| Page 1 of 2 | 1 | 2 |
|
|
Incoming radio wave polarisation
I have on order a tilting system for my antenna to probe the
polarisation of incoming signals for maximum audio clarity and gain. There are instruments out there that can automatically tell you the polarisation without one taking the trouble to pan the antenna in different directions. Anybody out there follow such a procedure with the antenna or use a homebrew or commercial instrument to save time? Regards Art |
Incoming radio wave polarisation
In article ,
"AI4QJ" wrote: "Art Unwin" wrote in message ... I have on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain. There are instruments out there that can automatically tell you the polarisation without one taking the trouble to pan the antenna in different directions. Anybody out there follow such a procedure with the antenna or use a homebrew or commercial instrument to save time? Regards Art How do you change the polarity of a helical antenna? You wind the Helix in the OPPOSITE Direction....... Duh..... |
Incoming radio wave polarisation
On Sat, 15 Mar 2008 08:52:01 -0700 (PDT), Art Unwin
wrote: Anybody out there follow such a procedure with the antenna Phase steerable array. 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
On Sat, 15 Mar 2008 14:32:57 -0400, "AI4QJ" wrote:
How do you change the polarity of a helical antenna? Swap the feeds. 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
"AI4QJ" wrote in
: "Richard Clark" wrote in message ... On Sat, 15 Mar 2008 14:32:57 -0400, "AI4QJ" wrote: How do you change the polarity of a helical antenna? Swap the feeds. Ha ha Richard, I assume you are aware that this is a joke given that a helical antenna is circularly polarized. I am not so sure about this AI4QJ, perhaps you have a different understanding of the meaning of circular polarisation to most of us. Owen |
Incoming radio wave polarisation
Art Unwin wrote: I have on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain. There are instruments out there that can automatically tell you the polarisation without one taking the trouble to pan the antenna in different directions. Never saw one that didn't need an antenna capable of being switched (either electronically or machanically) beween different polarizations. Which instrument did you see? Alan |
Incoming radio wave polarisation
"AI4QJ" wrote in
: .... Are you talking about the possibility of Art communicating with other people who are transmitting on similar helical circularly polarized antennas where CW vs CCW direction must be considered? I dismissed If this is his compact wonder, it is probably not an axial mode helical. (I don't know that one could ever describe an axial mode helical as 'compact'.) Normal mode helicals deliver linear polarisation. this possibility entirely. Most hams's signals arrive either veritcal, norizontal or somewhere in between (not rotating) originating at a linear polarized source. Is he communicating with satellites? I really haven't heard of helix antennas on the HF bands other than the Unwin compact model. If so, then yes, you can only switch the feedpoint to Normal mode helicals are commonly used on HF. change from CW to CCW and that can make a BIG difference in gain. The probability of Art finding another HF helical to QSO with should be negligible to null. Satellites are another matter. Owen |
Incoming radio wave polarisation
On Mar 16, 12:55 am, Owen Duffy wrote:
"AI4QJ" wrote : ... Are you talking about the possibility of Art communicating with other people who are transmitting on similar helical circularly polarized antennas where CW vs CCW direction must be considered? I dismissed If this is his compact wonder, it is probably not an axial mode helical. (I don't know that one could ever describe an axial mode helical as 'compact'.) Normal mode helicals deliver linear polarisation. this possibility entirely. Most hams's signals arrive either veritcal, norizontal or somewhere in between (not rotating) originating at a linear polarized source. Is he communicating with satellites? I really haven't heard of helix antennas on the HF bands other than the Unwin compact model. If so, then yes, you can only switch the feedpoint to Normal mode helicals are commonly used on HF. change from CW to CCW and that can make a BIG difference in gain. The probability of Art finding another HF helical to QSO with should be negligible to null. Satellites are another matter. Owen See recent posting on E ham Art |
Incoming radio wave polarisation
In article ,
You wrote: In article , "AI4QJ" wrote: "Art Unwin" wrote in message ... I have on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain. There are instruments out there that can automatically tell you the polarisation without one taking the trouble to pan the antenna in different directions. Anybody out there follow such a procedure with the antenna or use a homebrew or commercial instrument to save time? Regards Art How do you change the polarity of a helical antenna? You wind the Helix in the OPPOSITE Direction....... Duh..... Just for "Grins" consider this..... What Polorization would you get if you mounted the Dipole Feed of a Corner Reflector Antenna, at 45° instead of inline with the Axis of the Reflector? |
Incoming radio wave polarisation
Art wrote:
"Normal mode helicals are commonly used on HF." Yes. Such antennas include small diameter coils making up solenoids. The turns act as small stacked loops. A small loop acts as a short dipole but with its E and H fields interchanged. See page 58 of the 3rd edition of "Antennas" by Kraus, Marthefka, et al. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
On Mar 16, 2:48 pm, (Richard Harrison)
wrote: Art wrote: "Normal mode helicals are commonly used on HF." Yes. Such antennas include small diameter coils making up solenoids. The turns act as small stacked loops. A small loop acts as a short dipole but with its E and H fields interchanged. See page 58 of the 3rd edition of "Antennas" by Kraus, Marthefka, et al. Best regards, Richard Harrison, KB5WZI I did not say that. The quote is from somewhere else. I am sure that he will be happy about the facts that you have revealed to him as a personal favor and a book that he can read up for himself what "Normal mode" means Then explain it to you so you understand what you read In the mean time I will try loading up a solenoid on 20 M to see how many people are using them.. |
Incoming radio wave polarisation
Art wrote:
"I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
I apologize to Art Unwin. It was Owen Duffy who wrote:
"Normal mode helicals are commonly used on HF." A normal mode helical antenna radiates perpendicularly to the axis of the helix. The axial mode helix antenna invented by John Kraus radiates in the direction of the axis of the helix. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
"Owen Duffy" wrote in message ... "AI4QJ" wrote in : ... Are you talking about the possibility of Art communicating with other people who are transmitting on similar helical circularly polarized antennas where CW vs CCW direction must be considered? I dismissed If this is his compact wonder, it is probably not an axial mode helical. (I don't know that one could ever describe an axial mode helical as 'compact'.) Normal mode helicals deliver linear polarisation. this possibility entirely. Most hams's signals arrive either veritcal, norizontal or somewhere in between (not rotating) originating at a linear polarized source. Is he communicating with satellites? I really haven't heard of helix antennas on the HF bands other than the Unwin compact model. If so, then yes, you can only switch the feedpoint to Normal mode helicals are commonly used on HF. change from CW to CCW and that can make a BIG difference in gain. The probability of Art finding another HF helical to QSO with should be negligible to null. Satellites are another matter. Owen Hi Owen I have no disagreement with your thoughts. I do want to point out that the short helical antenna named Quad Helix does give good CP normal to the helix axis. Jerry KD6JDJ |
Incoming radio wave polarisation
Art wrote:
"Anybody out there follow such a procedure with the antenna or use a homebrew or commercial instrument to save time?" Search on goniometer. I was doing my thing in Argentina when El Jefe or the boss called me into his office to ask me why my assistant had requisitioned a goniometer instead of the company doctor. I had to explain that it was not a medical diagnostic instrument. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
My apology to Edmund A. Laport, author of a marvelous book: "Radio
Antenna Engineering". He does not add an "e" after the "t" in his name. I was the culprit that did it in an earlier post. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
"Jerry" wrote in
news:dniDj.714$Nr1.510@trnddc01: .... Hi Owen I have no disagreement with your thoughts. I do want to point out that the short helical antenna named Quad Helix does give good CP normal to the helix axis. Hi Jerry, John Kraus' explanation of "normal mode" is where the radiation normal to the helix axis dominates. On that basis, the Quad Helix (which he discusses in his book) is neither an axial mode helix nor a normal mode helix, it is large enough that it has significant radiation both normal and axial, but not large enough to be dominated by the axial lobe, and it is a multi-filar helix which allows CP normal to the helix axis. The Quadrifilar Helix is an interesting antenna, and I was aware of your particular interest from previous reading. I don't know of a mono-filar normal mode helix that gives CP, but I expect that two of them with phased feeds could be used in the same way as crossed dipoles. We are of course all guessing what Art had in mind, there is a conspicous and familiar lack of coherent detail. Owen |
Incoming radio wave polarisation
"Owen Duffy" wrote in message ... "Jerry" wrote in news:dniDj.714$Nr1.510@trnddc01: ... Hi Owen I have no disagreement with your thoughts. I do want to point out that the short helical antenna named Quad Helix does give good CP normal to the helix axis. Hi Jerry, John Kraus' explanation of "normal mode" is where the radiation normal to the helix axis dominates. On that basis, the Quad Helix (which he discusses in his book) is neither an axial mode helix nor a normal mode helix, it is large enough that it has significant radiation both normal and axial, but not large enough to be dominated by the axial lobe, and it is a multi-filar helix which allows CP normal to the helix axis. The Quadrifilar Helix is an interesting antenna, and I was aware of your particular interest from previous reading. I don't know of a mono-filar normal mode helix that gives CP, but I expect that two of them with phased feeds could be used in the same way as crossed dipoles. We are of course all guessing what Art had in mind, there is a conspicous and familiar lack of coherent detail. Owen Hi Owen Art who?? Again, I am in full agreement with you on the limited application of nthe term "Normal" to the radiation of a helix. In addition, I suspect there is little need to elaborate, but, if a person had need, he could make a bi-directional CP radiator from 1/2 of a Quad helix. Jerry KD6JDJ |
Incoming radio wave polarisation
Art Unwin wrote:
I have on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain. There are instruments out there that can automatically tell you the polarisation without one taking the trouble to pan the antenna in different directions. Anybody out there follow such a procedure with the antenna or use a homebrew or commercial instrument to save time? Regards Art There's lots of ways to do this. calibration is always an issue. For instance, two helices wound with opposite senses can be run through a variable combiner. (the helices can be on the same form, and are coincident. There'a variety of tripole antennas used for this sort of thing, too. 3 crossed short, resistively loaded dipoles or loops is also used. A very clever scheme uses half loops sticking out of a conductive sphere as a simultaneous E and H field probe. The electronics is all inside the sphere, and you bring the data out on fiber optics. |
Incoming radio wave polarisation
Richard Harrison wrote:
Art wrote: "I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. Or, use diversity combining. Several researchers in France have done work with this, and discovered there's very little correlation between the ordinary and extraordinary rays, so diversity combining is extremely effective on HF skywave paths. They used physically co-located antennas that had different polarization sensitivities (a loop and a whip, as I recall). E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Interference polarization is not necessarily the case. (I believe there are measurements that show it is essentially random). More what it is has to do with the antenna pattern of horizontal and vertical antennas for sources at ground level and reasonably close. For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
On Mar 17, 11:27 am, Jim Lux wrote:
Richard Harrison wrote: Art wrote: "I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. Or, use diversity combining. Several researchers in France have done work with this, and discovered there's very little correlation between the ordinary and extraordinary rays, so diversity combining is extremely effective on HF skywave paths. They used physically co-located antennas that had different polarization sensitivities (a loop and a whip, as I recall). E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Interference polarization is not necessarily the case. (I believe there are measurements that show it is essentially random). More what it is has to do with the antenna pattern of horizontal and vertical antennas for sources at ground level and reasonably close. For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation. Best regards, Richard Harrison, KB5WZI Jim' My 160M antenna is totaly at 70 feet. Not below or above. With the tilting and pan mechanism and a couple of relays it is possible to automate it so that every so often it will cycle thru all modes using the single antenna. When a louder signal arises then it is simple to stay on that polarisation .. This combiation thus is a reduction of land space required for two or more separate antennas. I was just curious as to what other hams were doing and it appears to be nothing in this area. Regards Art |
Incoming radio wave polarisation
On Mon, 17 Mar 2008 09:17:01 -0700, Jim Lux
wrote: run through a variable combiner Hi Jim, As Richard pointed out, a goniometer (what, a 100 years old already?) works fine for this. I bought one at a Ham swap when I was a teenager. I also pointed this goniometer/antenna application out to Arthur to demonstrate what he thought was novel was quite old (in reference to the work of Tosi and Bellini). Arthur does not acknowledge prior inventors, so this topic consistently re-emerges with a fair periodicity. It should reappear around July again. For those who want to see a schematic of the goniometer and antenna application, here is a perfectly good example: http://www.elektronikschule.de/~krau...ng%20-%205.htm 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
Richard Clark wrote:
On Mon, 17 Mar 2008 09:17:01 -0700, Jim Lux wrote: run through a variable combiner Hi Jim, As Richard pointed out, a goniometer (what, a 100 years old already?) works fine for this. A potential problem with a goniometers is that they aren't particularly broadband, although, I suppose that if the relative coupling ratios change with frequency, at least they're consistent. The example cited below is an example of this. You adjust for best null/peak on your desired signal, which is narrow band. The setting for one frequency isn't likely to be the same as the setting for another frequency. In an application where you want to combine multiple skywave paths, one probably wants something that can be automatically adjusted. I bought one at a Ham swap when I was a teenager. I also pointed this goniometer/antenna application out to Arthur to demonstrate what he thought was novel was quite old (in reference to the work of Tosi and Bellini). Arthur does not acknowledge prior inventors, so this topic consistently re-emerges with a fair periodicity. It should reappear around July again. For those who want to see a schematic of the goniometer and antenna application, here is a perfectly good example: http://www.elektronikschule.de/~krau...ng%20-%205.htm 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
Art Unwin wrote:
On Mar 17, 11:27 am, Jim Lux wrote: Richard Harrison wrote: Art wrote: "I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. Or, use diversity combining. Several researchers in France have done work with this, and discovered there's very little correlation between the ordinary and extraordinary rays, so diversity combining is extremely effective on HF skywave paths. They used physically co-located antennas that had different polarization sensitivities (a loop and a whip, as I recall). E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Interference polarization is not necessarily the case. (I believe there are measurements that show it is essentially random). More what it is has to do with the antenna pattern of horizontal and vertical antennas for sources at ground level and reasonably close. For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation. Best regards, Richard Harrison, KB5WZI Jim' My 160M antenna is totaly at 70 feet. Not below or above. With the tilting and pan mechanism and a couple of relays it is possible to automate it so that every so often it will cycle thru all modes using the single antenna. When a louder signal arises then it is simple to stay on that polarisation . This combiation thus is a reduction of land space required for two or more separate antennas. I was just curious as to what other hams were doing and it appears to be nothing in this area. Lots of hams have done things with polarization diversity combining for HF. Check out Ralph, W0RPK's site at: http://showcase.netins.net/web/wallio/POLAR.html He has some actual recorded levels over a 20-30 second interval on a 10m skywave signal. The problem with physically moving the antenna is that you need a fairly fast positioner, since the fades (in any one polarization) are on the order of 1 second. With a single antenna, you also don't know, a priori, which way to move it or when to move it (is that an overall fade, or is the polarization changing). You can use a scanning or dithering technique (much like conical scan for high gain parabolas), as long as the scan period is much less than the fading time scale. With two co-located antennas, you've got lots more possibilities, and with modern signal processing hardware, it's cheap. (and, of course, most FM car radios use some form of diversity combining these days, as do virtually all Wireless LAN access points) Regards Art |
Incoming radio wave polarisation
On Mar 17, 12:53 pm, Art Unwin wrote:
On Mar 17, 11:27 am, Jim Lux wrote: Richard Harrison wrote: Art wrote: "I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. Or, use diversity combining. Several researchers in France have done work with this, and discovered there's very little correlation between the ordinary and extraordinary rays, so diversity combining is extremely effective on HF skywave paths. They used physically co-located antennas that had different polarization sensitivities (a loop and a whip, as I recall). E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Interference polarization is not necessarily the case. (I believe there are measurements that show it is essentially random). More what it is has to do with the antenna pattern of horizontal and vertical antennas for sources at ground level and reasonably close. For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation. Best regards, Richard Harrison, KB5WZI Jim' My 160M antenna is totaly at 70 feet. Not below or above. With the tilting and pan mechanism and a couple of relays it is possible to automate it so that every so often it will cycle thru all modes using the single antenna. When a louder signal arises then it is simple to stay on that polarisation . This combiation thus is a reduction of land space required for two or more separate antennas. I was just curious as to what other hams were doing and it appears to be nothing in this area. Regards Art Jim, Allow mw to share my thoughts with you on my antenna design and where my experimental trail is leading. I say experimental because the trail cannot be pursued in the mind only unless one is absolutely sure one knows everything and thus cannot be faultedn I constantly experiment to prove that my mind is correct or corrected if experimentation proves it to be in error which thus require re evalution and redirection. without experimentaion you have nothing but a talking head sitting on a couch. My antenna is actually several antennas rolled up into one. As a contra wound helix on top of each other we have a ambidextrious antenna that with tilting provides horizontal and vertical polarisation because the windings and counter windings cancel each other out. If one circular sign al is dominant I expected the cancellation remainder will be added to the horizontal and vertical polarisation signal. At the same time eithe of the cancelled polarities can be issollated from all otheres by shorting it out. I also wanted purity of polarisation to which I have referred to in the past where signals are not at 90 degrees to earth but tipped 10 degrees plus. Hopefully this will all work out as I have solve the combination polarisation problem while keeping the readiator small enough for three degree movement. I have to do all this to first confirm that the direction that I am taking so I can move on to arrays using tilted radiators fashhioned in a a array in equilibrium where two degrees of freedom with respect to volume which is forcasted by the combination of Gauss with Maxwell. Obviously every structure has to have the ability of many experiments as possible to flush out any errors in my analysis as possible in the early stages. Fortunately my single radiator pursuit with respect to size came out o.k. and thus with the incoming mechanism for tilt and scan operation can now procede without the huge mechanical difficulties imposed by planar and large radiators. This comming portion of the experimental trail is of utmost im portance to ensure that the comming arrays are truly in equilibrium such that the spacings of the individual small radiators can be reduceded over those of planar arrays. In my work with the small signal radiator I have found it possible to make them directive such that it may well render the idea of small arrays as moot when considering the advances made by zeroing on the signal polarity and pursuing a delay phase addition circuit with what I have at present. A long trail that was started years ago which I find very rewarding where I can now see the light at the end of the tunnel. Best regards Art Unwin KB9MZ.....XG (uk) |
Incoming radio wave polarisation
On Mon, 17 Mar 2008 11:57:21 -0700, Jim Lux
wrote: In an application where you want to combine multiple skywave paths, one probably wants something that can be automatically adjusted. Hi Jim, That would be called a telephone. The objection to adjustments being necessary is duly noted; the same characterisitic is one that has been historically prized within the Ham world. My goniometer was untuned. 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
On Mar 17, 2:03 pm, Jim Lux wrote:
Art Unwin wrote: On Mar 17, 11:27 am, Jim Lux wrote: Richard Harrison wrote: Art wrote: "I have an on order a tilting system for my antenna to probe the polarisation of incoming signals for maximum audio clarity and gain." That may be interesting but do you ever recall cross polarization of an incoming ionosphere reflected signal being unreadable because polarization was wrong? So many different and quickly changing path variations exist in the ionosphere that the best antenna to use is based on probability. Or, use diversity combining. Several researchers in France have done work with this, and discovered there's very little correlation between the ordinary and extraordinary rays, so diversity combining is extremely effective on HF skywave paths. They used physically co-located antennas that had different polarization sensitivities (a loop and a whip, as I recall). E.A. Laporte says on page 215 of "Radio Antenna Engineering": "To make best use of this effect (randomness of ionospheric waves) it is desirable to employ complimentary antennas for transmitting and receiving." Most commercial HF circuits I`ve experienced and seen use horizontal polarization. It is because much severe man made interference arriving at a receiving antenna is vertically polarized. Interference polarization is not necessarily the case. (I believe there are measurements that show it is essentially random). More what it is has to do with the antenna pattern of horizontal and vertical antennas for sources at ground level and reasonably close. For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation. Best regards, Richard Harrison, KB5WZI Jim' My 160M antenna is totaly at 70 feet. Not below or above. With the tilting and pan mechanism and a couple of relays it is possible to automate it so that every so often it will cycle thru all modes using the single antenna. When a louder signal arises then it is simple to stay on that polarisation . This combiation thus is a reduction of land space required for two or more separate antennas. I was just curious as to what other hams were doing and it appears to be nothing in this area. Lots of hams have done things with polarization diversity combining for HF. Check out Ralph, W0RPK's site at:http://showcase.netins.net/web/wallio/POLAR.html He has some actual recorded levels over a 20-30 second interval on a 10m skywave signal. The problem with physically moving the antenna is that you need a fairly fast positioner, since the fades (in any one polarization) are on the order of 1 second. With a single antenna, you also don't know, a priori, which way to move it or when to move it (is that an overall fade, or is the polarization changing). You can use a scanning or dithering technique (much like conical scan for high gain parabolas), as long as the scan period is much less than the fading time scale. With two co-located antennas, you've got lots more possibilities, and with modern signal processing hardware, it's cheap. (and, of course, most FM car radios use some form of diversity combining these days, as do virtually all Wireless LAN access points) Regards Art Can't afford more land, I have to economise or do nothing Art |
Incoming radio wave polarisation
Jim Lux wrote:
"Interference polarization is not necessarily the case. --------For example, A horizontal antenna not too high over a ground plane has a null right at zero elevation." Good point. The worst noise is likely local and arrives via ground wave. Ground waves are vertically polarized because horizontal components of an electric field are exactly canceled at the surface of a perfect reflector. Examination of the radiation patterns of horizontal antennas confirms that they invariably have zero response at zero elevation on their best azimuths. From researching susceptibility of antennas to noise I came across a statement interesting to me in Terman`s 1955 opus on page 929: "----a loop antenna responds much less to the electric induction field than does a simple wire antenna of comparable intercept area. This is of importance because electric induction fields predominate in the man-made noise that causes disturbances in radio receivers, and this explains in part the popularity of loop antennas in broadcast receivers." Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
Richard Clark wrote:
On Mon, 17 Mar 2008 11:57:21 -0700, Jim Lux wrote: In an application where you want to combine multiple skywave paths, one probably wants something that can be automatically adjusted. Hi Jim, That would be called a telephone. Or a reliable communications system. The objection to adjustments being necessary is duly noted; the same characterisitic is one that has been historically prized within the Ham world. More knobs better? My goniometer was untuned. Most Iv'e seen are basically just coils and not designed to be narrow band. My comment was more that the transfer function varies not only as a function of the moving coil position, but also frequency. I suppose one could build a tuned one. 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
Examination of the radiation patterns of horizontal antennas confirms
that they invariably have zero response at zero elevation on their best azimuths. _____________ If this were true then most television broadcast stations would have nearly zero field strength near the earth over much of their present coverage areas. Instead, the fields there are directly related to the peak ERP of the TV station -- which typically is radiated in, or a few tenths of a degree below the horizontal plane. RF |
Incoming radio wave polarisation
Richard Fry in a private e-mail noted that I had misquoted E. A. Laport
who wrote: "---it is desirable to employ complementary antennas for transmitting and receiving." I typed "complimentary" which means praise or a gift. Surely Laport meant antennas which work together to perfection which is even better than getting them free. I made a typo. I apologize for my mistake. Best regards, Richard Harrison, KB5WZI |
Incoming radio wave polarisation
"Richard Clark" wrote in message ... On Mon, 17 Mar 2008 09:17:01 -0700, Jim Lux wrote: run through a variable combiner Hi Jim, As Richard pointed out, a goniometer (what, a 100 years old already?) works fine for this. I bought one at a Ham swap when I was a teenager. I also pointed this goniometer/antenna application out to Arthur to demonstrate what he thought was novel was quite old (in reference to the work of Tosi and Bellini). Arthur does not acknowledge prior inventors, so this topic consistently re-emerges with a fair periodicity. It should reappear around July again. For those who want to see a schematic of the goniometer and antenna application, here is a perfectly good example: http://www.elektronikschule.de/~krau...ng%20-%205.htm 73's Richard Clark, KB7QHC Hi Richard Is it possible that Sheldon Remington is trying to acknowledge Art's previous work as indicated by his naming him in the title of his article? J |
Incoming radio wave polarisation
On Mar 17, 5:29 pm, "Richard Fry" wrote:
Examination of the radiation patterns of horizontal antennas confirms that they invariably have zero response at zero elevation on their best azimuths. _____________ If this were true then most television broadcast stations would have nearly zero field strength near the earth over much of their present coverage areas. Instead, the fields there are directly related to the peak ERP of the TV station -- which typically is radiated in, or a few tenths of a degree below the horizontal plane. RF So you are saying that Termqn's book has errors? Amazing! |
Incoming radio wave polarisation
On Mar 17, 3:28 pm, (Richard Harrison)
wrote: "----a loop antenna responds much less to the electric induction field than does a simple wire antenna of comparable intercept area. This is of importance because electric induction fields predominate in the man-made noise that causes disturbances in radio receivers, and this explains in part the popularity of loop antennas in broadcast receivers." Best regards, Richard Harrison, KB5WZI I'll have to ponder his statement, but my reg flag is waving... This almost seems akin to the shielded loop controversy. It may well be true in whatever manner he is considering, but for some reason it doesn't seem quite right to me. Maybe I'm missing something, so I'll await further comments. MK |
Incoming radio wave polarisation
On Mon, 17 Mar 2008 23:19:43 GMT, "Jerry"
wrote: Is it possible that Sheldon Remington is trying to acknowledge Art's previous work as indicated by his naming him in the title of his article? Hi Jerry, Well..... It does in many ways suggest prior Art is responsible, yes. 73's Richard Clark, KB7QHC |
Incoming radio wave polarisation
"Art Unwin" wrote:
If this were true then most television broadcast stations would have nearly zero field strength near the earth over much of their present coverage areas. Instead, the fields there are directly related to the peak ERP of the TV station -- which typically is radiated in, or a few tenths of a degree below the horizontal plane. RF So you are saying that Termqn's book has errors? Amazing! ______________ art, Your post above shows that you don't understand this subject, and what Terman wrote about it. Not so sure about "Termqn," though. Doesn't your common sense and life experience support what I stated in my post? If not, why not? Please consider using "due diligence" and proofreading before you click your send button. Such will serve you better. RF |
Incoming radio wave polarisation
Richard Harrison wrote:
. . . From researching susceptibility of antennas to noise I came across a statement interesting to me in Terman`s 1955 opus on page 929: "----a loop antenna responds much less to the electric induction field than does a simple wire antenna of comparable intercept area. This is of importance because electric induction fields predominate in the man-made noise that causes disturbances in radio receivers, and this explains in part the popularity of loop antennas in broadcast receivers." Like so many bons mots lifted from Terman, we have to use a bit of care in extending it to everyday amateur applications. A very small loop responds less strongly to the electric field than a very small dipole only within a fraction of a wavelength of the antenna. Beyond that, it actually responds more strongly to the electric field than the dipole does. So at HF, for example, it would be helpful only in rejecting electric field noise being radiated within a few feet of the antenna. Roy Lewallen, W7EL |
Incoming radio wave polarisation
Roy Lewallen wrote in
: A very small loop responds less strongly to the electric field than a very small dipole only within a fraction of a wavelength of the antenna. I have seen this expressed as a sensitivity to E and H that imply an impedance that varies with distance from the antenna, and that it "bounces around" (that is a technical term, you know) eventually converging on 120*pi. Is that correct? Beyond that, it actually responds more strongly to the electric field than the dipole does. So at HF, for example, it would be helpful only in Roy, accepting that the response of the loop and dipole to electric and magnetic fields are different close the the antenna, do they not eventually converge on sensitivity to E and H in the ratio of 120*pi when immersed in the far radiation field? I don't know if I have put that sensibly. My understanding was that when placed a very long way from the sources, neither one had any advantage in response to the desired signal just by virtue of their type (loop vs dipole). Owen |
Incoming radio wave polarisation
Owen Duffy wrote:
Roy Lewallen wrote in : A very small loop responds less strongly to the electric field than a very small dipole only within a fraction of a wavelength of the antenna. I have seen this expressed as a sensitivity to E and H that imply an impedance that varies with distance from the antenna, and that it "bounces around" (that is a technical term, you know) eventually converging on 120*pi. Is that correct? They do converge, but only after one change in slope. More below. Beyond that, it actually responds more strongly to the electric field than the dipole does. So at HF, for example, it would be helpful only in Roy, accepting that the response of the loop and dipole to electric and magnetic fields are different close the the antenna, do they not eventually converge on sensitivity to E and H in the ratio of 120*pi when immersed in the far radiation field? Yes. I don't know if I have put that sensibly. My understanding was that when placed a very long way from the sources, neither one had any advantage in response to the desired signal just by virtue of their type (loop vs dipole). That's correct. E/H is the impedance of the field and, close to a small loop, the impedance is small as expected. (As a receiving antenna, this means that it's relatively more sensitive to the H field than the E field if the source is very close.) However, the impedance rises rapidly as you get farther from the loop, and at a fraction of a wavelength, it actually overshoots 276 ohms. Then, after reaching its peak, it monotonically approaches 276 ohms from the high side as you get farther and farther away. A short dipole acts just the same, but with E and H reversed: the impedance is high very close to the antenna, then overshoots on the low side, and from there approaches 276 ohms at a great distance. So at all points except very close, the impedance of the loop's field is actually higher than that of the dipole's. In practice, the difference is negligible except perhaps for a very small region, so they behave virtually the same for signals coming from any distance of, say, a wavelength or further away. You can very easily see this behavior with NEC-2 or EZNEC modeling, using the near field analysis. The free demo version of EZNEC is adequate. Roy Lewallen, W7EL |
Incoming radio wave polarisation
Roy Lewallen wrote in
: ..... actually overshoots 276 ohms. Then, after reaching its peak, it monotonically approaches 276 ohms from the high side as you get 120*pi or 377? Owen |
| All times are GMT +1. The time now is 03:43 PM. |
|
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com