Interesting 144 foot Dipole
A ham over on eHam.net wanted to know if a 40m EDZ
would work on 80m. Of course it will if fed correctly since it is about 166 feet long. The question is: Is there a fixed length of ladder-line that will work both on 40m and 80m? I fired up EZNEC and started cut and trying. I found that a 144 foot 40m "EDZ" would yield some interesting results. I went out and extended my 130 foot dipole to 144 feet and was impressed. I found that a 144 foot center-fed dipole fed with ~88 feet of 450 ohm ladder-line was resonant on 7.150 MHz and my IC-756PRO would tune it over the entire 40m band. 40m is my favorite band. In addition, the IC-756PRO tuner will tune the same antenna system over a 3.7-3.9 MHz range on 80m. In addition, the IC-756PRO tuner will tune the same antenna system on 30m and 17m. I've already got a rotatable dipole for 20m-10m and this antenna tunes on 80m, 40m, and 30m. -- 73, Cecil http://www.w5dxp.com |
Interesting 144 foot Dipole
In article ,
Cecil Moore wrote: A ham over on eHam.net wanted to know if a 40m EDZ would work on 80m. Of course it will if fed correctly since it is about 166 feet long. The question is: Is there a fixed length of ladder-line that will work both on 40m and 80m? I fired up EZNEC and started cut and trying. I found that a 144 foot 40m "EDZ" would yield some interesting results. I went out and extended my 130 foot dipole to 144 feet and was impressed. I found that a 144 foot center-fed dipole fed with ~88 feet of 450 ohm ladder-line was resonant on 7.150 MHz and my IC-756PRO would tune it over the entire 40m band. 40m is my favorite band. In addition, the IC-756PRO tuner will tune the same antenna system over a 3.7-3.9 MHz range on 80m. In addition, the IC-756PRO tuner will tune the same antenna system on 30m and 17m. I've already got a rotatable dipole for 20m-10m and this antenna tunes on 80m, 40m, and 30m. interesting , resonant too hmm wonder how the waves look on that dipole? |
Interesting 144 foot Dipole
ml wrote:
interesting , resonant too hmm wonder how the waves look on that dipole? The free demo copy of EZNEC available from www.eznec.com will display the current waveform. Here's a copy of a posting I made to eHam.net The following results are approximate but show the resonance trend on 80m Vs dipole length. Take a certain length dipole and adjust the length of the 450 ohm ladder-line for resonance on 7.15 MHz. i.e. NOTE: All of the following antenna systems are resonant on 7.15 MHz. and cover the entire 40m band with an SWR of 3.5:1 or less (good for built-in autotuners). Here are the approximate results: dipole length : feedline length : resonance on 80m 170' : ~85' : 3.62 MHz (3.52-3.72) 160' : ~87' : 3.7 MHz (3.6-3.8) 150' : ~89' : 3.8 MHz (3.7-3.9) 140' : ~91' : 3.92 MHz (3.82-4) 130' : ~92.8' : 4.06 MHz (resonant out of band) 120' : ~94.7' : 4.23 MHz (resonant out of band) Yesterday I had a 130' dipole that exhibited the above characteristics. I have changed it to a 144' dipole and now, with one length of ladder-line, the antenna covers all of 40m and 200 kHz of 80m using the limited range autotuner built into my IC-756PRO. A bonus is that the autotuner also tunes this fixed antenna system on 30m and 17m. -- 73, Cecil http://www.w5dxp.com |
Interesting 144 foot Dipole
Cecil Moore wrote:
The following results are approximate but show the resonance trend on 80m Vs dipole length. Take a certain length dipole and adjust the length of the 450 ohm ladder-line for resonance on 7.15 MHz. i.e. NOTE: All of the following antenna systems are resonant on 7.15 MHz. and cover the entire 40m band with an SWR of 3.5:1 or less (good for built-in autotuners). Here are the approximate results: dipole length : feedline length : resonance on 80m 170' : ~85' : 3.62 MHz (3.52-3.72) 160' : ~87' : 3.7 MHz (3.6-3.8) 150' : ~89' : 3.8 MHz (3.7-3.9) 140' : ~91' : 3.92 MHz (3.82-4) 130' : ~92.8' : 4.06 MHz (resonant out of band) 120' : ~94.7' : 4.23 MHz (resonant out of band) Yesterday I had a 130' dipole that exhibited the above characteristics. I have changed it to a 144' dipole and now, with one length of ladder-line, the antenna covers all of 40m and 200 kHz of 80m using the limited range autotuner built into my IC-756PRO. A bonus is that the autotuner also tunes this fixed antenna system on 30m and 17m. Happy New Year, Cecil. Really neat design. Can you describe the balun you used? Thanks, Jim, AC6XG |
Interesting 144 foot Dipole
Jim Kelley wrote:
Can you describe the balun you used? When one feeds the antenna system at a current maximum point, the balun is non-critical. I am presently using ten turns of RG-400 on an FT-240-61 toroid with no measurable common mode current on an MFJ-853. As you know, the stress on the balun is reduced when the resonant current maximum point is located at the output of the balun-choke. That's another bonus for the matching system that I use. -- 73, Cecil http://www.w5dxp.com |
Choke balun (was: Interesting 144 foot Dipole)
Cecil Moore wrote:
When one feeds the antenna system at a current maximum point, the balun is non-critical. I am presently using ten turns of RG-400 on an FT-240-61 toroid with no Hi Cecil, It seems like it's been a decade since we debated on RRAP. I hope all is well with you. I plan on erecting a multi-band inverted V with several insulators and associated shorting connectors along each leg so that with all connectors open, the antenna is resonant on 10m; with the first insulator on each leg shorted, the antenna is resonant on 15m; with the first and second insulators on each leg shorted the antenna is resonant on 20m; et cetera. Shorting and opening insulators is easier than winding accurate chokes! For a balun, I'm considering N4UJW's "Ugly Balun" (see http://www.hamuniverse.com/balun.html). UJW leaves the diameter of the coil form to the reader, only specifying that 18-21 feet of coax be used. Can you (or anyone else on RRAA) tell me if there is an optimum diameter, considering that most of my operations will be on 20m? (On that page, UJW has two balun projects -- see the first one.) Warmest regards, Jeff KH6O Chief Petty Officer, U.S. Coast Guard Mathematics Lecturer, University of Hawaii System -- |
Choke balun
Jeffrey Herman wrote:
Hi Cecil, It seems like it's been a decade since we debated on RRAP. I hope all is well with you. Things are terrible. I can't dunk a basketball anymore. :-) Good to hear from you. For a balun, I'm considering N4UJW's "Ugly Balun" (see http://www.hamuniverse.com/balun.html). UJW leaves the diameter of the coil form to the reader, only specifying that 18-21 feet of coax be used. Can you (or anyone else on RRAA) tell me if there is an optimum diameter, considering that most of my operations will be on 20m? This subject was recently beat to death over on QRZ.com or eHam.net, I can't remember which. Here's some actual measurements showing how the choking impedance varies with frequency: http://www.k1ttt.net/technote/airbalun.html An ugly balun (N turns of coax) will not cover a 10:1 frequency range very well. If it performs well on 10m, it doesn't have very much choking impedance on 80m. If it performs well on 80m, it will have reached its series resonant low impedance point before it reaches 10m. An ugly balun performs reasonably well over a 3:1 frequency range. And the choking problem worsens considerably with non-resonant antenna systems. However, the necessary choking impedance is minimized if the antenna is low impedance resonant as yours will be. I made some measurements on 20 turns of coax on a 2 liter pop bottle. It was parallel resonant at 14 MHz (good high impedance) and series resonant at 28 MHz (bad low impedance). It would probably function pretty well from 40m to 15m. A toroidal 1:1 choke-balun is much more broadbanded than an ugly balun. For your antenna, ten turns of RG-400 on a FT-240-61 toroid would, like mine, be good enough. The AB-240-kit contains that toroid and comes with instructions for winding a 1:1 choke-balun, all for $9. However, I would not recommend that balun for non- resonant antenna systems where three of those toroids stacked would be about right. That web page is at: http://www.amidoncorp.com/aai_cost_experimenter.htm -- 73, Cecil http://www.w5dxp.com |
Choke balun (was: Interesting 144 foot Dipole)
"Jeffrey Herman" wrote in message ... Cecil Moore wrote: When one feeds the antenna system at a current maximum point, the balun is non-critical. I am presently using ten turns of RG-400 on an FT-240-61 toroid with no Hi Cecil, It seems like it's been a decade since we debated on RRAP. I hope all is well with you. I plan on erecting a multi-band inverted V with several insulators and associated shorting connectors along each leg so that with all connectors open, the antenna is resonant on 10m; with the first insulator on each leg shorted, the antenna is resonant on 15m; with the first and second insulators on each leg shorted the antenna is resonant on 20m; et cetera. Shorting and opening insulators is easier than winding accurate chokes! For a balun, I'm considering N4UJW's "Ugly Balun" (see http://www.hamuniverse.com/balun.html). UJW leaves the diameter of the coil form to the reader, only specifying that 18-21 feet of coax be used. Can you (or anyone else on RRAA) tell me if there is an optimum diameter, considering that most of my operations will be on 20m? (On that page, UJW has two balun projects -- see the first one.) Warmest regards, Jeff KH6O Chief Petty Officer, U.S. Coast Guard Mathematics Lecturer, University of Hawaii System -- How do you plan on actuating the switches? I tried some knife swithes and thought I could switch them using a hook on a pole. This didnt work very well for an all band antenna. |
Choke balun
Jimmie D wrote:
How do you plan on actuating the switches? I tried some knife swithes and thought I could switch them using a hook on a pole. This didnt work very well for an all band antenna. When I was in high school, I built my dipole with a pulley at each end. For changing bands, I just let the dipole down and either installed or removed the jumper wires across the insulators. An Inv-V would only require one pulley. -- 73, Cecil http://www.w5dxp.com |
Choke balun
"Cecil Moore" wrote in message et... Jimmie D wrote: How do you plan on actuating the switches? I tried some knife swithes and thought I could switch them using a hook on a pole. This didnt work very well for an all band antenna. When I was in high school, I built my dipole with a pulley at each end. For changing bands, I just let the dipole down and either installed or removed the jumper wires across the insulators. An Inv-V would only require one pulley. -- 73, Cecil http://www.w5dxp.com Yeah I thought about this but was trying to stay away from raising and lowering the antenna. I used to have the antenna on a pulley but found that sometimes the neighbor kids would lower it for me. The ones who were doing it arent around anymore so I guess its safe to put it back up now. |
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