Re: Topband: no response to query: feeding phased verticals at half wave spacing
This is quite true although some patterns will be closer to theory than others. In a commercial phasor as is used for broadcast there are several elements that must be taken into account. The first is the matching at each vertical element. It must take the actual drive impedance of the elements and match to the transmission line (usually 50 ohms). These networks all have phase shift which must be taken into account as a part of the total system design. The next important element is the power divider. There are various designs but in the end they all permit the adjustment of power to each element so the currents are correct. The ARRL patterns are idealized examples where the current in both elements are equal but in the real world this is not often the case. A power divider also has phase shift. The final element is the means of making the phases of each tower the desired value while taking into account the fixed phase shift of the matching network and the power divider. There are two common methods used. The first is a lumped constant network which adds or subtracts phase to achieve the correct values after transmission line phase delay is added into the system. The other method is to use the transmission line to achieve the proper phase relationships. Even when transmission lines are used it is necessary to have a small lumped constant network to trim for minor variations in phase. It is apparent that such a system is very sensitive to a change in frequency. Adjusting a typical phased array requires a means of measuring impedance and typically there is a phase monitor which shows the phase and current ratio of each tower. This is all verified by field measurements that require a calibrated field intensity meter and a lot of paperwork to plot the pattern or a more complex (and expensive) GPS based measurement system. It should be obvious at this point that no amateur phased arrays are built as described above and do not have the same requirements. Commercial arrays are usually designed to provide protection to other stations on the same or adjacent frequencies. Amateur arrays are generally intended for gain in a desired direction and must have at least a small amount frequency agility. While the ARRL patterns are very much theoretical a few can be implemented for practical amateur use. The broadside two tower array spaced 180 degrees is probably the best if space is available. One drawback is the figure 8 pattern has zero db front to back ratio. This could be handled with a parasitic reflector but at the expense of more complexity and space. The bottom line is that practical amateur arrays will not achieve performance close to theoretical. On 11/24/11 10:59 AM, Rik van Riel wrote: > On 11/22/2011 08:06 PM, Gerry Treas, K8GT wrote: >> Hi Dale, >> >> I'm no antenna expert, but certainly read as much of the experts >> publications as I can get my hands on, but having a Teflon brain, it doesn't >> stick very well. >> >> That said, the ARRL Antenna Book has a page that shows the patterns of >> various spacings and phasings of vertical antennas, which I found very >> enlightening. >> > Enlightening, but also somewhat misleading... > > The patterns in the ARRL Antenna Book are correct if the > current in both elements is the same. > > However, if you feed an array of antennas with delay lines, > those delay lines will act as impedance transformers for > the antenna impedance of each element (like all feedlines do). > > This can result in each element getting different currents, > and the pattern no longer being what it was. > > This makes feeding a phased array with delay lines much > trickier than one would imagine at first glance. > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
- Original Message - From: "Rik van Riel" To: Sent: Thursday, November 24, 2011 10:59 AM Subject: Re: Topband: no response to query: feeding phased verticals at half wave spacing > On 11/22/2011 08:06 PM, Gerry Treas, K8GT wrote: >> Hi Dale, >> >> I'm no antenna expert, but certainly read as much of the experts >> publications as I can get my hands on, but having a Teflon brain, it >> doesn't stick very well. >> >> That said, the ARRL Antenna Book has a page that shows the patterns of >> various spacings and phasings of vertical antennas, which I found very >> enlightening. >> > Enlightening, but also somewhat misleading... > > The patterns in the ARRL Antenna Book are correct if the > current in both elements is the same. > > However, if you feed an array of antennas with delay lines, > those delay lines will act as impedance transformers for > the antenna impedance of each element (like all feedlines do). > > This can result in each element getting different currents, > and the pattern no longer being what it was. > > This makes feeding a phased array with delay lines much > trickier than one would imagine at first glance. For 2 elements coax phasing is sufficient if 15dB or a bit better F/B is acceptable especially when using low noise receiving antennas. I was more than satisfied with a pair of sloping wires on 160 (NE/SW cardiod, NW/SE figure 8) and was happy to not be wasting power in a dummy load. I used a noise bridge and the rig to cut the lines to exact lengths and about 18dB FB was the norm, sometimes a bit better or worse but I could also load it up to about 1950 in a contest without wasting more RF in a tuner. Carl KM1H ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
On 11/22/2011 08:06 PM, Gerry Treas, K8GT wrote: > Hi Dale, > > I'm no antenna expert, but certainly read as much of the experts publications > as I can get my hands on, but having a Teflon brain, it doesn't stick very > well. > > That said, the ARRL Antenna Book has a page that shows the patterns of > various spacings and phasings of vertical antennas, which I found very > enlightening. > Enlightening, but also somewhat misleading... The patterns in the ARRL Antenna Book are correct if the current in both elements is the same. However, if you feed an array of antennas with delay lines, those delay lines will act as impedance transformers for the antenna impedance of each element (like all feedlines do). This can result in each element getting different currents, and the pattern no longer being what it was. This makes feeding a phased array with delay lines much trickier than one would imagine at first glance. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
A wide spaced array offers many benefits when possible. In general the is less coupling between the elements results in better less mutual impedance interdependence. When enough space is available a simple Ham array would be 1/2 wave spaced elements fed from the center point with open wire. This will produce familiar figure 8 pattern where the major lobe is perpendicular to the line of the towers. Basically the energy if equal from both towers will cancel along the line of the towers but since the towers are in phase, points perpendicular, beginning at 45 degrees between the line of the towers will add in phase with the resultant lobe at 90 degrees. If the phasing is 180 degrees the energy will add along the line of the towers and also produce a figure 8 but rotated 90 degrees. A useful unidirectional mode with 180 degree spaced towers is 45 degree phasing which produces a wide forward lobe with deep nulls at an angle to the rear and a 'tail' peaking up at the rear. Towers spaced around 90 degrees produce better cardioid patterns. The ARRL Antenna Handbook goes into pretty detailed explanation of phased arrays and gets into multitower arrays, showing three and four tower designs. I would also suggest EZNEC as good entry modelling software. while with modeling the devil is always in how close to life the modeling details are, simple two towers models play out pretty well with basic models. If I had the space I would consider a 180 deg spaced two tower array with as I mentioned earlier open transmission with 4 positions. The first in the center for normal figure 8 operation, the second a transmission line to either one of the towers to rotate the figure 8 90 degrees and the third and forth to taps in either direction along the TX line to achieve 45 degree phasing for quasi unidirectional operation along the line of the towers in either direction. This would be one of the least expensive arrays that could be built with a minimum parts count. But have 360 deg coverage. On 11/22/11 8:06 PM, Gerry Treas, K8GT wrote: > Hi Dale, > > I'm no antenna expert, but certainly read as much of the experts publications > as I can get my hands on, but having a Teflon brain, it doesn't stick very > well. > > That said, the ARRL Antenna Book has a page that shows the patterns of > various spacings and phasings of vertical antennas, which I found very > enlightening. > > 73, Gerry, K8GT > > > Dale Long wrote: > > = > Gentlemen: > > > > I am not one who thinks the whole world revolves around my concerns. And I > recognize that some research on my part may be necessary. ( I have read > ON4UN's Low-Band Dxing) > > > > But I do think this is a reasonable question, and think that there are > knowledgeable folks who might provide some advice. Unfortunately I have > never done any antenna modeling. > > > > Please let me know your thoughts. > > > > Thanks, > > > > Dale N3BNA > > > > From: Dale Long [mailto:dale.l...@prodigy.net] > Sent: Saturday, November 19, 2011 3:05 PM > To: 'Topband@contesting.com' > Subject: feeding phased verticals at half wave spacing > > > > Gentlemen: > > > > I have been told repeatedly that phased verticals should be spaced 1/4 > wavelength apart. Ok, I am willing to accept that. > > > > My question is if you have verticals that are 1/2 wave apart, would it not > give some pattern, whatever that should be? > > > > If you were looking for an endfire pattern how should you feed such > verticals? > > > > If you have specific questions, you may contact me directly at > dale.l...@prodigy.net > > > > Thanks and 73, > > > > Dale N3BNA > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
There is no single spacing for phased elements. There is a continuous variation of both spacing and phasing which has a gazillion outcomes. Two antennas spaced a halfwave apart and fed 180 degrees out of phase are only one configuration that will exhibit an end-fire pattern. The answer to seeing the nearly infinite variability to antennas, spacing and phasing is called EZNEC or one of the other antenna modeling programs. It's the first place to go to see what stuff will do. EZNEC is a particularly good modeling program and well worth the cost. The help section in it is very extensive, and exceptionally well written in a format that makes it completely searchable. It has a start easy section that is as good as stuff like that ever gets. 73, Guy. On Tue, Nov 22, 2011 at 9:16 AM, Dale Long wrote: > Gentlemen: > > > > I am not one who thinks the whole world revolves around my concerns. And I > recognize that some research on my part may be necessary. ( I have read > ON4UN's Low-Band Dxing) > > > > But I do think this is a reasonable question, and think that there are > knowledgeable folks who might provide some advice. Unfortunately I have > never done any antenna modeling. > > > > Please let me know your thoughts. > > > > Thanks, > > > > Dale N3BNA > > > > From: Dale Long [mailto:dale.l...@prodigy.net] > Sent: Saturday, November 19, 2011 3:05 PM > To: 'Topband@contesting.com' > Subject: feeding phased verticals at half wave spacing > > > > Gentlemen: > > > > I have been told repeatedly that phased verticals should be spaced 1/4 > wavelength apart. Ok, I am willing to accept that. > > > > My question is if you have verticals that are 1/2 wave apart, would it not > give some pattern, whatever that should be? > > > > If you were looking for an endfire pattern how should you feed such > verticals? > > > > If you have specific questions, you may contact me directly at > dale.l...@prodigy.net > > > > Thanks and 73, > > > > Dale N3BNA > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: no response to query: feeding phased verticals at half wave spacing
Hi Dale, I'm no antenna expert, but certainly read as much of the experts publications as I can get my hands on, but having a Teflon brain, it doesn't stick very well. That said, the ARRL Antenna Book has a page that shows the patterns of various spacings and phasings of vertical antennas, which I found very enlightening. 73, Gerry, K8GT Dale Long wrote: = Gentlemen: I am not one who thinks the whole world revolves around my concerns. And I recognize that some research on my part may be necessary. ( I have read ON4UN's Low-Band Dxing) But I do think this is a reasonable question, and think that there are knowledgeable folks who might provide some advice. Unfortunately I have never done any antenna modeling. Please let me know your thoughts. Thanks, Dale N3BNA From: Dale Long [mailto:dale.l...@prodigy.net] Sent: Saturday, November 19, 2011 3:05 PM To: 'Topband@contesting.com' Subject: feeding phased verticals at half wave spacing Gentlemen: I have been told repeatedly that phased verticals should be spaced 1/4 wavelength apart. Ok, I am willing to accept that. My question is if you have verticals that are 1/2 wave apart, would it not give some pattern, whatever that should be? If you were looking for an endfire pattern how should you feed such verticals? If you have specific questions, you may contact me directly at dale.l...@prodigy.net Thanks and 73, Dale N3BNA ___ UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: no response to query: feeding phased verticals at half wave spacing
Gentlemen: I am not one who thinks the whole world revolves around my concerns. And I recognize that some research on my part may be necessary. ( I have read ON4UN's Low-Band Dxing) But I do think this is a reasonable question, and think that there are knowledgeable folks who might provide some advice. Unfortunately I have never done any antenna modeling. Please let me know your thoughts. Thanks, Dale N3BNA From: Dale Long [mailto:dale.l...@prodigy.net] Sent: Saturday, November 19, 2011 3:05 PM To: 'Topband@contesting.com' Subject: feeding phased verticals at half wave spacing Gentlemen: I have been told repeatedly that phased verticals should be spaced 1/4 wavelength apart. Ok, I am willing to accept that. My question is if you have verticals that are 1/2 wave apart, would it not give some pattern, whatever that should be? If you were looking for an endfire pattern how should you feed such verticals? If you have specific questions, you may contact me directly at dale.l...@prodigy.net Thanks and 73, Dale N3BNA ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
