end. I only need to look at the first half wavelength since it just repeats itself. I find the lowest impedance occurs at 240 degrees and is 28+j30. The highest is 120 -j12 at near a half wave. Now either of these should be possible for your tuner to tune. Your right the impedance changes between these values and if your very careful you can get close to 50 +j0. But why? Now in my house I have a 88 foot dipole fed in the center with 450 ohm windowed feed line of random electrical length. The SWR can get to 12:1 on some bands and the loss goes up to near 5%. I get out just fine and am Net Control for several nets on 80 and 40 meters. I am sorry but my experience and training make it hard to understand your results. 73 Karl K5DI PS: If you want the Smith Chart I can mail it to you. > Both with coax and ladder line sometimes you have to add or subtract a > bit for impedance mismatch. You can look it up in the ARRL handbook In > fact, you can even do a fair matching job with ladder line bypassing a > tuner with the correct lengths.I added two feet of feedline and it > loaded right up sweet as pie. I also should have realized it wasn't a > shorted feedline as it still took some power and signal strengths were > not hugely different as when there's nothing connected. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Dan Presley-2
I believe two points need to be made about this:
First, if the SWR on the feedline was 1:1, changing the length of the feedline would have no effect. The conclusion is that the original SWR had to have been something other than 1:1. Secondly, the inductance and capacitance range of the KXAT1 is limited (3 inductors and 3 capacitors), the result of that is the impedance matching range decreases as the frequency is reduced. On 80 meters, the matching range is quite narrow, a bit better on 40, but on 30 and 20, the range becomes broader so that one can match most anything on 20 meters. 73, Don W3FPR > -----Original Message----- > Sorry Karl-Ron had it exactly right.Feedline length is always a > potential factor; I've run into it before and just forgot.Both with > coax and ladder line sometimes you have to add or subtract a bit for > impedance mismatch. You can look it up in the ARRL handbook In fact, > you can even do a fair matching job with ladder line bypassing a > tuner with the correct lengths.I added two feet of feedline and it > loaded right up sweet as pie. I also should have realized it wasn't a > shorted feedline as it still took some power and signal strengths > were not hugely different as when there's nothing connected. > -- > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Changing feedline length makes two important differences. One in the
internal path length (which makes an impedance transformation) and one in the external path (if there is not an adequately effective balun at the feedpoint). The impedance of this outside path can vary over a considerable range, and depending on the impedance of the antenna this extra wire connected to the antenna can have a wide range of effects. Model your antenna as a simple vee with a source in the middle, and then attach a wire equal in length to the feedline and see how the current and impedance are disrupted. The extra wire (outside of the coax) is end loaded by the rig and whatever else is at that end of things, so it is hard to model precisely. The end loading will make the extra conductor much longer than actual length, and it may be strongly coupled to earth. -- Alan wb6zqz At 06:42 PM 8/23/2006, Don Wilhelm wrote: >I believe two points need to be made about this: >First, if the SWR on the feedline was 1:1, changing the length of the >feedline would have no effect. The conclusion is that the original SWR had >to have been something other than 1:1. >Secondly, the inductance and capacitance range of the KXAT1 is limited (3 >inductors and 3 capacitors), the result of that is the impedance matching >range decreases as the frequency is reduced. On 80 meters, the matching >range is quite narrow, a bit better on 40, but on 30 and 20, the range >becomes broader so that one can match most anything on 20 meters. > >73, >Don W3FPR > > > > -----Original Message----- > > Sorry Karl-Ron had it exactly right.Feedline length is always a > > potential factor; I've run into it before and just forgot.Both with > > coax and ladder line sometimes you have to add or subtract a bit for > > impedance mismatch. You can look it up in the ARRL handbook In fact, > > you can even do a fair matching job with ladder line bypassing a > > tuner with the correct lengths.I added two feet of feedline and it > > loaded right up sweet as pie. I also should have realized it wasn't a > > shorted feedline as it still took some power and signal strengths > > were not hugely different as when there's nothing connected. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Karl Larsen
At 7:27 PM -0600 8/23/06, Karl Larsen wrote:
> Now either of these should be possible for your tuner to tune. Your >right the impedance changes between these values and if your very >careful you can get close to 50 +j0. But why? Well, I think you answered my question.Changing the feedline length changed the impedance to a value the tuner could handle, which was the original issue.Remember that this is a coax fed antenna, not ladder line (which I have at my home QTH). I know that swr is very high and not an issue with ladder line; that's what I use at home.The tuner is simply a device to allow maximum transfer of power from the transmitter to the feedline. At 9:42 PM -0400 8/23/06, Don Wilhelm wrote: >I believe two points need to be made about this: >First, if the SWR on the feedline was 1:1, changing the length of the >feedline would have no effect. The conclusion is that the original SWR had >to have been something other than 1:1. Don- I think you may have missed my original post, where the issue was a high swr when trying to use the tuner on my coax fed dipole. Adding a few feet of RG 174 allowed the tuner to find a match.Neither the tuner nor added feedline changes the true state of the antenna, but only provides the best match between rig and feedline. -- Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71 [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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