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Installing a Ladder Line to the house
On Jan 8, 11:31*am, Roy Lewallen wrote:
But amateurs tend to use multiband antennas without any thought at all to radiation pattern. When the frequency gets considerably higher than a dipole's resonant frequency, the pattern changes. So there's a good chance that the pattern will have nulls in at least some directions where you might want to communicate. In those cases, the difference between a half wavelength dipole and much longer dipole can be striking. That's another reason why I prefer the separate elements for multi band use, vs the single wire. I generally prefer the normal dipole pattern on most of the bands I use. It's relatively easy to measure tuner efficiency when it's working into a nice resistive load. But I'm curious about how you measured the power the tuner was delivering to a more realistic non-resonant load impedance. The only way I can think of to do it with any semblance of accuracy is to connect two identical tuners back-to-back and measure the power out of the combination. Is that how you did it? If not, how? It's been so long since I did that, I forgot exactly how I came to that conclusion. But I think I was using my resonant coax fed dipole as the load, and pretty sure I had dual watt meters. One before the tuner, and another after the tuner. The tuner has an antenna switch to bypass the tuner. I believe what I did was measure the power on both meters with the tuner bypassed, and then tried using the tuner as a "line flattener", more than an actual tuner, being the system was already resonant. I tried various settings of the tuner, trying quite a few variations in inductance vs cap settings to see if I could notice much loss with the tuner inline. The radio was my old IC 730 and I used full power for the tests. The meter after the radio was used to verify the appx power from the radio, and it stayed fairly constant in all the tests. The meter after the tuner was used to check the power at that point in the line. In all cases, the tuner would indicate a "flat" match with all the various settings, so any variation in the output of the radio should have been small, and the meter after it verified this. But the meter on the other side of the tuner could vary anywhere from about 20% less, to almost unnoticeable difference, depending on the inductance setting of the tuner. This test didn't tell me much about the losses using non resonant loads fed with ladder line, but I suspect that the loss would still be greatly defendant on the inductance setting. I would think the loss would greatly vary just depending on the load at the moment. Could be high, as if feeding a half size dipole with a T network tuner, or pretty low with other longer wire lengths. I didn't try to worry about the exact loss in numbers, but I could see the problem cropping up fairly easy if one were lazy about using the least inductance setting, or if using a tuner with a tapped coil that was not the optimum setting. My tuner uses a roller inductor, which lets me tune to exactly the best spot on the coil, but some tuners tap and switch the coil position. With some of those, loss could be more noticeable if it's compromise setting was way off from optimum. Another thing I noticed that was it didn't take a whole lot of extra inductance for the losses to begin to show. Basically, I found there is only one tuner setting that will give you fairly low loss in such a case. The one using the least inductance to get a usable match for the radio. All the other settings would show quite a bit more loss, and it didn't take too much more inductance to start seeing 10-15-20 % decreases in output from the tuner. And all these settings show a perfect match to the radio. But if using the least inductance in such a case, the meter reading was so close as to almost be the same vs bypassing the tuner. So you can use a tuner and have low loss if you are careful about tuning. Sure, even 20% won't make much of a difference on the other end, but I'd prefer not to lose it none the less. I'm usually on the noisy lower bands, and I rarely run an amp anymore. That's why I insist on every drop. In the summer, I usually need every drop.. :/ I also prefer coax anyway just due to the convenience. But if I run ladder line, I run ladder line the whole way. I don't like running coax to ladder line. I either use one or the other. |
Installing a Ladder Line to the house
On Jan 8, 12:48*pm, Cecil Moore wrote:
wrote: When comparing the ladder line and tuner system vs the coax system, if I had a signal that was 40 db over S9 on the tuner system, it would bump up to about 45 db over S9 with the coax feed. Balanced tuner or balun plus unbalanced tuner? If balun, what kind? Was the balun seeing its designed-for impedance? What do you think would be the A/B results for a resonant coax-fed dipole vs my notuner dipole? Probably about the same. In theory you would have slightly less loss than the coax, but at the lower frequencies even the coax has very low loss. So being the losses for both are very low, I don't think you would be able to see much difference. Or that's my gut hunch anyway.. Yours would probably be better than the coax if the run was several hundred feet. At that distance, the slight difference might begin to show up more. Also if used at fairly high frequencies, you might have an advantage. Depends on how good the coax is how much it would be. |
Installing a Ladder Line to the house
Ed Cregger wrote:
"Dave" wrote in message If I did want to use non-resonant antennas I would locate a tuner at the antenna feedpoint, not at the generator (transmitter). Then you would cheat yourself of a fair amount of propagation and some of the lower and higher frequencies available with such a set up. You're not going to keep RF out of the shack, regardless of which system you use. You might be able to keep some of the hot spots outside, but often times they are close enough to the station that it is really a waste of time. This fascination with resonance is a leftover from CB thinking. How many warships utilize resonant antennas? Yet they communicate the world over. The aversion to transmatches is a ham cultural trait that has no basis in reality, just as the CB'ers are hooked on resonant 50 ohm antennas. It's a characteristic of the culture(s) of both types of operators, with no basis in practical operating engineering. Ed, N2ECW You don't read very well. And you seem a tad hostile. I stated no "aversion" whatsoever to what are called "non-resonant" antennas. I said that I'd locate the tuner at the antenna feedpoint. A transmatch between the radio and the transmission line does little to make the antenna work better. CB thinking? You really have issues. |
Installing a Ladder Line to the house
Dave wrote:
A transmatch between the radio and the transmission line does little to make the antenna work better. That statement is true for a very lossy system but not necessarily true for low-loss real-world systems. Establishing a conjugate match at the antenna feedpoint makes the antenna work better by allowing maximum available power transfer to the antenna. A remote autotuner at the base of the antenna can accomplish that feat. There seems to be developing the myth that a tuner at the shack cannot accomplish that feat. Although strictly technically true, a low-loss tuner and low-loss transmission line can come close enough to achieving a conjugate match at the antenna that almost all of the available power is transferred to the antenna (if losses are made negligible by good engineering practice). It can be proved mathematically that in a lossless system, a conjugate match is established at the antenna feedpoint by the tuner located back in the shack. A near-conjugate match is established in the case of a low-loss system resulting in near-maximum available power transfer to the antenna. -- 73, Cecil http://www.w5dxp.com |
Installing a Ladder Line to the house
On Jan 9, 8:24*am, Cecil Moore wrote:
There seems to be developing the myth that a tuner at the shack cannot accomplish that feat. Although strictly technically true, a low-loss tuner and low-loss transmission line can come close enough to achieving a conjugate match at the antenna that almost all of the available power is transferred to the antenna (if losses are made negligible by good engineering practice). It can be proved mathematically that in a lossless system, a conjugate match is established at the antenna feedpoint by the tuner located back in the shack. A near-conjugate match is established in the case of a low-loss system resulting in near-maximum available power transfer to the antenna. -- 73, Cecil *http://www.w5dxp.com Judging from my mobile antenna tinkering, I'd have to say that is true. As an example, with a short run of coax that feeds the antenna, you would think that it would be required to place the matching device or tuner at the feed point of the vertical. And strictly speaking, it would be the best place for it. But... I've found that you can have very good results if the tuner is at the radio end of the coax. In actual operation, there seems to be little difference in performance. But the short piece of coax "maybe 10 ft long" is fairly low loss on the lower HF frequencies. So it's not a lossless system, but fairly low loss considering the frequency and short length of the line. But if I run a long coax to the same antenna, I would prefer to keep the tuner at the same place, in front of the short 10 ft piece, and then run my long cable from the radio to the tuner, which is still at the car. I often did this when using the radio at picnic tables, tents, while using the mobile antenna on the car. My most recent installs on the two trucks place the matching device at the antenna. But in my older car I once used, I used the tuner at the radio end. It was convenient, and let me fine tune the match while driving. There seems to be little difference in performance that I can see using the short fairly low loss pieces of coax. Not much difference where I place the tuner. So this tends to back up your theory. |
Installing a Ladder Line to the house
"Dave" wrote in message m... Ed Cregger wrote: "Dave" wrote in message If I did want to use non-resonant antennas I would locate a tuner at the antenna feedpoint, not at the generator (transmitter). Then you would cheat yourself of a fair amount of propagation and some of the lower and higher frequencies available with such a set up. You're not going to keep RF out of the shack, regardless of which system you use. You might be able to keep some of the hot spots outside, but often times they are close enough to the station that it is really a waste of time. This fascination with resonance is a leftover from CB thinking. How many warships utilize resonant antennas? Yet they communicate the world over. The aversion to transmatches is a ham cultural trait that has no basis in reality, just as the CB'ers are hooked on resonant 50 ohm antennas. It's a characteristic of the culture(s) of both types of operators, with no basis in practical operating engineering. Ed, N2ECW You don't read very well. And you seem a tad hostile. I stated no "aversion" whatsoever to what are called "non-resonant" antennas. I said that I'd locate the tuner at the antenna feedpoint. A transmatch between the radio and the transmission line does little to make the antenna work better. CB thinking? You really have issues. ----------- Actually, I read very well. We are talking on a worldwide forum. Folks that take every single comment personally have missed that point of view and usually react negatively, as you. If I wanted to raise hell and berate someone, this would be the last usenet group that I would use. Most folks here are scientifically oriented and would be no fun to irritate. I am interested in two-way radio cultures. I own and use CB radios in addition to my amateur gear. I had my FCC commercial ticket long before encountering CB or ham radio. I was introduced to two-way radio while in the USAF, so my view of the cultures is quite different than many civilian radio cultures. No insult was or is intended. When I say someone is oriented toward radio in a CB fashion, it is not necessarily an insult. Why would I insult myself? I may be a bit hostile, that's true. Anyone in the amount of pain that I am in (and there are certainly millions with worse pain than mine) will be a bit short or curt at times. My apologies. The marketing campaigns for CB gear in the seventies placed emphasis on a 50 ohm match with a resonant antenna. Many CB folks received all of their education in radio via those commercials. Many hams, especially those that came from CB, would probably faint if they knew that commercial broadcast stations often have an "antenna tuner" at the base of their broadcast antennas. After all, tuners are no good, right? That was one of the points that I was trying to make. Kind of a preemptive strike on my part to reduce the number of complaints about folks running a dipole antenna configuration while using twinlead feedline with a transmatch at the station. I was not picking on you, nor was I trying to show you in a bad light. Ed, N2ECW |
Installing a Ladder Line to the house
wrote:
But if I run a long coax to the same antenna, I would prefer to keep the tuner at the same place, in front of the short 10 ft piece, and then run my long cable from the radio to the tuner, which is still at the car. When the SWR is not 1:1 but is of a reasonable value: A short coax run is usually low-loss. A long coax run is usually not low-loss. When the tuner is located at the transmitter, the near-conjugate match at the antenna can only be achieved in a low-loss system. Open-wire HF transmission line systems are usually low-loss systems. -- 73, Cecil http://www.w5dxp.com |
Installing a Ladder Line to the house
"Cecil Moore" wrote If one doesn't know what magnitude of impedance is being encountered by the balun, the best balun solution is a husky 1:1 current (choke) balun, not a 4:1 voltage balun which is designed to deal with 200 ohms, not 2000+j2000 ohms. -- 73, Cecil http://www.w5dxp.com ----------- I used to be good at this stuff, Cecil, but that was long ago. The only balun that has worked with any success so far has been the built-in balun (4:1 allegedly) in my MFJ-989C. That I can get to work. When hooking up other baluns and using the coax output on my tuner, none of the other baluns work worth a hoot with one exception. I have an LDG 1:1 200 watt balun that will tune my Van Gordon All Bander from one end to the other of the HF spectrum, using just the internal tuner of my Yaesu FT-890AT. Go figure. I used to be a fairly sharp cookie at this stuff, but those days are in the past. Got a serious case of "brick brain syndrome", if you know what I mean? To my way of thinking (which is probably incorrect), using the 4:1 balun would broaden the impedances that I could match versus the 1:1 balun. What you are saying is just the opposite. Please elaborate. I will be most grateful. Ed, N2ECW |
Installing a Ladder Line to the house
Ed Cregger wrote:
I have an LDG 1:1 200 watt balun that will tune my Van Gordon All Bander from one end to the other of the HF spectrum, using just the internal tuner of my Yaesu FT-890AT. Go figure. If this is the 80m dipole with 100' of ladder-line, one can look at my notuner all-band-HF antenna to see why 100' is a good fixed length for the ladder-line. 100' is near a current maximum point (loop) on all HF bands. If one varies the length of the ladder-line from 90' to 115', one doesn't even need a tuner and a 1:1 current- balun-choke is ideal. http://www.w5dxp.com/pnts130.gif To my way of thinking (which is probably incorrect), using the 4:1 balun would broaden the impedances that I could match versus the 1:1 balun. What you are saying is just the opposite. Please elaborate. I will be most grateful. A 4:1 balun is a very good transformer over a narrow range. Most are voltage baluns that do not balance currents and therefore do little to discourage common-mode currents. Test a balun looking into 2000+j2000 and see what happens. One of my 4:1 baluns got so hot I couldn't touch the case. The best balun design, IMO, is one where flux in the ferrite is caused only by common-mode current and not by differential-mode current. Here's some useful information: http://www.dxengineering.com/TechArticles.asp?ID={3E5220F7-2D0F-45B5-85F7-3B654F804C4F} -- 73, Cecil http://www.w5dxp.com |
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