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#71
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An antenna question--43 ft vertical
In message , John S
writes On 7/3/2015 10:17 AM, Ian Jackson wrote: In message , John S writes On 6/29/2015 10:48 AM, Wayne wrote: As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat metal roof. The antenna is fed with about 25 feet of RG-8, and there is a tuner at the transmit end. While I'm pretty happy with the antenna, I'd like to simplify the matching. Thus, the question: what is the purpose of a 1:4 unun on a 43 foot vertical? ( I assume the "4" side is on the antenna side.) I'd expect a better coax to antenna match when the antenna feedpoint is a high Z (example, at 30 meters), but I'd also expect a worse coax to antenna match when the feedpoint is a low Z (example, at 10 meters). Is that the way it works, or is there other magic involved? I think we strayed off the path to answering your original question. The short answer is that you are correct and there is no magic involved. A bit longer answer is: A 43ft vertical will present a feed impedance of 1010 + J 269.2 ohms at 30 meters. Using a 1:4 transformer at the feed point will reduce that to 253 + J 67 ohms. That is a bit closer to your 50 ohm line. A fixed-tuned TX will still need a matcher. That was not part of the original question(s). At 10 meters, the antenna will present a 147 + J 133 ohms impedance. A 1:4 transformer will reduce that to 37 + J 33 ohms. A fixed-tuned TX will probably be reasonably happy with a direct connection - although maybe even happier with a series capacitor of -J22 ohms. That was not part of the original question(s). There are several disclaimers I could include, but I think you understand that the answers cannot be exact with the info presented. I hope this helps. The question is really whether the losses with the 4:1 transformer, plus those of any matcher at the TX end, exceed those when there is no transformer (but with higher loss on the coax), plus a matcher. Put another way, for short feeder lengths, is it better to use the transformer? That was not the question he asked. Please re-read the OP. I was trying to address his original question(s) as best as I could. In addition I also said that there were "several disclaimers I could include" which may involve your personal concerns. I did not want to muddy the waters. I think I answered Wayne's question(s), but I will wait to hear from him to see if that is so. You have certainly answered "Thus, the question: what is the purpose of a 1:4 unun on a 43 foot vertical?" (ie to reduce the horrendous mismatch). However, don't you think there's any virtue in wondering whether, in the circumstances described (with the relatively short feeder), it will be any better than a direct connection to the antenna, and to do all the matching at the TX end? Also, would you use a transformer if there was hardly any feeder at all, or (in an extreme case) if the antenna was fed directly from the TX? I'm not advocating anything - only wondering. -- Ian |
#72
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An antenna question--43 ft vertical
"rickman" wrote in message ... On 7/2/2015 8:53 PM, Wayne wrote: "rickman" wrote in message ... On 7/2/2015 3:52 PM, Wayne wrote: Why will the reflections not have losses? Because the assumption I posed was for a lossless line. In that case, with a conjugate match on both ends, wouldn't there be maximum power transmission regardless of the SWR? You aren't grasping the issue. Losses are *not* only in the transmission line. When a reflected wave returns to the transmitter output, it is not reflected 100%. If the output and transmission line are matched exactly, 50% of the reflected wave reaching the output will be reflected and 50% will be dissipated in the output stage. I don't think I've ever heard that anywhere before. Could you elaborate? Are you suggesting that the conjugate match will reflect back to the antenna 100% of the original reflected wave from the antenna? Well, yes. Minus losses in matching networks and transmission lines. In examples with lossless lines and lossless matching networks, wouldn't it be 100%. |
#73
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An antenna question--43 ft vertical
On 7/3/2015 1:34 PM, Ian Jackson wrote:
In message , John S writes On 7/3/2015 10:17 AM, Ian Jackson wrote: In message , John S writes On 6/29/2015 10:48 AM, Wayne wrote: As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat metal roof. The antenna is fed with about 25 feet of RG-8, and there is a tuner at the transmit end. While I'm pretty happy with the antenna, I'd like to simplify the matching. Thus, the question: what is the purpose of a 1:4 unun on a 43 foot vertical? ( I assume the "4" side is on the antenna side.) I'd expect a better coax to antenna match when the antenna feedpoint is a high Z (example, at 30 meters), but I'd also expect a worse coax to antenna match when the feedpoint is a low Z (example, at 10 meters). Is that the way it works, or is there other magic involved? I think we strayed off the path to answering your original question. The short answer is that you are correct and there is no magic involved. A bit longer answer is: A 43ft vertical will present a feed impedance of 1010 + J 269.2 ohms at 30 meters. Using a 1:4 transformer at the feed point will reduce that to 253 + J 67 ohms. That is a bit closer to your 50 ohm line. A fixed-tuned TX will still need a matcher. That was not part of the original question(s). At 10 meters, the antenna will present a 147 + J 133 ohms impedance. A 1:4 transformer will reduce that to 37 + J 33 ohms. A fixed-tuned TX will probably be reasonably happy with a direct connection - although maybe even happier with a series capacitor of -J22 ohms. That was not part of the original question(s). There are several disclaimers I could include, but I think you understand that the answers cannot be exact with the info presented. I hope this helps. The question is really whether the losses with the 4:1 transformer, plus those of any matcher at the TX end, exceed those when there is no transformer (but with higher loss on the coax), plus a matcher. Put another way, for short feeder lengths, is it better to use the transformer? That was not the question he asked. Please re-read the OP. I was trying to address his original question(s) as best as I could. In addition I also said that there were "several disclaimers I could include" which may involve your personal concerns. I did not want to muddy the waters. I think I answered Wayne's question(s), but I will wait to hear from him to see if that is so. You have certainly answered "Thus, the question: what is the purpose of a 1:4 unun on a 43 foot vertical?" (ie to reduce the horrendous mismatch). However, don't you think there's any virtue in wondering whether, in the circumstances described (with the relatively short feeder), it will be any better than a direct connection to the antenna, and to do all the matching at the TX end? Also, would you use a transformer if there was hardly any feeder at all, or (in an extreme case) if the antenna was fed directly from the TX? I'm not advocating anything - only wondering. Yes, I agree that there is virtue in fully examining all the possibilities. I may or may not use a transformer with a direct connection to the antenna. It depends on my source's capabilities. Of course, anything added to improve a match also causes a bit of loss. It's all tradeoffs, as you well know. |
#74
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An antenna question--43 ft vertical
Okay. This data set is for a 43' carbon steel antenna on a perfect
ground fed with 25' of RG8A/U. No transformer. Freq R X SWR 4.000 2.52 -12.74 21.140 5.000 20.16 20.82 2.977 6.000 28.78 -30.81 2.586 7.000 8.04 -5.76 6.307 8.000 5.68 12.25 9.337 9.000 6.08 30.66 11.344 10.000 8.95 56.02 12.703 11.000 20.21 104.84 13.685 12.000 137.06 277.80 14.297 13.000 126.21 -267.32 14.174 14.000 19.15 -95.40 12.417 15.000 11.09 -43.81 8.067 16.000 17.90 -11.07 2.949 17.000 56.99 -15.98 1.384 18.000 20.29 -31.49 3.568 19.000 9.29 -12.21 5.711 20.000 6.95 3.56 7.236 21.000 6.99 19.13 8.217 22.000 9.03 38.15 8.829 23.000 15.83 67.71 9.161 24.000 48.70 132.94 9.150 25.000 418.45 49.46 8.488 26.000 60.45 -119.25 6.589 27.000 28.69 -45.41 3.465 28.000 46.51 -9.99 1.245 29.000 62.03 -48.79 2.397 30.000 21.38 -41.26 4.116 This data set is the same except with a 1:4 transformer at the antenna. Freq R X SWR 4.000 4.07 19.59 14.187 5.000 25.57 74.28 6.633 6.000 153.39 -83.56 4.058 7.000 25.51 -38.52 3.333 8.000 15.35 -6.11 3.312 9.000 16.11 18.43 3.567 10.000 26.59 49.05 3.970 11.000 87.00 102.27 4.497 12.000 180.75 -114.05 5.136 13.000 28.87 -72.84 5.814 14.000 11.18 -31.02 6.256 15.000 8.52 -4.23 5.914 16.000 13.30 23.05 4.607 17.000 50.10 61.48 3.196 18.000 107.24 -32.07 2.383 19.000 36.37 -30.20 2.135 20.000 22.85 -5.54 2.222 21.000 22.77 16.08 2.474 22.000 33.85 41.69 2.827 23.000 85.10 73.92 3.268 24.000 165.89 -60.03 3.790 25.000 39.38 -70.12 4.323 26.000 15.47 -31.46 4.605 27.000 12.03 -4.86 4.197 28.000 18.81 20.71 3.175 29.000 54.98 43.57 2.257 30.000 85.50 -14.78 1.786 Is this of any help? |
#75
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An antenna question--43 ft vertical
On 7/4/2015 1:34 AM, John S wrote:
Okay. This data set is for a 43' carbon steel antenna on a perfect ground fed with 25' of RG8A/U. No transformer. I made a mistake. I used 3" copper pipe. I will re-do with 3" carbon steel pipe. No transformer: Freq R X SWR 4.000 2.61 -12.68 20.382 5.000 20.92 20.65 2.867 6.000 28.18 -30.18 2.600 7.000 8.03 -5.57 6.304 8.000 5.70 12.35 9.317 9.000 6.11 30.75 11.314 10.000 9.00 56.13 12.662 11.000 20.37 105.05 13.626 12.000 139.02 278.20 14.204 13.000 125.69 -265.07 14.021 14.000 19.40 -94.97 12.182 15.000 11.41 -43.56 7.809 16.000 18.65 -11.02 2.830 17.000 56.19 -17.88 1.426 18.000 19.92 -31.06 3.599 19.000 9.26 -12.02 5.720 20.000 6.96 3.68 7.228 21.000 7.02 19.23 8.195 22.000 9.09 38.27 8.792 23.000 15.99 67.89 9.102 24.000 49.53 133.22 9.057 25.000 412.93 41.45 8.343 26.000 60.97 -117.33 6.399 27.000 29.70 -44.72 3.324 28.000 48.31 -10.74 1.247 29.000 60.26 -49.68 2.445 30.000 21.05 -40.86 4.142 1:4 transformer: Freq R X SWR 4.000 4.21 19.69 13.745 5.000 26.48 74.45 6.450 6.000 149.09 -82.20 3.972 7.000 25.55 -37.90 3.288 8.000 15.45 -5.81 3.285 9.000 16.25 18.68 3.549 10.000 26.91 49.36 3.954 11.000 88.45 102.31 4.478 12.000 177.47 -114.21 5.105 13.000 28.81 -72.20 5.756 14.000 11.31 -30.71 6.152 15.000 8.73 -3.99 5.767 16.000 13.78 23.29 4.469 17.000 51.75 60.81 3.109 18.000 104.23 -32.25 2.336 19.000 36.12 -29.39 2.111 20.000 22.93 -5.09 2.210 21.000 22.96 16.44 2.467 22.000 34.32 42.05 2.819 23.000 86.65 73.65 3.255 24.000 162.78 -61.65 3.764 25.000 39.08 -69.10 4.270 26.000 15.65 -30.95 4.510 27.000 12.38 -4.51 4.075 28.000 19.52 20.93 3.075 29.000 56.33 42.38 2.197 30.000 83.40 -15.44 1.755 |
#76
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An antenna question--43 ft vertical
"John S" wrote in message ... On 7/4/2015 1:34 AM, John S wrote: Okay. This data set is for a 43' carbon steel antenna on a perfect ground fed with 25' of RG8A/U. No transformer. I made a mistake. I used 3" copper pipe. I will re-do with 3" carbon steel pipe. No transformer: Freq R X SWR 4.000 2.61 -12.68 20.382 5.000 20.92 20.65 2.867 6.000 28.18 -30.18 2.600 7.000 8.03 -5.57 6.304 8.000 5.70 12.35 9.317 9.000 6.11 30.75 11.314 10.000 9.00 56.13 12.662 11.000 20.37 105.05 13.626 12.000 139.02 278.20 14.204 13.000 125.69 -265.07 14.021 14.000 19.40 -94.97 12.182 15.000 11.41 -43.56 7.809 16.000 18.65 -11.02 2.830 17.000 56.19 -17.88 1.426 18.000 19.92 -31.06 3.599 19.000 9.26 -12.02 5.720 20.000 6.96 3.68 7.228 21.000 7.02 19.23 8.195 22.000 9.09 38.27 8.792 23.000 15.99 67.89 9.102 24.000 49.53 133.22 9.057 25.000 412.93 41.45 8.343 26.000 60.97 -117.33 6.399 27.000 29.70 -44.72 3.324 28.000 48.31 -10.74 1.247 29.000 60.26 -49.68 2.445 30.000 21.05 -40.86 4.142 1:4 transformer: Freq R X SWR 4.000 4.21 19.69 13.745 5.000 26.48 74.45 6.450 6.000 149.09 -82.20 3.972 7.000 25.55 -37.90 3.288 8.000 15.45 -5.81 3.285 9.000 16.25 18.68 3.549 10.000 26.91 49.36 3.954 11.000 88.45 102.31 4.478 12.000 177.47 -114.21 5.105 13.000 28.81 -72.20 5.756 14.000 11.31 -30.71 6.152 15.000 8.73 -3.99 5.767 16.000 13.78 23.29 4.469 17.000 51.75 60.81 3.109 18.000 104.23 -32.25 2.336 19.000 36.12 -29.39 2.111 20.000 22.93 -5.09 2.210 21.000 22.96 16.44 2.467 22.000 34.32 42.05 2.819 23.000 86.65 73.65 3.255 24.000 162.78 -61.65 3.764 25.000 39.08 -69.10 4.270 26.000 15.65 -30.95 4.510 27.000 12.38 -4.51 4.075 28.000 19.52 20.93 3.075 29.000 56.33 42.38 2.197 30.000 83.40 -15.44 1.755 Yes, very interesting. Throw in 75 feet of cable, and things get "better". The lowest SWR is about 2:1 at 19 MHz. It is about 6:1 on 20 meters. |
#77
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An antenna question--43 ft vertical
On 7/4/2015 10:55 AM, Wayne wrote:
Yes, very interesting. Throw in 75 feet of cable, and things get "better". The lowest SWR is about 2:1 at 19 MHz. It is about 6:1 on 20 meters. Of course. More loss in the cable makes it "better" (but, you know that). |
#78
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An antenna question--43 ft vertical
On 7/4/2015 10:55 AM, Wayne wrote:
By the way, Wayne... Are you aware of a companion Excel application for EZNEC called AutoEZ? You can run many test cases in a few seconds using it. You can find it on the EZNEC site. It is how I generated the data I posted. |
#79
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An antenna question--43 ft vertical
"John S" wrote in message ... On 7/4/2015 10:55 AM, Wayne wrote: By the way, Wayne... Are you aware of a companion Excel application for EZNEC called AutoEZ? You can run many test cases in a few seconds using it. You can find it on the EZNEC site. It is how I generated the data I posted. Thanks, I'll look for that. I run the old wood burning version 3.0. |
#80
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An antenna question--43 ft vertical
On 7/3/2015 3:27 PM, Wayne wrote:
"rickman" wrote in message ... On 7/2/2015 8:53 PM, Wayne wrote: "rickman" wrote in message ... On 7/2/2015 3:52 PM, Wayne wrote: Why will the reflections not have losses? Because the assumption I posed was for a lossless line. In that case, with a conjugate match on both ends, wouldn't there be maximum power transmission regardless of the SWR? You aren't grasping the issue. Losses are *not* only in the transmission line. When a reflected wave returns to the transmitter output, it is not reflected 100%. If the output and transmission line are matched exactly, 50% of the reflected wave reaching the output will be reflected and 50% will be dissipated in the output stage. I don't think I've ever heard that anywhere before. Could you elaborate? I'm not so sure now. I think I mentioned before that I learned about transmission lines in the digital context where source and loads are largely resistive. Resistance dissipates power. So when matched the source dissipates as much power as delivered to the load (or transmission line). Likewise, matched impedance will not reflect power, but rather it is all absorbed. That is what happens at the antenna for sure. But I'm not clear about what this conjugate network is really. If it is purely reactive, then it will not have losses other than the parasitics. I have to admit I am not fluent in the complex math of networks. So off hand an impedance of 1063 -j0 says to me resistive. The imaginary part implies phase shifting, no? With that term being 0 doesn't that say the capacitive and inductive parts cancel out leaving only resistance? If you can, please explain how I am wrong. Are you suggesting that the conjugate match will reflect back to the antenna 100% of the original reflected wave from the antenna? Well, yes. Minus losses in matching networks and transmission lines. In examples with lossless lines and lossless matching networks, wouldn't it be 100%. I don't get how the matching network will reflect the wave from the antenna 100%. Is that something you can explain? -- Rick |
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