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80 Meter Horizontal Loop
I put up an 80 meter full wave loop using about 280 of #14 wire in
almost a square. Each end of the loop was soldered to an SO-239 connector. Im feeding the loop via RG-8 coax, about a 30 run. Using an MFJ Antenna Analyzer I cant find a nice low SWR point. The lowest I can find is at 2.5 MHz, the SWR at that point is still high at 3.4:1. In the 80 mtr band its 8:1 and in the 40 mtr band its 7:1. My installation is far from ideal. First, the antenna for about ½ the loop is at about 20 high and the second half is about 15 high. Next, in the center of the loop is the metal frame work for a screen-room over the swimming pool (50 x 30) which Im sure interacts with the loop antenna to some degree. The screening is not metal however the frame work is. Of course I can use my MFJ-949 tuner to get a low SWR on any band but by doing so am I loosing efficiency? I also notice that trying to tune the loop the tuner seems to be very touchy! I have noticed on 20 meters the loop received on average about 2 S-Units better than my 20 meter dipole. On 40 meters it receives almost 1 S-unit better than a 160 randomwire. On 80 meters just slightly better than a 160 randomwire. (all antennas Im comparing are all at about 20 high). I would have started making the loop shorter to bring up the resonate frequency to 80 meters however Im concerned as to why the lowest SWR I can find anywhere on the HF band is still over 3:1. Is it because the loop low to the ground (20)? Or do I need a balum? 1:1 balum? 4:1 balum? Looking for any suggestions. TNX George KI4FIA http://www.MilAirComms.com |
On Sun, 05 Jun 2005 16:57:03 GMT, GeorgeF
wrote: I put up an 80 meter full wave loop using about 280 of #14 wire in almost a square. Hi George, That was certainly a good beginning, but questions abound as we proceed. Each end of the loop How many "ends" does a loop have? This is something akin to how many sides to a circle. was soldered to an SO-239 connector. One is enough, why two (or more, we still don't know how many ends there are)? This statement is enough to give pause. If there is more than one 239 inserted inline, it must of necessity break continuity of the loop. This, then, means that you no longer have a loop, but rather a fullwave dipole (presuming the loop has 2 ends). Im feeding the loop via RG-8 coax, about a 30 run. You say nothing of choking the feedpoint, and given the symptoms that you describe, this sounds like a major omission. In the 80 mtr band its 8:1 and in the 40 mtr band its 7:1. Sounds like full wave dipoles (or even multiples). In other words, consistent with previous descriptions. My installation is far from ideal. No one here has it any better, but by degrees. If you can do better by trying harder, fine, but if there's no way to get the antenna higher, or to blow away the obstructions.... Of course I can use my MFJ-949 tuner to get a low SWR on any band but by doing so am I loosing efficiency? In trying to tune full wave dipoles? Could be, but being so close to the dirt is probably lowering your antenna's wicked Z to something easier to tune (your efficiency is already dominated by ground loss). I also notice that trying to tune the loop the tuner seems to be very touchy! Lack of choking at the feed point - or - you are tuning an anti-resonant antenna. I have noticed on 20 meters the loop received on average about 2 S-Units better than my 20 meter dipole. On 40 meters it receives almost 1 S-unit better than a 160 randomwire. On 80 meters just slightly better than a 160 randomwire. (all antennas Im comparing are all at about 20 high). Now all your previous complaints sound like whining. Do you want a tuned antenna, or a gain antenna? BOTH!? 73's Richard Clark, KB7QHC |
"GeorgeF" wrote in message hlink.net... I put up an 80 meter full wave loop using about 280 of #14 wire in almost a square. Each end of the loop was soldered to an SO-239 connector. Im feeding the loop via RG-8 coax, about a 30 run. Using an MFJ Antenna Analyzer I cant find a nice low SWR point. The lowest I can find is at 2.5 MHz, the SWR at that point is still high at 3.4:1. In the 80 mtr band its 8:1 and in the 40 mtr band its 7:1. My installation is far from ideal. First, the antenna for about ½ the loop is at about 20 high and the second half is about 15 high. Next, in the center of the loop is the metal frame work for a screen-room over the swimming pool (50 x 30) which Im sure interacts with the loop antenna to some degree. The screening is not metal however the frame work is. Of course I can use my MFJ-949 tuner to get a low SWR on any band but by doing so am I loosing efficiency? I also notice that trying to tune the loop the tuner seems to be very touchy! I have noticed on 20 meters the loop received on average about 2 S-Units better than my 20 meter dipole. On 40 meters it receives almost 1 S-unit better than a 160 randomwire. On 80 meters just slightly better than a 160 randomwire. (all antennas Im comparing are all at about 20 high). I would have started making the loop shorter to bring up the resonate frequency to 80 meters however Im concerned as to why the lowest SWR I can find anywhere on the HF band is still over 3:1. Is it because the loop low to the ground (20)? Or do I need a balum? 1:1 balum? 4:1 balum? Looking for any suggestions. TNX George KI4FIA http://www.MilAirComms.com Sounds like s successful installation. The tuner doesn't reduce efficiency - - it just tunes out reactance, leaving a resistive load for your rig to work with. Don't worry about SWR - - your radio doesn't worry about SWR (with the reactance tuned out) - - it sees stronger signals. You did good. Chuck W6PKP |
Now all your previous complaints sound like whining. Do you want a tuned antenna, or a gain antenna? BOTH!? 73's Richard Clark, KB7QHC There is one SO-239 connector, there is one piece of wire which is 280' in lenght. On end of the wire is connected to the center pin of the SO-239 connector while the other end of the wire is connected to the braid side of the SO-239. Hope that clears up the configuration questions. No I am not choking at the feed point. I was not told about a choke by other hams who mentioned I should give an 80 meter loop a try. Is a choke the same as a 1:1 balun? I was told (and found it also illistrated in print) that I could directly hook 50 ohm coax to the feedpoint. Tell me what I need to do to choke the feedpoint. I had seen (believe it was one of the ARRL handbooks) that this antenna should have no SWR higher than 3:1, mine is 7+:1 so I think either I did something wrong or am missing something. Don't think I'm whining yet.... George |
"GeorgeF" wrote in message hlink.net... Now all your previous complaints sound like whining. Do you want a tuned antenna, or a gain antenna? BOTH!? 73's Richard Clark, KB7QHC There is one SO-239 connector, there is one piece of wire which is 280' in lenght. On end of the wire is connected to the center pin of the SO-239 connector while the other end of the wire is connected to the braid side of the SO-239. Hope that clears up the configuration questions. No I am not choking at the feed point. I was not told about a choke by other hams who mentioned I should give an 80 meter loop a try. Is a choke the same as a 1:1 balun? I was told (and found it also illistrated in print) that I could directly hook 50 ohm coax to the feedpoint. Tell me what I need to do to choke the feedpoint. I had seen (believe it was one of the ARRL handbooks) that this antenna should have no SWR higher than 3:1, mine is 7+:1 so I think either I did something wrong or am missing something. Don't think I'm whining yet.... George George, Since you have an MFJ Antenna Analyzer, is there some frequency, regardless of the SWR, where the reactive part of the impedance goes to 0? I don't know about horizontal loops, but vertical loops are not 50 Ohm antennas. Tam/WB2TT |
GeorgeF wrote:
I would have started making the loop shorter to bring up the resonate frequency to 80 meters however Im concerned as to why the lowest SWR I can find anywhere on the HF band is still over 3:1. Is it because the loop low to the ground (20)? Or do I need a balum? 1:1 balum? 4:1 balum? Looking for any suggestions. Common mode current could be upsetting your measurements as you are feeding a balanced antenna with coax. Your loop seems to be too long to resonate on the 75m band. By shortening it, you can probably move that 3.4:1 point into the 75m band. But why not just feed it with 450 ohm ladder-line through a balun at a tuner output and alleviate most of your problems? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Chuck Olson wrote:
The tuner doesn't reduce efficiency - - There's no such thing as a 100% efficient tuner. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
"Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. |
...
"Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. Well, at the risk of David going into conflict with the Goliaths of the newsgroups, I would reckon that a tuner (matcher ?) must be a pretty efficient device as it doesn't get very warm from wasting energy as heat - or perhaps my aerials are a reasonably good match and the tuner isn't doing any / much work. Also a tuner, I would suggest, is a fairly useful bit of kit in that it enables the transmitter to see the sort of load it wants to and allows it to deliver more power to the antenna system without the internal protection devices limiting the power it produces (to avoid self destruction) even if not all arrives at the antenna....... Is this a fairly correct understanding of what is going on, Reg / Cecil ? Nick |
Reg Edwards wrote:
Chuck Olson wrote: The tuner doesn't reduce efficiency - - "Cecil Moore" says - There's no such thing as a 100% efficient tuner. Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? Some ARRL publication said the losses in a tuner average about 0.5 dB. If true, a tuner indeed reduces efficiency by about 12%. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
nick smith wrote:
Is this a fairly correct understanding of what is going on, Reg / Cecil ? Yep, Nick, all I was doing was taking a tongue-in-cheek poke at the idea that "The tuner doesn't reduce efficiency." -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
"Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. Well, at the risk of David going into conflict with the Goliaths of the newsgroups, I would reckon that a tuner (matcher ?) must be a pretty efficient device as it doesn't get very warm from wasting energy as heat - or perhaps my aerials are a reasonably good match and the tuner isn't doing any / much work. Also a tuner, I would suggest, is a fairly useful bit of kit in that it enables the transmitter to see the sort of load it wants to and allows it to deliver more power to the antenna system without the internal protection devices limiting the power it produces (to avoid self destruction) even if not all arrives at the antenna....... Is this a fairly correct understanding of what is going on, Reg / Cecil ? Nick ==================================== Nick, your response indicates a 'perfect' understanding of what goes on inside tuner boxes. If it runs cold or cool with 100 watts there's nothing to worry about. Most Guru's over-exaggerate the importance of tuner losses. But in a practical case they never state what the efficiency actually is. Such omissions illustrate their ignorance of the subject. From the frequency of occurrence at which 'tuner loss' appears in these columns, novices and even experienced amateurs can gain the frightening impression that tuner loss is the most serious loss in the system and is to be avoided at all costs, even to the extent of dispensing with the tuner. In answer to my own question, the efficiency of a typical tuner when used with a typical antenna does not differ significantly from 100 percent. Even if it is as poor as 90% this corresponds to an undetectable loss in signal strength of 0.5dB or 1/13 of an S-unit. Less than the thickness of the S-meter needle. So forget it. ---- Reg, G4FGQ |
"Reg Edwards" wrote in message ... "Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. Well, at the risk of David going into conflict with the Goliaths of the newsgroups, I would reckon that a tuner (matcher ?) must be a pretty efficient device as it doesn't get very warm from wasting energy as heat - or perhaps my aerials are a reasonably good match and the tuner isn't doing any / much work. Also a tuner, I would suggest, is a fairly useful bit of kit in that it enables the transmitter to see the sort of load it wants to and allows it to deliver more power to the antenna system without the internal protection devices limiting the power it produces (to avoid self destruction) even if not all arrives at the antenna....... Is this a fairly correct understanding of what is going on, Reg / Cecil ? Nick ==================================== Nick, your response indicates a 'perfect' understanding of what goes on inside tuner boxes. If it runs cold or cool with 100 watts there's nothing to worry about. Most Guru's over-exaggerate the importance of tuner losses. But in a practical case they never state what the efficiency actually is. Such omissions illustrate their ignorance of the subject. From the frequency of occurrence at which 'tuner loss' appears in these columns, novices and even experienced amateurs can gain the frightening impression that tuner loss is the most serious loss in the system and is to be avoided at all costs, even to the extent of dispensing with the tuner. In answer to my own question, the efficiency of a typical tuner when used with a typical antenna does not differ significantly from 100 percent. Even if it is as poor as 90% this corresponds to an undetectable loss in signal strength of 0.5dB or 1/13 of an S-unit. Less than the thickness of the S-meter needle. So forget it. ---- Reg, G4FGQ Well, I was actually pretty sure I was right, but its good to have it confirmed and hope this was useful to others in their understanding or otherwise of the job a tuner (matcher) does. Thanks Gentlemen, Nick |
On Mon, 06 Jun 2005 07:40:49 GMT, "nick smith"
wrote: ... "Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. Well, at the risk of David going into conflict with the Goliaths of the newsgroups, I would reckon that a tuner (matcher ?) must be a pretty efficient device as it doesn't get very warm from wasting energy as heat - or perhaps my aerials are a reasonably good match and the tuner isn't doing any / much work. Let me refer to you to this link: http://users.triconet.org/wesandlinda/ladder.htm and suggest that you also follow the imbedded link to my letter to Dean. There you will find an analysis if what tuner losses can be. But let's also answer this issue of "It doesn't get hot, so it must not be lossy." First let's say that, unless the op is a real blabbermouth, the transmit duty cycle will be 50%. Transmit half the time, listen half the time. If the op is on CW then the duty cycle of the transmit cycle is ~44%. (The standard word "PARIS" sent repeatedly with 1:3:7 spacing. So for CW operation, the overall duty cycle is .5 * .44 = 22%. On SSB it's more complicated. Without speech processing, the peak to average ratio is variously given, but 14:1 (11.5 dB) is typical. Most rigs have some form of speech compression or clipping these days (most used to excess). Really effective clippers, (ahem) http://users.triconet.org/wesandlinda/s_proc.pdf can improve this quite a bit so let's say that it's 6 dB. So the average power is 6 dB below the peak or 25% of the peak. Our overall duty cycle is .5 * .25 = 12.5% Of course the digital modes and FM are full carrier so the duty cycle is 50%. Not many using FM on hf where tuners are the norm, the PSK guys pride themselves on QRP, which leaves only the special case RTTY contesters running full power. So back to the guy running 100 W CW through a tuner driving a ladder line fed antenna. If his tuner burns up half of the power will it get hot? Are 11 W (22% of 50) going to smoke most components? What if the tuner loss is 6 dB? The average power dissipation climbs to a whopping 16.5 W. (22% of 75) Is this a big thermal management issue? Certainly, KW rigs running RTTY are going to be a bigger concern, but the tuners (and component parts) are commensurately bigger and can dissipate more power without "getting hot". |
Let's put this an easier way, how many of you have a low pass filter in
line. Most manufacturers claim a .25dB or less insertion loss. These filters consist of a boat load of coils and caps. A tuner normally has 2 varible caps and a single silver plated coil. While any device indeed has loss, here we are picking fly crap out of pepper. Let me refer to you to this link: http://users.triconet.org/wesandlinda/ladder.htm and suggest that you also follow the imbedded link to my letter to Dean. There you will find an analysis if what tuner losses can be. But let's also answer this issue of "It doesn't get hot, so it must not be lossy." First let's say that, unless the op is a real blabbermouth, the transmit duty cycle will be 50%. Transmit half the time, listen half the time. If the op is on CW then the duty cycle of the transmit cycle is ~44%. (The standard word "PARIS" sent repeatedly with 1:3:7 spacing. So for CW operation, the overall duty cycle is .5 * .44 = 22%. On SSB it's more complicated. Without speech processing, the peak to average ratio is variously given, but 14:1 (11.5 dB) is typical. Most rigs have some form of speech compression or clipping these days (most used to excess). Really effective clippers, (ahem) http://users.triconet.org/wesandlinda/s_proc.pdf can improve this quite a bit so let's say that it's 6 dB. So the average power is 6 dB below the peak or 25% of the peak. Our overall duty cycle is .5 * .25 = 12.5% Of course the digital modes and FM are full carrier so the duty cycle is 50%. Not many using FM on hf where tuners are the norm, the PSK guys pride themselves on QRP, which leaves only the special case RTTY contesters running full power. So back to the guy running 100 W CW through a tuner driving a ladder line fed antenna. If his tuner burns up half of the power will it get hot? Are 11 W (22% of 50) going to smoke most components? What if the tuner loss is 6 dB? The average power dissipation climbs to a whopping 16.5 W. (22% of 75) Is this a big thermal management issue? Certainly, KW rigs running RTTY are going to be a bigger concern, but the tuners (and component parts) are commensurately bigger and can dissipate more power without "getting hot". |
Unfortunately, simply counting the number of coils and capacitors isn't
even an approximate way to judge loss. What counts, mainly, is how much current is flowing in those inductors and how large their wire is (and, if the capacitors have other than air dielectric, perhaps how much voltage is across the capacitors)(*). If you do an analysis of a tuner, you'll find that for a given applied power, the inductor current can vary a huge amount depending on the load impedance. Consequently, the loss can vary a greatly. Lowpass filters are invariably specified when in a circuit with a fixed, specified impedance load. It's not hard at all to design a lowpass filter which has low loss under that condition. Likewise, it's not hard to design a matching network (tuner) which has low loss when the load isn't too far away from 50 ohms resistive. The trick is to maintain reasonable loss when the impedance transformation is extreme. Roy Lewallen, W7EL Fred W4JLE wrote: Let's put this an easier way, how many of you have a low pass filter in line. Most manufacturers claim a .25dB or less insertion loss. These filters consist of a boat load of coils and caps. A tuner normally has 2 varible caps and a single silver plated coil. While any device indeed has loss, here we are picking fly crap out of pepper. |
Fred W4JLE wrote:
Let's put this an easier way, how many of you have a low pass filter in line. Most commercial rigs already meet the FCC spec so usually no low pass filter is needed. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
In article ,
Fred W4JLE wrote: Let's put this an easier way, how many of you have a low pass filter in line. Most manufacturers claim a .25dB or less insertion loss. These filters consist of a boat load of coils and caps. A tuner normally has 2 varible caps and a single silver plated coil. While any device indeed has loss, here we are picking fly crap out of pepper. I think you're making an inapplicable comparison. The low-pass filters you're referring to have a relatively low loss when used as directed, it's true... but the "use as directed" condition usually mandates having the proper source and sink impedances on either side. The loaded Q is usually modest. A transmatch being used to match a difficult load can be in a distinctly different situation. If the load is a harsh one (low R, high magnitude of X), tuning up can create a situation with a high network Q and high circulating currents in the tuner components. The April '95 QST has an article which shows some actual calculations (and if I recall correctly the Handbook has a bunch of tuner loss tables). One example in the QST article shows the results of using a T tuner to tune an antenna which is just too darned short. The tuner sees a load of 4.40 - j35 ohms. Although a match can be established with the specified tuner components, the estimated power loss in the tuner is almost 2/3 of the input (4.54 dB!). The transmission line eats enough 11.6 dB, in their example. Granted, this is a rather pathological situation, but it does occur from time to time in the real world. I've heard numerous reports of people "burning up" their tuners by trying to match a low-resistance, highly-reactive load, and frying the coil. Some of the MFJ tuners seem to have a reputation for suffering from heat damage to the coils (the plastic coil form melts). -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
Can you give us a typical loss for a tuner matching a G5RV?
"Roy Lewallen" wrote in message ... Unfortunately, simply counting the number of coils and capacitors isn't even an approximate way to judge loss. What counts, mainly, is how much current is flowing in those inductors and how large their wire is (and, if the capacitors have other than air dielectric, perhaps how much voltage is across the capacitors)(*). If you do an analysis of a tuner, you'll find that for a given applied power, the inductor current can vary a huge amount depending on the load impedance. Consequently, the loss can vary a greatly. Lowpass filters are invariably specified when in a circuit with a fixed, specified impedance load. It's not hard at all to design a lowpass filter which has low loss under that condition. Likewise, it's not hard to design a matching network (tuner) which has low loss when the load isn't too far away from 50 ohms resistive. The trick is to maintain reasonable loss when the impedance transformation is extreme. Roy Lewallen, W7EL Fred W4JLE wrote: Let's put this an easier way, how many of you have a low pass filter in line. Most manufacturers claim a .25dB or less insertion loss. These filters consist of a boat load of coils and caps. A tuner normally has 2 varible caps and a single silver plated coil. While any device indeed has loss, here we are picking fly crap out of pepper. |
Fred W4JLE wrote:
Can you give us a typical loss for a tuner matching a G5RV? No, sorry, I can't, and I don't believe there is such a thing. It's possible of course to find the input impedance of any wire antenna like the G5RV at each of the frequencies of interest. But transmission line lengths and impedances vary, which transforms the impedance seen by the tuner. Those impedance changes can be dramatic, and can result in widely varying tuner efficiency. On top of that, you have the variations in tuner topology and construction which makes a "typical" tuner also an elusive beast. I'd be very suspicious of any "typical" tuner loss figure, and wouldn't expect to see it in practice unless the conditions are spelled out really well and my setup was very similar. You see, I'm not a true Guru. A real one wouldn't waffle like this, but would give you a positive answer, and you'd very probably never have reason to doubt it. Roy Lewallen, W7EL |
"Reg Edwards" wrote in message ... "Cecil Moore" says - There's no such thing as a 100% efficient tuner. ==================================== Cecil, not a very surprising statement. There's nothing which is 100% efficient. What is the typical efficiency of a typical tuner with a typical antenna. Does it differ significantly from 100% ? Yes or no? ---- Reg. I did some measurments on a MFJ tuner into a dummy load. While I am not sure if the losses would be more or less than to an acutal antenna, I would assume it should be the best case . The losses were around 5 to 10 watts starting with 100 watts input depending on the band. I think 80 meters was the worse from 80 to 10 meters. This is a small tumer rated around 200 or 300 watts and has a built in wattmeter. This may account for a small aditional loss. I did not use this meter but did use 2 Bird meters , one on the input and one on the output to keep the input power constant at 100 watts. |
Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50
feet of 50 ohm coax. Is it .5 or 5 dB? Or we can be more specific and say we want to match a 50 Ohm source to R 5000 -J720 using an MFJ989C. What loss is to be expected? Granted there are cases of attempting to load a short (with respect to frequency) antenna that has extremely low values of R can cause large losses. I would think that a general statement could be made about antennas that are 1/2 wavelength or longer at the operating frequency and the magnitude of losses one could expect from the typical tuner. Is there no way to quantify the losses, no rule of thumb, should we all throw our tuners away because they may have unpredictable horrendous losses? What steps should be taken by the average amateur to obviate these losses. I am at a loss to understand how bad the losses are that you and Cecil refer to. Can you lead me from the darkness Sir!. "Roy Lewallen" wrote in message ... Fred W4JLE wrote: Can you give us a typical loss for a tuner matching a G5RV? No, sorry, I can't, and I don't believe there is such a thing. It's possible of course to find the input impedance of any wire antenna like the G5RV at each of the frequencies of interest. But transmission line lengths and impedances vary, which transforms the impedance seen by the tuner. Those impedance changes can be dramatic, and can result in widely varying tuner efficiency. On top of that, you have the variations in tuner topology and construction which makes a "typical" tuner also an elusive beast. I'd be very suspicious of any "typical" tuner loss figure, and wouldn't expect to see it in practice unless the conditions are spelled out really well and my setup was very similar. You see, I'm not a true Guru. A real one wouldn't waffle like this, but would give you a positive answer, and you'd very probably never have reason to doubt it. Roy Lewallen, W7EL |
"Fred W4JLE" wrote in message ... Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50 feet of 50 ohm coax. Is it .5 or 5 dB? .................................................. ....... ................................. QST has on several occasions tested antenna tuners. The most recent one I found was from last year. The worst case I saw was something like 40% loss when matching an impedance of 6.25 Ohms on, I think, 40 meters. It is worth noting that the 2KW tuners will have less loss than the 300W jobs. Also, the loss depends on the impedance it sees, rather than the SWR. So, for an 8:1 SWR, the loss at 6.25 Ohms will be a lot worse than at 400 Ohms. Among other things, the loss will then depend on the length of the feedline. The high power tuners had a loss of less than 10% over most of the range. Tam/WB2TT |
Fred W4JLE wrote:
Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50 feet of 50 ohm coax. Is it .5 or 5 dB? Sorry again, I can't help you much. There are a number of tuner topologies in use (L, pi, high and lowpass tee, LCC, "ultimate transmatch" to name a few), and the loss of one compared to another can be quite different depending on the load impedance, even if all use the same inductor(s). The information you gave is enough to calculate the impedance seen by the tuner, though, assuming your G5RV is 102 feet long and not one of the countless variations. Assuming a height of 40 feet over average ground, the impedance at 3.8 MHz seen at the input end of 50 feet of 50 ohm coax should be about 2.5 + j23 ohms (SWR ~ 27:1) if the coax is RG-8, or about 4.1 + j22 ohms (SWR ~ 17:1) if the coax is RG-58. (The SWR at the load will be greater than 60:1. You should maybe be worrying more about feedline loss than tuner loss.) I didn't take into account the effect of feedline radiation, which I'll assume is suppressed with a balun. Or we can be more specific and say we want to match a 50 Ohm source to R 5000 -J720 using an MFJ989C. What loss is to be expected? Using the Z you specified or the Z I calculated, all that's necessary then is to obtain a schematic of the tuner and information about the physical construction of the inductor(s), calculate what settings will achieve a match, and find out which of these settings you're using. Then calculate the coil currents and from that the loss. I don't have a schematic of the tuner nor a physical tuner -- I haven't used one for 30 years or more except for a small homebrew tuner for correcting small mismatches to keep my QRP Field Day rig happy. So I don't have a clue. Perhaps someone else who has the tuner, the math ability, the patience, and the time will be willing to help you. Granted there are cases of attempting to load a short (with respect to frequency) antenna that has extremely low values of R can cause large losses. I would think that a general statement could be made about antennas that are 1/2 wavelength or longer at the operating frequency and the magnitude of losses one could expect from the typical tuner. I think you can say that if the SWR is no greater than 2:1 or maybe 3:1, the loss in a properly designed tuner should be pretty low. Outside that range, like your 17 - 27 SWR example, I wouldn't speculate. Is there no way to quantify the losses, no rule of thumb, should we all throw our tuners away because they may have unpredictable horrendous losses? Hm, are those the only two options? Why not use the tuner, make contacts, and be happy? And if the tuner has a horrendous loss, why will throwing it away help? You'll still be better off with it than without it. What steps should be taken by the average amateur to obviate these losses. Adjust the feedline length for each band to present a moderate impedance to the tuner. Cecil has posted quite a bit about this in the past. And use a tuner with the largest coil(s) possible. You could set up jumpers so you can change the topology of the tuner to pi, L, tee, etc. On each band, try each configuration and, among those which effect a match, choose the one that gives you the greatest field strength from your antenna or the highest current to it. Of course, you could do what I do -- I settle for other than all-band operation, and make my antennas resonant or nearly resonant. When matching is required, I do it at the feedpoint with components I've characterized -- I know the antenna Z and the inductor Qs, so I can calculate the loss. But most people don't want to do this, and happily put up with whatever losses they get in exchange. Or you can get something like the B&W terminated folded dipole, and put the losses at the antenna instead of the tuner. I am at a loss to understand how bad the losses are that you and Cecil refer to. Can you lead me from the darkness Sir!. Nope, sorry, I can't. What's the approximate value of resistors? I can't answer that one, either. Roy Lewallen, W7EL |
For efficiency of the L-network tuner on different bands, and losses
in transmission lines and other data, download program DIPOLE3 from website below. The program covers dipole + balanced line + balun + coax line + tuner L and C settings. With one hit of a key the antenna system can be modelled as a G5RV. Download program DIPOLE3 in a few seconds. It is also easy to find the resonant frequencies of the G5RV. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
On Mon, 6 Jun 2005 15:06:13 -0400, "Fred W4JLE"
wrote: Let's put this an easier way, how many of you have a low pass filter in line. Most manufacturers claim a .25dB or less insertion loss. These filters consist of a boat load of coils and caps. A tuner normally has 2 varible caps and a single silver plated coil. While any device indeed has loss, here we are picking fly crap out of pepper. Clearly you didn't read the links or you wouldn't be asking all of the questions. |
Is there no way to quantify the losses, no rule of thumb, should we
all throw our tuners away because they may have unpredictable horrendous losses? In general I do....I don't use a tuner for any of my everyday antennas... What steps should be taken by the average amateur to obviate these losses. Quite simple really. Use the very minimum inductance needed to get a usable match. I once did tests to determine the appx amount of tuner loss when tuning properly vs improperly. When using an excess of inductance to match, I saw tuner losses approach 20%. IE: 20w out of 100w. When carefully tuning, using the very least inductance, this loss could be reduced to a value nearly unreadable. BUT!!! This was on a resonant 50 ohm system. You could expect the losses of an extreme mismatch to be higher, even if you tuned very carefully. The losses and coil warming when feeding a 1/2 size dipole with a T net tuner are well known. Thats how I got a free MFJ 989c when a friend of mine couldn't keep from frying the plastic coil forms. He bought a nye viking, and gave me the 989c. Which I've used since with no problems at all....It wasn't really the tuners fault...He was abusing it trying to feed a 1/2 size dipole, and then running a TL-922 flat out on top of that...:( MK |
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My 2 cents on the subject of tuner loss.
A tuner will Always introduce more loss to the system. If the total power output of the transmitter is not improved(ie, at 2:1 SWR), then using the tuner to reduce SWR to 1:1 is counter productive, isn't it? In other words, getting the SWR down to 1:1 from anything = 2:1, will always cause a reduction in total power out. Pat W0OPW |
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Do you have a need to be so supercilious?.
"Wes Stewart" wrote in message ... On Mon, 6 Jun 2005 15:06:13 -0400, "Fred W4JLE" Clearly you didn't read the links or you wouldn't be asking all of the questions. |
If you can't get the internal SWR meter on an Icom 735 (or similar
rigs) down to exactly 1:1 then either there's something wrong with the tuner or with the tuner operator. The tuner either works or it doesn't. There's no half-way house. Without a tuner anything can happen. And it usually does. There are far too many sleepless nights unnecessarily caused by the SWR meter not being in the right imagined ballpark. Just ask yourselves is the transmitter loaded with roughly 50 ohms or isn't it. The SWR on the feedline hardly matters two hoots - the so called SWR meter doesn't measure it anyway. Do G5RV addicts realise that under even the best conditions the SWR on the feedline is as high as 10-to-1 regardless of what the meter says. But it doesn't seem to worry them. ---- Reg. |
All my feedlines have a 9:1 SWR by design.
"Reg Edwards" wrote in message ... If you can't get the internal SWR meter on an Icom 735 (or similar rigs) down to exactly 1:1 then either there's something wrong with the tuner or with the tuner operator. The tuner either works or it doesn't. There's no half-way house. Without a tuner anything can happen. And it usually does. There are far too many sleepless nights unnecessarily caused by the SWR meter not being in the right imagined ballpark. Just ask yourselves is the transmitter loaded with roughly 50 ohms or isn't it. The SWR on the feedline hardly matters two hoots - the so called SWR meter doesn't measure it anyway. Do G5RV addicts realise that under even the best conditions the SWR on the feedline is as high as 10-to-1 regardless of what the meter says. But it doesn't seem to worry them. ---- Reg. |
Reg Edwards wrote:
If you can't get the internal SWR meter on an Icom 735 (or similar rigs) down to exactly 1:1 then either there's something wrong with the tuner or with the tuner operator. What you say is true for roller inductor tuners, Reg, but most tuners have switched inductors. The perfect inductance may not be possible. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Fred W4JLE wrote:
All my feedlines have a 9:1 SWR by design. Heh, heh, I understand perfectly. Don't know how many others do. :-) All my feedlines have an SWR between 5:1 and 13:1 by design. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Sun, 05 Jun 2005 19:21:27 -0500, Cecil Moore
wrote: Chuck Olson wrote: The tuner doesn't reduce efficiency - - There's no such thing as a 100% efficient tuner. I realize that a tuner is not 100% efficient, but when I hook up my 80 meter dipole and listen on 20 meters (the wire is fed with coax), the signals are stronger when tuned thru the tuner rather than direct from the antenna. Not to mention that when I transmit, the radio is operating on reduced power with the dipole direct. I realize that there is considerable loss in my coax (I am using garbage and know it) and that I am taking a loss thru the tuner, but it is a better option than direct thru the coax alone. ;) -- 73 for now Buck N4PGW |
On Tue, 07 Jun 2005 12:17:43 -0500, Cecil Moore
wrote: Reg Edwards wrote: If you can't get the internal SWR meter on an Icom 735 (or similar rigs) down to exactly 1:1 then either there's something wrong with the tuner or with the tuner operator. My TS870 has an menu option for setting the "good enough" SWR using the built-in tuner. The limits can be 1.2:1 or 1.6:1. 1:1 is not an option nor is it desired. If the feedback loop was tight enought to always try to achieve 1:1 it would probably never stop hunting. What you say is true for roller inductor tuners, Reg, but most tuners have switched inductors. The perfect inductance may not be possible. Nor is it required. With three reactances, coarse setting one and varying the other two can achieve a perfect match. As I have said many times, this may not be optimum from a loss or BW standpoint, but you can get a match. |
Wes Stewart wrote:
... but you can get a match. Apparently not, if you define a match as Reg apparently does. :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Tue, 7 Jun 2005 12:19:23 -0400, "Fred W4JLE"
wrote: All my feedlines have a 9:1 SWR by design. Really, and how is that? |
On Tue, 07 Jun 2005 12:22:05 -0500, Cecil Moore
wrote: Fred W4JLE wrote: All my feedlines have a 9:1 SWR by design. Heh, heh, I understand perfectly. You do? |
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