![]() |
Multiband dipole, coax fed, no tuner
Good afternoon, all. I would like to put up a dipole antenna for 80 and 40 meters, and a frequency near 4.5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. For illustration purposes, let's say that the 80-meter dipole will run east-west, the 4.5-MHz dipole will run northeast-southwest, and the 40-meter dipole will run north-south. Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ |
I had a 5 band trapped dipole at 90 degrees to a 17M dipole fed with a
single coax and the math held true. I did have some tuning to do but just trimming to my desired center frequency. So that was 2 dipoles (albeit one was a five band) at 90 digress and it worked a treat. -- Charlie Ham Radio - AD5TH www.ad5th.com Live Blues Music www.492acousticblues.com "C. J. Clegg" wrote in message ... Good afternoon, all. I would like to put up a dipole antenna for 80 and 40 meters, and a frequency near 4.5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. For illustration purposes, let's say that the 80-meter dipole will run east-west, the 4.5-MHz dipole will run northeast-southwest, and the 40-meter dipole will run north-south. Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ |
On Sat, 21 May 2005 16:32:14 -0400, C. J. Clegg
wrote: Good afternoon, all. I would like to put up a dipole antenna for 80 and 40 meters, and a frequency near 4.5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. For illustration purposes, let's say that the 80-meter dipole will run east-west, the 4.5-MHz dipole will run northeast-southwest, and the 40-meter dipole will run north-south. Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? I'd put the 80M and 4.5 MHz dipoles normal to each other with the 40 in between. I'd prune the 80M first and then the 4.5 and then 40M. I run an 75-80 dipole paired with a 40 spaced about 45 deg. Can't remember whether the formula held or not. Make 'em too long and prune. I have extensions on the 75 that I physically connect to go from the phone to CW bands. Don't remember any change in the 40, if it does, it's minor. |
My first suggestion would be to use a terminated folded dipole cut large
enough for 80m and the rest would just work. Have a look at Mr Cebik's website for details. http://www.cebik.com/wire/t2fd.html http://www.cebik.com/wire/wbfd.html Your idea for the design is the kind of setup that would be easy to model in Eznec/4nec2 etc. I did this once (only) for a 10m/6m design 90 degree offset inverted V. I noted that there was a much narrower SWR bandwidth on the 10M side. I didnt delve into why because I never built it. Apologies for not answering your question directly though. Cheers Bob VK2YQA C. J. Clegg wrote: ----- Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ |
On Sun, 22 May 2005 10:34:19 +1000, Bob Bob
wrote: My first suggestion would be to use a terminated folded dipole cut large enough for 80m and the rest would just work. Have a look at Mr Cebik's website for details. http://www.cebik.com/wire/t2fd.html http://www.cebik.com/wire/wbfd.html Good morning, Bob. Wouldn't the terminated folded dipole be too lossy at the lowest frequencies of interest? In any case it looks like a terminated folded dipole would cost at least a full "S" unit over a dipole, at any frequency (and much more than that down by the low end of the design range). However, looking through L.B.'s website gave me another idea ... what about a triband full wave loop similar to what is shown in the attached JPEG? There would be a single wire on the "fed" side of the loop, tapped off at points along its length to create anchor points for the other three sides of a loop for each frequency. Have any of you tried anything like that, and how did it work? CJ |
C. J. Clegg wrote:
However, looking through L.B.'s website gave me another idea ... what about a triband full wave loop similar to what is shown in the attached JPEG? Have any of you tried anything like that, and how did it work? Unlike dipoles, there would be heavy interaction between the loops on 40m. The feedpoint impedance of an 80m dipole is very high on 40m and most of the power goes into the 40m dipole. The feedpoint impedance of an 80m loop is low on 40m so the power is shared with sometimes unexpected results. You can probably model it with the free demo version of EZNEC available at www.eznec.com -- 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 =--- |
"C. J. Clegg" wrote in message ... Good afternoon, all. I would like to put up a dipole antenna for 80 and 40 meters, and a frequency near 4.5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. For illustration purposes, let's say that the 80-meter dipole will run east-west, the 4.5-MHz dipole will run northeast-southwest, and the 40-meter dipole will run north-south. Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ It should work just fine. I have an 18 MHz dipole, which also serves as the support, and a 40 m inverted V hanging below that, fed through a current balun. There will be interaction, so it would be a good idea to model it in EZNEC first. You will want to trim the longest antennas first. Cut them a little long to start with, and when you go to shorten one, don't cut off all the extra wire, in case you have to go back. If the 4.5 is for receiving only, it may not be worth the bother. It took a lot of going back and forth, but I have an EZNEC simulation of a 75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up the 4.5 antenna, you can probably use that to extend the bandwidth of the 80 m antenna on the high side. Tam/WB2TT |
On Sat, 21 May 2005 16:32:14 -0400, C. J. Clegg
wrote: Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? near, yes, but it will be a little short In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ Wes and I disagree, so you will have to toss a coin on this one. I have built many of these multiband parallel dipoles over the years. I still use them. Here is how I do mine. I space the wires about 6-8 inches apart using the longest wire on top and they get shorter as they go down. What I generally do is use a long formula to set up the initial wires such as 495/f = length in feet. Then I hang all the wires with the spacers. I trim the highest frequency first and measure it out. I reverse the calculations to get the X more accurately in the formula, X/f = L in Feet. I trim the other two and I am done. I have not tried this with an element so close in frequency as your 80/4.5 MHz elements, but I don't expect a problem. If you have an antenna analyzer, you can see what the different elements are resonant on and then calculate the reverse formula trimming only once per band. The only real difference I see in the multiband parallel dipole is that the bandwidth on 80 and 40 seem to be broader than on a single dipole cut to frequency. I have read on some of these forums that others are getting narrower bandwidth. I can't explain that. FWIW -- 73 for now Buck N4PGW |
I'll admit that I havent played with the TFD but would agree that the
resistive termination would introduce a 3dB power loss. One has to ask though whether that will be a problem at 80m given band noise etc. To tell you the truth if I was trying for a 3.5, 4.5 and 7Mhz antenna I'd probably use just two (crossed) dipoles and figure a way to mechanically tune between the lower frequencies. Even lumped C comes to mind. Only HF loop I ever played with was a 40m NVIS.. Cheers Bob VK2YQA C. J. Clegg wrote: --- Wouldn't the terminated folded dipole be too lossy at the lowest frequencies of interest? Have any of you tried anything like that, and how did it work? |
"Tam/WB2TT" wrote in message ... "C. J. Clegg" wrote in message ... Good afternoon, all. I would like to put up a dipole antenna for 80 and 40 meters, and a frequency near 4.5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. For illustration purposes, let's say that the 80-meter dipole will run east-west, the 4.5-MHz dipole will run northeast-southwest, and the 40-meter dipole will run north-south. Questions... Is the standard 468/F formula likely to be anywhere near accurate, or will the three antennas interact with one another to throw the calculations off? In particular, is the 4.5-MHz frequency too near the 80-meter band such that interaction will be greater than otherwise? If the interactions are sufficient to throw the formula off, will my antennas end up being longer or shorter than the formula length? Thanks.... CJ It should work just fine. I have an 18 MHz dipole, which also serves as the support, and a 40 m inverted V hanging below that, fed through a current balun. There will be interaction, so it would be a good idea to model it in EZNEC first. You will want to trim the longest antennas first. Cut them a little long to start with, and when you go to shorten one, don't cut off all the extra wire, in case you have to go back. If the 4.5 is for receiving only, it may not be worth the bother. It took a lot of going back and forth, but I have an EZNEC simulation of a 75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up the 4.5 antenna, you can probably use that to extend the bandwidth of the 80 m antenna on the high side. Tam/WB2TT CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. Tam/WB2TT |
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote: I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. Good evening, Tam. Thanks for running the simulation for me. Your results don't surprise me much. (I'm going to have to get that EZNEC program and play with it for a while ... thanks to all for mentioning it.) The 4.5-MHz antenna will be used for transmitting as well as receiving, and so I need to get the SWR down to something reasonable. I guess there's no reason why I can't just put up a separate dipole for 4.5 MHz and the crossed dipoles, fed with a single coax, for 80 and 40. I could also (and I might...) just put up an 80-meter dipole fed with ladder line and use a tuner, though I was trying to avoid the tuner. Thanks (to you and to all) for saving me a bunch of work. :-) CJ |
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote: [snip] CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. I'd be interested to see your Eznec file. |
It took a lot of going back and forth, but I have an EZNEC simulation of a 75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up the 4.5 antenna, you can probably use that to extend the bandwidth of the 80 m antenna on the high side. Tam/WB2TT Could you post what the antenna looks like that will do that bandwidth ? de KU4PT |
.... draw a picture of a discone in your mind... yep, that is kinda what it
looks like... only made by Martians... grin Warmest regards, John "Ralph Mowery" wrote in message ink.net... It took a lot of going back and forth, but I have an EZNEC simulation of a 75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up the 4.5 antenna, you can probably use that to extend the bandwidth of the 80 m antenna on the high side. Tam/WB2TT Could you post what the antenna looks like that will do that bandwidth ? de KU4PT |
A cheap and effective solution is to purchase a Van Gordon 130 foot all band
dipole $29.95 with 100 feet of ladder line. Purchase an additional 100 foot of 450 ohm ladderline $12.00. find 7 4PDT relays and 2 digitran decimal to binary switches. use the relays to switch in 1,2,4,8,10,20, and 40 feet of additional ladder line. cut 10 feet off of the 100 feet that came with the antenna. Now use the relays to add length as needed to tune. For example to tune your 4.5 would require switching in an additional 78 feet. E-Mail me and I will send you a chart of frequency Vs what you need to switch in. I found the relays for a buck a piece and the digital rotary switches for 3 bucks. feed with your choice of coax with ferrite beads to act as a balun and your good to go. Less than $50.00 and I cover nearly DC to Daylight, no tuner and worst SWR anywhere 1.4:1 "C. J. Clegg" wrote in message ... On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. Good evening, Tam. Thanks for running the simulation for me. Your results don't surprise me much. (I'm going to have to get that EZNEC program and play with it for a while ... thanks to all for mentioning it.) The 4.5-MHz antenna will be used for transmitting as well as receiving, and so I need to get the SWR down to something reasonable. I guess there's no reason why I can't just put up a separate dipole for 4.5 MHz and the crossed dipoles, fed with a single coax, for 80 and 40. I could also (and I might...) just put up an 80-meter dipole fed with ladder line and use a tuner, though I was trying to avoid the tuner. Thanks (to you and to all) for saving me a bunch of work. :-) CJ |
"Wes Stewart" wrote in message ... On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: [snip] CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. I'd be interested to see your Eznec file. Gladly, but, how do I get an ASCII file out of it. I thought I had opened EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when I click on View File, I get the same garbage as Notepad. The only questionable thing I did would be the 0.2 foot stub in the middle that the other wires are connected to; but that works for other configurations. Tam/WB2TT |
"Ralph Mowery" wrote in message ink.net... It took a lot of going back and forth, but I have an EZNEC simulation of a 75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put up the 4.5 antenna, you can probably use that to extend the bandwidth of the 80 m antenna on the high side. Tam/WB2TT Could you post what the antenna looks like that will do that bandwidth ? de KU4PT Easy, two dipoles at right angles. One wire is 133 feet long, the other is 119. The height I used was 75 feet over average ground. I double checked the SWR. It is below 2:1 from 3.5 to 4.0. If you do it at 75 Ohms, the SWR is below 1.5:1 from 3.55 to 3.975. Tam/WB2TT |
On Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT"
wrote: "Wes Stewart" wrote in message .. . On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: [snip] CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. I'd be interested to see your Eznec file. Gladly, but, how do I get an ASCII file out of it. I thought I had opened EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when I click on View File, I get the same garbage as Notepad. The only questionable thing I did would be the 0.2 foot stub in the middle that the other wires are connected to; but that works for other configurations. Tam/WB2TT Just send him the *.ez file. Wes can handle that. Danny |
"Dan Richardson arrl net" k6mhatdot wrote in message ... On Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT" wrote: "Wes Stewart" wrote in message . .. On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: [snip] CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. I'd be interested to see your Eznec file. Gladly, but, how do I get an ASCII file out of it. I thought I had opened EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when I click on View File, I get the same garbage as Notepad. The only questionable thing I did would be the 0.2 foot stub in the middle that the other wires are connected to; but that works for other configurations. Tam/WB2TT Just send him the *.ez file. Wes can handle that. Danny Will do. I wanted to post it here.Now that I think about it, it's the SWCAD files that are ASCII, not the EZNEC Tam |
Fred W4JLE wrote:
Less than $50.00 and I cover nearly DC to Daylight, no tuner and worst SWR anywhere 1.4:1 Speaking of broad-banding an antenna ... :-) -- 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 Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT"
wrote: "Wes Stewart" wrote in message .. . On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: [snip] CJ, I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz, with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the 4.5 really messes up the 3.7. Among other things the impedance at 3.7 and 4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average ground. If the 4.5 is for receive only, I would forget about it, and take the 10:1 SWR that the 80 meter dipole gives you. I'd be interested to see your Eznec file. Gladly, but, how do I get an ASCII file out of it. I thought I had opened EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when I click on View File, I get the same garbage as Notepad. The only questionable thing I did would be the 0.2 foot stub in the middle that the other wires are connected to; but that works for other configurations. Tam was kind enough to send me his EZNEC file. I asked for this file since I went through this myself unsuccessfully (so far) and wanted to see if someone else had a better idea. My suspicions were confirmed: there are some NEC guideline violations. I'm don't want this to come off as picking on Tam publicly, but to keep others from making the same mistakes, (*I* would never make a mistake [g]) here's what I see. Tam uses a single wire at the middle of the dipole to contain the source. This is necessary because NEC doesn't allow a source at a wire junction. (EZNEC has a split source that works at a wire junction, but not a multiple wire junction.) The EZNEC manual recommends that this wire be at least 0.02 wavelengths long and consist of three segments. I believe the three segment rule is stipulated to force the segments adjacent to the source wire to be equal to it. If we are careful about this, we can go to one segment. Tam's center wire is only 0.2 feet long and has 11 segments. The segment length of .018 feet is way too short; the wire needs to be ~16' long at 3.5 MHz to meet the guidelines. Of course with this gross violation comes another one when the connecting wires are a more appropriate segment length. Tam, I suggest that you got to Options--Segmentation Check and make it "Auto". I'm still looking at this issue and will report back if I see any progress. Wes N7WS |
"Wes Stewart" wrote in message ... On Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT" wrote: "Wes Stewart" wrote in message . .. On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT" wrote: [snip] Tam uses a single wire at the middle of the dipole to contain the source. This is necessary because NEC doesn't allow a source at a wire junction. (EZNEC has a split source that works at a wire junction, but not a multiple wire junction.) The EZNEC manual recommends that this wire be at least 0.02 wavelengths long and consist of three segments. I believe the three segment rule is stipulated to force the segments adjacent to the source wire to be equal to it. If we are careful about this, we can go to one segment. Tam's center wire is only 0.2 feet long and has 11 segments. The segment length of .018 feet is way too short; the wire needs to be ~16' long at 3.5 MHz to meet the guidelines. Of course with this gross violation comes another one when the connecting wires are a more appropriate segment length. Tam, I suggest that you got to Options--Segmentation Check and make it "Auto". I'm still looking at this issue and will report back if I see any progress. Wes N7WS Wes, Thanks for pointing it out. I did this in a hurry, and did not notice the 11 segments in the .2 ft wire. I will take a look to see if it is any different for 1 segment. In fact, I might make it +/- 1 foot long. Tam/WB2TT |
All times are GMT +1. The time now is 09:26 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com