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RF Grounding and Shorting a G5RV for use on 160 Meters
I'm thinking of tossing up a G5RV and perhaps using it at times on 160
meters by shorting the braid and center conductor. What do I need for buried radials ? Will several 40' - 50' radials work satisfactorially or would one ~125' radial be best ? I could run a 125' radial but not in a straight line I'm planning on using No. 14 Ga solid insulated wire. I think I've read in this newsgroup that the buried wire doesn't have to be bare ? Also does anyone have a more elegant way of shorting the inner conductor and braid together than the half axxed contraption I'd cobble together ;) ? Thanks in advance. Gary |
Gary wrote:
I'm thinking of tossing up a G5RV and perhaps using it at times on 160 meters by shorting the braid and center conductor. What do I need for buried radials ? Will several 40' - 50' radials work satisfactorially or would one ~125' radial be best ? I could run a 125' radial but not in a straight line Several shorter radials will definitely be better than a single long one. I'm planning on using No. 14 Ga solid insulated wire. I think I've read in this newsgroup that the buried wire doesn't have to be bare ? Yes, that's correct. Also does anyone have a more elegant way of shorting the inner conductor and braid together than the half axxed contraption I'd cobble together ;) ? It's hard to say how to make something better than something for which we have no description. Surely it can't be too hard to short two conductors together. Roy Lewallen, W7EL |
On Tue, 10 May 2005 18:39:16 -0700, Roy Lewallen
wrote: Gary wrote: I'm thinking of tossing up a G5RV and perhaps using it at times on 160 meters by shorting the braid and center conductor. What do I need for buried radials ? Will several 40' - 50' radials work satisfactorially or would one ~125' radial be best ? I could run a 125' radial but not in a straight line Several shorter radials will definitely be better than a single long one. I'm planning on using No. 14 Ga solid insulated wire. I think I've read in this newsgroup that the buried wire doesn't have to be bare ? Yes, that's correct. Also does anyone have a more elegant way of shorting the inner conductor and braid together than the half axxed contraption I'd cobble together ;) ? It's hard to say how to make something better than something for which we have no description. Surely it can't be too hard to short two conductors together. Roy Lewallen, W7EL Thanks Roy, I can certainly short two conductors together. I was just thinking of minimizing any amount of stray RF that might arrise given my propensity to make Rube Goldberg type contraptions out of something that should be an easy task. ;) Gary |
On Tue, 10 May 2005 18:39:16 -0700, Roy Lewallen
wrote: Gary wrote: I'm thinking of tossing up a G5RV and perhaps using it at times on 160 meters by shorting the braid and center conductor. What do I need for buried radials ? Will several 40' - 50' radials work satisfactorially or would one ~125' radial be best ? I could run a 125' radial but not in a straight line Several shorter radials will definitely be better than a single long one. I'm planning on using No. 14 Ga solid insulated wire. I think I've read in this newsgroup that the buried wire doesn't have to be bare ? Yes, that's correct. Also does anyone have a more elegant way of shorting the inner conductor and braid together than the half axxed contraption I'd cobble together ;) ? It's hard to say how to make something better than something for which we have no description. Surely it can't be too hard to short two conductors together. Roy Lewallen, W7EL One question, if shorting the leads to feed the g5rv "marconi style", would it be better to connect the single wire to the antenna tuner's random wire connection, or to the coax connection, or does it matter? bob k5qwg |
Hi,
Say, I've got a question about something I've read about the Swift gamma ray detection satellite. It's detector consisted of an antenna composed of 52,000 lead blocks arranged by computer generated pseudo-random locations and glued to the back of a sheet of 4x8 plywood. The actual detectors where located in the spaces between the blocks. It wasn't mentioned but I think these were probably crystals which give off a pulse of electricity every time they are struck by a gamma ray. Anyways my question is, in your opinion, what is the purpose of the pseudo random arrangement of this "apperture mask" antenna? I suspect it has something statistical related to the nature of ambient noise signals. I tried making a pc simulation of this but I get the same answer whether the array is in rows or pseudo-random. I tried with noise but I saw no reduction. I haven't tried adding a signal to the noise in the simulation yet though... A*s*i*m*o*v .... Three types of lies: lies, damn lies, and statistics - Mark Twain. |
It's hard to say how to make something better than something for which
we have no description. Surely it can't be too hard to short two conductors together. Roy Lewallen, W7EL One question, if shorting the leads to feed the g5rv "marconi style", would it be better to connect the single wire to the antenna tuner's random wire connection, or to the coax connection, or does it matter? bob k5qwg How much current will actually flow in the center conductor of the shorted coaxial feedline? The single wire connection makes much more sense. I never liked the G5RV antenna since it just seemed like a high loss method of feeding a 102 ft piece of wire. Frank VE6CB |
What is the basis of your "high loss method" statement?
"Frank" wrote in message news:O7pge.61496$tg1.25181@edtnps84... I never liked the G5RV antenna since it just seemed like a high loss method of feeding a 102 ft piece of wire. Frank VE6CB |
"Fred W4JLE" wrote in message ... What is the basis of your "high loss method" statement? "Frank" wrote in message news:O7pge.61496$tg1.25181@edtnps84... I never liked the G5RV antenna since it just seemed like a high loss method of feeding a 102 ft piece of wire. Frank VE6CB The following is based on an analysis I did for a ham Friend. Consider a 102 ft bent dipole (REF: Richards Antenna v4), fed in the center with 33ft of 300 ohm tubular, followed by 25 ft of 75 ohm twin. Frequency Total feedline loss (MHz) (dB) 1.8 24.8 3.8 4.9 7.1 2.4 10.1 10.2 14.1 1.4 18.1 3.0 21.2 9.1 24.9 2.7 28.5 3.9 If you are interested I can e-mail you the complete analysis in Microsoft Word showing various feedline combinations from 1.8 to 30 MHz. If you have a particular structure in mind I can also do the analysis. I use NEC2 based software in combination with the ARRL's transmission line analysis program. Regards, Frank VE6CB |
"Fred W4JLE" wrote in message ... Frank, with all due respect I disagree with your analysis. I would appreciate your sending me the data so we may both start at the same discussion point. will get the info to me. 73 Fred Thanks Fred, I am happy when people disagree with me, since then I have a chance of learning something. I will e-mail you my analysis. 73, Frank |
Frank wrote:
How much current will actually flow in the center conductor of the shorted coaxial feedline? Good question. In this case, the more difference in the two currents, the greater the radiation from the horizontal section. I never liked the G5RV antenna since it just seemed like a high loss method of feeding a 102 ft piece of wire. Actually, if the purpose of the matching section is to lower the SWR (and thus the losses) on the coax, it does a reasonable job on 80m, 40m, 20m, and 12m. But forget the other four bands unless you change the length of the matching section. -- 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! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Wednesday, 11 May 2005 09:06:36 -500, "Asimov"
wrote: Anyways my question is, in your opinion, what is the purpose of the pseudo random arrangement of this "apperture mask" antenna? Hi Isaac, The random code of the "coded aperture mask" can be correlated to the grid pattern of detectors to make a virtual lens. I haven't tried adding a signal to the noise in the simulation yet though... You probably won't unless you have deconvolution math behind it. 73's Richard Clark, KB7QHC |
Bob Miller wrote:
One question, if shorting the leads to feed the g5rv "marconi style", would it be better to connect the single wire to the antenna tuner's random wire connection, or to the coax connection, or does it matter? It's hard to say, because too many variables are involved. What I'd do is to model the antenna with EZNEC and if the impedance is high use the random wire connection and if low the coax connection. Roy Lewallen, W7EL |
Asimov,
I believe you have misinterpreted the geometry. The detector array is some distance behind the aperture array, perhaps one meter or more. The concept is that of a simple shadow mask. There are 52000 shadows on 32000 detectors, so the details of the computation are probably a bit complex. I recommend a paper by Scott Barthelmy, which is available at http://swift.gsfc.nasa.gov/docs/swif...SBarthelmy.pdf 73, Gene W4SZ Asimov wrote: Hi, Say, I've got a question about something I've read about the Swift gamma ray detection satellite. It's detector consisted of an antenna composed of 52,000 lead blocks arranged by computer generated pseudo-random locations and glued to the back of a sheet of 4x8 plywood. The actual detectors where located in the spaces between the blocks. It wasn't mentioned but I think these were probably crystals which give off a pulse of electricity every time they are struck by a gamma ray. Anyways my question is, in your opinion, what is the purpose of the pseudo random arrangement of this "apperture mask" antenna? I suspect it has something statistical related to the nature of ambient noise signals. I tried making a pc simulation of this but I get the same answer whether the array is in rows or pseudo-random. I tried with noise but I saw no reduction. I haven't tried adding a signal to the noise in the simulation yet though... A*s*i*m*o*v ... Three types of lies: lies, damn lies, and statistics - Mark Twain. |
"Gene Fuller" bravely wrote to "All" (11 May 05 21:02:18)
--- on the heady topic of " Apperture Mask Antenna" GF From: Gene Fuller GF Xref: aeinews rec.radio.amateur.antenna:30137 GF Asimov, GF I believe you have misinterpreted the geometry. The detector array is GF some distance behind the aperture array, perhaps one meter or more. The original release mentions that the gamma rays can only penetrate inbetween the lead blocks but doesn't mention how far back the detectors were located or how they were arranged. GF The concept is that of a simple shadow mask. There are 52000 shadows GF on 32000 detectors, so the details of the computation are probably a GF bit complex. "The mask together with a set of gamma-ray detectors, totaling 32,768 pieces of cadmium-zinc-telluride each measuring four square millimeters are the main components of Swift's Burst Alert Telescope (BAT). BAT will locate hundreds of bursts to better than 4-arcminute accuracy and provide enhanced sensitivity to faint bursts that earlier detectors have missed." Maybe it is a little less complex than we might assume... GF I recommend a paper by Scott Barthelmy, which is available at GF http://swift.gsfc.nasa.gov/docs/swif..._SBarthelmy.pd GF f "For an image of the coded aperture mask, refer to: http://swift.gsfc.nasa.gov/news/coded_app_mask.html." That's all I have... A*s*i*m*o*v .... "Beware of all enterprises that require new clothes." -- THOREAU |
"Richard Clark" bravely wrote to "All" (11 May 05 12:05:28)
--- on the heady topic of " Apperture Mask Antenna" RC The random code of the "coded aperture mask" can be correlated to the RC grid pattern of detectors to make a virtual lens. I haven't tried adding a signal to the noise in the simulation yet though... RC You probably won't unless you have deconvolution math behind it. Would you please, explain? A*s*i*m*o*v .... Essay: Describe the universe in 500 words or less & name 2 examples. |
"Asimov" wrote in message ... Hi, Say, I've got a question about something I've read about the Swift gamma ray detection satellite. It's detector consisted of an antenna composed of 52,000 lead blocks arranged by computer generated pseudo-random locations and glued to the back of a sheet of 4x8 plywood. The actual detectors where located in the spaces between the blocks. It wasn't mentioned but I think these were probably crystals which give off a pulse of electricity every time they are struck by a gamma ray. Anyways my question is, in your opinion, what is the purpose of the pseudo random arrangement of this "apperture mask" antenna? I suspect it has something statistical related to the nature of ambient noise signals. I tried making a pc simulation of this but I get the same answer whether the array is in rows or pseudo-random. I tried with noise but I saw no reduction. I haven't tried adding a signal to the noise in the simulation yet though... A*s*i*m*o*v .... Three types of lies: lies, damn lies, and statistics - Mark Twain. Plywood on a satellite? 73 Roger ZR3RC |
On Thursday, 12 May 2005 00:09:36 -500, "Asimov"
wrote: RC You probably won't unless you have deconvolution math behind it. Would you please, explain? Hi Isaac, The technique is one of a suite of tools derived from Fourier analysis. The background signal contains a random response that is largely immutable. That signal can be used as a key (if we were to use the parlance of cryptography). The signal of interest still appears to be just as random - in isolation. However, when both are "mixed" (if we were to use the idiom of electronics), then the signal of interest rises out of the noise. It is not a simple mixing process, however, because in that idiom we don't know the center frequency - so to speak (and instead of getting clear speech in the typical SSB application we get something that sounds like Donald Duck at best). However, in Fourier analysis, you can slip the two signals past each other (akin to matching the key of the "Gold Code" of a spread spectrum signal to the incoming signal) in what is called cross correlation and the deconvolved signal will spring out as a result (when done with what is called confidence math, also found in the Fourier repertoire). To return to the idiom of the SSB application, the background noise becomes the center frequency. The same application has been done to map the ocean floor using natural wave and wildlife noise. 73's Richard Clark, KB7QHC |
Roger Conroy wrote: "Asimov" wrote in message ... Hi, Say, I've got a question about something I've read about the Swift gamma ray detection satellite. It's detector consisted of an antenna composed of 52,000 lead blocks arranged by computer generated pseudo-random locations and glued to the back of a sheet of 4x8 plywood. The actual detectors where located in the spaces between the blocks. It wasn't mentioned but I think these were probably crystals which give off a pulse of electricity every time they are struck by a gamma ray. Anyways my question is, in your opinion, what is the purpose of the pseudo random arrangement of this "apperture mask" antenna? I suspect it has something statistical related to the nature of ambient noise signals. I tried making a pc simulation of this but I get the same answer whether the array is in rows or pseudo-random. I tried with noise but I saw no reduction. I haven't tried adding a signal to the noise in the simulation yet though... A*s*i*m*o*v ... Three types of lies: lies, damn lies, and statistics - Mark Twain. Plywood on a satellite? 73 Roger ZR3RC Honeycomb composite, about 2" thick and about 1/4 the area of a sheet of plywood. http://swift.gsfc.nasa.gov/docs/swif.../bat_desc.html According to the web page, the answer to the original question is the geometry of the mask elements allows the telescope to maintain its field of view and angular resolution in the event of a wide variety of different sensor failures. ac6xg |
"Richard Clark" bravely wrote to "All" (12 May 05 08:23:37)
--- on the heady topic of " Apperture Mask Antenna" RC From: Richard Clark RC Xref: aeinews rec.radio.amateur.antenna:30190 RC On Thursday, 12 May 2005 00:09:36 -500, "Asimov" RC wrote: RC You probably won't unless you have deconvolution math behind it. Would you please, explain? RC Hi Isaac, RC The technique is one of a suite of tools derived from Fourier RC analysis. [,,,] RC The same application has been done to map the ocean floor using RC natural wave and wildlife noise. Okay, thanks but not Isaac rather Mike... Is this something like the noise forming a "bell curve" and the desired signal appearing on the outside? A*s*i*m*o*v .... Isn't Fourier and it's applications a bitch! |
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