Hi,
I'm a CW operator who dwells in the lower end of the HF bands. My current antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm ladder line. This connects to a 4 to 1 balun (common mode choke?) which is attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57' for 40 meters. A hypothetical question to the wise ones on this list is would I expect any practical improvement in performance of my antenna system (on 40 meters and above) by reducing my 200' delta loop to 143.57' and feeding it with 71.78' of ladder line so that the sum of the antenna length plus twice the ladder line length is 287'? This seems to make theoretical sense since the entire system would be resonant at 7mhz and integral multiples thereof. However, the performance of my current 200' loop appears to be quite good from 80 to 6 meters and my small tuner matches whatever impedance this system is presenting to it so I'm hesitant to take a pair of snippers to my antenna. I would like to increase the length of the loop to 287' feet and feed it with 71.78' of ladderline but that is another story. Also, would I expect to be able to tune any of the these three antennas on 160 meters if I were to purchase either a KXAT100 or KAT500 tuner which presumably have a wider tuning ranges than the Dentron Jr. Monitor tuner? Rick McClelland, AA5S Fort Collins, CO ______________________________________________________________ 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 |
I have a full size 80 meter delta loop that is vertical, hung from a support
on my tower at the 75 foot point. The shape is not ideal (too much horizontal but I can't do any better). I feed it with 450 ohm line at the 0.64 wave point down from the top. The antenna is then tuned with an AT-Auto (Palstar) and I've used other tuners as well. This antenna does not tune at all well on 160. The Q is out of sight (very sharp) and if you can get a match (I would with an old Murch but not the AT-Auto) it was only good for a few kHz before you had to retune and tuning was very touchy. I never tried lengthening the feedline -- I just put up a true 160 meter antenna, a Double-L which works OK. After three years of very casual operating, I made DXCC on top band. Pete, W1RM -----Original Message----- From: Rick McClelland, AA5S [mailto:[hidden email]] Sent: Thursday, January 05, 2012 10:14 AM To: [hidden email] Subject: [Elecraft] Horizontal Delta Loop Questions Hi, I'm a CW operator who dwells in the lower end of the HF bands. My current antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm ladder line. This connects to a 4 to 1 balun (common mode choke?) which is attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57' for 40 meters. A hypothetical question to the wise ones on this list is would I expect any practical improvement in performance of my antenna system (on 40 meters and above) by reducing my 200' delta loop to 143.57' and feeding it with 71.78' of ladder line so that the sum of the antenna length plus twice the ladder line length is 287'? This seems to make theoretical sense since the entire system would be resonant at 7mhz and integral multiples thereof. However, the performance of my current 200' loop appears to be quite good from 80 to 6 meters and my small tuner matches whatever impedance this system is presenting to it so I'm hesitant to take a pair of snippers to my antenna. I would like to increase the length of the loop to 287' feet and feed it with 71.78' of ladderline but that is another story. Also, would I expect to be able to tune any of the these three antennas on 160 meters if I were to purchase either a KXAT100 or KAT500 tuner which presumably have a wider tuning ranges than the Dentron Jr. Monitor tuner? Rick McClelland, AA5S Fort Collins, CO ______________________________________________________________ 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 Rick McClelland, AA5S
In an antenna design where one is already committed to a broadband feedline
and a tuner, particularly one that is working, making the antenna "resonant" may actually WORSEN your results. Efficiency is not hide bound to "resonance". What most people mean by resonance is a low Z feedpoint that has no reactive component, and also want to feed it with 50 ohm coax with no further devices. In other words what they want is SIMPLICITY. I'm not knocking that at all, but it is NOT the only way to fly. The doublet with the most gain is something called a double extended zepp, is NOT resonant, needs a low loss balanced feedline and a tuner to feed it. Working wire solutions for most gain, best efficiency in a given space is a tricky science that involves modeling, and RARELY produces resonant solutions that feed with nothing except 50 ohm coax. In critiquing one person's work, he had defeated himself by forcing the wires to produce a no-tuning-device 50 ohm feed. When he dropped that requirement and got used to the idea of designing for results and matching it to coax afterward, he very quickly designed something that fit his back yard and worked well. In your case what screams at me is "If it ain't broke, don't fix it!" and "Model it, and see what is going on." "Resonance" is way, way over-rated. 73, Guy K2AV On Thu, Jan 5, 2012 at 10:13 AM, Rick McClelland, AA5S <[hidden email]>wrote: > Hi, > > I'm a CW operator who dwells in the lower end of the HF bands. My current > antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm > ladder line. This connects to a 4 to 1 balun (common mode choke?) which is > attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a > spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57' > for 40 meters. > > A hypothetical question to the wise ones on this list is would I expect any > practical improvement in performance of my antenna system (on 40 meters and > above) by reducing my 200' delta loop to 143.57' and feeding it with 71.78' > of ladder line so that the sum of the antenna length plus twice the ladder > line length is 287'? This seems to make theoretical sense since the > entire system would be resonant at 7mhz and integral multiples thereof. > However, the performance of my current 200' loop appears to be quite good > from 80 to 6 meters and my small tuner matches whatever impedance this > system is presenting to it so I'm hesitant to take a pair of snippers to my > antenna. > > I would like to increase the length of the loop to 287' feet and feed it > with 71.78' of ladderline but that is another story. Also, would I expect > to be able to tune any of the these three antennas on 160 meters if I were > to purchase either a KXAT100 or KAT500 tuner which presumably have a wider > tuning ranges than the Dentron Jr. Monitor tuner? > > Rick McClelland, AA5S > Fort Collins, CO > ______________________________________________________________ > 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 |
Guy,
Thank you for taking the time to respond, I had a feeling that I would be well served by posting this question. I was aware that doublets needed to trimmed to non-resonant lengths but I didn't realize the same might be true regarding loops. Looking at the current system on my spreadsheet, there aren't any resonant points at the low end of any of the ham bands so your advice seems to have some objective truth evident. Last weekend I trimmed my ladder line by removing 13' from the 100' length and I notice that I'm having much better results when adjusting the tuner and I'm also now able to achieve a decent match on 10 and 6 meters. I'll take your advice and leave things as they are (unless the irrational urge to extend the length of the loop by 20' to 40' overwhelms me in the spring.) Best Wishes, Rick, AA5S On Thu, Jan 5, 2012 at 9:27 AM, Guy Olinger K2AV <[hidden email]>wrote: > In an antenna design where one is already committed to a broadband > feedline and a tuner, particularly one that is working, making the antenna > "resonant" may actually WORSEN your results. Efficiency is not hide bound > to "resonance". What most people mean by resonance is a low Z feedpoint > that has no reactive component, and also want to feed it with 50 ohm coax > with no further devices. In other words what they want is SIMPLICITY. I'm > not knocking that at all, but it is NOT the only way to fly. The doublet > with the most gain is something called a double extended zepp, is NOT > resonant, needs a low loss balanced feedline and a tuner to feed it. > > Working wire solutions for most gain, best efficiency in a given space is > a tricky science that involves modeling, and RARELY produces resonant > solutions that feed with nothing except 50 ohm coax. In critiquing one > person's work, he had defeated himself by forcing the wires to produce a > no-tuning-device 50 ohm feed. When he dropped that requirement and got > used to the idea of designing for results and matching it to coax > afterward, he very quickly designed something that fit his back yard and > worked well. > > In your case what screams at me is "If it ain't broke, don't fix it!" and > "Model it, and see what is going on." > > "Resonance" is way, way over-rated. > > 73, Guy K2AV > > On Thu, Jan 5, 2012 at 10:13 AM, Rick McClelland, AA5S < > [hidden email]> wrote: > >> Hi, >> >> I'm a CW operator who dwells in the lower end of the HF bands. My current >> antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm >> ladder line. This connects to a 4 to 1 balun (common mode choke?) which >> is >> attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a >> spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57' >> for 40 meters. >> >> A hypothetical question to the wise ones on this list is would I expect >> any >> practical improvement in performance of my antenna system (on 40 meters >> and >> above) by reducing my 200' delta loop to 143.57' and feeding it with >> 71.78' >> of ladder line so that the sum of the antenna length plus twice the ladder >> line length is 287'? This seems to make theoretical sense since the >> entire system would be resonant at 7mhz and integral multiples thereof. >> However, the performance of my current 200' loop appears to be quite good >> from 80 to 6 meters and my small tuner matches whatever impedance this >> system is presenting to it so I'm hesitant to take a pair of snippers to >> my >> antenna. >> >> I would like to increase the length of the loop to 287' feet and feed it >> with 71.78' of ladderline but that is another story. Also, would I expect >> to be able to tune any of the these three antennas on 160 meters if I were >> to purchase either a KXAT100 or KAT500 tuner which presumably have a wider >> tuning ranges than the Dentron Jr. Monitor tuner? >> >> Rick McClelland, AA5S >> Fort Collins, CO >> ______________________________________________________________ >> 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 >> > > -- Rick McClelland, AA5S Fort Collins, CO ______________________________________________________________ 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 Rick McClelland, AA5S
At 08:13 AM 1/5/2012 -0700, you wrote:
>Hi, > >I'm a CW operator who dwells in the lower end of the HF bands. My current >antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm >ladder line. This connects to a 4 to 1 balun (common mode choke?) which is >attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a >spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57' >for 40 meters. > >A hypothetical question to the wise ones on this list is would I expect any >practical improvement in performance of my antenna system (on 40 meters and >above) by reducing my 200' delta loop to 143.57' and feeding it with 71.78' >of ladder line so that the sum of the antenna length plus twice the ladder >line length is 287'? This seems to make theoretical sense since the >entire system would be resonant at 7mhz and integral multiples thereof. >However, the performance of my current 200' loop appears to be quite good >from 80 to 6 meters and my small tuner matches whatever impedance this >system is presenting to it so I'm hesitant to take a pair of snippers to my >antenna. Changing the length of the feed line will not change the dimension or performance of the loop. A loop of dimension (X) will present a feed point impedance (Y) at particular frequency (Z). Attached to the loop at the feed point is a 450 ohm balanced feed line (as pointed out in your case). There will be an impedance mismatch which will produce standing waves on the feed line which will produce varying RF current/voltages along its length. A matching device at the end of the feed line must convert the resultant impedance to the 50 ohm unbalanced impedance accepted by your radio. If the resulting impedance falls outside the range of your coupling/matching device changing the length of the feed line may solve the problem and bring the impedance back into the range of the matching device. However this will not change the performance characteristics of the loop. However, 1, 2, 3 wavelength loops have interesting characteristics on the fundamental and multiple frequencies. A 1 wavelength loop radiates broadside to the loop and more off the sides on multiple wavelengths. A 140 ft horizontal loop is a 'cloud burner' on 40m and a much better dx performer on 20m and up. Making the loop 1.4 wave lengths on 40m probably won't make much difference on 40m but I am not quite sure what will happen to the radiation angle at harmonic frequencies. Probably not a great deal of difference. >I would like to increase the length of the loop to 287' feet and feed it >with 71.78' of ladderline but that is another story. Also, would I expect >to be able to tune any of the these three antennas on 160 meters if I were >to purchase either a KXAT100 or KAT500 tuner which presumably have a wider >tuning ranges than the Dentron Jr. Monitor tuner? There is no doubt that a 280' loop will provide much better dx performance on 40m and up. Choosing the feed line length with the intent of changing the antenna radiation pattern is not fruitful. However certain line lengths present a better opportunity of matching the end to the radio. Check the antenna handbook for suggested line lengths that fall into this category. Another caveat is that a particular antenna tuner may not work beyond a certain power level. It doesn't mean that the impedance is different between the different power levels ... but that the resulting RF voltages or currents my go beyond the component capabilities ... eg arc over or melt hi hi. 73 Jim, VE3CI ______________________________________________________________ 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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