Home |
Search |
Today's Posts |
#21
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
Russ wrote:
Doesn't the delta P of a fuel-air bomb travel at greater than the speed of sound? No. Roy Lewallen, W7EL |
#22
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
The denotation is supersonic, while the flame spread is subsonic.
"Roy Lewallen" wrote in message ... Russ wrote: Doesn't the delta P of a fuel-air bomb travel at greater than the speed of sound? No. Roy Lewallen, W7EL |
#23
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
On Sun, 18 Dec 2005 12:39:09 -0800, Roy Lewallen
wrote: Russ wrote: Doesn't the delta P of a fuel-air bomb travel at greater than the speed of sound? No. Roy Lewallen, W7EL The definition of dentonation includes the flame front moving at supersonic speeds. http://www.globalsecurity.org/milita...itions/fae.htm R |
#25
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
Russ wrote:
On Sun, 18 Dec 2005 12:39:09 -0800, Roy Lewallen wrote: Russ wrote: Doesn't the delta P of a fuel-air bomb travel at greater than the speed of sound? No. Roy Lewallen, W7EL The definition of dentonation includes the flame front moving at supersonic speeds. http://www.globalsecurity.org/milita...itions/fae.htm Yes, I can understand the flame front moving faster than sound, if it's not a pressure wave. I don't know the mechanism, but presume it's propagated by radiant heat. That is, a flame occurs, and its heat radiates and superheats nearby material, causing it to flame. That would be propagation by electromagnetic wave, i.e., infrared "light". The radiation would travel at the speed of light, with the apparent speed of the front being dictated by how fast the material is heated and ignited by the radiated heat. Propagation by this mechanism and at this speed would end as soon as the flame front reached the outside of the vapor cloud, beyond which the resulting pressure wave would travel at the speed of sound. I'm not an expert at this, but I'm quite sure that the only way you can get a mechanical wave to travel faster than sound is if the behavior of the air becomes nonlinear at some compression level. That could conceivably happen as a result of an explosion, but I don't think so. If anyone has any references describing such nonlinear behavior, I'd love to learn more about it. Roy Lewallen, W7EL |
#26
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
"Robert11" wrote
is it better to just leave the now "floating" antenna alone, or is it better to ground one end of it ? ______________ Most MW broadcast stations use series-fed, insulated towers that usually are (by far) the highest structures in the area. These stations operate successfully in lightning storms using a combination of means. First is an arc gap connected across the tower feedpoint to a very low resistance earth ground (120 1/4-wave, buried radials). The gap is set to flash over at some margin above the peak voltage present during normal operation. They also use a "static drain choke" to earth ground, which is a high Z at the MW frequency, but doesn't let high static potentials develop on the tower. The last part of the protection system is supplied by transmitter circuitry that senses instantaneous phase changes in transmission line current, and kills r-f output for some milliseconds so as not to sustain any arc that occurs in the antenna system. Maybe some of these techniques could be useful in amateur radio installations. RF |
#27
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
Roy Lewallen wrote:
I'm not an expert at this, but I'm quite sure that the only way you can get a mechanical wave to travel faster than sound is if the behavior of the air becomes nonlinear at some compression level. Carrier velocity is linear and must be taken into account. Relative to a measurement point at the center of the earth, sound waves traveling East in the surface atmosphere are moving faster than Mach 2. Do the carriers move during an explosion? -- 73, Cecil http://www.qsl.net/w5dxp |
#28
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
"Robert11" wrote is it better to just leave the now "floating" antenna alone, or is it better to ground one end of it ? ______________ In anticipation of a thunder storm just leave it floating. Not that it will prevent a direct lightning strike but it MIGHT prevent damage to equipment and, more important, to yourself. But it is advisable not to attempt to disconnect it using bare fingers during the progress of a thunder storm. I am a little superstitious so I use the XYL's rubber kitchen gloves. There's only one thing you can be absolutely certain of - lightning exactly obeys the Mathematical Laws of Probability. See the works of Sir Ronald Arthur Fisher, the greatest statistician of all time. Beautifully explained in plain English. He dabbled mainly in Genetics, Agriculture, the Weather, and the mathematics thereof. But I'm not aware of anything specifically he had to say about the statistics of lightning strikes. You will have to work things out for yourself. In all probability nothing seriously will happen to YOU. So don't worry about it. Just DON'T fly kites using 1/2-wavelength metal wires during thunder storms. Not even on the 10m band. Or shelter from the rain under solitary trees. It's asking for trouble but you probably won't get any. As for me, I'm 80 years of age, and I'm still alive. I've never won the national lottery. But perhaps that can be explained by the fact that I've never entered it. I hope the foregoing has helped to set your mind at rest. ---- Reg, G4FGQ ========================================== |
#29
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
Reg Edwards wrote:
. . . See the works of Sir Ronald Arthur Fisher, the greatest statistician of all time. Beautifully explained in plain English. He dabbled mainly in Genetics, Agriculture, the Weather, and the mathematics thereof. But I'm not aware of anything specifically he had to say about the statistics of lightning strikes. You will have to work things out for yourself. In all probability nothing seriously will happen to YOU. So don't worry about it. . . . As for me, I'm 80 years of age, and I'm still alive. I've never won the national lottery. But perhaps that can be explained by the fact that I've never entered it. I hope the foregoing has helped to set your mind at rest. I'd be willing to wager that there are places in Florida which have more lightning strikes in a single summer than have occurred at your QTH (or mine) in the past 80 years. Roy Lewallen, W7EL |
#30
|
|||
|
|||
Ground Or Not To Ground Receiving Antenna In Storm ?
"Reg Edwards" wrote
In anticipation of a thunder storm just leave it floating. Not that it will prevent a direct lightning strike but it MIGHT prevent damage to equipment and, more important, to yourself. .... etc etc removed by major clippage I hope the foregoing has helped to set your mind at rest. __________ Possibly you thought this relevant to the original post. But then why not thread it so, rather than to mine? RF |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Grounding | Shortwave | |||
No CounterPoise - Portable Antenna System | Shortwave | |||
The "Almost" Delta Loop Antenna for Limited Space Shortwave Listening (SWL) made from TV 'type' Parts | Shortwave | |||
FS: sma-to-bnc custom fit rubber covered antenna adapter | Scanner | |||
This product any good? | Scanner |