Pecipitation Static or P-static
also see Beverages
During inclement weather, when using antennas that are relatively high compared to surrounding structures, a severe increase in noise may occur. This is commonly reported by people with high antennas. By looking at stations with identical antennas at widely varying heights we can logically conclude the real reason behind the noise increase in inclement weather. Contest forums and repeaters are both useful places to gather information on "p-static" or precipitation static.
Logical Analysis of Systems
Case 1, multiple contest stations
Here's a sample of typical posts on contest reflectors. This one is from NQ4I on the 3830 reflector:
Case 2, my Yagi antennas
My contest station has a similar feature. Operators can change to lower antennas on receive to mitigate precipitation static during inclement weather. My 40-meter Yagi antennas are 3-element plumber's delight construction. Reflector and director elements are directly connected to the grounded booms, while the driven elements have a hair-pin match that grounds the elements to the boom. The upper antenna is around 185-feet above ground level, and with a 50-foot boom and 70-foot long elements the elements. During foul weather, such as severe blowing snow, rain, or heavy overcast with the threat of rain, the upper antenna makes a raspy note that sounds like a steadily increasing frying noise. It can easily be mistaken for particles striking the antenna, except close observation shows the noise does not track the moisture striking the antenna.
A second observation is even before the moisture gets here, the noise can start. When a distant lightning bolt flashes the noise often abruptly stops.
All of this by itself would indicate the noise is not related to particles discharging against the antenna. If it was noise from particles, the noise would often track the volume of particles striking the antenna. It does not. If the noise was from moisture or charged particles striking the antenna, it would not stop at the moment a lightning flash and then rapidly and steadily rebuild from a slow popping or crackle to a rapid intense sizzle...only to abruptly die again at the next lightning flash.
Case 3, my 160 meter dipoles
My 160-meter dipoles are on a 318-foot tall tower. The upper antenna is at 300 feet or more, the lower antenna around 130 feet above ground. The upper antenna is insulated #10 gauge solid copper, the lower antenna is bare #16 copper weld wire.
On a typical clear day the noise from both antennas is very low, barely moving the S meter on my receivers. The background is a smooth steady hiss with an occasional faint pop from an electric fence about 1/2 mile away. During inclement weather or the threat of inclement weather, the upper antenna suddenly has an S-9 plus musical sizzling noise. The noise starts slowly at a low pitch, and builds to a higher pitch and stronger level as a storm approaches. Despite the upper antenna being insulated and the lower antenna bare, the upper antenna is also by far the most problematic.
Logically if the problem was charged particles striking the antenna, the insulated antenna should fair much better. It does not.
Case 4, repeater antennas
In the 1960's and 70's, I was associated with WA8MNR and W8VWQ. Both were experienced repeater builders. W8VWQ Gail worked on the City of Toledo public safety systems, and WA8MNR Kaz worked with Gail on some of the original two-meter VHF and 440 MHz UHF repeater systems. Both Gail and Kaz constantly warned about being the "top antenna" on a building or tower. They said it was no place to be if the repeater had to function during foul weather without noise.
We had the opportunity to move a 146.94 repeater to the roof of a tall building in Toledo. The fiberglass covered Stationmaster antenna was immune to p-static when side mounted on a 350-foot tower, but when relocated to the roof of the building it because useless during storms. The receiver was overwhelmed with noise during high winds or other foul weather.
A significant reduction of noise occurred when a mast taller than the repeater antenna was installed 30 to 50 feet from the repeater antenna. For the most part the system became useable in bad weather.
Logic would tell us again if the problem was particles striking the antenna, the fiberglass radome would reduce or eliminate noise. Adding the mast would have had no effect.
While on the roof during one p-static event, I could hear and see a distinct sizzle from the tip of the antenna out into the air around the antenna. The audible pitch of the acoustical noise precisely matched the noise on the receiver.
The cases above are typical of what many stations with stacked or multiple high antennas report.
Despite having grounded antennas and the same rain or precipitation striking physically identical antennas, the highest antennas are always noisy and the lowest antennas are always the quietest. This occurs on a variety of antennas. Antennas with grounded elements and antennas with insulated elements all behave the same way. Antennas near the top of towers, especially those without taller towers nearby, all have severe p-static in storms. Lower antennas show very little noise under the same conditions, even though they are being struck by the same particles.
I recently received a request to design a phased stacking system. The engineering specifications for this large commercial stacked log periodic antenna switching system require disabling the uppermost antenna in the tall stack of logs when receiving! The specifications call for all six antennas to be active during transmit, but include an operator selected "p-static" mode to disable the upper antenna.
Obviously others have the same observations even if they don't understand the cause.
The cause of noise most commonly called p-static or precipitation static is obviously not from charged particles striking the antenna. While some of this might occur under some conditions, the overwhelming cause appears to be corona discharge from protruding points into space around the antennas or antenna structures. On dark nights with closing storms, I can look at my upper 40-meter Yagi with binoculars and see a faint St. Elmo's fire from the element tips. This is similar to what I saw on the VHF antenna that noised-up during foul weather. Sailors have seen it on salt-water soaked wooden masts, and we are plagued by it also. We just have not paid enough attention to the evidence and have missed the real root cause. We consider it particles striking the antenna was nearly all cases appear to be the simple phenomena known as St. Elmo's fire.
We can't cure precipitation static, but it can be reduced through the following steps:
As a general rule the following makes little difference:
hits since created April 2, 2009