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Dish reflector
"Art Unwin" wrote in message ... I made a helical end fed antenna that is inside a cone shaped reflector The reflector is made from 1/2" mesh steel with an aluminum foil liner and connected to the braid of the feed coax. No baluns are used, just direct connections. I was surprised to hear signals from the rear! I thought that a dish reflector prevented such signals getting to the receiver. So what can be wrong with the reflector or can signals get reflected back from the frontal area? Antenna is at a 40 foot height Any ideas as to what the fault could be? Regards Art I have no experience with dishes thus the question Note, the helical antenna does not protrude beyond the dish envelope. Art There is a lot of very important information missing here. What frequency are we talking about and what is the dish diameter? Do you have any idea as to what your edge taper is or sidelobes? Dale W4OP |
#2
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Dish reflector
Dale Parfitt wrote:
"Art Unwin" wrote in message ... I made a helical end fed antenna that is inside a cone shaped reflector The reflector is made from 1/2" mesh steel with an aluminum foil liner and connected to the braid of the feed coax. No baluns are used, just direct connections. I was surprised to hear signals from the rear! I thought that a dish reflector prevented such signals getting to the receiver. So what can be wrong with the reflector or can signals get reflected back from the frontal area? Antenna is at a 40 foot height Any ideas as to what the fault could be? Regards Art I have no experience with dishes thus the question Note, the helical antenna does not protrude beyond the dish envelope. Art There is a lot of very important information missing here. What frequency are we talking about and what is the dish diameter? Do you have any idea as to what your edge taper is or sidelobes? Dale W4OP The last time he talked about it, it was "designed" to operate on the 160 meter band and the "reflector" was 3 meters in diameter. No, those numbers are not typos. -- Jim Pennino Remove .spam.sux to reply. |
#3
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Dish reflector
On Apr 10, 10:15*am, wrote:
Dale Parfitt wrote: "Art Unwin" wrote in message ... I made a helical end fed antenna that is inside a cone shaped reflector The reflector is made from 1/2" mesh steel with an aluminum foil liner and connected to the braid of the feed coax. No baluns are used, just direct connections. I was surprised to hear signals from the rear! I thought that a dish reflector prevented such signals getting to the receiver. So what can be wrong with the reflector or can signals get reflected back from the frontal area? Antenna is at a 40 foot height Any ideas as to what the fault could be? Regards Art I have no experience with dishes thus the question Note, the helical antenna does not protrude beyond the dish envelope. Art There is a lot of very important information missing here. What frequency are we talking about and what is the dish diameter? Do you have any idea as to what your edge taper is or sidelobes? Dale W4OP The last time he talked about it, it was "designed" to operate on the 160 meter band and the "reflector" was 3 meters in diameter. No, those numbers are not typos. -- Jim Pennino Remove .spam.sux to reply. That antenna was when I used an old parabolic satellite dish which was unsuitable. Scanning past antenna papers point to the use of a cone shape similar to a horn of 2 metres diameter produces better results. The antenna needs a longer mast so at the moment I can't compare F/R. Either way, with the radiator within the reflector envelope it is difficult to understand what creates a rearward lobe regardles of scale or frequency of use with respect to receive. At the moment I see nothing that points away from the Rutherford particle experiments with foil .ie penetration when at right angles , deflection at other angles. |
#4
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Dish reflector
That antenna was when I used an old parabolic satellite dish which was unsuitable. Scanning past antenna papers point to the use of a cone shape similar to a horn of 2 metres diameter produces better results. The antenna needs a longer mast so at the moment I can't compare F/R. Either way, with the radiator within the reflector envelope it is difficult to understand what creates a rearward lobe regardles of scale or frequency of use with respect to receive. At the moment I see nothing that points away from the Rutherford particle experiments with foil .ie penetration when at right angles , deflection at other angles. As usual Art you are avoiding answering the questions and choose to confuse the issues with you own preconceived ideas and terminology. The fact that the feed is totally within the "reflector envelope" tells you or us nothing about sidelobes and edge taper. I really don't think you want answers, but I'll try once mo 1. What frequency 2. What is the dish diameter 3. What is the dish focal length to diameter ratio (F/D) Dale W4OP |
#5
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Dish reflector
On Apr 10, 6:00*pm, "Dale Parfitt" wrote:
*That antenna was when I used an old parabolic satellite dish which was unsuitable. Scanning past antenna papers point to the use of a cone shape similar to a horn of 2 metres diameter produces better results. The antenna needs a longer mast so at the moment I can't compare F/R. Either way, with the radiator within the reflector envelope it is difficult to understand what creates a rearward lobe regardles of scale or frequency of use with respect to receive. At the moment I see nothing that points away from the Rutherford particle experiments with foil .ie penetration when at right angles , deflection at other angles. As usual Art you are avoiding answering the questions and choose to confuse the issues with you own preconceived ideas and terminology. The fact that the feed is totally within the "reflector envelope" tells you or us nothing about sidelobes and edge taper. I really don't think you want answers, but I'll try once mo 1. What frequency 2. What is the dish diameter 3. What is the dish focal length to diameter ratio (F/D) Dale W4OP I am not avoiding questions, just those that appear irrelevant, but here goes Anything to make you happy, this should be interesting how you use these answers with respect to the posted question 1 160 metres upto 2 metres, tunable 2 2 metres 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. At least to the best of my knowledge which is why I posed the question Hopefully we will all stay on subject and not get side tracked. I will leave it to others to respond to Richard when they determine what he is talking about. |
#6
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Dish reflector
On Fri, 10 Apr 2009 16:49:31 -0700 (PDT), Art Unwin
wrote: 1. What frequency 2. What is the dish diameter 3. What is the dish focal length to diameter ratio (F/D) I am not avoiding questions, just those that appear irrelevant, 20 postings to get to the point (not unanticipated, however) which Art calls "irrelevant." As for those answers? 1 160 metres upto 2 metres, tunable 2 2 metres Hence the wholesale disregard for first principles in size vs. wavelength. Elementary analysis need not go any further when failure is so obviously designed in. 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. -Well, maybe not obvious to everyone.- But why don't we chalk this design up to S U C C E S S and call it a thread? If this bier gets anymore wreaths tossed onto it, it will kill the pallbearers. 73's Richard Clark, KB7QHC |
#7
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Dish reflector
On Apr 10, 7:19*pm, Richard Clark wrote:
On Fri, 10 Apr 2009 16:49:31 -0700 (PDT), Art Unwin wrote: 1. What frequency 2. What is the dish diameter 3. What is the dish focal length to diameter ratio (F/D) I am not avoiding questions, just those that appear irrelevant, 20 postings to get to the point (not unanticipated, however) which Art calls "irrelevant." As for those answers? 1 160 metres upto 2 metres, tunable 2 2 metres Hence the wholesale disregard for first principles in size vs. wavelength. *Elementary analysis need not go any further when failure is so obviously designed in. * 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. -Well, maybe not obvious to everyone.- But why don't we chalk this design up to S U C C E S S and call it a thread? *If this bier gets anymore wreaths tossed onto it, it will kill the pallbearers. 73's Richard Clark, KB7QHC The posting is about dishes not antennas. I have not read about a dish that does not emit signals to the rear. Now I have built one and find to my surprize that it does accept signals from the rear ! All very simple, the radiator is resting at the bottom of a cone and the top of the radiator does not stick out beyond the reflector. Since you do not know what you are talking about and intent is to disrupt this thread why on earth are you muttering about nothing at length? Simple question has been posed and obviously you do not know the answers that antenna engineering knowledge would provide as you are not an engineer but a actor or actress by day and by night. My question remains unanswered after all these posts.How do signals arrive or depart from the rear of a dish or horn? We all know that you don't know the answer but there are qualified engineers in this group who possibly doand willing to share. |
#8
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Dish reflector
Art Unwin wrote:
I am not avoiding questions, just those that appear irrelevant, but here goes Anything to make you happy, this should be interesting how you use these answers with respect to the posted question 1 160 metres upto 2 metres, tunable 2 2 metres 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. At least to the best of my knowledge which is why I posed the question Hopefully we will all stay on subject and not get side tracked. I will leave it to others to respond to Richard when they determine what he is talking about. While this provide some details regarding your antenna, it is not sufficient for me to visualize it. If one can't visualize what you are talking about, getting help with your questions will be difficult. You could try a simple experiment: Remove the active part of your antenna and replace it with a dummy load. Leave the reflector/dish/whatever in place. If you still pick up signals, then the antenna itself may not be the problem. By 'active part', I mean the helix antenna. You have a web site, a link to a picture would help me understand what you are doing. |
#9
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Dish reflector
"joe" wrote in message ... Art Unwin wrote: I am not avoiding questions, just those that appear irrelevant, but here goes Anything to make you happy, this should be interesting how you use these answers with respect to the posted question 1 160 metres upto 2 metres, tunable 2 2 metres 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. At least to the best of my knowledge which is why I posed the question Hopefully we will all stay on subject and not get side tracked. I will leave it to others to respond to Richard when they determine what he is talking about. While this provide some details regarding your antenna, it is not sufficient for me to visualize it. take an aluminum foil dunce cap, wide a curly pigs tail helix inside of it and feed it with coax. most likely he attached the shield to the foil and the center conductor to the helix, so all he has is an ugly dipole all folded up on itself at hf. he would be better off putting the dunce cap over his head to prevent damage from the brain probes. |
#10
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Dish reflector
On Apr 11, 2:48*pm, joe wrote:
Art Unwin wrote: I am not avoiding questions, just those that appear irrelevant, but here goes Anything to make you happy, this should be interesting how you use these answers with respect to the posted question 1 160 metres upto 2 metres, tunable 2 2 metres 3 Doesn't have a focal length, it is an end fed ( series connection) helix antenna. At least to the best of my knowledge which is why I posed the question Hopefully we will all stay on subject and not get side tracked. I will leave it to others to respond to Richard when they determine what he is talking about. While this provide some details regarding your antenna, it is not sufficient for me to visualize it. If one can't visualize what you are talking about, getting help with your questions will be difficult. You could try a simple experiment: Remove the active part of your antenna and replace it with a dummy load. Leave the reflector/dish/whatever in place. If you still pick up signals, then the antenna itself may not be the problem. By 'active part', I mean the helix antenna. You have a web site, a link to a picture would help me understand what you are doing. Joe This debate has been going on for years. It is all in the archives. I am not interested in hearing the cacophony of sound all over again every time a newcomer comes along Believe it or not this thread started with a question and you may have read the responses. You may not be different from the others and time would be wasted again. Read the archives for yourself instead of asking favours of me, it is all printed in the archives and it goes back half a dozen years or more. If you are a qualified engineer like me it will take only a short time to get to the gist of the material and possibly fall in place with your support. But I will not hold my breath. Note Both previous advisors of Radcom amateur radio magazine in the UK and also Roy formerly of QST have formally debunked my position in public tho neither has provided proof so you might want to use your time else where Or maybe hook up with Richard. wink wink !! Either way I am readying to get out of here again these guys are ruthless. Nothing personal intended |
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