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A' little' db extra gain !
Most people have added an amplifier only to find out that the
difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art |
art wrote:
I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? I lowered my 20m dipole from 40 ft. to 30 ft. because that gave me a better skip into Arizona where a lot of my friends are. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Cecil wrote - I lowered my 20m dipole from 40 ft. to 30 ft. because that gave me a better skip into Arizona where a lot of my friends are. ======================= No Cecil, it didn't. It just gave you worse skip into where you didn't want it. --- Reg |
On 28 Jan 2005 12:48:52 -0800, "art" wrote:
Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art I have always thought that if one changed the azimuth angle of a beam it would improve a number of contact signals, pending the angle they are reflected from the atmosphere. -- Buck N4PGW |
So true ! Many a DXer loses signals because his TOA is to low
Art "Cecil Moore" wrote in message ... art wrote: I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? I lowered my 20m dipole from 40 ft. to 30 ft. because that gave me a better skip into Arizona where a lot of my friends are. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
You can move the antenna boom up or down some 10 degrees and you would not
be able to tell the difference per Lawson W2PV Art "Buck" wrote in message ... On 28 Jan 2005 12:48:52 -0800, "art" wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art I have always thought that if one changed the azimuth angle of a beam it would improve a number of contact signals, pending the angle they are reflected from the atmosphere. -- Buck N4PGW |
Hi Art
I'd say that every little bit helps when conditions are marginal. Even 10dB extra mean pretty well nothing in readability when the signal is already 20dB above the noise, but a few dB *can* make a difference when the signal is in noise. Antenna efficiency and gain in the right direction all helps but it is going to be a compromise. I mean if you want to chat to the "locals" 30 degrees takeoff is better again! I'll admit that I havent done any huge a amount of modelling on this but (IMO) ground conditions and height over are far more important and are very difficult to design an antenna for all situations. Maybe the trick is to design your antenna for free space for "good" gain and then be able to raise and lower it for the best angles.. Cheers Bob VK2YQA art wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art |
"Bob Bob" wrote in message ... Hi Art I'd say that every little bit helps when conditions are marginal. Even 10dB extra mean pretty well nothing in readability when the signal is already 20dB above the noise, but a few dB *can* make a difference when the signal is in noise. I don't see that! would not the S/N stay the same? Antenna efficiency and gain in the right direction all helps but it is going to be a compromise. I mean if you want to chat to the "locals" 30 degrees takeoff is better again! Agreed, that is what Cecil did. I'll admit that I havent done any huge a amount of modelling on this but (IMO) ground conditions and height over are far more important and are very difficult to design an antenna for all situations. For horizontal waves the ground conditions relative to 1 wavelength is of little concern Height as always helps with low TOA so one has to determine the average incoming signal angle of choice QSO's and design to suit. Maybe the trick is to design your antenna for free space for "good" gain and then be able to raise and lower it for the best angles.. Agreed but I would like to see smaller turning radius ( moving away from the boom length mantra , ) without the necessity for dual driven stacked array This would require a fixed feed point with moveable elements for desired TOA to suit desired QSO.. I am sure it can be done, and since 'every thing is known about antennas' all that is reguired is for a Guru to come forward to share how it is done. Regards Art Cheers Bob VK2YQA art wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art |
I say ignore the TOA. (For those unfamiliar with the term, it's the
"takeoff angle", which usually means the elevation angle at which the antenna pattern is strongest.) What counts is the gain at the elevation angle at which you want to communicate. This, in turn, depends on the distance and the propagation conditions. If you need a strong signal at an elevation angle of 15 degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or zero. All that counts is the gain at 15 degrees. And an antenna with TOA of 15 degrees doesn't necessarily have the most gain at 15 degrees of any antenna. Consider the following three 40 meter antennas: A vertical antenna with about 8 radials (18 ohm ground system resistance), a dipole at 30 feet, and a dipole at 40 feet, all over average ground. Antenna TOA deg Gain at 26 deg. Gain at 15 deg. Vert 26 -1.76 dBi -2.72 dBi Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi Dipole @ 40' 51 3.9 dBi 0.32 dBi -- Which one has the lowest takeoff angle? -- Which one is the best for communicating at 26 deg. elevation angle? -- Which one is the best for communciating at 15 deg. elevation angle? What does the takeoff angle have to do with which antenna is best? Roy Lewallen, W7EL art wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art |
Hi Art
I'd say that every little bit helps when conditions are marginal. Even 10dB extra mean pretty well nothing in readability when the signal is already 20dB above the noise, but a few dB *can* make a difference when the signal is in noise. I don't see that! would not the S/N stay the same? Well to tell you the truth this was one of those "told by someone else" things that I never did get around to proving myself (thinking it was general knowledge) I have of course noticed it on 2M FM where the recovered audio S/N falls off very rapidly as the usable senitivity of the radio is reached. In that case a 1 or 2dB signal increase can make the difference between readable 1 and readable 4. I have a funny feeling the discussion I heard on the topic may have been on front end NF of VHF/UHF receivers where a 1dB lower number there yielded a much larger dB result. Note this was for SSB. I have some work to do here understanding this. When I look at building another preamp for 2/70 I'll do it then! However if the noise is -110dBm and the signal was -114dBm, the margin (s/n) would become less (of a negative number) when the signal level is increased. You may not be able to resolve it but you can measure the difference. You can of course use DSP techniques to resolve signals weaker than noise. WRSS60 for example will enable you to resolve signals 26dB below the noise level. FSK441/JT44 is another example of signal below noise reception. For horizontal waves the ground conditions relative to 1 wavelength is of little concern Height as always helps with low TOA so one has to determine the average incoming signal angle of choice QSO's and design to suit. Something about brewster angles and phase reversal in horizontal but not vertical polarisation? (Note I work in IT, not RF!) I always thought that the poorer the ground (eg sand/clay) the higher the takeoff angle and over seawater was the lowest one could attain. (Keep in mind that VK dropped CW earlier this year and I was one of those that has been playing VHF+ for the last 25 years!) Agreed but I would like to see smaller turning radius ( moving away from the boom length mantra , ) without the necessity for dual driven stacked array This would require a fixed feed point with moveable elements for desired TOA to suit desired QSO.. I would also expect that F/B & F/S are major contributors to design to. Very handy when you neighbours son a few miles away wants to tune his VW engine! I like the idea of a quad, simply because of its smaller turning radius! I once had a think about ways to tune a 3 element quad for best F/B. Maybe some way to roll the wire up on a small motor shaft or tune it with some C on the end of some tuned length feeder? Didnt figure out an easy way to change the element spacing though. Maybe bending the spreaders would have a similar effect of changing the feedpoint positions on a stacked array? You could also change the length of the phasing sections for a dual driven stacked array - rather than moving the feedpoint. If I was experimenting with this idea I'd probably start (modeling) with 3 parallel horizontal dipoles arranged such that when viewed from the ends the (end point) shape was a triangle. All would be fed in parallel but with different phase relationships between them. I am sure it can be done, and since 'every thing is known about antennas' all that is reguired is for a Guru to come forward to share how it is done. Not me sorry. If however I stumble onto something that defies all the theory and works better than anyone else, this NG will be the first to know - and I'll make the design like GPL software! Free... Cheers Bob VK2YQA |
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote: What does the takeoff angle have to do with which antenna is best? That would depend on the desired contact. If you want 80 meters DX, you want a very high antenna, if you just want to talk to your local buddies, a lower antenna provides a better NVIS. Verticals provide better omni-directional pattern but a slanted dipole provides better directivity than a vertical. Beams are obvious. -- Buck N4PGW |
*Sigh*
I tried. Roy Lewallen, W7EL Buck wrote: On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen wrote: What does the takeoff angle have to do with which antenna is best? That would depend on the desired contact. If you want 80 meters DX, you want a very high antenna, if you just want to talk to your local buddies, a lower antenna provides a better NVIS. Verticals provide better omni-directional pattern but a slanted dipole provides better directivity than a vertical. Beams are obvious. |
Jim Lawson, W2PV, solved the TOA problem on 20 M with a l o n g yagi at
~150' to open the band and his either/or/both stack(top antenna at about 70-80', as I remember) for normal band condition. Oh yes, Alpha 77s on most bands, too! Phil, KB2HQ, former neighbor of W2PV " wrote in message news:ODzKd.33178$IV5.6955@attbi_s54... You can move the antenna boom up or down some 10 degrees and you would not be able to tell the difference per Lawson W2PV Art "Buck" wrote in message ... On 28 Jan 2005 12:48:52 -0800, "art" wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art I have always thought that if one changed the azimuth angle of a beam it would improve a number of contact signals, pending the angle they are reflected from the atmosphere. -- Buck N4PGW |
On Fri, 28 Jan 2005 21:28:20 -0800, Roy Lewallen
wrote: I say ignore the TOA. (For those unfamiliar with the term, it's the "takeoff angle", which usually means the elevation angle at which the antenna pattern is strongest.) What counts is the gain at the elevation angle at which you want to communicate. This, in turn, depends on the distance and the propagation conditions. If you need a strong signal at an elevation angle of 15 degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or zero. All that counts is the gain at 15 degrees. And an antenna with TOA of 15 degrees doesn't necessarily have the most gain at 15 degrees of any antenna. Consider the following three 40 meter antennas: A vertical antenna with about 8 radials (18 ohm ground system resistance), a dipole at 30 feet, and a dipole at 40 feet, all over average ground. Antenna TOA deg Gain at 26 deg. Gain at 15 deg. Vert 26 -1.76 dBi -2.72 dBi Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi Dipole @ 40' 51 3.9 dBi 0.32 dBi -- Which one has the lowest takeoff angle? -- Which one is the best for communicating at 26 deg. elevation angle? -- Which one is the best for communciating at 15 deg. elevation angle? What does the takeoff angle have to do with which antenna is best? Roy Lewallen, W7EL Dear Roy, 3 cheers. Bob, W9DMK, Dahlgren, VA Replace "nobody" with my callsign for e-mail http://www.qsl.net/w9dmk http://zaffora/f2o.org/W9DMK/W9dmk.html |
Roy Lewallen wrote: *Sigh* I tried. Let me have a shot at it, Roy. possible blather alert! Perhaps there is confusion by some people with the idea that the takeoff angle. I suspect that a lot of people think of their RF leaving the antenna as a "blob" that leaps out at some desired or undesired angle. Instead, the RF is heading off in all directions, with some angles having more relative power. So even if an antenna has a lower TOA, it might be less gain than an antenna that has a higher TOA has at that angle. An inefficient antenna with a low TOA can be less efficient at that low TOA than a more efficient antenna with a higher TOA is at that same low TOA. Oy. - Mike KB3EIA - rest snipped |
Mike Coslo wrote:
Perhaps there is confusion by some people with the idea that the takeoff angle. I suspect that a lot of people think of their RF leaving the antenna as a "blob" that leaps out at some desired or undesired angle. Instead, the RF is heading off in all directions, with some angles having more relative power. So even if an antenna has a lower TOA, it might be less gain than an antenna that has a higher TOA has at that angle. An inefficient antenna with a low TOA can be less efficient at that low TOA than a more efficient antenna with a higher TOA is at that same low TOA. Maybe a picture is worth a thousand words. Here's a comparison radiation pattern for my 130 ft dipole Vs my 40m vertical with elevated radials. In the dipole's favored direction, it's TOA is greater than the vertical's yet the dipole radiates more power than the vertical even at the vertical's TOA. Here's the pictu http://www.qsl.net/w5dxp/dipvsver.htm -- 73, Cecil, W5DXP ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Sat, 29 Jan 2005 13:11:20 GMT, "Phil"
wrote: Jim Lawson, W2PV, solved the TOA problem on 20 M with a l o n g yagi at ~150' to open the band and his either/or/both stack(top antenna at about 70-80', as I remember) for normal band condition. Oh yes, Alpha 77s on most bands, too! Phil, KB2HQ, former neighbor of W2PV I imagine that you had an interesting ham life when you shared the same band and he communicated in your direction. -- Buck N4PGW |
On 28 Jan 2005 12:48:52 -0800, "art" wrote:
Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art Someone correct me if I am wrong, but isn't gain derived by narrowing focussing all the energy into a more narrow path? Besides, TOA is important to the location of an antenna in respect to its relative position to the ground and the surrounding terrain. I have heard that people surrounded by mountains prefer a 1/4 whip on their cars for 2 meters and up when trying to hit repeaters due to its higher angle of radiation, but in the flat areas, the preferred antennas are the 5/8 wave etc due to its horizontal gain. Being on the side of a hill, I can't use an antenna at roof-top level with a low angel of radiation as there isn't enough power to get the signal through the miles of land mass under my neighbor's houses. I did an experiment when I first received my General license to see if I could sign into the GA SSB NTS Net. I rolled out a spool of wire on the ground approximately 1/4 wave for 3975 kc. Without a tuner I was able to get acceptable SWR and checked into the net. I wasn't the strongest signal but I did well enough to hold several QSOs. It wasn't as good as my dipole when I raised one, but it worked better than my 40 meter dipole at the time. I believe that a horizontal dipole will have about the same TOA as a vertical dipole when both are sufficiently high. However, the dipole is more bidirectional and the vertical is omni directional. Therefore the horizontal dipole may display some gain broadside over the vertical. I believe that Cecil's picture reinforces the idea that on HF especially, the TOA is largely affected by the antenna's elevation above ground. However, I was reading in CQ or QST last year about a DX operator who uses verticals near the sea and wins his contests because of his antennas. He finds the best location for his antennas near the ocean. I believe he said he had tried beams before but there is an ocean effect that makes the verticals better suited for his operations. That same vertical would be lousy for me as my house is on a hill that forms a very close valley. I used a Taylor Radio vertical years ago in this yard and it sucked. However, when I used it in Charleston and Jacksonville, it was fantastic (not near the ocean). Another DX operator suggests that most people will have a better chance of communicating with him if they use a slanted dipole pointed in the direction of their QTH. The angle of radiation and gain make it a great DX antenna. Different antennas work differently depending on their locations. I think your better question would be, what is the best antenna for my QTH and operating style? -- Buck N4PGW |
Buck, in my posting I refered to 20 meters and also the incoming angles and
average signals thereof coming from Europe. Thus my interest was in the lower half of the main lobe. The thickness of the lobe of the lobe would thus not be important, only the contour of the underside of the lobe. It is this portion of the lobe where a DXer referers to the fact that a db means a lot as opposed to adding a db gain to angles contained within a lobe. Note that the thickness of the lobe can vary even tho both anternnas may have the same take of angle as can be seen by comparing a monster boom length antenna to that of a stacked beam which admittedly has a feed point which is very high. When comparing these two types an optimum would be a low feed point (1 WL) with a small turning radius with means to compress the main lobe downwards for those DX signals arrive and where the 'silly' db becomes everything Regards Art. "Buck" wrote in message ... On 28 Jan 2005 12:48:52 -0800, "art" wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art Someone correct me if I am wrong, but isn't gain derived by narrowing focussing all the energy into a more narrow path? Besides, TOA is important to the location of an antenna in respect to its relative position to the ground and the surrounding terrain. I have heard that people surrounded by mountains prefer a 1/4 whip on their cars for 2 meters and up when trying to hit repeaters due to its higher angle of radiation, but in the flat areas, the preferred antennas are the 5/8 wave etc due to its horizontal gain. Being on the side of a hill, I can't use an antenna at roof-top level with a low angel of radiation as there isn't enough power to get the signal through the miles of land mass under my neighbor's houses. I did an experiment when I first received my General license to see if I could sign into the GA SSB NTS Net. I rolled out a spool of wire on the ground approximately 1/4 wave for 3975 kc. Without a tuner I was able to get acceptable SWR and checked into the net. I wasn't the strongest signal but I did well enough to hold several QSOs. It wasn't as good as my dipole when I raised one, but it worked better than my 40 meter dipole at the time. I believe that a horizontal dipole will have about the same TOA as a vertical dipole when both are sufficiently high. However, the dipole is more bidirectional and the vertical is omni directional. Therefore the horizontal dipole may display some gain broadside over the vertical. I believe that Cecil's picture reinforces the idea that on HF especially, the TOA is largely affected by the antenna's elevation above ground. However, I was reading in CQ or QST last year about a DX operator who uses verticals near the sea and wins his contests because of his antennas. He finds the best location for his antennas near the ocean. I believe he said he had tried beams before but there is an ocean effect that makes the verticals better suited for his operations. That same vertical would be lousy for me as my house is on a hill that forms a very close valley. I used a Taylor Radio vertical years ago in this yard and it sucked. However, when I used it in Charleston and Jacksonville, it was fantastic (not near the ocean). Another DX operator suggests that most people will have a better chance of communicating with him if they use a slanted dipole pointed in the direction of their QTH. The angle of radiation and gain make it a great DX antenna. Different antennas work differently depending on their locations. I think your better question would be, what is the best antenna for my QTH and operating style? -- Buck N4PGW |
On Sat, 29 Jan 2005 10:52:05 -0500, Buck wrote:
Someone correct me if I am wrong, but isn't gain derived by narrowing focussing all the energy into a more narrow path? Hi Buck, Thanks for the invitation (but we are a rabble of party crashers anyway). What you say about narrowing to achieve gain is a useful analogy, but there are some problems on down the line: Besides, TOA is important to the location of an antenna in respect to its relative position to the ground and the surrounding terrain. True, except to invert the inference: location and terrain is important to the TOA (put the horse before the cart, in other words). I have heard that people surrounded by mountains prefer a 1/4 whip on their cars for 2 meters and up when trying to hit repeaters due to its higher angle of radiation, but in the flat areas, the preferred antennas are the 5/8 wave etc due to its horizontal gain. This reveals the problem with testimonial in place of measurement. Unless you are in the Grand Canyon, you stand a chance of communication at a very much greater distance to a mountain than you are to another rig on the same plain. Even an HT has enough power to communicate with a sattelite (or space shuttle). This reveals that power is not the problem for considerable distance. However, at this frequency (2M) line of sight on the plains is not that very far away (less than 5 miles with your HT in your hand). On the other hand, if on the plains you can see a mountain 50 miles away, you are as likely as not to be able to talk to it to (presuming a repeater inhabits its peak). Hence the gain differential of quarterwave and 5/8ths is not necessarily required for the Power nor the TOA - other issues are at work. When the issues are not discussed, nor investigated, then changing the antenna system from one to the other may resolve that hidden issue and the difference attributed to the antenna - voila! testimony offered. I did an experiment when I first received my General license to see if I could sign into the GA SSB NTS Net. I rolled out a spool of wire on the ground approximately 1/4 wave for 3975 kc. Without a tuner I was able to get acceptable SWR and checked into the net. I wasn't the strongest signal but I did well enough to hold several QSOs. It wasn't as good as my dipole when I raised one, but it worked better than my 40 meter dipole at the time. You have a bad habit of comparing the qualities of one antenna on one band to the qualities of a second antenna on another band. This is called testimonial, and it is not very useful in demonstrating correlations. Trying to draw two different observations under the same umbrella of discussion does not lead to any general conclusion. Your 80M antenna on the ground would match, certainly when so obviously in the grip of ground. You could have probably qualified that installation to match at nearly any frequency - if we confine the goal of matching to present no reflected power. A ground hugger so qualifies and the ground is content to absorb (without reflecting) all the power you pour into it. What you fail to compare is how it worked "better" than your elevated 40M: how far were you working 80M contacts? The ground laid antenna was used in Desert Storm for just this quality and it provided useful contacts in missions there, but they were not interested in skip. However, I was reading in CQ or QST last year about a DX operator who uses verticals near the sea and wins his contests because of his antennas. He finds the best location for his antennas near the ocean. I believe he said he had tried beams before but there is an ocean effect that makes the verticals better suited for his operations. This, again, is testimonial. However, it is often attended with compelling testing and theory that dovetail. The simple explanation is that the vertical's radiation is constructively reinforced at low angles by the sea, a horizontal's radiation is destructively combined by the sea at low take off angles. The difference at very low angles is far in excess of a 'little' db. If you look over your shoulder to all that sand behind you, then that same vertical becomes a miserable performer in comparison to those beams turned to follow your eye. Another DX operator suggests that most people will have a better chance of communicating with him if they use a slanted dipole pointed in the direction of their QTH. The angle of radiation and gain make it a great DX antenna. It's surprising how many Hams have missed this gem of wisdom. It must mean that 1. We are a particularly dull and stupid lot; or 2. It doesn't really offer all that much for the effort. 73's Richard Clark, KB7QHC |
Amen.
Let us use TOA for the elevation angle where an antenna's pattern is strongest and ATOA for the actual elevation angle used over a long HF path. At least from 7 MHz to 21 MHz, when DX ionosphere propagation is likely the ATOA is between about 12 degrees and about 2 degrees. When comparing antennas to be used for HF DX contacts, it is appropriate to note the gain at 3, 6, and 9 degrees as being the numbers to compare. The actual TOA (as defined above) is only interesting. That said, it is possible to have a single horizontally polarized antenna that is so high that it suffers in comparison to a lower antenna for ATOAs of about 10 degrees (by more than the one db that is being talked about). For one horizontally polarized antenna to be used for DX contacts the desired heights are two to three wavelengths above earth. If one can use a plurality of horizontally polarized antennas, interesting results are possible. For instance: on receive, combining a lower second antenna with a tall first antenna can effect the approximate cancellation of the second lobe. The second lobe has a high TOA and can contribute significantly to the noise and interference received from relatively short distances. Nulling the second lobe can significantly increase the received SNR. For closer spacing of multiple antennas, one can effect more gain than that of one antenna - with trade-offs. I emphasize what has been said by Roy and others: TOA (as defined above) is interesting, but it is not the most important number for DX contacts. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Roy Lewallen" wrote in message ... I say ignore the TOA. (For those unfamiliar with the term, it's the "takeoff angle", which usually means the elevation angle at which the antenna pattern is strongest.) What counts is the gain at the elevation angle at which you want to communicate. This, in turn, depends on the distance and the propagation conditions. If you need a strong signal at an elevation angle of 15 degrees, it doesn't matter whether the TOA is 10 degrees, 15, or 20 or zero. All that counts is the gain at 15 degrees. And an antenna with TOA of 15 degrees doesn't necessarily have the most gain at 15 degrees of any antenna. Consider the following three 40 meter antennas: A vertical antenna with about 8 radials (18 ohm ground system resistance), a dipole at 30 feet, and a dipole at 40 feet, all over average ground. Antenna TOA deg Gain at 26 deg. Gain at 15 deg. Vert 26 -1.76 dBi -2.72 dBi Dipole @ 30' 90 (straight up) 2.58 dBi -1.28 dBi Dipole @ 40' 51 3.9 dBi 0.32 dBi -- Which one has the lowest takeoff angle? -- Which one is the best for communicating at 26 deg. elevation angle? -- Which one is the best for communciating at 15 deg. elevation angle? What does the takeoff angle have to do with which antenna is best? Roy Lewallen, W7EL |
On Sat, 29 Jan 2005 17:04:14 GMT, "
wrote: Buck, in my posting I refered to 20 meters and also the incoming angles and average signals thereof coming from Europe. Thus my interest was in the lower half of the main lobe. The thickness of the lobe of the lobe would thus not be important, only the contour of the underside of the lobe. It is this portion of the lobe where a DXer referers to the fact that a db means a lot as opposed to adding a db gain to angles contained within a lobe. Note that the thickness of the lobe can vary even tho both anternnas may have the same take of angle as can be seen by comparing a monster boom length antenna to that of a stacked beam which admittedly has a feed point which is very high. When comparing these two types an optimum would be a low feed point (1 WL) with a small turning radius with means to compress the main lobe downwards for those DX signals arrive and where the 'silly' db becomes everything Regards Art. "Buck" wrote in message .. . On 28 Jan 2005 12:48:52 -0800, "art" wrote: Most people have added an amplifier only to find out that the difference in signal was very small. Thus many people deride the value of a 'silly' db gain whereas DX'ers say that a single db extra is a lot ! Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. So where a dxer points to the extra 1db gain as being everything in fact it is the lowering of the TOA that comes with the extra gain. In my opinion if one designs his antenna for a lower TOA say 10 to 11 degrees then even tho its gain may well be below the dxers choise( a very long boom or stacked antennas) the lower TOA with less gain will show little difference to the antenna of choics because the lower edge of the radiation lobe will follow the same line and any extra gain provided will have the same effect of adding an amplifier which is minimal compared to the ability of capturing signals that arrive at low angles. I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. What say ? Art Someone correct me if I am wrong, but isn't gain derived by narrowing focussing all the energy into a more narrow path? Besides, TOA is important to the location of an antenna in respect to its relative position to the ground and the surrounding terrain. I have heard that people surrounded by mountains prefer a 1/4 whip on their cars for 2 meters and up when trying to hit repeaters due to its higher angle of radiation, but in the flat areas, the preferred antennas are the 5/8 wave etc due to its horizontal gain. Being on the side of a hill, I can't use an antenna at roof-top level with a low angel of radiation as there isn't enough power to get the signal through the miles of land mass under my neighbor's houses. I did an experiment when I first received my General license to see if I could sign into the GA SSB NTS Net. I rolled out a spool of wire on the ground approximately 1/4 wave for 3975 kc. Without a tuner I was able to get acceptable SWR and checked into the net. I wasn't the strongest signal but I did well enough to hold several QSOs. It wasn't as good as my dipole when I raised one, but it worked better than my 40 meter dipole at the time. I believe that a horizontal dipole will have about the same TOA as a vertical dipole when both are sufficiently high. However, the dipole is more bidirectional and the vertical is omni directional. Therefore the horizontal dipole may display some gain broadside over the vertical. I believe that Cecil's picture reinforces the idea that on HF especially, the TOA is largely affected by the antenna's elevation above ground. However, I was reading in CQ or QST last year about a DX operator who uses verticals near the sea and wins his contests because of his antennas. He finds the best location for his antennas near the ocean. I believe he said he had tried beams before but there is an ocean effect that makes the verticals better suited for his operations. That same vertical would be lousy for me as my house is on a hill that forms a very close valley. I used a Taylor Radio vertical years ago in this yard and it sucked. However, when I used it in Charleston and Jacksonville, it was fantastic (not near the ocean). Another DX operator suggests that most people will have a better chance of communicating with him if they use a slanted dipole pointed in the direction of their QTH. The angle of radiation and gain make it a great DX antenna. Different antennas work differently depending on their locations. I think your better question would be, what is the best antenna for my QTH and operating style? -- Buck N4PGW Ok, Art, I think I am with you now. I just re-read all the previous posts. Roy Lewallen first referred to the 40 meters and I think he introduced the picture of the angles from a vertical and a dipole. Sorry to have been so slow picking up on this, and thank you all for your patience with me. With all this discussion, I am learning. I echo back my thoughts at the time that may be subject to change upon correction or even possibly due to misinformation, hihi. I have been studying antenna theory for a while now, off and on. Not like a college professor, just on my own. Let's start by getting back to your original post. You are interested in DXing on 20 meters in which most signals come in at 11 degrees or less. Therefore antenna designers should focus their attention, not on antenna gain, but on getting the gain to the incident angle of radiation. You mentioned that Amps turn out to be of little help if the antenna angle is wrong. (I'll save the amp for another discussion and deal with the antennas.) I have been studying about antennas for a while now. (not like a college professor, probably more accurately I have been reading a lot.) I understand what you are saying about the amplifier. From my experience I have learned a simple truth. Either one has the propagation to make a contact, or one doesn't make contact. Last year I totally surprised myself when I called a DX station in a pileup and he answered. I was running an FT-817 into a dipole about 65 feet high. There have been times I couldn't break a pileup with a 400 watt Swan on the same antenna. Getting back to your topic, from what I understand, the terrain and antenna elevation are as, or more, important in establishing the angle of incidence as the antenna is. IIRC, a Yagi has a recommended minimum height above terrain for optimum operation. I believe that 20 meters is 125 feet. BTW, I am curious to know, from where did you get the information that the incoming signals are at 11 degrees? Speaking of Yagi's and gain, I know that the gain (and inversely the bandwidth) of a yagi is increased by extending the spacing between elements. A wide spaced gives a little more gain than narrow spaced elements. I believe it also narrows the beam width of the signal. I don't think it affects that TOA, though, except maybe by its relationship to the ground and its surrounding terrain. -- Buck N4PGW |
On Sat, 29 Jan 2005 19:22:12 -0500, Buck wrote:
Speaking of Yagi's and gain, I know that the gain (and inversely the bandwidth) of a yagi is increased by extending the spacing between elements. A wide spaced gives a little more gain than narrow spaced elements. I believe it also narrows the beam width of the signal. Hi Buck, This is fine. I don't think it affects that TOA, though, except maybe by its relationship to the ground and its surrounding terrain. It is unlikely that anything you do in such a small footprint will bring any geometric change that brings even a perceptible change to the TOA. However, by simply increasing gain, the entire lobe structure of the antenna increases (same shape balloon, but now a larger balloon) which does impact the TOA; but not its angle, instead more its magnitude. This, in a sense, was the comparison Roy was drawing upon with the different examples. In a sense, increasing the antenna gain (all other factors held constant) would be indistinguishable from simply boosting the transmitter gain (or adding an Amp). 73's Richard Clark, KB7QHC |
On Sat, 29 Jan 2005 15:35:21 -0500, "J. Mc Laughlin"
wrote: 73 Mac N8TT Let me re-iterate what you said, assuming I understand it. Art is saying that it is better to have a more accurate TOA than the last db of antenna gain, but you are saying that a better s/n ratio (as handled by the antenna) is better than the last db of gain. Of course, Art started his statement with something about a person turning up their amplifier and having no better results. Therefore he must also be considering being heard as well as hearing. I would think that an amplifier will, for the most part, increase the radiation strength of every angle radiated at all by the antenna. If the amp represents a 6dB gain over the radio, it will represent a 6 dB gain in the any direction in which the lobe points. At least for the transmission, that should provide the 1 db difference we are talking about. This doesn't address that time of day in which the west hears from the east in one way propagation. Correct me if I am wrong here. -- Buck N4PGW |
Just to clarify -
The angle of elevation of the radio path between points A and B on the Earth's surface is always a constant which depends purely on the Earth's geometry and the number of hops. It has nothing to do with the radiation patterns, beam widths of either the receiving or transmitting antennas, vary as they may. There may of course be short term variations due to ionospheric effects. --- Reg |
Dear Buck (N4PGW):
I am having a difficult time finding what I thought that I said in your paraphrasing. Your bio on QRZ.COM does not indicate an interest in DX, so it is possible that all of my comments were misdirected. Perhaps the essence of what I was trying to say, in addition to agreeing with Roy, is that it is desirable with (single) horizontally polarized antennas at HF to have as much gain as possible appear in the direction that is expected to be used for DX contacts. In turn, that suggests that it is desirable to have a height above ground (or above the applicable "refection" area) be between 2 and 3 wavelengths. I do not recall writing anything about power amplifiers or something called "one way propagation." 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Buck" wrote in message ... On Sat, 29 Jan 2005 15:35:21 -0500, "J. Mc Laughlin" wrote: 73 Mac N8TT Let me re-iterate what you said, assuming I understand it. Art is saying that it is better to have a more accurate TOA than the last db of antenna gain, but you are saying that a better s/n ratio (as handled by the antenna) is better than the last db of gain. snip Correct me if I am wrong here. -- Buck N4PGW |
On Sat, 29 Jan 2005 16:45:29 -0800, Richard Clark
wrote: On Sat, 29 Jan 2005 19:22:12 -0500, Buck wrote: Speaking of Yagi's and gain, I know that the gain (and inversely the bandwidth) of a yagi is increased by extending the spacing between elements. A wide spaced gives a little more gain than narrow spaced elements. I believe it also narrows the beam width of the signal. Hi Buck, This is fine. I don't think it affects that TOA, though, except maybe by its relationship to the ground and its surrounding terrain. It is unlikely that anything you do in such a small footprint will bring any geometric change that brings even a perceptible change to the TOA. However, by simply increasing gain, the entire lobe structure of the antenna increases (same shape balloon, but now a larger balloon) which does impact the TOA; but not its angle, instead more its magnitude. This, in a sense, was the comparison Roy was drawing upon with the different examples. In a sense, increasing the antenna gain (all other factors held constant) would be indistinguishable from simply boosting the transmitter gain (or adding an Amp). 73's Richard Clark, KB7QHC I think you and I are in agreement except for what Art believes. (see his statement below:) I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. He agrees that the antenna is better as it improves receive as well as transmit, but I can't see the TOA being more important than the gain unless it is really off by a long way. An NVIS antenna has a different purpose than a DX antenna so he would need an antenna that fits his needs. I am not sure what would reduce the TOA over a Yagi unless it is a Yagi pointed downward. Maybe what we need to be doing is asking Art what his situation is and trying to find the antenna that best fits his needs. I can't help but think that this question arose because he can't seem to find the antenna that helps him make successful DX contacts. I used a TA-33JR for years. It was a fantastic 3 element beam. It was small, fit on my roof and could be turned by a RadShak TV Rotor. Even though it wasn't the ideal height above ground, it made a world of difference chasing mobiles for the WA counties award. I try to learn a lot about antennas. I don't claim to be an expert and certainly don't want anyone to think I am trying to make Art (or anyone else) look like they don't know what they are talking about. BTW, Art, have you looked at the N4GG antenna? It is on the ARRL site for members. I built one and didn't understand it so I took it down and made a new antenna. Then I got the details of it, but it was promoted as being a low angle of radiation. I don't know the degrees, though. It was certainly a much quieter antenna than the dipole. I talked to N4GG by email. He is a real nice person. Good luck, Buck -- Buck N4PGW |
I occasionally chase counties when I am sitting at my desk doing other
things and have the radio available. Right now I am using a horizontal dipole antenna to make contacts. The downside of this is that many times I can't hear the mobiles or they can't hear me. I am thinking that I might be able to improve my contacts by using a vertical antenna since most mobiles use vertical antennas. I have heard that once the signal bounces off the ionosphere, polarity isn't as important as it is for local communications. However, when I was assembling a 2 meter dipole antenna, I held it horizontal and turned it vertical. I saw the s-meter go from nothing to s-7 and the repeater go from silent to full quieting when I did this. I can't help but wonder how much difference it will make with the mobiles. Thanks for the comments. Buck N4PGW -- Buck N4PGW |
Yes, you've got it. Hopefully some of the folks who didn't understand my
explanation will understand yours. Roy Lewallen, W7EL Mike Coslo wrote: Let me have a shot at it, Roy. possible blather alert! Perhaps there is confusion by some people with the idea that the takeoff angle. I suspect that a lot of people think of their RF leaving the antenna as a "blob" that leaps out at some desired or undesired angle. Instead, the RF is heading off in all directions, with some angles having more relative power. So even if an antenna has a lower TOA, it might be less gain than an antenna that has a higher TOA has at that angle. An inefficient antenna with a low TOA can be less efficient at that low TOA than a more efficient antenna with a higher TOA is at that same low TOA. Oy. - Mike KB3EIA - rest snipped |
Thanks, Cecil.
Roy Lewallen, W7EL Cecil Moore wrote: Maybe a picture is worth a thousand words. Here's a comparison radiation pattern for my 130 ft dipole Vs my 40m vertical with elevated radials. In the dipole's favored direction, it's TOA is greater than the vertical's yet the dipole radiates more power than the vertical even at the vertical's TOA. Here's the pictu http://www.qsl.net/w5dxp/dipvsver.htm -- 73, Cecil, W5DXP |
On Sat, 29 Jan 2005 20:35:56 -0500, "J. Mc Laughlin"
wrote: I do not recall writing anything about power amplifiers or something called "one way propagation." The paragraph you quoted is the paragraph I reiterated what I thought you were saying. All that follows was not from you, but a followup continuing the topic. As for DXing. I don't chase it, but I don't turn it down either. We do seem to be in agreement that TOA isn't the most important factor. {Break from that} I have heard where antennas, beams in particular, have been mounted too high and thus not been as good for the contact. I don't remember the numbers, two to three wavelengths sounds right, but there seems to be an optimum height for beam antennas. Art first mentioned the amps and I threw in the one-way propagation statement, which probably neither of which really contributes to the real question for discussion. -- Buck N4PGW |
Buck wrote:
. . . He agrees that the antenna is better as it improves receive as well as transmit, but I can't see the TOA being more important than the gain unless it is really off by a long way. . . It's important to realize that at HF (where atmospheric rather than receiver noise dominates), different criteria are important for receiving than transmitting antenna improvement. If you simply increase the gain of an antenna without changing the pattern (by, for example, improving the efficiency of a vertical by adding more radials), it improves the S/N ratio at the station you're talking to, but it doesn't help the S/N ratio at your end. The reason is that both of you are getting noise from elsewhere. When you increase your gain, it improves the signal at the other end, while the noise at the other end stays the same, hence the S/N ratio improvement. But the gain increase causes both the signal and the noise to increase at your end, both in the same proportion. So you've improved your transmit effectiveness but haven't improved your ability to receive. You've done no more than you would by turning up the volume control. The only way to improve your ability to receive at HF is to improve the directivity of the antenna, so it has less gain in the direction the noise, or some of the noise, is coming from compared to the direction of the station you're talking with. Deep pattern nulls are usually an important factor in doing this. If the signal and bulk of the noise both come from the same direction, you're stuck. The pattern makes no difference for transmitting, only the gain in a single direction. (I'll ignore the possibility of multipath propagation or surface/sky wave interference for this simplified explanation.) But for receiving, the ability to have different gains in different directions is important. Because the absolute gain isn't important, a small and inefficient but rotatable antenna with some good nulls can be an excellent receiving antenna. At VHF/UHF, where the noise primarily comes from the receiver front end, antenna gain helps the S/N ratio for both transmitting and receiving. Roy Lewallen, W7EL |
Let me encourage you to build a vertical antenna and arrage a switch so
you can switch back and forth between it and your dipole. Be sure to use a current balun or two in your dipole feedline so it doesn't become part of the test. Here's what I think you'll find, as I have when comparing a vertical to a horizontal antenna. At times, one antenna will be spectacularly better than the other -- by 20 dB or more. After a while, maybe a minute or so, the signal on the good antenna will fade, and when you switch you'll find that the other antenna is now a lot better than the formerly good one, by about the same amount. This cycle can go on for quite a while. This is likely due to polarization rotation (although multipath can cause a similar effect, if the antennas are spaced far enough apart); whichever antenna has the right polarization for the moment will be much better than the other. I don't believe you'll find any spectacular overall improvement by using the vertical. When doing these tests, don't make the mistake of assuming the units on your S-meter are some particular number of dB, unless you have the abililty to actually measure them. Any assumption you make could be WAY off. Roy Lewallen, W7EL Buck wrote: I occasionally chase counties when I am sitting at my desk doing other things and have the radio available. Right now I am using a horizontal dipole antenna to make contacts. The downside of this is that many times I can't hear the mobiles or they can't hear me. I am thinking that I might be able to improve my contacts by using a vertical antenna since most mobiles use vertical antennas. I have heard that once the signal bounces off the ionosphere, polarity isn't as important as it is for local communications. However, when I was assembling a 2 meter dipole antenna, I held it horizontal and turned it vertical. I saw the s-meter go from nothing to s-7 and the repeater go from silent to full quieting when I did this. I can't help but wonder how much difference it will make with the mobiles. Thanks for the comments. Buck N4PGW |
"Buck" wrote in message ... On Sat, 29 Jan 2005 16:45:29 -0800, Richard Clark wrote: On Sat, 29 Jan 2005 19:22:12 -0500, Buck wrote: Speaking of Yagi's and gain, I know that the gain (and inversely the bandwidth) of a yagi is increased by extending the spacing between elements. A wide spaced gives a little more gain than narrow spaced elements. I believe it also narrows the beam width of the signal. Hi Buck, This is fine. I don't think it affects that TOA, though, except maybe by its relationship to the ground and its surrounding terrain. It is unlikely that anything you do in such a small footprint will bring any geometric change that brings even a perceptible change to the TOA. However, by simply increasing gain, the entire lobe structure of the antenna increases (same shape balloon, but now a larger balloon) which does impact the TOA; but not its angle, instead more its magnitude. This, in a sense, was the comparison Roy was drawing upon with the different examples. In a sense, increasing the antenna gain (all other factors held constant) would be indistinguishable from simply boosting the transmitter gain (or adding an Amp). 73's Richard Clark, KB7QHC I think you and I are in agreement except for what Art believes. (see his statement below:) I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. He agrees that the antenna is better as it improves receive as well as transmit, but I can't see the TOA being more important than the gain unless it is really off by a long way. But Buck that is exactly what I am talking about. Just think about what types of antenna can be considered a band opener. Somebody mentioned a 150 foot boom yagi which tho it has lots of gain it is at a low height. I suspect the lobe it is projecting will be around 13 degrees and the lobe will be fat suchg that the lower portion of the main lobe may well encompass a 10 degree signal. Another band opener will be say a three element antenna at a height of say 150 to 200 feet. The three element antenna is not a ground shaker but the lobe is made lower than a normal height antenna thus even tho the antenna is relative low gain this low gain is directed at a low angle say 10 to 11 degrees that can intercept signals just as the band is opening. Another band opener is vertically stacked three element beams solely because there is three db gain to be had purely by stacking that can be added to the uppermost antenna which also lowers the interception angle area by virtue of a fatter lobe. Now look at the band when it is well established, most antennas will now intercept a lot of the DX signals but at the same time many of the band opening antennas may well fail to hear the signals as the signals may well be coming in at a higher angle which coincides with the null supplied between the first and second lobe . In all of this you must take note of what Reg said in that communicating signals must have the same hop distance which revolves around lobe interception and not gain. If the lobe intersection of the two stations vary by say a few hundred miles no amount of extra gain is going to make communication possible. I am a member of the RSGB and not the ARRL. Regards Art snip. Good luck, Buck -- Buck N4PGW |
From URL:
http://www.astronantennas.com/polarization.html On line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more. -- Caveat Lector "Buck" wrote in message ... I occasionally chase counties when I am sitting at my desk doing other things and have the radio available. Right now I am using a horizontal dipole antenna to make contacts. The downside of this is that many times I can't hear the mobiles or they can't hear me. I am thinking that I might be able to improve my contacts by using a vertical antenna since most mobiles use vertical antennas. I have heard that once the signal bounces off the ionosphere, polarity isn't as important as it is for local communications. However, when I was assembling a 2 meter dipole antenna, I held it horizontal and turned it vertical. I saw the s-meter go from nothing to s-7 and the repeater go from silent to full quieting when I did this. I can't help but wonder how much difference it will make with the mobiles. Thanks for the comments. Buck N4PGW -- Buck N4PGW |
On Sun, 30 Jan 2005 03:09:54 GMT, "
wrote: But Buck that is exactly what I am talking about. Just think about what types of antenna can be considered a band opener. Somebody mentioned a 150 foot boom yagi which tho it has lots of gain it is at a low height. I suspect the lobe it is projecting will be around 13 degrees and the lobe will be fat suchg that the lower portion of the main lobe may well encompass a 10 degree signal. Another band opener will be say a three element antenna at a height of say 150 to 200 feet. The three element antenna is not a ground shaker but the lobe is made lower than a normal height antenna thus even tho the antenna is relative low gain this low gain is directed at a low angle say 10 to 11 degrees that can intercept signals just as the band is opening. Another band opener is vertically stacked three element beams solely because there is three db gain to be had purely by stacking that can be added to the uppermost antenna which also lowers the interception angle area by virtue of a fatter lobe. Now look at the band when it is well established, most antennas will now intercept a lot of the DX signals but at the same time many of the band opening antennas may well fail to hear the signals as the signals may well be coming in at a higher angle which coincides with the null supplied between the first and second lobe . In all of this you must take note of what Reg said in that communicating signals must have the same hop distance which revolves around lobe interception and not gain. If the lobe intersection of the two stations vary by say a few hundred miles no amount of extra gain is going to make communication possible. I am a member of the RSGB and not the ARRL. Fair enough, I can't know where everyone is on the internet. On the air, I get the advantage of having their callsign. I'll be glad to send you the antenna design if you wish. (I see that isn't your problem here). Regards Art It appeared to me that you were looking for that lower lobe, not the higher one when the band opens. The longer the beam, the narrower its pattern is, and like better the rejection from other directions (f/b, f/s rejection, etc. I took that as an understood.) )While answering both you and in part, Roy,) from the OP: Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. end quote. I was under the impression that you felt a need for designers to find a lower TOA. closer to ten or eleven degrees. I am confused, there can be no doubt of that in your minds at this point I am sure :). I do realize that at least in a yagi, as you increase the forward gain (f/b and s/b ratios), generally by adding elements that it narrows the forward lobe horizontally and vertically. A 150 foot boom (say 20 elements for example) beam might be perfect for picking up the lower angle, which is what I thought you were looking for. The three element beam will bring in higher angle signals as the lobe will have a higher angle. A dipole will likely have even a higher, possibly a NVIS angle. As for being quieter, I didn't define it but I mentioned that the N4GG antenna was much quieter than my dipoles. It also has a low angle of radiation, which fits very well with what you and Roy are telling me. It doesn't have a high gain, in fact the designer doesn't even try to calculate it except to say it is a little higher than a dipole. He also said it was designed for the DX and not to expect to chat with many nearby stations. For a small real estate layout, I imagine that the N4GG can be used with a dipole or small beam for continuous DX operation. Of course the N4GG antenna is larger than a dipole. It is one wave long and has quarter wave legs hanging off it. .... from the OP I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. Are you looking for a small antenna that will pick up the DX before the other DX hounds start piling up? -- Buck N4PGW |
On Sat, 29 Jan 2005 18:41:35 -0800, Roy Lewallen
wrote: When doing these tests, don't make the mistake of assuming the units on your S-meter are some particular number of dB, unless you have the abililty to actually measure them. Any assumption you make could be WAY off. Thanks. My determining factor will be making the contact when I am up for it. Too many times I have heard an s5 or better signal but by the time it was my turn to call, or the pileup dies down, I can't hear the mobile. That may be the answer. I once considered phasing the vertical and horizontal together, but from everything I read, the advantages of one over the other often have to do with noise not picked up due to polarity. Horizontals have some noise, and verticals have different noise, but a combination of the two would have it all. Since I am dealing with 20 and 40 meters mostly, I would only concern myself with the 20 meter vertical. 40 doesn't seem to have the problem. It seems that if I hear them on 40 I can work them. On 20 I might get a 5-7 reply to a 22 report or vice-versa. If I hang the vertical here, the top will be about 65 feet above ground. The dipole feedline will be about 15 feet away and the center of the dipole about 50-55 feet high. I doubt they will interact with each other. Thanks for your comments. -- Buck N4PGW |
"Buck" wrote in message ... On Sun, 30 Jan 2005 03:09:54 GMT, " wrote: snipArt It appeared to me that you were looking for that lower lobe, not the higher one when the band opens. The longer the beam, the narrower its pattern is, and like better the rejection from other directions (f/b, f/s rejection, etc. I took that as an understood.) )While answering both you and in part, Roy,) from the OP: Fact is that most long distance signals on 20 metres come in at angles of 11 degrees or less where as the 'normal' antenna has a TOA of around 14 degrees. end quote. I was under the impression that you felt a need for designers to find a lower TOA. closer to ten or eleven degrees. Yes, that is exactly what I said and what I mean.We need to get away from the long boom high gain aproach which cannot be used in many places and look at other aproaches to getting a lower lobe trajectory with a small turning radius. Some will say that is impossible where as I would say it is possible when open minds are turned to the task. Just think of what I could be describing, a 20 metre antenna with a ten to eleven degree TOA, turning radius of a conventional dipole and a feed point of something less than 75 foot high. Now thats good for small real estate and a light duty rotor tho the U.K. authority may baulk at the height. I have built very long boom yagi.s. for 20 M some with a couple of reflectors and some with as many as 13 elements but this direction is limited by minimal advances compared to complexity, thus my statement as to what the hobby needs for it to grow Regards Art KB9MZ........XG I am confused, there can be no doubt of that in your minds at this point I am sure :). I do realize that at least in a yagi, as you increase the forward gain (f/b and s/b ratios), generally by adding elements that it narrows the forward lobe horizontally and vertically. A 150 foot boom (say 20 elements for example) beam might be perfect for picking up the lower angle, which is what I thought you were looking for. The three element beam will bring in higher angle signals as the lobe will have a higher angle. A dipole will likely have even a higher, possibly a NVIS angle. As for being quieter, I didn't define it but I mentioned that the N4GG antenna was much quieter than my dipoles. It also has a low angle of radiation, which fits very well with what you and Roy are telling me. It doesn't have a high gain, in fact the designer doesn't even try to calculate it except to say it is a little higher than a dipole. He also said it was designed for the DX and not to expect to chat with many nearby stations. For a small real estate layout, I imagine that the N4GG can be used with a dipole or small beam for continuous DX operation. Of course the N4GG antenna is larger than a dipole. It is one wave long and has quarter wave legs hanging off it. ... from the OP I believe it is time for antenna designers to concentrate less on obtaining gain and instead concentrate more on lowering the TOA. without the need of excessive real estate requirements. Are you looking for a small antenna that will pick up the DX before the other DX hounds start piling up? -- Buck N4PGW |
Roy Lewallen wrote: Let me encourage you to build a vertical antenna and arrage a switch so you can switch back and forth between it and your dipole. Be sure to use a current balun or two in your dipole feedline so it doesn't become part of the test. Here's what I think you'll find, as I have when comparing a vertical to a horizontal antenna. At times, one antenna will be spectacularly better than the other -- by 20 dB or more. After a while, maybe a minute or so, the signal on the good antenna will fade, and when you switch you'll find that the other antenna is now a lot better than the formerly good one, by about the same amount. This cycle can go on for quite a while. This is likely due to polarization rotation (although multipath can cause a similar effect, if the antennas are spaced far enough apart); whichever antenna has the right polarization for the moment will be much better than the other. Thats pretty close...They flip flop back and forth... I don't believe you'll find any spectacular overall improvement by using the vertical. Depends on the length of the path, and the frequency. On 40m at night, the improvement using the vertical is spectacular *if* the path is long enough. But that will vary. At 500 miles, usually the dipole will win. At 1000 miles, usually they will be about even. At 1500 miles the usual amount on the S meter is about 2 s units in favor of the vertical. At 4000+ miles, can be 4 s units. But of course, this will vary to the quality of the vertical. In my case, was a full size ground plane, 4 radials, up 36 feet at the base. The dipole was at 36 feet. Same height as the base of the GP. My 40 meter mobile antenna is almost always better than my 36 ft high dipole to either of the coasts. I've tested that many times to Fla. On say a 1500 mile path, usually the vertical will hold the best overall, maybe 90 percent of the time, but you will see the shift where they flip flop for a short time, and then flip back... Sometimes the flop will leave them about equal. When back to "normal", the vertical will be noticably better..2 s units in that 1500 mile case...The vertical will be better a lot larger percentage of the time, than the dipole. I've seen many cases where the dipole never is as loud as the vertical, no matter what the shift...But thats usually on the longer paths. The longer the path, the larger the vertical advantage. To say VK land, I've never seen the vertical less than 3-4 s units better than the dipole at 36 ft. And I was on about 3 times a week to check at that time. That dipole would have to be a whole lot higher than 36 ft to even come close to the ground plane I ran. When doing these tests, don't make the mistake of assuming the units on your S-meter are some particular number of dB, unless you have the abililty to actually measure them. Any assumption you make could be WAY off. True...I make no claim to actual db increase....But I do use switches, and get a good A/B comparison...BTW...I think the vertical advantage on long paths decreases as you go higher in frequency...Maybe cuz the dipoles are higher in wavelength??? Not sure...Seems to be more a lower band, nighttime thing...The types of propagation at night vs day may be a factor...MK |
Buck wrote:
. . . If I hang the vertical here, the top will be about 65 feet above ground. The dipole feedline will be about 15 feet away and the center of the dipole about 50-55 feet high. I doubt they will interact with each other. The dipole feedline and the vertical will interact a great deal unless you take steps to prevent it. That would be to insert one or more "current baluns" (otherwise known as choke baluns and common mode chokes) in the dipole feedline. Roy Lewallen, W7EL |
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