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Ladder line Vs. Coax
I have an efficiency question concerning feed lines. My present
system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? |
Ladder line Vs. Coax
... in practical terms... not worth the trouble. :)
- 'Doc |
Ladder line Vs. Coax
Sonny Hood wrote:
I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? ================================================== == Why not replace the complete coax feeder with twin lead feeder (if you can keep it away from soil and/or metal) , and use a matching box directly accepting the twin lead feeder ( without ferrite type balun), be it 300 or 450 Ohms or approx 600 Ohms ladder line ? It will improve efficiency and above all make the antenna multi-band. Frank GM0CSZ / KN6WH |
Ladder line Vs. Coax
On May 28, 10:16*am, Sonny Hood wrote:
* *I have an efficiency question concerning feed lines. *My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. *I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. *Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). *By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. *Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. *What do you think the increase will be? I think you left out the losses in the balun. With a kilowatt even a large (by ham standards) balun will get very warm if you leave the key down... my guess is it's not quite as much as you're saving but comparable. It all amounts to 10%, and that's such a tiny fraction of a S-unit. Now, if your antenna were an incredible mismatch to coax to begin with, then ladder line makes good sense. Say you want to use your same inv-V on 40M, then you'd run ladder line all the way to your tuner and be in fat city. Tim N3QE |
Ladder line Vs. Coax
Sonny Hood wrote in
: I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? One of the numbers that is hard to come up with is the loss through a balun. The only number I could find for a voltage balun is a matched loss of 0.075db, this would be times 2 in your setup. So there is loss, and it's well known that the loss goes up with miss match. I think you are neglecting the loss through the baluns and the miss match loss. Remember your antenna will not be 50 ohms over a very wide frequency range. Going open wire line all the way or changing to RG8 size coax will likely work just as well and be simpler to do. John W3JXP |
Ladder line Vs. Coax
Tim Shoppa wrote:
Hi, I think you left out the losses in the balun. With a kilowatt even a large (by ham standards) balun will get very warm if you leave the key down... my guess is it's not quite as much as you're saving but comparable. It all amounts to 10%, and that's such a tiny fraction of a S-unit. The other side probably wouldn`notice the difference. Now, if your antenna were an incredible mismatch to coax to begin with, then ladder line makes good sense. Say you want to use your same inv-V on 40M, then you'd run ladder line all the way to your tuner and be in fat city. I would not take TV ladderline if you have a high standing wave ratio, and this will happen if you use the dipol for multiband purpose. I`ve tested a dipol with about 20 m length (67 ft) for 80m. At first I got almost the same s-meter report compared with a W3DZZ trap dipol. But after a couple of month I noticed that the received signal was up to 20 db down compared with the trap dipol. I only used 100 watts but it broke the TV ladder line. Here I`ve learned what has happened: http://www.w8ji.com/vswr_reactive_power.htm I`m planning to build a new antenna with self built ladderline for multiband purposes for one of the traps of my W3DZZ is broken. I´ve only bought the spacers for the new ladder line. -- 73 DJ4PB |
Ladder line Vs. Coax
Highland Ham wrote:
Why not replace the complete coax feeder with twin lead feeder (if you can keep it away from soil and/or metal) , and use a matching box directly accepting the twin lead feeder ( without ferrite type balun), be it 300 or 450 Ohms or approx 600 Ohms ladder line ? It will improve efficiency and above all make the antenna multi-band. Let's see how much improvement. Assuming a 50 ohm antenna, 3.8 MHz, and using Owen's xmission line calculator at: http://www.vk1od.net/tl/tllc.php 85 feet of RG8x has a loss of 0.478 dB. 85 feet of 300 ohm twinlead has a loss of 0.424 dB. How much will that 0.054 dB improve efficiency? 1%? The coax has a 1:1 SWR. The 300 ohm twinlead has a 6:1 SWR. That makes the losses almost equal. If we were talking about RG-213, the losses would be 0.308 dB, 0.116 dB better than the 300 ohm twinlead. The following is becoming a myth: "One can ignore the losses in twinlead and ladder-line." Also - maybe he doesn't want to use a "matching box". -- 73, Cecil http://www.w5dxp.com |
Ladder line Vs. Coax
On May 28, 1:22*pm, (Dieter Kiel) wrote:
wrote: Hi, I think you left out the losses in the balun. With a kilowatt even a large (by ham standards) balun will get very warm if you leave the key down... my guess is it's not quite as much as you're saving but comparable. It all amounts to 10%, and that's such a tiny fraction of a S-unit. The other side probably wouldn`notice the difference. Now, if your antenna were an incredible mismatch to coax to begin with, then ladder line makes good sense. Say you want to use your same inv-V on 40M, then you'd run ladder line all the way to your tuner and be in fat city. I would not take TV ladderline if you have a high standing wave ratio, and this will happen if you use the dipol for multiband purpose. I`ve tested a dipol with about 20 m length (67 ft) for 80m. At first I got almost the same s-meter report compared with a W3DZZ trap dipol. But after a couple of month I noticed that the received signal was up to 20 db down compared with the trap dipol. I only used 100 watts but it broke the TV ladder line. Here I`ve learned what has happened: http://www.w8ji.com/vswr_reactive_power.htm I`m planning to build a new antenna with self built ladderline for multiband purposes for one of the traps of my W3DZZ is broken. I´ve only bought the spacers for the new ladder line. I have a 135-foot dipole fed with approx 100 feet of home-made ladder line and am incredibly happy with its performance from 80M all the way to 15M. Much of the joy of the ladderline was not in buying the parts to make it, but making it from stuff on hand. I had a sheet of 1/8" polycarbonate that I cut into 4"x3/8" strips, then drilled and notched, to put a spacer every foot using tie-wires. Others boil wooden dowels in paraffin for the spacers (the method recommended by the 1930's ARRL Handbook). Seeing the ladderline go up 85 feet to the middle of the dipole is a pure joy! Tim N3QE |
Ladder line Vs. Coax
11 - 20 watts represents only 0.5 - 1 dB, which would virtually never be
discernible by the other station. As others have noted, even this insignificant potential gain would be reduced by balun loss. But what no one else has mentioned is that the ladder line loss can increase significantly, possibly even dramatically, when it gets wet. Any improvement you'll see from the proposed change will be due entirely to placebo effect. Roy Lewallen, W7EL |
Ladder line Vs. Coax
Tim Shoppa wrote:
I have a 135-foot dipole fed with approx 100 feet of home-made ladder line and am incredibly happy with its performance from 80M all the way to 15M. Why those are good choices for lengths can be seen on the following diagram: http://www.w5dxp.com/pnts130.gif You are relatively close to a low-impedance/current- maximum point on all HF bands. -- 73, Cecil http://www.w5dxp.com |
Ladder line Vs. Coax
On May 28, 9:16 am, Sonny Hood wrote:
I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? If you switch from coax to ladder line and baluns or tuners, you are going to lose a bit of efficiency I bet. I always have when I've compared the two on that band. You are converted from a pure and simple system which is a 50 ohm radio, feeding 50 ohm line, which BTW at 75m is very low loss, into an appx 50 ohm load. This "pure" system is probably 95%+ efficient on the 75m band as long as the coax is not junk. In my opinion there is no better method of feeding a single band dipole. Anything else is pretty much a step down as far as I'm concerned. The *only* reason I would ever run that way is if I wanted multi band use using ladder line and a tuner. But in my case, I prefer multiple dipoles fed with a single coax. The decrease in loss switching from coax to ladder line *on 75m* is so small as to be nothing. But then you have baluns and tuners. This is what is going to spoil the food. You will actually end up with a net loss at the end of the day. Maybe be a small loss, but I bet it will be measurable on a meter if you used an A/B switch. It was in my cases. Then you have the moisture issues, etc.. Do what you want, I prefer coax when feeding dipoles. I usually use 213 on HF here at the house. But at 3 mhz, even RG-58 is fairly low loss. The mini 8 you are using should be a bit better than rg-58. I think it's slightly larger and using foam if I remember right. |
Ladder line Vs. Coax
Sonny Hood wrote in
: I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? Sonny, I have resisted the temptation to tell you that the question is wrong rather than to answer the question... however... You are trying to compare two configurations that are not optimal. An optimal coax configuration would have a balun, usually at the antena feed point so your coax loss budget is short changed a balun. I assume from the fact that you have proposed coax that this is a one band antenna. You haven't made it clear whether you can use an ATU to transform the load to suit the tx, I will assume you can. Why do you need two 4:1 baluns / transformers? The dipole is already an approximately balanced load and loss on open wire line with a VSWR of 4:1 is still quite low. You could just attach the feedline directly to the antenna, and use a 1:1 balun at the ATU. Alternatively, you could lengthen the feedline a little so that it was an electrical half wave and dispense with the ATU (still need the balun). In the case of the latter (an electrical half wave of open wire line, 1:1 balun at the tx) you will achieve the lowest loss, but it is just a few tenths of a db better than the balun/RG8X config if you work them through. The open wire line might not be as easy to route into and around the shack, and depending on construction, more affected by water. Owen |
Ladder line Vs. Coax
On Wed, 28 May 2008 10:16:45 -0400, Sonny Hood wrote:
Thanks Guys, I got some good replies and it cause me to reconsider the change. I find that the best and most simple change will be to remove the RG-8X and it's high attenuation and install all JT-2015 (RG-8 Type) from R&L Electronics. Also to put a good 1:1 balun at the feed point. I have a 160M windom and a G5RV and will dedicate this inverted vee antenna to 75M. This will be not used on 40M due to the high resistance on the second harmonic with the current balun. Yes the added baluns for the ladder line would increase the insertion loss and yes the wet ladder line is a poor conductor. And the cost will be spent for a more efficiency designed system. K4WYS |
Ladder line Vs. Coax
Sonny Hood wrote:
I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? There is so little loss at 3.5 mHz for RG8X you would have a hard time telling any difference. |
Ladder line Vs. Coax
Sonny Hood wrote in
: I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? In one short word: imperceptible. Using twinlead or ladder line is a good idea if you're feeding an antenna that has a high SWR at the feedpoint on some of the frequencies you're going to use it with, but at 75 meters, RG8X vs. ladder line will only make a small difference if the SWR is at all close to 1. Less than half a decibel, or a tenth of an S-unit! Sure, it might make enough difference on very weak paths, but most of the time nobody would be able to tell the difference on a direct on-air A-B test! And even that advantage almost disappears when the ladder line is wet. Like I said, the picture is quite different at high SWR. -- Dave Oldridge+ ICQ 1800667 |
Ladder line Vs. Coax
Sonny Hood wrote in
: On Wed, 28 May 2008 10:16:45 -0400, Sonny Hood wrote: Thanks Guys, I got some good replies and it cause me to reconsider the change. I find that the best and most simple change will be to remove the RG-8X and it's high attenuation and install all JT-2015 (RG-8 Type) from R&L Electronics. Sonny, run the numbers at http://www.vk1od.net/tl/tllc.php before you spend the money. BTW, it will make NO difference on receive since S/N ratio on 80m is almost entirely determined by band noise and small change in TL loss will make no significant difference. Change in TL loss will affect the strength of your transmitted signals. Also to put a good 1:1 balun at the feed point. Good move. Owen |
Ladder line Vs. Coax
"Sonny Hood" wrote in message ... On Wed, 28 May 2008 10:16:45 -0400, Sonny Hood wrote: Thanks Guys, I got some good replies and it cause me to reconsider the change. I find that the best and most simple change will be to remove the RG-8X and it's high attenuation and install all JT-2015 (RG-8 Type) from R&L Electronics. Also to put a good 1:1 balun at the feed point. I have a 160M windom and a G5RV and will dedicate this inverted vee antenna to 75M. This will be not used on 40M due to the high resistance on the second harmonic with the current balun. Yes the added baluns for the ladder line would increase the insertion loss and yes the wet ladder line is a poor conductor. And the cost will be spent for a more efficiency designed system. K4WYS YOu have had many answers to your question, but have drawn the wrong conclusion. If you replace the rg8x with some of the best low loss coax (lmr400 for my example) you go from about .7 db to .2 db of loss on 80 meters. That is .5 db less loss. You will almost need an electron microscope to see the s-meter move . Also 80 meters has so much noise on it most of the time, you will not be able to hear the difference. I think it was one db that was suppose to be the minimal detected difference in hearing when the db scale was first put into use. It may seem that if you have a 100 watt output transmitter you will go from about 85 to 95 watts in a matched system. This may seem to be a lot , but on the receving end it will not be noticed. On maybe 20 meters and higher, especially 2 meters and up it does make good use of the money to go to a higher grade of coax for weak signals. Spend your money on something more productive. |
Ladder line Vs. Coax
Owen Duffy wrote:
(Dieter Kiel) wrote in news:1ihnz3n.wxm0z7nvxaivN% : http://www.w8ji.com/vswr_reactive_power.htm I assume Dieter that this is your recommendation of the article. That article uses the term 'reactive power' in a non-conventional way, though the term is a well known one (ie has a conventional meaning). Conventional use is that the term 'apparent power' is applied to the product of RMS voltage and current flowing into a two terminal load, and the units are VoltAmps (VA), not Watts as used in the article. Reactive power is the reactive component of apparent power, and expressed in units of 'VoltAmpsReactive' (VAR). 'Real power' is the real component of apparent power and expressed in units of Watts (W). The relationship is that apparentpower = (realpower^2 + reactive power^2)^0.5 . This is all basic lumped component AC circuit theory, and holds at RF. True, but we still aren't there. It's very misleading to quote "VAR powers" in the kilowatt range, because the only power available to melt the feedline is 100W from the transmitter. There is no magnification of real power. The high value of "VAR power" is a theoretical result of the large RF currents in the system. These result from an antenna feedpoint impedance that has a very low resistive part and is almost entirely reactive. The large RF currents are a genuine physical phenomenon, as also are the high voltages a quarter-wavelength back along the feedline (if the feedline is long enough, of course)... but if there were no losses in the feedline, these would have no further effect. In spite of the wild values of impedance, current, voltage, VSWR etc, if there were no losses in the feedline then all of the RF power would still reach the antenna. In a real feedline, the effect of the high currents is to divert almost all of the available RF power away from the antenna and into the feedline's own resistive losses - skin-effect losses in the copper conductor, and dielectric losses in the plastic. Both of these result in heating and softening of the plastic, which makes the dielectric loss even higher. This tends to divert even more of the available power into the weak spots, where the plastic finally melts. But there is still only 100W available to do the damage. No argument about the final conclusion - it ain't gonna work - but I don't care for the explanation. There's no problem with "VAR power" for anyone who already has a firm grip on the concepts, but it is not a good way to explain those concepts to a newcomer. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ladder line Vs. Coax
Ian White GM3SEK wrote:
.... a very good posting with the exception (IMO) of the choice of the word "magnification". There is no magnification of real power. There is indeed no net increase in real average power. However, "magnification" seems to be a poor choice of words since its definition contains such words as "apparent", "seems", "exaggerate", "overstate", ... "magnify - to cause to *seem* greater" certainly describes a feedline with 100W source power and 200W forward power. But there is still only 100W available to do the damage. True, but a 100W laser can do a lot of damage. :-) And a *magnifying* glass can start a fire. -- 73, Cecil http://www.w5dxp.com |
Ladder line Vs. Coax
Ian White GM3SEK wrote:
Owen Duffy wrote: (Dieter Kiel) wrote in news:1ihnz3n.wxm0z7nvxaivN% : http://www.w8ji.com/vswr_reactive_power.htm I assume Dieter that this is your recommendation of the article. That article uses the term 'reactive power' in a non-conventional way, though the term is a well known one (ie has a conventional meaning). Conventional use is that the term 'apparent power' is applied to the product of RMS voltage and current flowing into a two terminal load, and the units are VoltAmps (VA), not Watts as used in the article. Reactive power is the reactive component of apparent power, and expressed in units of 'VoltAmpsReactive' (VAR). 'Real power' is the real component of apparent power and expressed in units of Watts (W). The relationship is that apparentpower = (realpower^2 + reactive power^2)^0.5 . This is all basic lumped component AC circuit theory, and holds at RF. True, but we still aren't there. It's very misleading to quote "VAR powers" in the kilowatt range, because the only power available to melt the feedline is 100W from the transmitter. There is no magnification of real power. The high value of "VAR power" is a theoretical result of the large RF currents in the system. These result from an antenna feedpoint impedance that has a very low resistive part and is almost entirely reactive. The large RF currents are a genuine physical phenomenon, as also are the high voltages a quarter-wavelength back along the feedline (if the feedline is long enough, of course)... but if there were no losses in the feedline, these would have no further effect. In spite of the wild values of impedance, current, voltage, VSWR etc, if there were no losses in the feedline then all of the RF power would still reach the antenna. In a real feedline, the effect of the high currents is to divert almost all of the available RF power away from the antenna and into the feedline's own resistive losses - skin-effect losses in the copper conductor, and dielectric losses in the plastic. Both of these result in heating and softening of the plastic, which makes the dielectric loss even higher. This tends to divert even more of the available power into the weak spots, where the plastic finally melts. But there is still only 100W available to do the damage. No argument about the final conclusion - it ain't gonna work - but I don't care for the explanation. There's no problem with "VAR power" for anyone who already has a firm grip on the concepts, but it is not a good way to explain those concepts to a newcomer. I think you are right, the referenced link of W8JI mixed up the definitions. He used "kilowatts" instead of "1000 VAs". But for me the text was very helpful. It also will give newcomers some information about problems with short antennas. If you ask: What is responsible for the losses of an antenna construction ? The answer would be: The losses are proportional to the " Apparent Power VA" It`s "Scheinleistung" in German language. I didn`t even know the term before it was mentioned here.:( I found this schematic in the wikipedia with the different terms Real Power, Reactive Power, and Apparent Power: http://en.wikipedia.org/wiki/Image:P...riangle_01.png So if we use a short antenna, e.g. 20m for the 80m band or even the G5RV we should use parts that can handle the "Apparent Power". I`ve seen Sonny has already made up his mind using koax for the 80m Band. This probably is a good idea, and I`m planning to build a monoband for my favorite band and multiband antenna fed with a low loss ladder line to cover all the bands. I`m not quite sure if a folded dipol as a monoband antenna fed with ladder line would give better results as a coax fed dipol. I have the equipment to match both kinds of feeding lines. |
Ladder line Vs. Coax
Sonny Hood wrote:
I have a 160M windom and a G5RV and will dedicate this inverted vee antenna to 75M. There's your answer. And here's the readers digest version of it. As a rule of thumb, if you are going to use an antenna cut for a specific band, cut it for that, and use coax, and a balun. If you want to have multiple bands from one antenna without traps or tricks, use ladder line and a tuner. The ladder line can handle the wildly varying VSWR, and the tuner will, well, allow the Xciever to see an impedence it likes. - 73 de Mike N3LI - |
Ladder line Vs. Coax
Cecil Moore wrote:
Ian White GM3SEK wrote: ... a very good posting with the exception (IMO) of the choice of the word "magnification". There is no magnification of real power. There is indeed no net increase in real average power. However, "magnification" seems to be a poor choice of words since its definition contains such words as "apparent", "seems", "exaggerate", "overstate", ... "magnify - to cause to *seem* greater" certainly describes a feedline with 100W source power and 200W forward power. But there is still only 100W available to do the damage. True, but a 100W laser can do a lot of damage. :-) And a *magnifying* glass can start a fire. I have no intention of allowing *that* particular fire to start again! -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ladder line Vs. Coax
"Sonny Hood" wrote in message ... I have an efficiency question concerning feed lines. My present system is RG-8X to my 75 meter inverted vee which is about 85 feet away from the shack. I propose to replace some 88 feet of coax with 300 ohm window ladder line that is inserted into the coax run with 4:1 baluns to match the coax on each end. Also at the feed point of the antenna switch from a voltage balun to a current balun (ferrite chock type). By my calculations with a 98 watt generator I will increase the power to the load by about 11-20 watts and with a 985 watt generator, 117-210 more watts will reach the load. Figuring theoretical total system (A) against total System (B) or by just the difference in the 88 feet of ladder line versus coax. What do you think the increase will be? ---------- In all likelihood, no one on the other end will ever be able to tell the difference after you make the changes. Neither will you. Ed, NM2K |
Ladder line Vs. Coax
On May 30, 6:46 pm, "Ed Cregger" wrote:
---------- In all likelihood, no one on the other end will ever be able to tell the difference after you make the changes. Neither will you. Ed, NM2K Maybe not from any practical standpoint, but I could see the difference on a meter when I fed both a coax dipole, and a ladder line dipole using the same tuner, which has antenna switch, and meter built in. So I could A/B real fast. I could see a slight difference on receive switching between the two. And if it's enough to see on a meter, I consider it a noticeable amount. Most of the signals were in the 20-40 over 9 range being 75m, and I'd see about 5 db worth of difference between the two antenna/feed lines. Course, I make no claim as to the exact DB amount of difference, but I could see it on a meter. After many years of 75 and 40 m operating using mostly NVIS paths, I've come to the conclusion nothing will beat a dipole/loop/ turnstile fed with good coax for sheer system efficiency unless say you had a run of several hundred feet or something... Which of those three doesn't really matter much, although I prefer the turnstile over the other two if I had a choice. Nothing wrong with a loop, but in my cases, some sections end up sagging closer to the ground, and you are often a bit more prone to ground losses, and also overall performance if sections of heavy current are low to the ground. With a dipole or turnstile, max current is at the feed point, so the ends of the wires height above the ground is often not quite as critical. As far as I can think of, only Cecil's no tuner/no choke system would let a ladder line fed dipole equal or slightly beat a coax fed. And in that case, I'm not sure how noticeable it would be, being as the 213 I use is quite low loss at 3-4 mhz. But like you say, for on the air, many would probably not notice much. #1, you would have to do quick A/B transmit tests for them to notice any difference, and also make sure fading doesn't skew the results. It would be best to test with a stable ground or space wave signal. But... I still prefer coax.. I want every drop out I can get, and I also much prefer the convenience of coax. IE: with most antennas, no tuner required. And really not even a "balun" required if you roll a choke out of the feed line itself and tie wrap it. Weather is no issue with coax. I can have it sitting in standing water with no problems. The only time I use ladder line is mostly experimental antennas where the feed point impedance is not the usual 50 ohms. If the mismatch to coax is high, ladder and the tuner makes sense. |
Ladder line Vs. Coax
wrote in message ... On May 30, 6:46 pm, "Ed Cregger" wrote: ---------- In all likelihood, no one on the other end will ever be able to tell the difference after you make the changes. Neither will you. Ed, NM2K Maybe not from any practical standpoint, but I could see the difference on a meter when I fed both a coax dipole, and a ladder line dipole using the same tuner, which has antenna switch, and meter built in. So I could A/B real fast. I could see a slight difference on receive switching between the two. And if it's enough to see on a meter, I consider it a noticeable amount. Most of the signals were in the 20-40 over 9 range being 75m, and I'd see about 5 db worth of difference between the two antenna/feed lines. Course, I make no claim as to the exact DB amount of difference, but I could see it on a meter. Most of it had to be the antennas. Going from almost no loss open wire to much higher loss rg58 would be only 1 db at the most on 75 meters. You still need a magnifing glass to see the smeter move this much on a ham receiver. |
Ladder line Vs. Coax
On May 31, 8:17 pm, "Ralph Mowery" wrote:
Most of it had to be the antennas. Going from almost no loss open wire to much higher loss rg58 would be only 1 db at the most on 75 meters. You still need a magnifing glass to see the smeter move this much on a ham receiver. What about the tuner loss? And.. I was using the least amount of inductance needed to tune.. The difference was noticeable on a meter. So that would tend to indicate the difference was more than 1 db. The 213 I use at the house would be even lower loss than the 58, but I do use rg-58 sometimes when portable, etc.. Doesn't do any good to use a slightly lower loss feed line, if the tuner needed to match causes more loss than the feed line saves vs coax. And tuners will vary also. Also setting the tuner itself can lose even more power if the minimum inductance is not use. It's not too hard to lose up to 20% of your power if the inductance settings are wrong. I'll still stick with coax and no tuner. :) |
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