Helix antenna
in [Wireless Internet]
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From: miso on 8 Aug 2008 03:56 On Aug 7, 1:23 pm, jimmi...(a)gmail.com wrote: > 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 antennashttp://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. > > Ian is extremely knowledgable on the subject. > > Jimmie I could see the stacked yagis interacting. The problem with beam antennas is from the top and bottom, they more or less look like dipoles because the driven element is not shielded from those directions. I never stacked any beams, but if I did, I'd consider antenna designs that had what amounts to a corner reflector at the back of each antenna. That would shield the driven element. I've been trying to DF vertically polarized UHF signals with a yagi. I find it really hard to find a peak and suspect there is just too much gain from the dipole as view from top and bottom. I've DFed HF with loop using the null, and that works very well. The particular UHF signal is heavily modulated, so the cheap double ducky box doesn't work.
From: jimmie68 on 8 Aug 2008 16:20 On Aug 8, 3:56 am, m...(a)sushi.com wrote: > On Aug 7, 1:23 pm, jimmi...(a)gmail.com wrote: > > > > > > > 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 antennashttp://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. > > > Ian is extremely knowledgable on the subject. > > > Jimmie > > I could see the stacked yagis interacting. The problem with beam > antennas is from the top and bottom, they more or less look like > dipoles because the driven element is not shielded from those > directions. I never stacked any beams, but if I did, I'd consider > antenna designs that had what amounts to a corner reflector at the > back of each antenna. That would shield the driven element. > > I've been trying to DF vertically polarized UHF signals with a yagi. I > find it really hard to find a peak and suspect there is just too much > gain from the dipole as view from top and bottom. I've DFed HF with > loop using the null, and that works very well. The particular UHF > signal is heavily modulated, so the cheap double ducky box doesn't > work.- Hide quoted text - > > - Show quoted text - I use a "Little L-per" direction finder and sometimes use a Yagi with a little handheld VHF UHF radio. When I use the YAGI sometimes I turn it around backwards and search for the null instead of the peak. Also you need to check the pattern of your yagi. Some can be rather skewed from what you think they should be. Jimmie
From: miso on 8 Aug 2008 22:40 On Aug 8, 1:20 pm, jimmi...(a)gmail.com wrote: > On Aug 8, 3:56 am, m...(a)sushi.com wrote: > > > > > On Aug 7, 1:23 pm, jimmi...(a)gmail.com wrote: > > > > 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 antennashttp://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. > > > > Ian is extremely knowledgable on the subject. > > > > Jimmie > > > I could see the stacked yagis interacting. The problem with beam > > antennas is from the top and bottom, they more or less look like > > dipoles because the driven element is not shielded from those > > directions. I never stacked any beams, but if I did, I'd consider > > antenna designs that had what amounts to a corner reflector at the > > back of each antenna. That would shield the driven element. > > > I've been trying to DF vertically polarized UHF signals with a yagi. I > > find it really hard to find a peak and suspect there is just too much > > gain from the dipole as view from top and bottom. I've DFed HF with > > loop using the null, and that works very well. The particular UHF > > signal is heavily modulated, so the cheap double ducky box doesn't > > work.- Hide quoted text - > > > - Show quoted text - > > I use a "Little L-per" direction finder and sometimes use a Yagi with > a little handheld VHF UHF radio. When I use the YAGI sometimes I turn > it around backwards and search for the null instead of the peak. Also > you need to check the pattern of your yagi. Some can be rather skewed > from what you think they should be. > > Jimmie I've tried the backward yagi. The trouble is you get a lot of reflection. One oddball scheme I have used with control channels, ie. digital signals, is to view the eye pattern via software demodulation. The widest open eye corresponds to the cleanest and thus most direct signal. I've also done the "remove the antenna" trick once you get close. The L-per is a bit expensive for hobby use unless there are DIY scheme.
From: jimmie68 on 9 Aug 2008 19:48 On Aug 8, 10:40 pm, m...(a)sushi.com wrote: > On Aug 8, 1:20 pm, jimmi...(a)gmail.com wrote: > > > > > > > On Aug 8, 3:56 am, m...(a)sushi.com wrote: > > > > On Aug 7, 1:23 pm, jimmi...(a)gmail.com wrote: > > > > > 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 antennashttp://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. > > > > > Ian is extremely knowledgable on the subject. > > > > > Jimmie > > > > I could see the stacked yagis interacting. The problem with beam > > > antennas is from the top and bottom, they more or less look like > > > dipoles because the driven element is not shielded from those > > > directions. I never stacked any beams, but if I did, I'd consider > > > antenna designs that had what amounts to a corner reflector at the > > > back of each antenna. That would shield the driven element. > > > > I've been trying to DF vertically polarized UHF signals with a yagi. I > > > find it really hard to find a peak and suspect there is just too much > > > gain from the dipole as view from top and bottom. I've DFed HF with > > > loop using the null, and that works very well. The particular UHF > > > signal is heavily modulated, so the cheap double ducky box doesn't > > > work.- Hide quoted text - > > > > - Show quoted text - > > > I use a "Little L-per" direction finder and sometimes use a Yagi with > > a little handheld VHF UHF radio. When I use the YAGI sometimes I turn > > it around backwards and search for the null instead of the peak. Also > > you need to check the pattern of your yagi. Some can be rather skewed > > from what you think they should be. > > > Jimmie > > I've tried the backward yagi. The trouble is you get a lot of > reflection. One oddball scheme I have used with control channels, ie. > digital signals, is to view the eye pattern via software demodulation. > The widest open eye corresponds to the cleanest and thus most direct > signal. I've also done the "remove the antenna" trick once you get > close. > > The L-per is a bit expensive for hobby use unless there are DIY > scheme.- Hide quoted text - > > - Show quoted text - A variable attenuator in line with the Yagi will help a lot with reflections. I have one of those binary switch selected attenuators. I think it can switch in 3-20 db pads a 10, a 5, a 3 . If you can monitor the AGC voltage on the rx with a voltmeter this give a much better indication of the strongest signal than an S meter. I work at an airport an people used to think I was nuts but when I used to look for Emergency Locator Transmitters I would start by climping the Control Tower. By getting up high I didnt have as much problems with reflections and could often point directly at the offending aircraft from the catwalk of the tower. Jimmie
From: miso on 10 Aug 2008 00:56 On Aug 9, 4:48 pm, jimmi...(a)gmail.com wrote: > On Aug 8, 10:40 pm, m...(a)sushi.com wrote: > > > > > On Aug 8, 1:20 pm, jimmi...(a)gmail.com wrote: > > > > On Aug 8, 3:56 am, m...(a)sushi.com wrote: > > > > > On Aug 7, 1:23 pm, jimmi...(a)gmail.com wrote: > > > > > > 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 antennashttp://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm. > > > > > > Ian is extremely knowledgable on the subject. > > > > > > Jimmie > > > > > I could see the stacked yagis interacting. The problem with beam > > > > antennas is from the top and bottom, they more or less look like > > > > dipoles because the driven element is not shielded from those > > > > directions. I never stacked any beams, but if I did, I'd consider > > > > antenna designs that had what amounts to a corner reflector at the > > > > back of each antenna. That would shield the driven element. > > > > > I've been trying to DF vertically polarized UHF signals with a yagi.. I > > > > find it really hard to find a peak and suspect there is just too much > > > > gain from the dipole as view from top and bottom. I've DFed HF with > > > > loop using the null, and that works very well. The particular UHF > > > > signal is heavily modulated, so the cheap double ducky box doesn't > > > > work.- Hide quoted text - > > > > > - Show quoted text - > > > > I use a "Little L-per" direction finder and sometimes use a Yagi with > > > a little handheld VHF UHF radio. When I use the YAGI sometimes I turn > > > it around backwards and search for the null instead of the peak. Also > > > you need to check the pattern of your yagi. Some can be rather skewed > > > from what you think they should be. > > > > Jimmie > > > I've tried the backward yagi. The trouble is you get a lot of > > reflection. One oddball scheme I have used with control channels, ie. > > digital signals, is to view the eye pattern via software demodulation. > > The widest open eye corresponds to the cleanest and thus most direct > > signal. I've also done the "remove the antenna" trick once you get > > close. > > > The L-per is a bit expensive for hobby use unless there are DIY > > scheme.- Hide quoted text - > > > - Show quoted text - > > A variable attenuator in line with the Yagi will help a lot with > reflections. > > I have one of those binary switch selected attenuators. I think it can > switch in 3-20 db pads a 10, a 5, a 3 . If you can monitor the AGC > voltage on the rx with a voltmeter this give a much better indication > of the strongest signal than an S meter. > > I work at an airport an people used to think I was nuts but when I > used to look for Emergency Locator Transmitters I would start by > climping the Control Tower. By getting up high I didnt have as much > problems with reflections and could often point directly at the > offending aircraft from the catwalk of the tower. > > Jimmie I have a HP RF attenuator. I forgot to bring it with me when I was DFing these repeater sites, but will do so this time. I used a Minicircuits 4 way splitter as an adhoc attenuator, but it wasn't enough.
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