Home |
Search |
Today's Posts |
#14
![]() |
|||
|
|||
![]()
J. Mc Laughlin wrote:
P-noise is not found on an antenna imbedded in a clump of trees when an antenna out in the open (many wavelengths from the first antenna) has P-noise. The follow-on is that since most sites are urban or suburban, few radio amateurs will experience P-noise. That does not disagree with anything I said. A lower antenna surrounded by taller objects is not subject to the same high voltage gradient as an antenna out in a flat clear field. P-noise is observed when there is no rain nor thunderstorms, but plenty of wind. This is suggestive of moving charge discharging into the antenna. So how does it get there? How does it build up? Where is the spark arc or sizzle? Of course, one could define this action as being "corona." Of course, if one places enough charge on a piece of metal eventually there will be "corona." Many antennas have a conductive path to earth that makes such an accumulation of charge unlikely. The fact is grounded or ungrounded antennas all behave the very same way. Ask anyone who has yagis on towers. It is a potential difference between earth and the atmosphere around the antenna. It isn't the antenna charging up so much differently than earth. It is the difference in potential between the antenna and the space around the antenna. Remember those old tall mast wooden sailing ships soaked with sal****er and the fire off the yardarms at night? Your #6 is interesting. Unfortunately, there is so much radiation from what else is on a tall building that it is difficult to sort out where excess noise is coming from. An antenna inside of a slightly conductive radome that is placed a long distance from anything that could radiate might be different. You can walk right up to the noise source, and even see the corona at night. It's very easy to take a FSM with audio monitor or AM receiver with S meter and walk the roof for strongest noise, and it will generally take you right to the tallest sharpest object (grounded or not) on the roof. The last place you want to be is the tallest antenna on the building. Get high winds or inclement weather and you will be destined for noise....grounded antenna or not. We serviced dozens of repeaters and a few STL or Remote links in the 70's, it was a pattern that repeated. I have a suggestion. Go to a forum where there are many people with antennas at various heights, like a contesting reflector. Ask people who have similar or identical antennas at various heights on a single tall tower what they observe during high winds, nasty weather, or rain. The very same wind and the very same moisture is impacting all of the antennas, but without fail they will tell you the lower antennas are always much better and the taller antennas are the first to go. If the P-staic is actually coming from the particles or moisture in air striking the antenna, and if the same basic sample of weather is at all the antennas, why are the upper antennas affected more? If it is the conductor charging, why do plumber's delight antennas or folded elements with grounded centers have the same noise as insulated elements? If it is moisture or particles striking the antenna causing the problem, why is an insulated antenna with a single sharp protrusion just as noisey as a bare antenna? Why doesn't the noise follow the pattern of the particle rate, and why does it occur (as you even seemed to say) when there is no actual precipitation? Since I've always had towers taller than 100 feet, and since I've worked on VHF and UHF systems that had to stay up during storms, I've spent a lot of time looking at this. I've not found anything that points to the antenna charging differently than earth or being struck by charged particles. 73 Tom |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Passive Repeater | Antenna | |||
Is magnetic field affected by metal conductor? | Homebrew | |||
F/A New Motorola VHF portable antennas (Motorola Branded!!) | Swap | |||
FA Motorola VHF rubber duck Antennas $4.99 ea. Dealer cost $8.70 List $11.80 | Swap | |||
How was antenna formula for uV/Meter Derived? | Antenna |