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Dish reflector
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 |
Dish reflector
On Thu, 9 Apr 2009 20:05:20 -0700 (PDT), Art Unwin
wrote: No baluns are used That alone is at least one thing wrong with the design. Ignoring the obvious, the design suffers from the basic disregard for scale and wavelength. There are probably other issues beyond these violations of first principles. 73's Richard Clark, KB7QHC |
Dish reflector
In message
, Art Unwin writes 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? Diffraction off the edge of the reflector. It causes backlobes. It's not a fault. Brian GM4DIJ -- Brian Howie |
Dish reflector
On Apr 9, 11:59*pm, Richard Clark wrote:
On Thu, 9 Apr 2009 20:05:20 -0700 (PDT), Art Unwin wrote: No baluns are used That alone is at least one thing wrong with the design. Ignoring the obvious, the design suffers from the basic disregard for scale and wavelength. There are probably other issues beyond these violations of first principles. 73's Richard Clark, KB7QHC The radiator is totally within the reflector envelope ! It is possible that the transmission line is picking up some signal but a brief scan of the books show that dishes do some how obtain some signals from the rear.. "Ignoring the obvious" is a nonsense aproach, as is scale and wavelength. I was hoping for somebody who is familiar with dish design and not from one who is a talking head bent on agitation and slander |
Dish reflector
In message , Richard Clark
writes On Thu, 9 Apr 2009 20:05:20 -0700 (PDT), Art Unwin wrote: No baluns are used That alone is at least one thing wrong with the design. Do you use a balun with a helix and a dish reflector? Surely that bit at least is right! -- Ian |
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 |
Dish reflector
Brian Howie wrote:
In message , Art Unwin writes 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? Diffraction off the edge of the reflector. It causes backlobes. It's not a fault. Brian GM4DIJ Ask him the working frequency and dimensions of his "dish reflector". Don't be drinking anything when you read his answer. -- Jim Pennino Remove .spam.sux to reply. |
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. |
Dish reflector
On Apr 10, 9:50*am, "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 Dale I thought that if the radiator was in the reflector envelope, that is the radiator is below the top of the cone then there should be no radiation from the rear though possibly a little edge refraction. I know little regarding dish reflectors thus the question. I am of the opinion that radio is a matter of particles and not waves so I can easily visualize impregnation of the shield at the center as per Rutherford foil and particle experiments, but I am not ready to jump because of edge taper and other things that I am not aware of What is very clear from dish radiation patterns in the books that there is a localised radiation congregation at the dish axis rear which appears unexplainable. at the rear at the dishes axis tho it is in the area of direct impact I appreciate the comments and thoughts applied but not the nonsensicle writings of Richard who is wired so differently from the rest of us. These signals appear at all frequencies though I fail to see what the impact of frequency is because of the reflector envelope or umbrella. |
Dish reflector
Art Unwin wrote:
On Apr 10, 9:50 am, "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 Dale I thought that if the radiator was in the reflector envelope, that is snip These signals appear at all frequencies though I fail to see what the impact of frequency is because of the reflector envelope or umbrella. Dale You will, of course, have noted that he hasn't given a couple of the important items that you requested. Based upon some of his earlier babblings, I suspect that this is a helical antenna of perhaps UHF dimensions that he is attempting to use on 160 or 80. tom K0TAR |
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