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
Topband: corona noise
Hi would a static discharge wick mounted on the lightning rod be helpful? They seem to work well for aircraft AM radios. ___ Topband reflector - topband@contesting.com
Re: Topband: corona noise
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
