|
I will be sending you some photos of my final installation. I did a number
of tests comparing how tight you can wind the loops. I was amazed at how non critical it was, considering all the dire warnings one receives from the old wife's tales. Aside from all the ham bands, I have the need to get down to 3.347 MHz as well. My setup with the thumbwheel digital rotary switches lets me look at my chart, see 3.5 MHz needs 39 additional feet and set 39 in the switches, I built a box outside the house with 4 dowel rods to wind the loops around. It worked out great both mechanically and electrically. After I inserted the relay box, I cut additional feedline off the 90 foot feedline so the output side at the end of the coax agreed with the original readings. Once that was accomplished all the plots were in agreement with the predicted except on 40 meters. Predicted should have been 7.3, actual was 6.8 MHz. Easy enough to correct for, but have not yet figured out what causes it. All other freqs were spot on. Worst SWR is 1.8:1 I am a happy camper. On 75 an A/B test shows no difference was noted between it and a 75 meter dipole. I need to A/B it on the other bands yet. My method of 1,2,4,8 and 10,20,and 40 feet uses extra feed line, but is made up for in the ability to enter feet directly on the switches. Three other folks here are constructing a duplicate. "Cecil Moore" wrote in message ... 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 =---- |
Of Course you are, all horror stories aside.
Don't confuse the angels dancing on the pinheads around here with practical world experiences. The best solution is to increase the length of your dipole to 130 feet and feed it with 100 foot of 450 Ohm ladderline. Connect a piece of coax with a ferrite bead choke to the 450 Ohm line. Your tuner will love you and you can use all bands from 80 on up. The electrical plug on your rig has losses that are about as meaningful real world.. "Buck" wrote in message ... 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 |
My 132 foot dipole is fed by lengths of 450 Ohm line of lengths depending on
frequency. The first part acts as a matching section to achieve 50 Ohms. This feeds an electrical 1/2 wavelength 450 Ohm section the 50 ohm impeadence is seen by the rig, while maintaning a 9:1 swr on the 1/2 wave section. 450/50=9:1 "Wes Stewart" wrote in message ... 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? |
Fred W4JLE wrote:
Once that was accomplished all the plots were in agreement with the predicted except on 40 meters. Predicted should have been 7.3, actual was 6.8 MHz. Easy enough to correct for, but have not yet figured out what causes it. All other freqs were spot on. What causes it is the feedpoint impedance of a one wavelength dipole is very high and therefore easily upset by the surroundings. A low impedance feedpoint impedance is not easily upset by the surroundings. It's the same concept as using a 20k ohms/volt voltmeter to measure the cathode voltage or the screen voltage of a tube. One will give correct results and one won't. -- 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 =--- |
Wes Stewart wrote:
Cecil Moore wrote: Fred W4JLE wrote: All my feedlines have a 9:1 SWR by design. Heh, heh, I understand perfectly. You do? Of course! The feedline Z0 equals 450 ohms. 450/9=50 Fred is using my design from: http://www.qsl.net/w5dxp/notuner.htm -- 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 =--- |
On Tue, 7 Jun 2005 15:01:23 -0400, "Fred W4JLE"
wrote: My 132 foot dipole is fed by lengths of 450 Ohm line of lengths depending on frequency. The first part acts as a matching section to achieve 50 Ohms. This feeds an electrical 1/2 wavelength 450 Ohm section the 50 ohm impeadence is seen by the rig, while maintaning a 9:1 swr on the 1/2 wave section. 450/50=9:1 Because you see 50 ohm (more or less) at the input of your "450 ohm" (more like 400 ohm) line with an arbitrary impedance at the other end, you incorrectly conclude the 450 ohm, variable length line is operating at 9:1. It appears that you've copied Cecil's design (ingenious BTW) but even he admits to anywhere from 6:1 to 13:1 on his line. For discussion purposes let's say that a 132 foot dipole, 50' above average ground operated on 3.5 MHz has a feedpoint Z of about 61 -j63. That's about SWR = 7.5 using 450 ohm as a normalizing factor. Except for the effects of loss, the SWR *everywhere* on the line is 7.5:1. You don't get to say that 1/2 wavelength of it is operating at 9:1 and some other part is operating at something else. Change the frequency to 7 MHz and the SWR is ~10:1 and so forth. |
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. Each end of the loop was soldered to an SO-239 connector. Im feeding the loop via RG-8 coax, about a 30 run. I have a 400 foot loop that is more triangular than square but it still seems to work pretty well. The biggest difference between our antennas is how they are fed. I use 450 ohm ladder-line to a balanced tuner (Johnson Matchbox) to my FT-897D. According the Yaesu's display a suitable match can be obtained on all bands except 30 and 60 meters. I can also use the antenna on six meters with a homebrew matchbox for that band. A two meter matchbox is in the works. 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. The impedance, is that the right word?, of a loop can be several hundred to several thousand ohms. As you have found, the antenna is not a fifty ohm load. 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. The antenna is what it is. Although a little more elevation would be FB I wouldn't be too concerned with what is in the middle of the loop. 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. Ack, do not shrink the loop!!!!! The tuner you have can be used with a balanced feeder, the built-in balun should be satisfactory. Try feeding your loop with 450 ohm ladder-line from the tuner and things should improve significantly. 73 de n4jvp Fritz |
Nonsense Wes, take the case of an antenna that is of sufficient length,
height, or what ever so that at the antenna is exactly R 50 J0. I feed it with an electrical 1/2 wave length of exactly 450 Ohm feedline. The 50 Ohms from my antenna is repeated at the other end of the feedline. An SWR bridge calibrated for 50 Ohms and my rig see 1:1. Would you deny that the SWR on the feedline is 9:1? What is my SWR? Can I say I have 1:1 at the ends and 9:1 anywhere on the feedline? I do get to say it! Now if you want to argue that it will never be exactly 9:1 because the feedline is never exactly 450 Ohms, or the antenna has a reactive portion, you will have to change the subject. No generalization is valid, including mine that I have a 9:1 by design. But I suspect you already new that and decided to increase the quantity of fly crap in the pepper. "Wes Stewart" wrote in message ... On Tue, 7 Jun 2005 15:01:23 -0400, "Fred W4JLE" wrote: You don't get to say that 1/2 wavelength of it is operating at 9:1 and some other part is operating at something else. |
On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE"
wrote: You started with this (mis)statement: All my feedlines have a 9:1 SWR by design. I challenged this crap and showed that, using your own example, this was not the case. You called my challenge "nonsense" and then go on to agree with my original point: No generalization is valid, including mine that I have a 9:1 by design. Simply amazing. |
You win Wes, pick up the marbles.
"Wes Stewart" wrote in message ... On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE" wrote: You started with this (mis)statement: All my feedlines have a 9:1 SWR by design. I challenged this crap and showed that, using your own example, this was not the case. You called my challenge "nonsense" and then go on to agree with my original point: No generalization is valid, including mine that I have a 9:1 by design. Simply amazing. |
On Tue, 7 Jun 2005 14:45:32 -0400, "Fred W4JLE"
wrote: I will be sending you some photos of my final installation. I did a number of tests comparing how tight you can wind the loops. I was amazed at how non critical it was, considering all the dire warnings one receives from the old wife's tales. Fred, any hints on winding your 450-ohm line around the wood dowels? I have a feedline I wouldn't mind lengthening if I could do it without loose ladderline everywhere. bob k5qwg |
Why bother, unless you're having a problem with the heat? 20% loss is
just about exactly 1 dB. That's 1 db I'd rather keep to myself...Why give it away if it's not required? If you pump up the power, heat will likely be a problem. But saying that, I'd rather avoid the tuner altogether... MK |
On Tue, 7 Jun 2005 14:55:25 -0400, "Fred W4JLE"
wrote: Of Course you are, all horror stories aside. Don't confuse the angels dancing on the pinheads around here with practical world experiences. The best solution is to increase the length of your dipole to 130 feet and feed it with 100 foot of 450 Ohm ladderline. Connect a piece of coax with a ferrite bead choke to the 450 Ohm line. Your tuner will love you and you can use all bands from 80 on up. The electrical plug on your rig has losses that are about as meaningful real world.. Thanks for the encouragement and antenna. I have two dipoles up right now. One is a 20 meter mono-bander that was setup specifically for 20 meters and to test a test design for a PVC 'cobra head' (whatever the generic name). The other is a piece made of junk that I put up using parts I already had available. (#14 electrical wire, PVC insulators and TV Coax). It started as a 20 meter dipole, I added 40 and then 80 meters. It wasn't supposed to be anything but a temporary antenna until I made a new one, but weather, timing and money won't cooperate with me. I have patched and patched it. Ice tore down one leg this winter and destroyed half the PVC insulators I was using for spacers. Yesterday I rewired the PL-259, cut the connection to the wires and re-wired it and cut off the 40 and 20 meter elements. It tunes and hears much better now. I have always wanted antennas that would cover all bands without a tuner. This was practical as a novice when all I could work was 80, 40, 15, and 10 meters. Three parallel dipoles hanging from one antenna feed worked well. When I advanced to General, I used two parallel dipoles and an antenna switch. (CW: 80, 40-15, 20, &10; and SSB: 75, 40, & 10). Today, my idea isn't as practical as it was. I now have a rig that covers 160-6 meters on one HF connector. That's eleven bands!! That's a lot of parallel dipoles on a feed even with the bands split up into two antennas. I acquired an antenna tuner recently and it tunes very quickly. I still don't like it, but I can operate anywhere from 160-6 meters on it (not that I have heard anyone on 6 yet.) I would like to build a portable antenna using 300 ohm TV- twin lead for the feed for the tuner. Is there a recommended length and feed point for all bands? Thanks Buck N4PGW -- 73 for now Buck N4PGW |
If you would send me an e-mail so I can get your address, I will send you
some photos. Are you on broadband or dial up? "Bob Miller" wrote in message ... On Tue, 7 Jun 2005 14:45:32 -0400, "Fred W4JLE" wrote: I will be sending you some photos of my final installation. I did a number of tests comparing how tight you can wind the loops. I was amazed at how non critical it was, considering all the dire warnings one receives from the old wife's tales. Fred, any hints on winding your 450-ohm line around the wood dowels? I have a feedline I wouldn't mind lengthening if I could do it without loose ladderline everywhere. bob k5qwg |
I can send you a copy of a program I wrote. It is based on Cecil's work. You
can put in the length of the dipole you want to use, the frequency, and type of feed line. It gives you the choice of giving you the length of feedline for that single case, or a start and stop frequency in which case it prints out a chart of frequency vs. total length.Add jumpers to make up the difference above 80 feet and your good to go! For portable operation a 130 foot dipole fed with 80 feet of 300 Ohm to a small piece of Plexiglas and two sets of banana jacks would allow you to put jumpers of various lengths into the jacks. The second set goes to the rig via a convenient length of 50 ohm coax with a choke balun of ferrites. Lengths of 1,2,4, and 8 foot would allow you to make up jumpers to enable 75 meters from 3.8 to 4 and all the other bands with the exception of 60 meters. It can be made smaller if your only interested in 40 and up etc. Easy to carry, no tuner and worst swr around 1.7:1 For example a 2 foot jumper would put you at 4.0, and a series of an 8,2, and 1 jumper for 3.8 "Buck" wrote in message ... I would like to build a portable antenna using 300 ohm TV- twin lead for the feed for the tuner. Is there a recommended length and feed point for all bands? Thanks Buck N4PGW -- 73 for now Buck N4PGW |
On Wed, 8 Jun 2005 11:13:19 -0400, "Fred W4JLE"
wrote: If you would send me an e-mail so I can get your address, I will send you some photos. Are you on broadband or dial up? I'm on cable modem broadband, Roadrunner. My address is Thanks much, Bob k5qwg "Bob Miller" wrote in message .. . On Tue, 7 Jun 2005 14:45:32 -0400, "Fred W4JLE" wrote: I will be sending you some photos of my final installation. I did a number of tests comparing how tight you can wind the loops. I was amazed at how non critical it was, considering all the dire warnings one receives from the old wife's tales. Fred, any hints on winding your 450-ohm line around the wood dowels? I have a feedline I wouldn't mind lengthening if I could do it without loose ladderline everywhere. bob k5qwg |
|
On Tue, 7 Jun 2005 15:51:51 +0000 (UTC), "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. 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. I know I'll be corrected if I am wrong, but if I am correct, the SWR is high (actually varies by band) on the feedline for the G5RV. The twin lead portion doesn't have the losses the coax does with that SWR so more of the signal gets to the antenna than it would if it were just coax going to a twenty meter dipole. -- 73 for now Buck N4PGW |
On Tue, 07 Jun 2005 15:16:47 -0500, Cecil Moore
wrote: Wes Stewart wrote: Cecil Moore wrote: Fred W4JLE wrote: All my feedlines have a 9:1 SWR by design. Heh, heh, I understand perfectly. You do? Of course! The feedline Z0 equals 450 ohms. 450/9=50 Fred is using my design from: http://www.qsl.net/w5dxp/notuner.htm Can the 17 and 10 meter bands be tuned to a better match or are they compromised so the antenna doesn't need additional matching sections? -- 73 for now Buck N4PGW |
Pardon me while I learn from this discussion.
The 450 ohm antenna is designed to be tuned by using exactly 1/2 electrical wave lengths to match both the transmitter and antenna. This should mean that any differing feedline should work equally as well (except for the losses) if I am correct.... On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE" wrote: I feed it with an electrical 1/2 wave length of exactly 450 Ohm feedline. The 50 Ohms from my antenna is repeated at the other end of the feedline. An SWR bridge calibrated for 50 Ohms and my rig see 1:1. -- 73 for now Buck N4PGW |
Thank you, Is this the same program he http://www.qsl.net/w5dxp/notuner.htm ? I have been looking at this awhile and wonder if the SWR on 17 and 10 meters can be better tuned by adding an additional 1/2 foot section. It probably doesn't matter at that SWR. another question related to the antenna: Do you think this would work? Instead of switching the lead in and out, could the leads be tapped at each band according to the matched setting? So that instead of a series of knife switches, a double-pole multi-throw switch could be used to select a band or frequency for use? Thanks again, gears are turning in my head again... ;) 73 for now Buck On Wed, 8 Jun 2005 11:40:10 -0400, "Fred W4JLE" wrote: I can send you a copy of a program I wrote. It is based on Cecil's work. You can put in the length of the dipole you want to use, the frequency, and type of feed line. It gives you the choice of giving you the length of feedline for that single case, or a start and stop frequency in which case it prints out a chart of frequency vs. total length.Add jumpers to make up the difference above 80 feet and your good to go! For portable operation a 130 foot dipole fed with 80 feet of 300 Ohm to a small piece of Plexiglas and two sets of banana jacks would allow you to put jumpers of various lengths into the jacks. The second set goes to the rig via a convenient length of 50 ohm coax with a choke balun of ferrites. Lengths of 1,2,4, and 8 foot would allow you to make up jumpers to enable 75 meters from 3.8 to 4 and all the other bands with the exception of 60 meters. It can be made smaller if your only interested in 40 and up etc. Easy to carry, no tuner and worst swr around 1.7:1 For example a 2 foot jumper would put you at 4.0, and a series of an 8,2, and 1 jumper for 3.8 -- 73 for now Buck N4PGW |
On Wed, 08 Jun 2005 12:52:01 -0400, Buck wrote:
Pardon me while I learn from this discussion. Hold on Buck. So far there has been very little "learning" to be done from this discussion. I dislike getting personal but I strongly suggest that you reject anything Fred has put forth. Some of what he says is correct, but for the most part you are being led astray. Since you don't yet have the skills to separate the good from the BS, the safest thing to do is ignore it all. For example he has suggested that an all-band antenna can be nothing more than a 130' dipole fed through 100' of 450 ohm line to which you connect a 50 ohm coax and "your rig will be happy." Let's examine this premise, shall we. If you don't already have it, download the free version of EZNEC. www.eznec.com If you have MS Excel do the following. If you don't skip down below the dotted line. Download the program XLZIZL.xls at: http://www.qsl.net/ac6la/xlzizl.html Using EZNEC set up a frequency sweep, for example 3.5 to 4.0 MHz in 50 KHz steps and check Microsmith Files as an output and give a file name ("80meter" for example) "Build" the 130' long antenna in the wires menu, add a source in the middle and do the frequency sweep. (I used a height of 50' and 12 AWG wire) Open xlzizl.xls and select the "ZIZL" worksheet if it isn't already active. "Press" the "Clear all freq..." button (near cell A25). Press the "Read file for Freq, R, X" button (near cell D25). Navigate to the file location where you specified the Microsmith files be located. The default is in the Smith subdirectory in the EZW directory. Select the file "80meter.gam" and open it. The calculated data will populate the Frequency, R at load and X at load cells. Press the "Refresh and show Smith" button (near cell I28). The Smith chart will open and display the calculated impedance data for the 130' antenna operated from 3.5 to 4.0 MHz. Now we are going to add a transmission line. Select the "ZIZL" worksheet again and press the "Set via Dialog" button (near cell A34). The "Network definition" window will open with "Element position 1" selected by default. Change it to "5". Under "Element type" select Transmission line. Under "Qualifier" scroll the dropdown menu to either "Generic 450 ohm window" or if you more more realistic numbers you can select one of the Wireman Ladder line types. (Ignore "wet" ones.) Mouse down to the "Element Value" area an type in "100" for the length and press the "Set This Element" button and then close the Network definition window. Press the Refresh and show Smith Chart button and you will now see two traces, the original "load" data and the feedpoint data at the input to the 100' transmission line. If you know anything about Smith charts you will immediately notice that the match is worse at the input of the line than it was at the antenna. So much for the "magic" 100' length that Fred proposes. Going back to the ZIZL sheet and looking in the "results" area you can see that at 3.5 MHz the SWR is 36:1. Without the "magic" 100' of ladderline, the SWR is 3:1. You can repeat this exercise at different frequency ranges and see just how awful this idea is. Let's continue... Assume that your 50-ohm coax is 50' long. Go back to the Network "Set via Dialog" button. Accept the "1" default for Element Position and again select Transmission Line for Element Type. For Qualifier, let's use Belden 9258 (RG8X), although you can use what you use. Set the length to 50' and press "Set this Element." Close the window. Press the Refresh and show Smith button and you will now see three traces on the chart: the load, the impedance at the inut of the 450 ohm line and the impedance at the input of the 50 ohm line. Return to the ZIZL sheet and under results note that the SWR at 3.5 MHz is down to "only" 17:1. This is what your rig is going to see. Also note that the network loss (the line loss) is over 3 dB. Now just for giggles, let's take out the 100' of ladderline and make the whole 150' run out of RG8X. You can just highlight the cells "G34 through G36" and delete them and then select cell C36 and type in 150 and tab out. Press "F9" and see the new results. The 3.5 MHz SWR is now 2.4:1 and the total network (line) loss is 1.2 dB. So replacing the "low loss" ladderline with "lossy" coax improved the match and lowered the loss. I don't know how much of this "magic" I can stand. ************************************************** ***************** If you don't have Excel there is a more labor intensive method that is just as accurate. Go to http://www.qsl.net/ac6la/tldetails.html and download the program and open it. Select a transmission line type, "Generic 450 ohm Window" for example. The line parameters will populate the boxes to the right. Under Set Frequency, type in 3.5. Run EZNEC one frequency at a time, beginning with 3.5 MHz. Look at the source data and note the Impedance R and X values. Pay attention to the sign of X. Copy these values to "R" and "X" in the TLdetails program. Remember the sign of X. For example I used R = 61, X = -64. In the "results" area under "At Input" you can see the R and X values at the input and note that the SWR in the 450 ohm line is about 7:1 and in the 50 ohm feeder Fred would have you connecting at this point the SWR is as before ~36:1. If you want to "add" the 50 ohm line, copy down the R and X at the input (132, -470) and enter them in the the R and X boxes above. Change the line type to Belden 9258 and the length to 50 feet and as above, the SWR at the input is ~17:1. To summarize: There are ample free tools to work these problems out without relying on bafflegab. You don't have to take my word or anyone else's; work the problem yourself and learn something while doing it. |
On Wed, 08 Jun 2005 12:23:50 -0700, Wes Stewart
wrote: [snip} Under "Qualifier" scroll the dropdown menu to either "Generic 450 ohm window" or if you more more realistic numbers you can select one of the Wireman Ladder line types. (Ignore "wet" ones.) This should of course read, "...if you want more realistic..." |
Bob Miller wrote:
Fred, any hints on winding your 450-ohm line around the wood dowels? I have a feedline I wouldn't mind lengthening if I could do it without loose ladderline everywhere. You can string a straight piece of nylon/dacron rope from one point to another and spiral the ladder-line using the rope for support. Black tie wraps keep the ladder-line in position. Another idea is to hang the ladder-line, accordion style, under the eaves of your house. -- 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:
I can send you a copy of a program I wrote. It is based on Cecil's work. You can put in the length of the dipole you want to use, the frequency, and type of feed line. That EXCEL program is nice. "imax.exe" is also available from my web page. It was written in Quickbasic and executes in a DOS window. -- 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 =---- |
Buck wrote:
I know I'll be corrected if I am wrong, but if I am correct, the SWR is high (actually varies by band) on the feedline for the G5RV. The twin lead portion doesn't have the losses the coax does with that SWR so more of the signal gets to the antenna than it would if it were just coax going to a twenty meter dipole. Here are the 50 ohm SWRs at the 300 ohm twinlead to 50 ohm coax junction that EZNEC produced in 2001 for a 102' dipole at 40 feet fed with 27.7' of 300 ohm ladder-line. 3.8 MHz 3.2:1, 7.2 MHz 3.6:1, 10.125 MHz 56:1, 14.2 MHz 4.1 18.14 MHz 37:1, 21.3 MHz 11:1, 24.95 MHz 7.6:1, 28.4 MHz 66:1 The G5RV was designed for 80m, 40m, & 20m operation and on those designed-for bands does a reasonable job. It works pretty well on 12m. Less well on 15m. Terrible for 30m, 17m, and 10m operation. However, if you are willing to vary the length of the 300 ohm (or 450 ohm) matching section, you can achieve a reasonable match on any HF band. -- 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 =---- |
Buck wrote:
Cecil Moore wrote: Fred is using my design from: http://www.qsl.net/w5dxp/notuner.htm Can the 17 and 10 meter bands be tuned to a better match or are they compromised so the antenna doesn't need additional matching sections? Each installation will vary depending upon the surroundings. My 50 ohm SWR on 17m was 1.6:1 and 1.7:1 on 10m. Those were acceptable to my IC-706 at the time - even more acceptable to me now that I have an IC-756PRO with its internal tuner. :-) In fact, one of the advantages/benefits of this matching method is that it allows internal tuners to achieve perfect matches on all HF bands - no external tuner necessary. -- 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 =---- |
Buck wrote:
Pardon me while I learn from this discussion. The 450 ohm antenna is designed to be tuned by using exactly 1/2 electrical wave lengths to match both the transmitter and antenna. This should mean that any differing feedline should work equally as well (except for the losses) if I am correct.... What you are missing is that first piece of matching section which can be any length less than 1/2WL. After that first piece of matching section, you could indeed switch to a different characteristic impedance. Congratulations, you have just invented the G5RV. :-) -- 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 =---- |
Buck wrote:
Do you think this would work? Instead of switching the lead in and out, could the leads be tapped at each band according to the matched setting? So that instead of a series of knife switches, a double-pole multi-throw switch could be used to select a band or frequency for use? Nope, that won't work because it leaves unterminated stubs in the transmission line system. You might be able to predict their effect but I have never tried to do that. It's rather like a bag of worms. -- 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 =---- |
This is what I use Buck. Mine is a 132 foot dipole and I insert the lengths
with Omron 4PDT relays controlled by 2 decimal thumbwheel switches. I just added another relay that ties the two sides of the twinlead together and feeds the center conductor of the coax. I plan to use it on 160. I have not tested it yet because conditions have been so bad with storms every day this week. "Buck" wrote in message ... Thank you, Is this the same program he http://www.qsl.net/w5dxp/notuner.htm ? I have been looking at this awhile and wonder if the SWR on 17 and 10 meters can be better tuned by adding an additional 1/2 foot section. It probably doesn't matter at that SWR. another question related to the antenna: Do you think this would work? Instead of switching the lead in and out, could the leads be tapped at each band according to the matched setting? So that instead of a series of knife switches, a double-pole multi-throw switch could be used to select a band or frequency for use? Thanks again, gears are turning in my head again... ;) 73 for now Buck On Wed, 8 Jun 2005 11:40:10 -0400, "Fred W4JLE" wrote: I can send you a copy of a program I wrote. It is based on Cecil's work. You can put in the length of the dipole you want to use, the frequency, and type of feed line. It gives you the choice of giving you the length of feedline for that single case, or a start and stop frequency in which case it prints out a chart of frequency vs. total length.Add jumpers to make up the difference above 80 feet and your good to go! For portable operation a 130 foot dipole fed with 80 feet of 300 Ohm to a small piece of Plexiglas and two sets of banana jacks would allow you to put jumpers of various lengths into the jacks. The second set goes to the rig via a convenient length of 50 ohm coax with a choke balun of ferrites. Lengths of 1,2,4, and 8 foot would allow you to make up jumpers to enable 75 meters from 3.8 to 4 and all the other bands with the exception of 60 meters. It can be made smaller if your only interested in 40 and up etc. Easy to carry, no tuner and worst swr around 1.7:1 For example a 2 foot jumper would put you at 4.0, and a series of an 8,2, and 1 jumper for 3.8 -- 73 for now Buck N4PGW |
No buck, the line is always longer than 1/2 wave. It is a matching section
from what is at the antenna to 50 ohms, and then 1/2 wave from that point. "Buck" wrote in message ... Pardon me while I learn from this discussion. The 450 ohm antenna is designed to be tuned by using exactly 1/2 electrical wave lengths to match both the transmitter and antenna. This should mean that any differing feedline should work equally as well (except for the losses) if I am correct.... On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE" wrote: I feed it with an electrical 1/2 wave length of exactly 450 Ohm feedline. The 50 Ohms from my antenna is repeated at the other end of the feedline. An SWR bridge calibrated for 50 Ohms and my rig see 1:1. -- 73 for now Buck N4PGW |
Did you miss the tuner part? The "magic antenna" is the same all band sold
by a number of folks, i.e. Van Gordon. .. "Wes Stewart" wrote in message ... On Wed, 08 Jun 2005 12:52:01 -0400, Buck wrote: Pardon me while I learn from this discussion. Hold on Buck. So far there has been very little "learning" to be done from this discussion. I dislike getting personal but I strongly suggest that you reject anything Fred has put forth. Some of what he says is correct, but for the most part you are being led astray. Since you don't yet have the skills to separate the good from the BS, the safest thing to do is ignore it all. |
On Wed, 08 Jun 2005 20:41:58 -0500, Cecil Moore
wrote: Buck wrote: Pardon me while I learn from this discussion. What you are missing is that first piece of matching section which can be any length less than 1/2WL. After that first piece of matching section, you could indeed switch to a different characteristic impedance. Congratulations, you have just invented the G5RV. :-) Hmmm, and I'm not even british..... ;) The G5RV is a twenty meter antenna, isn't it? It needs a tuner on all other bands if I am not mistaken. -- 73 for now Buck N4PGW |
Buck wrote:
The G5RV is a twenty meter antenna, isn't it? It needs a tuner on all other bands if I am not mistaken. The G5RV needs a tuner on all bands. Acceptable SWRs are very rare without a tuner. The G5RV is 1.5WL long on 20m. The resonant feedpoint impedance on 20m is in excess of 100 ohms giving a 50 ohm SWR in excess of 2:1 so a tuner is required, even on 20m. However, I have done to a G5RV what Fred has done to a 1/2WL 80m dipole. The matching section on my G5RV is a variable length between 22' and 38'. My G5RV has an SWR below 1.5:1 on all eight HF bands. I'm going to write it up one of these days. -- 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 =---- |
I am a little confused, so bare with me.....
I put up an antenna with 50 ohm of impedance. I feed it with any length of 300 ohm feed less than 1/2 L. Then I run 1/2 L of 50 ohm feed to the radio and I have the 50 ohm match? similar: I put up a 300 ohm antenna. I feed it with 300 ohm twin lead for less than 1/2 L and 1/2 L of 50 ohm feedline. Is this a 50 ohm match? (L=Lamda) Thanks Buck On Thu, 9 Jun 2005 00:27:26 -0400, "Fred W4JLE" wrote: No buck, the line is always longer than 1/2 wave. It is a matching section from what is at the antenna to 50 ohms, and then 1/2 wave from that point. "Buck" wrote in message .. . Pardon me while I learn from this discussion. The 450 ohm antenna is designed to be tuned by using exactly 1/2 electrical wave lengths to match both the transmitter and antenna. This should mean that any differing feedline should work equally as well (except for the losses) if I am correct.... On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE" wrote: I feed it with an electrical 1/2 wave length of exactly 450 Ohm feedline. The 50 Ohms from my antenna is repeated at the other end of the feedline. An SWR bridge calibrated for 50 Ohms and my rig see 1:1. -- 73 for now Buck N4PGW -- 73 for now Buck N4PGW |
On Thu, 09 Jun 2005 11:16:38 -0400, Buck Naked wrote:
I am a little confused, so bare with me..... I'm not about to get naked with you, but you are more than a little confused. You have listened to too much bafflegab in this thread. I showed you in detail how to answer your own questions. Did you not read my post? |
Buck wrote:
I am a little confused, so bare with me..... I put up an antenna with 50 ohm of impedance. I feed it with any length of 300 ohm feed less than 1/2 L. Then I run 1/2 L of 50 ohm feed to the radio and I have the 50 ohm match? Nope, 50 ohms is only one of an infinite number of impedances you might encounter. For 50 ohms, you feed it with 1/2WL of 300 ohm feedline. This is similar to (but not exactly like) a G5RV used on 20m. I put up a 300 ohm antenna. I feed it with 300 ohm twin lead for less than 1/2 L and 1/2 L of 50 ohm feedline. Is this a 50 ohm match? Nope, you cannot transform the impedance of a 300 ohm antenna using 300 ohm feedline. You need reflections to cause an impedance transformation. A 300 ohm antenna impedance is not within the green doughnut area below. The range of impedances that can be matched with a length of 450 ohm ladder-line are represented by the green doughnut at: http://www.qsl.net/w5dxp/smith.htm The impedances outside the green area cannot be matched by only one 450 ohm matching section. The area in the doughnut hole cannot be matched by only one 450 ohm matching section. -- 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 =--- |
On Thu, 09 Jun 2005 11:38:22 -0500, Cecil Moore
wrote: Buck wrote: I am a little confused, so bare with me..... I put up an antenna with 50 ohm of impedance. I feed it with any length of 300 ohm feed less than 1/2 L. Then I run 1/2 L of 50 ohm feed to the radio and I have the 50 ohm match? Nope, 50 ohms is only one of an infinite number of impedances you might encounter. For 50 ohms, you feed it with 1/2WL of 300 ohm feedline. This is similar to (but not exactly like) a G5RV used on 20m. I put up a 300 ohm antenna. I feed it with 300 ohm twin lead for less than 1/2 L and 1/2 L of 50 ohm feedline. Is this a 50 ohm match? Nope, you cannot transform the impedance of a 300 ohm antenna using 300 ohm feedline. You need reflections to cause an impedance transformation. A 300 ohm antenna impedance is not within the green doughnut area below. The range of impedances that can be matched with a length of 450 ohm ladder-line are represented by the green doughnut at: http://www.qsl.net/w5dxp/smith.htm The impedances outside the green area cannot be matched by only one 450 ohm matching section. The area in the doughnut hole cannot be matched by only one 450 ohm matching section. When I click on your links, I get connection refused from qsl.net -- 73 for now Buck N4PGW |
Buck wrote:
When I click on your links, I get connection refused from qsl.net qsl.net is not very fast or reliable. I just tried it and was refused. Maybe too many present users. Try again later. -- 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 =--- |
You can't match a 300 ohm antenna with 300 ohm line. A matching section
relies on SWR (read reflections) to match. once matched, any impeadence feed line may be used from the matched point as long as it is an electrical half wavelength or multiple at the frequency of interest. The only difference will be the SWR on the line. Your rig would still see the SWR ar the match point. Given an antenna that has 50 Ohms +J0, feed it with 50 ohm line and the swr for the system is 1:1, substitute a 1/2 wave of 450 ohm line and the antenna and the rig are both at 50 ohms. The SWR on the feedline is 450/50 or 9:1. Look at the half wave of feedline as two back to back 1/4 wave matching sections. The SWR on the feedline is of no consequece as the losses are so low as not to have a practical effect. "Buck" wrote in message ... I am a little confused, so bare with me..... I put up an antenna with 50 ohm of impedance. I feed it with any length of 300 ohm feed less than 1/2 L. Then I run 1/2 L of 50 ohm feed to the radio and I have the 50 ohm match? similar: I put up a 300 ohm antenna. I feed it with 300 ohm twin lead for less than 1/2 L and 1/2 L of 50 ohm feedline. Is this a 50 ohm match? (L=Lamda) Thanks Buck On Thu, 9 Jun 2005 00:27:26 -0400, "Fred W4JLE" wrote: No buck, the line is always longer than 1/2 wave. It is a matching section from what is at the antenna to 50 ohms, and then 1/2 wave from that point. "Buck" wrote in message .. . Pardon me while I learn from this discussion. The 450 ohm antenna is designed to be tuned by using exactly 1/2 electrical wave lengths to match both the transmitter and antenna. This should mean that any differing feedline should work equally as well (except for the losses) if I am correct.... On Tue, 7 Jun 2005 18:02:43 -0400, "Fred W4JLE" wrote: I feed it with an electrical 1/2 wave length of exactly 450 Ohm feedline. The 50 Ohms from my antenna is repeated at the other end of the feedline. An SWR bridge calibrated for 50 Ohms and my rig see 1:1. -- 73 for now Buck N4PGW -- 73 for now Buck N4PGW |
| All times are GMT +1. The time now is 12:53 PM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com