Helix antenna
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From: miso on 2 Aug 2008 16:31 On Aug 2, 8:58 am, Jeff Liebermann <je...(a)cruzio.com> wrote: > On Fri, 1 Aug 2008 23:18:03 -0700 (PDT), m...(a)sushi.com wrote: > >On Aug 1, 1:33 pm, jimmi...(a)gmail.com wrote: > >> Usually paralelling(stacking) antennas means a narrower bandwidth. > >> This statement assumes all the stacked antennas are identical. > >> Jimmie > >I see no reason for stacked antennas to have a narrower bandwidth. Can > >you elaborate? > > If your definition of bandwidth is the frequency between the -3dB > points, stacking two isolated resonant antennas together results in > exactly the same bandwidth as one antenna. An easier way to see this > is if the two antennas were simple parallel tuned circuits acting as a > bandpass filter. If you connect them together, using some means of > coupling that is critically coupled (i.e. maximum power tranfer), the > resultant circuit has exactly the same bandwidth. If you plot it on a > piece of graph paper, you could stack a dozen critically coupled tuned > circuits together and get exactly the same -3dB bandwidth. Obviously > the skirt factor and bandwidth at other refrence points will be > narrower as you add sections. > > Of course, such things fall apart when dealing with real world devices > and antennas. Two stacked antennas will couple to each other, causing > difficulties with such simplistic explanations. The traditional 2x2 > array of helixes heavily couple to each other, especially since > they're the same sense. Anyway, the only way to get it right is to > fire up your favorite NEC antenna modeling program, which takes such > things into consideration. 4NEC2 includes a helix generator. > > Specifically for a helix, the approximate -3dB bandwidth for a single > helix is roughly equal to the center frequency. In other words, if > you cut a helix for 2.4GHz, it will be usable from 1.2 to 3.6Ghz. > Stacking 4 of these together will theoretically not reduce this > bandwidth, but in reality, will reduce it somewhat. I don't think > operation in an 83.5MHz band is going to be affected with an antenna > with a 1 or 2Ghz bandwidth. > > -- > Jeff Liebermann je...(a)cruzio.com > 150 Felker St #D http://www.LearnByDestroying.com > Santa Cruz CA 95060http://802.11junk.com > Skype: JeffLiebermann AE6KS 831-336-2558 How about the impedance matching scheme? That must narrow the bandwidth. Also your comments on mixing Al and Cu?
From: jimmie68 on 2 Aug 2008 23:58 On Aug 2, 2:18 am, m...(a)sushi.com wrote: > On Aug 1, 1:33 pm, jimmi...(a)gmail.com wrote: > > > > > > > On Jul 31, 1:12 am, m...(a)sushi.com wrote: > > > > On Jul 30, 1:57 pm, jimmi...(a)gmail.com wrote: > > > > > On Jul 29, 11:47 pm, m...(a)sushi.com wrote: > > > > > > On Jul 29, 1:52 pm, jimmi...(a)gmail.com wrote: > > > > > > > In WiFi is there any standard convention for the polarity of a helical > > > > > > antenna. I am building a 40 turn unit and wanted to know whether I > > > > > > should build it right or left handed. > > > > > > > Yes I know this will only matter when trying to connect with other > > > > > > systems that use circular polarity. > > > > > > > Jimmie > > > > > > Please post how it works out. Also, have you considered building a 4 > > > > > 10 turn helix (heli?) and run in parallel. That gets around the > > > > > matching issue. > > > > > Yes, I thought about that but I have plans for the 40 turn unit > > > > including the matching device. Also I have access to a Network > > > > Analyzer and S pararamter test set for tuning it up. I think building > > > > the matching network may be easier than build a phasing harness for 4 > > > > Helix antennas. However I have never done this before so plans may > > > > change. Who knows, if things work out OK I may build a 4 X 40 turn > > > > device. > > > > > Jimmie > > > > My guess is paralleling the 4 helix antennas would have a broader > > > bandwidth than the impedance matched solution. Broadband is good in > > > the sense that it allows for more error in the construction.- Hide quoted text - > > > > - Show quoted text - > > > Usually paralelling(stacking) antennas means a narrower bandwidth. > > This statement assumes all the stacked antennas are identical. > > > Jimmie > > I see no reason for stacked antennas to have a narrower bandwidth. Can > you elaborate?- Hide quoted text - > > - Show quoted text - Sorry I was thinking of bandwidth in terms of frequency versus VSWR. This is usally the limiting factor as gain bandwidth is almost always much broader than VSWR bandwidth. As of yet I dont know whether this will be a serious consequence or not concerning the helix antenna. My plan is to build the antenna and tune it for greatest field strength A few years ago I stacked 2 2 meter 6 element quad antennas. I had plans to stack 4 but didnt do it because of the VSWR excursion from one end of the band to the other. My solidstate amp was not fond of the 2 to 1 VSWR near the band edges. In this situation the VSWR bandwidth of 2 antennas was less than 1 antenna and with 4 antennas it was even less. I am sure the array would have still exhibited considerable gain if I had a way to readily correct for the impedance changes seen by my amplifier. Jimmie
From: miso on 3 Aug 2008 23:49 On Aug 2, 8:58 pm, jimmi...(a)gmail.com wrote: > On Aug 2, 2:18 am, m...(a)sushi.com wrote: > > > > > On Aug 1, 1:33 pm, jimmi...(a)gmail.com wrote: > > > > On Jul 31, 1:12 am, m...(a)sushi.com wrote: > > > > > On Jul 30, 1:57 pm, jimmi...(a)gmail.com wrote: > > > > > > On Jul 29, 11:47 pm, m...(a)sushi.com wrote: > > > > > > > On Jul 29, 1:52 pm, jimmi...(a)gmail.com wrote: > > > > > > > > In WiFi is there any standard convention for the polarity of a helical > > > > > > > antenna. I am building a 40 turn unit and wanted to know whether I > > > > > > > should build it right or left handed. > > > > > > > > Yes I know this will only matter when trying to connect with other > > > > > > > systems that use circular polarity. > > > > > > > > Jimmie > > > > > > > Please post how it works out. Also, have you considered building a 4 > > > > > > 10 turn helix (heli?) and run in parallel. That gets around the > > > > > > matching issue. > > > > > > Yes, I thought about that but I have plans for the 40 turn unit > > > > > including the matching device. Also I have access to a Network > > > > > Analyzer and S pararamter test set for tuning it up. I think building > > > > > the matching network may be easier than build a phasing harness for 4 > > > > > Helix antennas. However I have never done this before so plans may > > > > > change. Who knows, if things work out OK I may build a 4 X 40 turn > > > > > device. > > > > > > Jimmie > > > > > My guess is paralleling the 4 helix antennas would have a broader > > > > bandwidth than the impedance matched solution. Broadband is good in > > > > the sense that it allows for more error in the construction.- Hide quoted text - > > > > > - Show quoted text - > > > > Usually paralelling(stacking) antennas means a narrower bandwidth. > > > This statement assumes all the stacked antennas are identical. > > > > Jimmie > > > I see no reason for stacked antennas to have a narrower bandwidth. Can > > you elaborate?- Hide quoted text - > > > - Show quoted text - > > Sorry I was thinking of bandwidth in terms of frequency versus VSWR. > This is usally the limiting factor as gain bandwidth is almost always > much broader > than VSWR bandwidth. > As of yet I dont know whether this will be a serious consequence or > not concerning the helix antenna. > > My plan is to build the antenna and tune it for greatest field > strength > > A few years ago I stacked 2 2 meter 6 element quad antennas. I had > plans to stack 4 but didnt do it because > of the VSWR excursion from one end of the band to the other. > My solidstate amp was not fond of the 2 to 1 VSWR near the band edges. > > In this situation the VSWR bandwidth of 2 antennas was less than 1 > antenna and with 4 antennas it was even less. > I am sure the array would have still exhibited considerable gain if I > had a way to readily correct for the impedance changes seen by my > amplifier. > > Jimmie I wonder if the VSWR effects were due to coupling between antennas?
From: jimmie68 on 7 Aug 2008 16:16 On Aug 3, 11:49 pm, m...(a)sushi.com wrote: > On Aug 2, 8:58 pm, jimmi...(a)gmail.com wrote: > > > > > > > On Aug 2, 2:18 am, m...(a)sushi.com wrote: > > > > On Aug 1, 1:33 pm, jimmi...(a)gmail.com wrote: > > > > > On Jul 31, 1:12 am, m...(a)sushi.com wrote: > > > > > > On Jul 30, 1:57 pm, jimmi...(a)gmail.com wrote: > > > > > > > On Jul 29, 11:47 pm, m...(a)sushi.com wrote: > > > > > > > > On Jul 29, 1:52 pm, jimmi...(a)gmail.com wrote: > > > > > > > > > In WiFi is there any standard convention for the polarity of a helical > > > > > > > > antenna. I am building a 40 turn unit and wanted to know whether I > > > > > > > > should build it right or left handed. > > > > > > > > > Yes I know this will only matter when trying to connect with other > > > > > > > > systems that use circular polarity. > > > > > > > > > Jimmie > > > > > > > > Please post how it works out. Also, have you considered building a 4 > > > > > > > 10 turn helix (heli?) and run in parallel. That gets around the > > > > > > > matching issue. > > > > > > > Yes, I thought about that but I have plans for the 40 turn unit > > > > > > including the matching device. Also I have access to a Network > > > > > > Analyzer and S pararamter test set for tuning it up. I think building > > > > > > the matching network may be easier than build a phasing harness for 4 > > > > > > Helix antennas. However I have never done this before so plans may > > > > > > change. Who knows, if things work out OK I may build a 4 X 40 turn > > > > > > device. > > > > > > > Jimmie > > > > > > My guess is paralleling the 4 helix antennas would have a broader > > > > > bandwidth than the impedance matched solution. Broadband is good in > > > > > the sense that it allows for more error in the construction.- Hide quoted text - > > > > > > - Show quoted text - > > > > > Usually paralelling(stacking) antennas means a narrower bandwidth. > > > > This statement assumes all the stacked antennas are identical. > > > > > Jimmie > > > > I see no reason for stacked antennas to have a narrower bandwidth. Can > > > you elaborate?- Hide quoted text - > > > > - Show quoted text - > > > Sorry I was thinking of bandwidth in terms of frequency versus VSWR. > > This is usally the limiting factor as gain bandwidth is almost always > > much broader > > than VSWR bandwidth. > > As of yet I dont know whether this will be a serious consequence or > > not concerning the helix antenna. > > > My plan is to build the antenna and tune it for greatest field > > strength > > > A few years ago I stacked 2 2 meter 6 element quad antennas. I had > > plans to stack 4 but didnt do it because > > of the VSWR excursion from one end of the band to the other. > > My solidstate amp was not fond of the 2 to 1 VSWR near the band edges. > > > In this situation the VSWR bandwidth of 2 antennas was less than 1 > > antenna and with 4 antennas it was even less. > > I am sure the array would have still exhibited considerable gain if I > > had a way to readily correct for the impedance changes seen by my > > amplifier. > > > Jimmie > > I wonder if the VSWR effects were due to coupling between antennas?- Hide quoted text - > > - Show quoted text - I dont know, the antennas came with printouts from NEC antenna modeling software. One of the parameters given was a diagram of their capture area. The antennas were place according to this data with their capture areas just touching. A local ham who is very much into antenna modeling verified the data that came with the antennas. At the time I was surprised by the reccomenced spacing thinking it was excessive until I discovered that rules saying 1/2 or 5/8 spacing was not always correct.
From: jimmie68 on 7 Aug 2008 16:23 On Aug 7, 4:16 pm, jimmi...(a)gmail.com wrote: > On Aug 3, 11:49 pm, m...(a)sushi.com wrote: > > > > > > > On Aug 2, 8:58 pm, jimmi...(a)gmail.com wrote: > > > > On Aug 2, 2:18 am, m...(a)sushi.com wrote: > > > > > On Aug 1, 1:33 pm, jimmi...(a)gmail.com wrote: > > > > > > On Jul 31, 1:12 am, m...(a)sushi.com wrote: > > > > > > > On Jul 30, 1:57 pm, jimmi...(a)gmail.com wrote: > > > > > > > > On Jul 29, 11:47 pm, m...(a)sushi.com wrote: > > > > > > > > > On Jul 29, 1:52 pm, jimmi...(a)gmail.com wrote: > > > > > > > > > > In WiFi is there any standard convention for the polarity of a helical > > > > > > > > > antenna. I am building a 40 turn unit and wanted to know whether I > > > > > > > > > should build it right or left handed. > > > > > > > > > > Yes I know this will only matter when trying to connect with other > > > > > > > > > systems that use circular polarity. > > > > > > > > > > Jimmie > > > > > > > > > Please post how it works out. Also, have you considered building a 4 > > > > > > > > 10 turn helix (heli?) and run in parallel. That gets around the > > > > > > > > matching issue. > > > > > > > > Yes, I thought about that but I have plans for the 40 turn unit > > > > > > > including the matching device. Also I have access to a Network > > > > > > > Analyzer and S pararamter test set for tuning it up. I think building > > > > > > > the matching network may be easier than build a phasing harness for 4 > > > > > > > Helix antennas. However I have never done this before so plans may > > > > > > > change. Who knows, if things work out OK I may build a 4 X 40 turn > > > > > > > device. > > > > > > > > Jimmie > > > > > > > My guess is paralleling the 4 helix antennas would have a broader > > > > > > bandwidth than the impedance matched solution. Broadband is good in > > > > > > the sense that it allows for more error in the construction.- Hide quoted text - > > > > > > > - Show quoted text - > > > > > > Usually paralelling(stacking) antennas means a narrower bandwidth.. > > > > > This statement assumes all the stacked antennas are identical. > > > > > > Jimmie > > > > > I see no reason for stacked antennas to have a narrower bandwidth. Can > > > > you elaborate?- Hide quoted text - > > > > > - Show quoted text - > > > > Sorry I was thinking of bandwidth in terms of frequency versus VSWR. > > > This is usally the limiting factor as gain bandwidth is almost always > > > much broader > > > than VSWR bandwidth. > > > As of yet I dont know whether this will be a serious consequence or > > > not concerning the helix antenna. > > > > My plan is to build the antenna and tune it for greatest field > > > strength > > > > A few years ago I stacked 2 2 meter 6 element quad antennas. I had > > > plans to stack 4 but didnt do it because > > > of the VSWR excursion from one end of the band to the other. > > > My solidstate amp was not fond of the 2 to 1 VSWR near the band edges.. > > > > In this situation the VSWR bandwidth of 2 antennas was less than 1 > > > antenna and with 4 antennas it was even less. > > > I am sure the array would have still exhibited considerable gain if I > > > had a way to readily correct for the impedance changes seen by my > > > amplifier. > > > > Jimmie > > > I wonder if the VSWR effects were due to coupling between antennas?- Hide quoted text - > > > - Show quoted text - > > I dont know, the antennas came with printouts from NEC antenna > modeling software. One of the parameters given was a diagram of their > capture area. The antennas were place according to this data with > their capture areas just touching. A local ham who is very much into > antenna modeling verified the data that came with the antennas. At the > time I was surprised by the reccomenced spacing thinking it was > excessive until I discovered that rules saying 1/2 or 5/8 spacing was > not always correct.- Hide quoted text - > > - Show quoted text - Source of info on stacking antennas http://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. Ian is extremely knowledgable on the subject. Jimmie
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