Re: Topband: corona noise
Tom, What is a lot taller? Would an aluminum or steel (or combination) mast extension with pointed tip, extending say 10-20 feet above the top beam -- let's say one for 20m -- help to reduce corona discharge noise in the top beam? 73/Jon AA1K On 11/16/2012 6:58 PM, Tom W8JI wrote: Hi would a static discharge wick mounted on the lightning rod be helpful? They seem to work well for aircraft AM radios. Anything a lot taller than the antenna being used and close to the antenna can help reduce corona from the antenna itself, because it is a better leak point. This is why lower antennas are quieter than higher antennas during storms. Static wicks would work especially great if our stations were in the air hundreds or thousands of feet above earth, with no earth contact. They would make the earth-isolated station assume the potential of the air or clouds around the station. Any corona (charge equalization) between the aircraft and air around the aircraft would come from the wicks, and not the antenna. The problem with having wicks work for terrestrial applications is getting the great big earth, which is larger than most aircraft, to assume the potential of the clouds or air around the antenna. The antenna has a path to earth, so the charge just keeps coming back. Lightning equalizes things between the sky and earth temporarily. Listen to an antenna during a storm, and watch out the window. When lightning flashes close by, the noise goes away. I'm not sure that is a safe way to operate though. :-) 73 Tom ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: corona noise
What is a lot taller? I can't answer that question specifically. It varies with e-field conditions and the type of antennas and structures. The corona is a micro power noise generator so it radiates noise, and the target has to neutralize the field near other points so they don't break into corona. Would an aluminum or steel (or combination) mast extension with pointed tip, extending say 10-20 feet above the top beam -- let's say one for 20m -- help to reduce corona discharge noise in the top beam? It should. I always put a sacrificial vertical of some type above my antennas for that reason, and to keep lightning off antenna element tips. The rule of guess I use is the target I use is over twice the antenna element radius length above the antenna. It seems to work here. When we took Bill Fisher's antennas down at his mountain QTH, his top antennas had element tips eaten up from lightning and corona. Antenna elements just 10-20 feet lower were clean. I played with this stuff a great deal in Ohio because my old two-way business had marine repeaters along the lake. Corona noise, right when ships and other services needed communications the most, could be severely hampered by p-static. Sharp points, like frayed ends of guylines, aggravated noise problems when antenna were around the guyline. I could climb the towers and hear the frayed or splayed guyline ends making the exact same acoustical noise pitch as the RF noise bothering antennas. The only way to cure it is to stop the corona (which means it moves somewhere else, usually) through rounded ends or by adding a taller leak or target that is away from the antenna. Changing antenna types, grounds or grounding, DC feedline pathsnone of that actually helped. The repeater systems had DC grounded hi-Q cavities, and noise was exactly the same with or without the cans. The same is true here at the house, where antenna with or without element grounding are all basically the same, although I do mitigate internal cable voltage buildup. 73 Tom ___ Topband reflector - topband@contesting.com
Topband: Corona
I used to have up all Telrex monobanders ( and by the way they are still great antennas despite what some think). The 8 el 15 and the 5 el 20 all had corona balls at the end of the elements. These were designed years ago (company defunct about 1995)... 73, John, W4NU ___ Topband reflector - topband@contesting.com
Re: Topband: Covered /bare antennn wire
The T Match tuner is what sits in the house Price. The T Match feed on the antenna is completely different, is grounded to the boom on the all metal design and is no more prone to P-static than any other feed system. My own yagis use a T Match from 28 to 432 MHz and work very well and without the pattern skewing of the gamma match. Carl KM1H No kidding Carl ! Price W0RI ___ Topband reflector - topband@contesting.com
Topband: Toroidal common mode choke
I've got an FT-240-43 core on which I'd like to wind RG58 to make a choke for the feedpoint of my inverted-L. I've seen articles that studied the optimum number of turns for air-core chokes, but don't recall seeing any for toroidal chokes. Can anyone offer a pointer (or empirical data) that might guide me. (20 turns?) (I sometimes also use the antenna for 80m - disconnecting part of the horizontal leg.) Tnx, /Bill, K2PO ___ Topband reflector - topband@contesting.com
Re: Topband: phasing line lengths for phased verticals
Joe...I was wrong in my post. My verticals are 1/2 wave apart on 80m, which is the same as 1/4 wave on 160. After writing my message, I went back and added the 66' for clarity, and should have been 132' You are correct, using RG8X with velocity factor of .78, the phasing lines are about 53.5' and there are two of them, making them a too short to reach the 132' I really DO have 80m verticals that are 1/2 wave apart. (incidentally I share the radial fields with the 160m antennas which are 1/4 wave apart) So the question remains, how to properly feed phased verticals that are physically 1/2 wave apart 73 Dale From: Joe Subich, W4TV li...@subich.com To: topband@contesting.com Sent: Saturday, November 17, 2012 7:18 PM Subject: Re: Topband: phasing line lengths for phased verticals 1. for 80m phased verticals that are 1/2 wave apart (66 feet), That is 1/4 wave separation - not half-wave. One half wave on 80 is roughly 139 feet (984/3.55/2 = 138.6 feet). Since you are using 1/4 wave spacing and a PVS-2 (which is a quadrature device if I remember correctly), two /14 wave cables (about 54' each when the velocity factor for foam is included) should *easily* reach the midpoint of the array. 73, ... Joe, W4TV On 11/17/2012 6:56 PM, DALE LONG wrote: Until recently, I had phased verticals on both 80m and 160m and lots of beverages. (this was in a woods, and not my property) Then the loggers came and destroyed all. In addition to the antennas, the phasing lines were torn up, and broken and needed replacement. For 160m I use the Christman method with .71 and .84 wavelength lines. For 80m I use a Comtek PVS-2 controller. In replacing the 80m phasing lines today I made a stupid mistake, I dont know what I was thinking, but I carefully measured and soldered two identical 1/4 wave lengths of new coax. I tested them on my AIM 4170 and they were nearly identical, exactly on the design frequency. Then I went to install them and guess what...of course they were too short. I have worked with phased verticals before and I know that you often need to use 3/4 wave phasing lines, but I was too intent on measuring and soldering and making the repairs. So now I have two questions. 1. for 80m phased verticals that are 1/2 wave apart (66 feet), what will be the pattern? It's not the same as 1/4 wave spacing, so what really is happening? 2. what is the best length of phasing line to use. Should I use 3/4 wave phasing lines? Should I avoid using 1/2 wave phasing lines? Thanks Dale - N3BNA ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: phasing line lengths for phased verticals
Joe...I was wrong in my post. My verticals are 1/2 wave apart on 80m, That changes things ... So the question remains, how to properly feed phased verticals that are physically 1/2 wave apart Seems to me you have two options ... feed them in phase which provides a bidirectional pattern *broadside* or feed them out of phase which provides a bidirectional pattern *endfire*. With the in/out of phase feed, I would use 1/2 wave lines from the verticals to the phasing unit. The phasing unit would consist of your two 1/4 wave lines with a half wave line in series with one of the two verticals - in line for endfire and bypassed for broadside. 73, ... Joe, W4TV On 11/17/2012 9:42 PM, DALE LONG wrote: Joe...I was wrong in my post. My verticals are 1/2 wave apart on 80m, which is the same as 1/4 wave on 160. After writing my message, I went back and added the 66' for clarity, and should have been 132' You are correct, using RG8X with velocity factor of .78, the phasing lines are about 53.5' and there are two of them, making them a too short to reach the 132' I really DO have 80m verticals that are 1/2 wave apart. (incidentally I share the radial fields with the 160m antennas which are 1/4 wave apart) So the question remains, how to properly feed phased verticals that are physically 1/2 wave apart 73 Dale From: Joe Subich, W4TV li...@subich.com To: topband@contesting.com Sent: Saturday, November 17, 2012 7:18 PM Subject: Re: Topband: phasing line lengths for phased verticals 1. for 80m phased verticals that are 1/2 wave apart (66 feet), That is 1/4 wave separation - not half-wave. One half wave on 80 is roughly 139 feet (984/3.55/2 = 138.6 feet). Since you are using 1/4 wave spacing and a PVS-2 (which is a quadrature device if I remember correctly), two /14 wave cables (about 54' each when the velocity factor for foam is included) should *easily* reach the midpoint of the array. 73, ... Joe, W4TV On 11/17/2012 6:56 PM, DALE LONG wrote: Until recently, I had phased verticals on both 80m and 160m and lots of beverages. (this was in a woods, and not my property) Then the loggers came and destroyed all. In addition to the antennas, the phasing lines were torn up, and broken and needed replacement. For 160m I use the Christman method with .71 and .84 wavelength lines. For 80m I use a Comtek PVS-2 controller. In replacing the 80m phasing lines today I made a stupid mistake, I dont know what I was thinking, but I carefully measured and soldered two identical 1/4 wave lengths of new coax. I tested them on my AIM 4170 and they were nearly identical, exactly on the design frequency. Then I went to install them and guess what...of course they were too short. I have worked with phased verticals before and I know that you often need to use 3/4 wave phasing lines, but I was too intent on measuring and soldering and making the repairs. So now I have two questions. 1. for 80m phased verticals that are 1/2 wave apart (66 feet), what will be the pattern? It's not the same as 1/4 wave spacing, so what really is happening? 2. what is the best length of phasing line to use. Should I use 3/4 wave phasing lines? Should I avoid using 1/2 wave phasing lines? Thanks Dale - N3BNA ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: phasing line lengths for phased verticals
This looks like the Engineering Phasing report mentioned. I have an older version, this one seems to be reformatted. Give it a try. http://www.classicinternational.eu/_clientfiles/info_extra/hygainphasedverticals.pdf' yui-spellcheck?http://www.classicinternational.eu/_clientfiles/info_extra/hygainphasedverticals.pdf;http://www.classicinternational.eu/_clientfiles/info_extra/hygainphasedverticals.pdf Arne N7KA ___ Topband reflector - topband@contesting.com
