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folded dipoles
Do folded dipoles have better noise rejection than single wire dipoles. I
was looking at a drawing one day and realized that they are a dc short. I know loop antennas are very good about noise. Loop antennas are difficult to install and a folded dipole would be a lot easier. |
folded dipoles
B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles. I was looking at a drawing one day and realized that they are a dc short. I know loop antennas are very good about noise. Loop antennas are difficult to install and a folded dipole would be a lot easier. Try this search: http://groups.google.com/groups?hl=e...-8&sa=N&tab=wg folded dipole noise reduction dipole - Google Groups Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-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 =---- |
folded dipoles
B29 wrote:
Do folded dipoles have better noise rejection than single wire dipoles? There's some controversy about that but here's my take. Folded dipoles receive *electromagnetic noise* just as well (or just as bad) as ordinary dipoles. However, IMO, there is one type of noise that is not as bad on folded dipoles as open-ended dipoles and that is precipitation static noise defined at: http://www.atis.org/tg2k/_precipitation_static.html If a charged particle dumps its charge on the floating wire of an open-ended bare wire dipole, there is only one discharge path to the other side of the dipole or to ground and that is through the transceiver. However, if a charged particle dumps its charge on one half of a folded dipole, there are two discharge paths to the other half of the dipole, one through the transceiver and one through the antenna wire. The antenna wire discharge path is usually a lower impedance than the discharge path through the transceiver and the entire folded dipole is usually referenced to ground. In addition, we know that insulated airplane antennas are less susceptible to precipitation static than uninsulated airplane antennas. Folded dipoles are often made out of insulated transmission line. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
chuck wrote:
Try this search: http://groups.google.com/groups?hl=e...-8&sa=N&tab=wg folded dipole noise reduction dipole - Google Groups This posting of yours is at the top of the list. :-) -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Cecil Moore wrote:
Folded dipoles receive *electromagnetic noise* just as well (or just as bad) as ordinary dipoles. Sorry, that should be *electromagnetic wave noise*. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
On Mon, 18 Dec 2006 15:14:06 GMT, Cecil Moore wrote:
B29 wrote: Do folded dipoles have better noise rejection than single wire dipoles? rain static discussion However, if a charged particle dumps its charge on one half of a folded dipole, there are two discharge paths to the other half of the dipole, one through the transceiver and one through the antenna wire. Three discharge paths --- if the folded dipole is grounded to a boom or mast at the center point of its 'unbroken' side. (As is common with a number of VHF yagis that employ folded (tubing) dipoles as the driven element.) It's my unscientific, unmeasured observation that my 2M yagi with a folded dipole is bothered less by rain/snow static than my 6M, 'traditional dipole' yagi. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 *** Killfiling google posts: http//jonz.net/ng.htm |
folded dipoles
Cecil Moore wrote:
B29 wrote: Do folded dipoles have better noise rejection than single wire dipoles? There's some controversy about that but here's my take. Folded dipoles receive *electromagnetic noise* just as well (or just as bad) as ordinary dipoles. However, IMO, there is one type of noise that is not as bad on folded dipoles as open-ended dipoles and that is precipitation static noise defined at: http://www.atis.org/tg2k/_precipitation_static.html If a charged particle dumps its charge on the floating wire of an open-ended bare wire dipole, there is only one discharge path to the other side of the dipole or to ground and that is through the transceiver. Hello Cecil, It is not certain that there will be a "discharge" (i.e., a change from a charged state to a neutral one) at all. One possibility is that charges on the wire will simply redistribute themselves after the addition of a new charge. It also depends, obviously, on whether the charged particle is of the same polarity as the preponderance of charges that may already be on the antenna. My pet hypothesis is that these charge redistributions cause changing magnetic fields which appear as noise impulses in the receiver. Remember from electrostatics that a grounded conductor, such as a tower or an antenna, may not be at ground potential due to induction caused by a cloud of oppositely charged particles, alien space ships, or whatever charge concentration is in the vicinity of the conductor. Even though the conductor is grounded! Of course, when the influence departs, the grounded conductor returns to is neutral status. Make sense? ;-) Chuck However, if a charged particle dumps its charge on one half of a folded dipole, there are two discharge paths to the other half of the dipole, one through the transceiver and one through the antenna wire. The antenna wire discharge path is usually a lower impedance than the discharge path through the transceiver and the entire folded dipole is usually referenced to ground. In addition, we know that insulated airplane antennas are less susceptible to precipitation static than uninsulated airplane antennas. Folded dipoles are often made out of insulated transmission line. ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-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 =---- |
folded dipoles
chuck wrote:
It is not certain that there will be a "discharge" (i.e., a change from a charged state to a neutral one) at all. Make sense? ;-) I may be using the wrong word. By "discharge", I didn't mean to imply that it would go to a neutral state, just that a concentrated charge deposited at a point on a conductor will be redistributed over the entire conductor. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Cecil Moore wrote:
chuck wrote: It is not certain that there will be a "discharge" (i.e., a change from a charged state to a neutral one) at all. Make sense? ;-) I may be using the wrong word. By "discharge", I didn't mean to imply that it would go to a neutral state, just that a concentrated charge deposited at a point on a conductor will be redistributed over the entire conductor. I do wonder whether alternatively the noise is not arcing or coronal discharges caused by the buildup of these high potentials on an antenna. An insulated antenna would resist charging and if charged, would have less opportunity to discharge by arcing. The arcing could actually occur in the receiver. I have noticed that the precipitation static I sometimes hear sounds very much like sand/dirt particles striking a glass window in a blow. Data consistent with either hypothesis, I guess. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-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 =---- |
folded dipoles
If you think a DC short will reduce noise, why not just put an RF choke
or moderate value resistor across the feedline conductors of a conventional dipole? Roy Lewallen, W7EL B29 wrote: Do folded dipoles have better noise rejection than single wire dipoles. I was looking at a drawing one day and realized that they are a dc short. I know loop antennas are very good about noise. Loop antennas are difficult to install and a folded dipole would be a lot easier. |
folded dipoles
Roy Lewallen wrote:
If you think a DC short will reduce noise, why not just put an RF choke or moderate value resistor across the feedline conductors of a conventional dipole? Because that still leaves only one path for the RF precipitation static, i.e. through the receiver. The RF is not going to travel through the high impedance of the RF choke but it will travel through the lower impedance of the other conductor in a folded dipole or loop if it exists. However, an RF choke will eliminate arcing which certainly does reduce noise. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
WOW
Thank you all for the information. I found some very positive reports about folded dipoles. I will try one this spring. I live in the North Country and it would be quite hazardous to try and hang one in all the snow and ice. I have seen these dipoles already constructed and made up for sale. I guess I will just have it all ready when the thaw hits. I will try to find one with a current balun. Michael |
folded dipoles
Michael, please do not spend good money for something you can build
yourself for a fraction of the cost, and learn good things in the process... An 8X10 piece of plexiglass storm window from the hardware store will supply strips for the end and center insulators... A chunk of 300 ohm TV twin lead will supply the folded dipole material... A roll of coax, some solder, and a pieces of small rope, and you are in business... A hack saw will cut the plexi (so will a skill saw or table saw)... Why not make one for 10 meters as a starter until spring comes... This can be hung between two trees or whatever so it is at least head high and will give you some fun when the band opens here and there..... You can check the formula for length versus resonant frequency... denny / k8do |
folded dipoles
Cecil Moore wrote: Roy Lewallen wrote: If you think a DC short will reduce noise, why not just put an RF choke or moderate value resistor across the feedline conductors of a conventional dipole? Because that still leaves only one path for the RF precipitation static, i.e. through the receiver. The RF is not going to travel through the high impedance of the RF choke but it will travel through the lower impedance of the other conductor in a folded dipole or loop if it exists. Then you also need a short across the other side of the folden dipole or loop (the feedpoint) and then all of those pesky noise problems are completely solved. If you add a 10 dB attenuator between there and the input to the transmission line then you will also have a nearly flat SWR too. A nearly perfect antenna. Completely flat SWR, totally noise free and with equal gain in all directions! What more could you ask for? Wes N7WS |
folded dipoles
Wes wrote:
A nearly perfect antenna. Completely flat SWR, totally noise free and with equal gain in all directions! What more could you ask for? :-) How about some functionality? Let's take a look at a G5RV that I bought when I moved to AZ and got back into HF operation. One side of the G5RV dipole was DC floating at the antenna tuner output while the other side was DC grounded. During AZ desert windstorms, this new G5RV of mine arced at the coax connector due to precipitation static, sometimes several times per second. Putting up a 40m folded dipole caused the arcing to cease. Seems to me, an antenna that doesn't arc is more functional and less noisy than an antenna that does arc. :-) In addition, even when the wind was not strong enough to cause arcing, the folded dipole delivered less noise to the receiver than did the G5RV. Folding and insulating are two methods of reducing precipitation static in airplane antennas. The G5RV was not folded - the folded dipole was. The G5RV was not insulated - the folded dipole was. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Cecil Moore wrote: Wes wrote: A nearly perfect antenna. Completely flat SWR, totally noise free and with equal gain in all directions! What more could you ask for? :-) How about some functionality? Let's take a look at a G5RV that I bought when I moved to AZ and got back into HF operation. One side of the G5RV dipole was DC floating at the antenna tuner output while the other side was DC grounded. During AZ desert windstorms, this new G5RV of mine arced at the coax connector due to precipitation static, sometimes several times per second. Hmm. I've lived in AZ for over 60 years (almost 50 of them as a ham) and am well familiar with dust storms and static build up on antennas but I've never heard of it being called precipitation static. Whatever you choose to call it, Roy's suggested rf choke would have solved your problem. Wes N7WS |
folded dipoles
Thanks for the suggestion. I have decided to make my own. There are
suggestions on the web that radio shack makes some good twin lead. However, I still would like to put up a balun. What would be the best balun for me? I intend to operate on 75 meters. I admit to being a ham since 1956. However, I have not been very active and now that I am retired would like to get on low band. I am not very knowledgeable on all the types of antennas. I do know how to make a random wire work but do not want that type of antenna again. Also, to keep the twin lead insulated, do I need to coat the ends where they are shorted? I do appreciate the successful reports of using this type of antenna. What might happen if I put an antenna tuner on the transmitter end and tried to operate a folded dipole for 75 meters on 40 meters? I cannot safely use my trees until they are thawed. I cannot climb them myself and I would not pay someone to do this until it is safer. Michael "Denny" wrote in message oups.com... Michael, please do not spend good money for something you can build yourself for a fraction of the cost, and learn good things in the process... An 8X10 piece of plexiglass storm window from the hardware store will supply strips for the end and center insulators... A chunk of 300 ohm TV twin lead will supply the folded dipole material... A roll of coax, some solder, and a pieces of small rope, and you are in business... A hack saw will cut the plexi (so will a skill saw or table saw)... Why not make one for 10 meters as a starter until spring comes... This can be hung between two trees or whatever so it is at least head high and will give you some fun when the band opens here and there..... You can check the formula for length versus resonant frequency... denny / k8do |
folded dipoles
Cecil Moore wrote:
During AZ desert windstorms, this new G5RV of mine arced at the coax connector due to precipitation static, sometimes several times per second. Hi Cecil - Just a small bit of elaboration on your point - the arc is the result of the accumulation of a sufficient amount of charge to facilitate an electrical discharge in air. Static is heard in the receiver as the charge is being acquired, but an AGC limited pop would be heard when an arc occurs. (And sometimes nothing at all after the latter :-) Putting up a 40m folded dipole caused the arcing to cease. That's right. The accumulated electrostatic charge would be distributed uniformly along the length of such an antenna. Both ends of the antenna would therefore be at the same potential, so there is no propensity to arc across them. If at least one of the antenna terminals on the rig is grounded, the likelihood that the antenna will accumulate a significant amount of charge is greatly reduced. The antenna is still just as likely to produce precipitation static noise however. If the receiver input was strictly differential, then it would indeed be completely insensitive to common mode signals and noise. 73, ac6xg |
folded dipoles
Wes wrote:
Hmm. I've lived in AZ for over 60 years (almost 50 of them as a ham) and am well familiar with dust storms and static build up on antennas but I've never heard of it being called precipitation static. Here's the definition of precipitation static. http://www.atis.org/tg2k/_precipitation_static.html -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Jim Kelley wrote:
The antenna is still just as likely to produce precipitation static noise however. It is unlikely that dissimilar antennas will produce identical responses to anything including static. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Jim Kelley wrote: Hi Cecil - Just a small bit of elaboration on your point - the arc is the result of the accumulation of a sufficient amount of charge to facilitate an electrical discharge in air. Static is heard in the receiver as the charge is being acquired, but an AGC limited pop would be heard when an arc occurs. (And sometimes nothing at all after the latter :-) Has anybody experienced this first hand? I was driving during a storm listening to talk radio and could distinctly hear a static rush build up from the radio 1 to 2 seconds before a lighting strike. The louder it was, the closer the strike was going to be. A little off topic. I know this was not antenna static build up, but found it interesting that you could listen to a charge building before a discharge. Chris KC8FRJ |
folded dipoles
Christopher Cox wrote:
Has anybody experienced this first hand? I was driving during a storm listening to talk radio and could distinctly hear a static rush build up from the radio 1 to 2 seconds before a lighting strike. The louder it was, the closer the strike was going to be. I have heard it to the point where the radio was desensed just before the lightning strike. This happened with AM radio in a fringe area. A little off topic. I know this was not antenna static build up, but found it interesting that you could listen to a charge building before a discharge. Here's some information on the subject. The electrons that discharge into the earth during a thunderstorm return to the atmosphere as fair weather current. http://www.auf.asn.au/meteorology/section11.html -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Cecil Moore wrote: Wes wrote: Hmm. I've lived in AZ for over 60 years (almost 50 of them as a ham) and am well familiar with dust storms and static build up on antennas but I've never heard of it being called precipitation static. Here's the definition of precipitation static. http://www.atis.org/tg2k/_precipitation_static.html -- I don't give a damn what they call it, here's a definition of precipitation: precipitation n. a: a deposit on the earth of hail, mist, rain, sleet or snow: also: the quantity of water deposited. I don't see anything about dirt. Wes N7WS |
folded dipoles
On Tue, 19 Dec 2006 18:11:27 GMT, "B29" wrote:
Thanks for the suggestion. I have decided to make my own. There are suggestions on the web that radio shack makes some good twin lead. www.thewireman.com is a good place to buy twinlead and stuff. However, I still would like to put up a balun. What would be the best balun for me? I intend to operate on 75 meters. I admit to being a ham since 1956. However, I have not been very active and now that I am retired would like to get on low band. I am not very knowledgeable on all the types of antennas. I do know how to make a random wire work but do not want that type of antenna again. Also, to keep the twin lead insulated, do I need to coat the ends where they are shorted? I do appreciate the successful reports of using this type of antenna. What might happen if I put an antenna tuner on the transmitter end and tried to operate a folded dipole for 75 meters on 40 meters? I cannot safely use my trees until they are thawed. I cannot climb them myself and I would not pay someone to do this until it is safer. You could attach a weight to a piece of rope or cord, throw it over a limb, and then hoist the end of the antenna up. Beats climbing, ice or not, and to adjust the antenna, you just loosen the rope, and let the antenna down. Bob k5qwg Michael "Denny" wrote in message roups.com... Michael, please do not spend good money for something you can build yourself for a fraction of the cost, and learn good things in the process... An 8X10 piece of plexiglass storm window from the hardware store will supply strips for the end and center insulators... A chunk of 300 ohm TV twin lead will supply the folded dipole material... A roll of coax, some solder, and a pieces of small rope, and you are in business... A hack saw will cut the plexi (so will a skill saw or table saw)... Why not make one for 10 meters as a starter until spring comes... This can be hung between two trees or whatever so it is at least head high and will give you some fun when the band opens here and there..... You can check the formula for length versus resonant frequency... denny / k8do |
folded dipoles
Wes wrote:
I don't give a damn what they call it, here's a definition of precipitation: precipitation n. a: a deposit on the earth of hail, mist, rain, sleet or snow: also: the quantity of water deposited. I don't see anything about dirt. As you know, words often have a different technical meaning than their common Webster's dictionary meaning. The adjective "precipitation" modifying "static" or "noise" has been extended to dust as well as rain or snow, just as the p-static definition indicates. Airplanes flying through rain, snow, and dust exhibit the same physical phenomena so dust has been included as one of the causes of precipitation static. A web search will prove that to be true. Example quotes: ************************************************** ***************** Volume 2, Issue 4 (December 1945) Journal of the Atmospheric Sciences Article: pp. 205–213 | PDF (801K) METEOROLOGICAL ASPECTS OF PRECIPITATION STATIC Robert C. Edwards, Lieutenant U.S.N.R. and George W. Brock, Captain U. S. A. A. F. ABSTRACT *Precipitation static*, a result of electrification of aircraft in flight, can cause loss of radio communication for long periods of time. Electrification may consist of either of two types, “autogenous” or “exogenous” electrification; autogenous electrification occurs when snow, *dust* or rain strike the surface of the aircraft, while exogenous electrification results from an aircraft being placed in a pre-existing atmospheric electric field. Serious autogenous electrification occurs only in snow and *dust* storms; ... ************************************************** *********** Please note the date. Precipitation static from dust has been recognized for more than half a century. There are many more references available. One advertisement asks the following question: ************************************************** *********** Ads by GoooooogleMicro Air *Dust* Collectors Tired of cleaning electrostatic *precipitator* cells? www.microaironline.com ************************************************** ************ SAE Technical Papers Title: *Precipitation-Static* (P-Static) Overview of Composite Aircraft, Document Number: 2001-01-2933 Author(s): Jerry W. Thornell - The Boeing Co. Abstract: Aircraft charging due to *p-static* results from two atmospheric conditions: 1) the vehicle's presence in a thunderstorm, and 2) the triboelectric charging (frictional) caused by neutral snow, rain, or *dust* particle bombardment of the vehicle frontal surface. ************************************************** ****************** Development of Transparent Materials Which Reduce Effects of *Precipitation Static* in Aircraft Authors: M. U. Cohen; George A. Dalin; BALCO RESEARCH LABS NEWARK NJ Abstract: Methods of laying a transparent electrically conductive film on plastic airplane canopies are discussed. The purpose of such films is to conduct to the aircraft frame the static charges developed on the canopies by friction with air, *dust*, snow, etc., during flight. ************************************************** ****************** From: http://www.faa.gov/ATpubs/AIM/Chap7/aim0705.html 7-5-11. Precipitation Static a. *Precipitation static* is caused by aircraft in flight coming in contact with uncharged particles. These particles can be rain, snow, fog, sleet, hail, volcanic ash, *dust*; any solid or liquid particles. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Thank you Cecil for your patience and service to ham radio humanity in
opening eyes and minds of many of us regardless of being shot at by some of the all-knowing. 73 and Merry Christmas to all! Yuri, K3BU "Cecil Moore" wrote in message ... Wes wrote: I don't give a damn what they call it, here's a definition of precipitation: precipitation n. a: a deposit on the earth of hail, mist, rain, sleet or snow: also: the quantity of water deposited. I don't see anything about dirt. As you know, words often have a different technical meaning than their common Webster's dictionary meaning. The adjective "precipitation" modifying "static" or "noise" has been extended to dust as well as rain or snow, just as the p-static definition indicates. Airplanes flying through rain, snow, and dust exhibit the same physical phenomena so dust has been included as one of the causes of precipitation static. A web search will prove that to be true. Example quotes: ************************************************** ***************** Volume 2, Issue 4 (December 1945) Journal of the Atmospheric Sciences Article: pp. 205–213 | PDF (801K) METEOROLOGICAL ASPECTS OF PRECIPITATION STATIC Robert C. Edwards, Lieutenant U.S.N.R. and George W. Brock, Captain U. S. A. A. F. ABSTRACT *Precipitation static*, a result of electrification of aircraft in flight, can cause loss of radio communication for long periods of time. Electrification may consist of either of two types, “autogenous” or “exogenous” electrification; autogenous electrification occurs when snow, *dust* or rain strike the surface of the aircraft, while exogenous electrification results from an aircraft being placed in a pre-existing atmospheric electric field. Serious autogenous electrification occurs only in snow and *dust* storms; ... ************************************************** *********** Please note the date. Precipitation static from dust has been recognized for more than half a century. There are many more references available. One advertisement asks the following question: ************************************************** *********** Ads by GoooooogleMicro Air *Dust* Collectors Tired of cleaning electrostatic *precipitator* cells? www.microaironline.com ************************************************** ************ SAE Technical Papers Title: *Precipitation-Static* (P-Static) Overview of Composite Aircraft, Document Number: 2001-01-2933 Author(s): Jerry W. Thornell - The Boeing Co. Abstract: Aircraft charging due to *p-static* results from two atmospheric conditions: 1) the vehicle's presence in a thunderstorm, and 2) the triboelectric charging (frictional) caused by neutral snow, rain, or *dust* particle bombardment of the vehicle frontal surface. ************************************************** ****************** Development of Transparent Materials Which Reduce Effects of *Precipitation Static* in Aircraft Authors: M. U. Cohen; George A. Dalin; BALCO RESEARCH LABS NEWARK NJ Abstract: Methods of laying a transparent electrically conductive film on plastic airplane canopies are discussed. The purpose of such films is to conduct to the aircraft frame the static charges developed on the canopies by friction with air, *dust*, snow, etc., during flight. ************************************************** ****************** From: http://www.faa.gov/ATpubs/AIM/Chap7/aim0705.html 7-5-11. Precipitation Static a. *Precipitation static* is caused by aircraft in flight coming in contact with uncharged particles. These particles can be rain, snow, fog, sleet, hail, volcanic ash, *dust*; any solid or liquid particles. -- 73, Cecil http://www.w5dxp.com |
folded dipoles
Cecil Moore wrote:
Jim Kelley wrote: The antenna is still just as likely to produce precipitation static noise however. It is unlikely that dissimilar antennas will produce identical responses to anything including static. Sorry if I gave that impression. I simply meant that a folded dipole is just as likely to produce precipitation static noise as a dipole antenna. Merry Christmas de AC6XG |
folded dipoles
Jim Kelley wrote:
Hi Cecil - Just a small bit of elaboration on your point - the arc is the result of the accumulation of a sufficient amount of charge to facilitate an electrical discharge in air. Static is heard in the receiver as the charge is being acquired, Hi Jim, Can you elaborate further on your understanding of just how an ungrounded antenna wire that receives an increment of charge causes a response in the receiver as the charge is being acquired? If dust particles are charged as raindrops are (mixed polarity and magnitude) a typical incremental charge is on the order of 8 picocoulomb. Do we have an understanding of how much power would be transmitted to the 50 ohm input impedance of the receiver by such an incremental charge and the mechanism by which that transmission takes place? Based on anecdotal info, it is not unusual for these impulses to appear at an average level of several S-units. Thanks for any insights you can share. Chuck, NT3G but an AGC limited pop would be heard when an arc occurs. (And sometimes nothing at all after the latter :-) Putting up a 40m folded dipole caused the arcing to cease. That's right. The accumulated electrostatic charge would be distributed uniformly along the length of such an antenna. Both ends of the antenna would therefore be at the same potential, so there is no propensity to arc across them. If at least one of the antenna terminals on the rig is grounded, the likelihood that the antenna will accumulate a significant amount of charge is greatly reduced. The antenna is still just as likely to produce precipitation static noise however. If the receiver input was strictly differential, then it would indeed be completely insensitive to common mode signals and noise. 73, ac6xg ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-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 =---- |
folded dipoles
chuck wrote:
Hi Jim, Can you elaborate further on your understanding of just how an ungrounded antenna wire that receives an increment of charge causes a response in the receiver as the charge is being acquired? Hi Chuck - given a large enough increment of charge it's pretty straightforward. Best example I can think of is a capacitor. Take a high gain amplifier with an input coupling capacitor and start daubing clumps of charge onto the unconnected input lead. When the amount of charge is big enough, you'll hear the pop that results from the instantaneous change in charge. Thousands of those per second and pretty soon we're talking some real noise. ;-) If dust particles are charged as raindrops are (mixed polarity and magnitude) a typical incremental charge is on the order of 8 picocoulomb. Do we have an understanding of how much power would be transmitted to the 50 ohm input impedance of the receiver by such an incremental charge and the mechanism by which that transmission takes place? Based on anecdotal info, it is not unusual for these impulses to appear at an average level of several S-units. Thanks for any insights you can share. Chuck, NT3G I've never worked these numbers before, but given your typical charge per particle of 8 picocoulombs, and a 16uV signal from a 50 ohm antenna (converted to uamps), I get about 4x10^4 of those particles per second. Given the density of air, that's a pretty low number I think. If I'm wrong, please don't blast me. The back of my envelope here is pretty messy and hard to read. :-) 73, Jim, AC6XG |
folded dipoles
Jim Kelley wrote:
I simply meant that a folded dipole is just as likely to produce precipitation static noise as a dipole antenna. Probably not true for a bare-wire dipole Vs a ladder-line folded dipole. Insulation is one well accepted method of reducing precipitation static on airplane antennas. In any case, the two wires in the folded dipole make it different from the single wire in the dipole. I'm away from my computer for the moment but consider your capacitor suggestion. Let's say we have a perfect ground plane and are testing a dipole Vs a folded dipole. They are in inverted-V configurations so we can discharge a capacitor between the end of the antenna and ground. For the dipole, there is only one path to ground through the receiver. For the folded dipole, there are two paths to ground, one through the receiver and one to ground. Why won't the charge applied to the folded dipole divide and take both paths? -- 73, Cecil, w5dxp.com |
folded dipoles
I have flown through dry snow over the Great Lakes that completely
desensed the receivers in the airplane - and this was a plane equipped with static discharge wicks... Rising noise to a roar, big discharge POP, receiver back on line for about 3-5 seconds until the rising roar blocks it up again- total cycle 15 to 20 seconds, only able to hear ATC for 3 to 5 seconds out of that... Not fun at O'dark thirty, it is 10F outside, you won't survive a ditching into the water, and your VOR receiver can't tell you where Windsor is... Yes, I believe in P-Static... denny Cecil Moore wrote: Wes wrote: I don't give a damn what they call it, here's a definition of precipitation: |
folded dipoles
Cecil Moore wrote: Jim Kelley wrote: I simply meant that a folded dipole is just as likely to produce precipitation static noise as a dipole antenna. Probably not true for a bare-wire dipole Vs a ladder-line folded dipole. Insulation is one well accepted method of reducing precipitation static on airplane antennas. In any case, the two wires in the folded dipole make it different from the single wire in the dipole. Any antenna/receiver combination is likely to be sensitive to p-static. Some more than others obviously. An indoor, heavily insulated folded dipole connected to an differential input receiver would probably not receive much - so I'll give you that one even though I never claimed it would. Happier now? I'm away from my computer for the moment but consider your capacitor suggestion. Let's say we have a perfect ground plane and are testing a dipole Vs a folded dipole. They are in inverted-V configurations so we can discharge a capacitor between the end of the antenna and ground. For the dipole, there is only one path to ground through the receiver. For the folded dipole, there are two paths to ground, one through the receiver and one to ground. Why won't the charge applied to the folded dipole divide and take both paths? -- 73, Cecil, w5dxp.com You seem like a guy who'd pick a fight with his own shadow sometimes, Cecil. 73, ac6xg |
folded dipoles
I will use a pulley. The branches I want to use are very high. I cannot
throw or even use my slingshot thingy for this. I have a handyman who has agreed to climb the trees in the spring. I will get everything ready this winter. I have some large trees on each corner of my lot. I can probably get 50 feet up. I was going to use nylon rope to attach to the trees but I read that polyester rope last longer. It is even cheaper. I erroneously thought that the more expensive nylon would last longer. "Bob Miller" wrote in message ... On Tue, 19 Dec 2006 18:11:27 GMT, "B29" wrote: Thanks for the suggestion. I have decided to make my own. There are suggestions on the web that radio shack makes some good twin lead. www.thewireman.com is a good place to buy twinlead and stuff. However, I still would like to put up a balun. What would be the best balun for me? I intend to operate on 75 meters. I admit to being a ham since 1956. However, I have not been very active and now that I am retired would like to get on low band. I am not very knowledgeable on all the types of antennas. I do know how to make a random wire work but do not want that type of antenna again. Also, to keep the twin lead insulated, do I need to coat the ends where they are shorted? I do appreciate the successful reports of using this type of antenna. What might happen if I put an antenna tuner on the transmitter end and tried to operate a folded dipole for 75 meters on 40 meters? I cannot safely use my trees until they are thawed. I cannot climb them myself and I would not pay someone to do this until it is safer. You could attach a weight to a piece of rope or cord, throw it over a limb, and then hoist the end of the antenna up. Beats climbing, ice or not, and to adjust the antenna, you just loosen the rope, and let the antenna down. Bob k5qwg Michael "Denny" wrote in message groups.com... Michael, please do not spend good money for something you can build yourself for a fraction of the cost, and learn good things in the process... An 8X10 piece of plexiglass storm window from the hardware store will supply strips for the end and center insulators... A chunk of 300 ohm TV twin lead will supply the folded dipole material... A roll of coax, some solder, and a pieces of small rope, and you are in business... A hack saw will cut the plexi (so will a skill saw or table saw)... Why not make one for 10 meters as a starter until spring comes... This can be hung between two trees or whatever so it is at least head high and will give you some fun when the band opens here and there..... You can check the formula for length versus resonant frequency... denny / k8do |
folded dipoles
On Thu, 21 Dec 2006 18:56:49 GMT, "B29" wrote:
I will use a pulley. The branches I want to use are very high. I cannot throw or even use my slingshot thingy for this. I have a handyman who has agreed to climb the trees in the spring. I will get everything ready this winter. I have some large trees on each corner of my lot. I can probably get 50 feet up. I was going to use nylon rope to attach to the trees but I read that polyester rope last longer. It is even cheaper. I erroneously thought that the more expensive nylon would last longer. As I understand, black Dacron Polyester is the good stuff. They have it at AES, the Wireman, RadioWorks, etcetera... I've been using some surplus olive drab Dacron I got from RadioWorks that is really long lasting and blends in nicely... Radioworks, by the way, has good marine-type pullys if that's the direction you're going. bob k5qwg "Bob Miller" wrote in message .. . On Tue, 19 Dec 2006 18:11:27 GMT, "B29" wrote: Thanks for the suggestion. I have decided to make my own. There are suggestions on the web that radio shack makes some good twin lead. www.thewireman.com is a good place to buy twinlead and stuff. However, I still would like to put up a balun. What would be the best balun for me? I intend to operate on 75 meters. I admit to being a ham since 1956. However, I have not been very active and now that I am retired would like to get on low band. I am not very knowledgeable on all the types of antennas. I do know how to make a random wire work but do not want that type of antenna again. Also, to keep the twin lead insulated, do I need to coat the ends where they are shorted? I do appreciate the successful reports of using this type of antenna. What might happen if I put an antenna tuner on the transmitter end and tried to operate a folded dipole for 75 meters on 40 meters? I cannot safely use my trees until they are thawed. I cannot climb them myself and I would not pay someone to do this until it is safer. You could attach a weight to a piece of rope or cord, throw it over a limb, and then hoist the end of the antenna up. Beats climbing, ice or not, and to adjust the antenna, you just loosen the rope, and let the antenna down. Bob k5qwg Michael "Denny" wrote in message egroups.com... Michael, please do not spend good money for something you can build yourself for a fraction of the cost, and learn good things in the process... An 8X10 piece of plexiglass storm window from the hardware store will supply strips for the end and center insulators... A chunk of 300 ohm TV twin lead will supply the folded dipole material... A roll of coax, some solder, and a pieces of small rope, and you are in business... A hack saw will cut the plexi (so will a skill saw or table saw)... Why not make one for 10 meters as a starter until spring comes... This can be hung between two trees or whatever so it is at least head high and will give you some fun when the band opens here and there..... You can check the formula for length versus resonant frequency... denny / k8do |
folded dipoles
Thanks Bob,
I did not even think to get pulleys and rope from amateur radio supply places. I will do some shopping there very soon. What do you think about feeding the dipole with some sort of balun? Michael W0EZI "Bob Miller" wrote in message ... On Thu, 21 Dec 2006 18:56:49 GMT, "B29" wrote: I will use a pulley. The branches I want to use are very high. I cannot throw or even use my slingshot thingy for this. I have a handyman who has agreed to climb the trees in the spring. I will get everything ready this winter. I have some large trees on each corner of my lot. I can probably get 50 feet up. I was going to use nylon rope to attach to the trees but I read that polyester rope last longer. It is even cheaper. I erroneously thought that the more expensive nylon would last longer. As I understand, black Dacron Polyester is the good stuff. They have it at AES, the Wireman, RadioWorks, etcetera... I've been using some surplus olive drab Dacron I got from RadioWorks that is really long lasting and blends in nicely... Radioworks, by the way, has good marine-type pullys if that's the direction you're going. bob k5qwg |
folded dipoles
"B29" wrote in
t: Thanks Bob, I did not even think to get pulleys and rope from amateur radio supply places. I will do some shopping there very soon. What do you think about feeding the dipole with some sort of balun? You'll want a 4:1 balun if you'll be using coax. - 73 de Mike KB3EIA - |
folded dipoles
Jim Kelley wrote:
Jim Kelley wrote: I simply meant that a folded dipole is just as likely to produce precipitation static noise as a dipole antenna. ... so I'll give you that one even though I never claimed it would. Happier now? Sorry, I thought you were claiming equal magnitudes of noise for two dissimilar antennas. You seem like a guy who'd pick a fight with his own shadow sometimes, Sorry, I seem to have inferred something you didn't mean to imply. I believe I can prove the difference in the two antennas using EZNEC but not until I get back to my home computer. -- 73, Cecil, w5dxp.com |
folded dipoles
Buying pulleys at radio supply places is as bad as buying at a marina. Get
the stainless stuff at your local hrdware for about half the cost. "B29" wrote in message t... Thanks Bob, I did not even think to get pulleys and rope from amateur radio supply places. I will do some shopping there very soon. What do you think about feeding the dipole with some sort of balun? Michael W0EZI "Bob Miller" wrote in message ... On Thu, 21 Dec 2006 18:56:49 GMT, "B29" wrote: I will use a pulley. The branches I want to use are very high. I cannot throw or even use my slingshot thingy for this. I have a handyman who has agreed to climb the trees in the spring. I will get everything ready this winter. I have some large trees on each corner of my lot. I can probably get 50 feet up. I was going to use nylon rope to attach to the trees but I read that polyester rope last longer. It is even cheaper. I erroneously thought that the more expensive nylon would last longer. As I understand, black Dacron Polyester is the good stuff. They have it at AES, the Wireman, RadioWorks, etcetera... I've been using some surplus olive drab Dacron I got from RadioWorks that is really long lasting and blends in nicely... Radioworks, by the way, has good marine-type pullys if that's the direction you're going. bob k5qwg |
folded dipoles
Jim Kelley wrote:
chuck wrote: Hi Jim, Can you elaborate further on your understanding of just how an ungrounded antenna wire that receives an increment of charge causes a response in the receiver as the charge is being acquired? Hi Chuck - given a large enough increment of charge it's pretty straightforward. Best example I can think of is a capacitor. Take a high gain amplifier with an input coupling capacitor and start daubing clumps of charge onto the unconnected input lead. When the amount of charge is big enough, you'll hear the pop that results from the instantaneous change in charge. Thousands of those per second and pretty soon we're talking some real noise. ;-) If dust particles are charged as raindrops are (mixed polarity and magnitude) a typical incremental charge is on the order of 8 picocoulomb. Do we have an understanding of how much power would be transmitted to the 50 ohm input impedance of the receiver by such an incremental charge and the mechanism by which that transmission takes place? Based on anecdotal info, it is not unusual for these impulses to appear at an average level of several S-units. Thanks for any insights you can share. Chuck, NT3G I've never worked these numbers before, but given your typical charge per particle of 8 picocoulombs, and a 16uV signal from a 50 ohm antenna (converted to uamps), I get about 4x10^4 of those particles per second. Given the density of air, that's a pretty low number I think. If I'm wrong, please don't blast me. The back of my envelope here is pretty messy and hard to read. :-) Hi Jim, Seems I misunderstood your original post as suggesting that each incremental charge produced a pop. I see that the typical current density of rain in a storm is on the order of 0.1 - 1 uA/square meter. Taking the usual obscene liberties with priors, that's on the order of 60 - 240 pA for a 40 meter long wire with a diameter of 2 mm. The average voltage developed at the receiver front end (50 ohms)would then be on the order of 12 nanovolts (240 pA x 50 ohms). This is obviously many orders of magnitude less than reported p-static signal levels. Using your capacitor-coupled amplifier example, a continuous, average current of 240 pA would be more like DC than what we seem to hear. I am persuaded that there may be some kind of relaxation process going on in which the charges build to some breakdown level and appear as a pulse (significantly greater than 12 nV) at the receiver input. But what breaks down? Diodes? Presumably we are not talking about arcing here. Does anyone recall this phenomenon in the vacuum tube receiver era? Also unknown is the state of charge of the ungrounded antenna wire just prior to the acquisition of an incremental charge. Is the antenna at some high positive or negative potential just prior to impact, allowing a small incremental charge to cause a breakdown? What I think we do know is that there are sometimes charged particles (dust, rain, snow, etc.) that impact an antenna and cause a characteristic type of noise in the receiver. Exactly which particles, with which charges, and under what conditions of pre-existing charge in the antenna do we see such noise and at what signal levels? I'm sort of at the analogous point of noting that crop growth is correlated with some periodic level of rainfall, without a clue as to the mechanism by which the raindrops and plant growth are related. ;-) Appreciate your comments, Jim. 73, Chuck 73, Jim, AC6XG ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-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 =---- |
folded dipoles
"chuck" wrote in message ... Jim Kelley wrote: chuck wrote: Hi Jim, Can you elaborate further on your understanding of just how an ungrounded antenna wire that receives an increment of charge causes a response in the receiver as the charge is being acquired? Hi Chuck - given a large enough increment of charge it's pretty straightforward. Best example I can think of is a capacitor. Take a high gain amplifier with an input coupling capacitor and start daubing clumps of charge onto the unconnected input lead. When the amount of charge is big enough, you'll hear the pop that results from the instantaneous change in charge. Thousands of those per second and pretty soon we're talking some real noise. ;-) If dust particles are charged as raindrops are (mixed polarity and magnitude) a typical incremental charge is on the order of 8 picocoulomb. Do we have an understanding of how much power would be transmitted to the 50 ohm input impedance of the receiver by such an incremental charge and the mechanism by which that transmission takes place? Based on anecdotal info, it is not unusual for these impulses to appear at an average level of several S-units. Thanks for any insights you can share. Chuck, NT3G I've never worked these numbers before, but given your typical charge per particle of 8 picocoulombs, and a 16uV signal from a 50 ohm antenna (converted to uamps), I get about 4x10^4 of those particles per second. Given the density of air, that's a pretty low number I think. If I'm wrong, please don't blast me. The back of my envelope here is pretty messy and hard to read. :-) Hi Jim, Seems I misunderstood your original post as suggesting that each incremental charge produced a pop. I see that the typical current density of rain in a storm is on the order of 0.1 - 1 uA/square meter. Taking the usual obscene liberties with priors, that's on the order of 60 - 240 pA for a 40 meter long wire with a diameter of 2 mm. The average voltage developed at the receiver front end (50 ohms)would then be on the order of 12 nanovolts (240 pA x 50 ohms). This is obviously many orders of magnitude less than reported p-static signal levels. Using your capacitor-coupled amplifier example, a continuous, average current of 240 pA would be more like DC than what we seem to hear. I am persuaded that there may be some kind of relaxation process going on in which the charges build to some breakdown level and appear as a pulse (significantly greater than 12 nV) at the receiver input. But what breaks down? Diodes? Presumably we are not talking about arcing here. Does anyone recall this phenomenon in the vacuum tube receiver era? Also unknown is the state of charge of the ungrounded antenna wire just prior to the acquisition of an incremental charge. Is the antenna at some high positive or negative potential just prior to impact, allowing a small incremental charge to cause a breakdown? What I think we do know is that there are sometimes charged particles (dust, rain, snow, etc.) that impact an antenna and cause a characteristic type of noise in the receiver. Exactly which particles, with which charges, and under what conditions of pre-existing charge in the antenna do we see such noise and at what signal levels? I'm sort of at the analogous point of noting that crop growth is correlated with some periodic level of rainfall, without a clue as to the mechanism by which the raindrops and plant growth are related. ;-) the noise is caused by corona on the antenna due to the electric field between the ground and cloud. this field can be many thousands of kv per meter which is enough to cause sharp points and tips of elements to generate corona which makes the hiss and pop noises. |
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