Pecipitation Static or P-static

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Receiving Antennas

During inclement weather, when using antennas that are relatively high compared to surrounding structures, a severe increase in noise may occur. This effect is commonly reported by people with antennas that are physically high compared to surroundings. 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.

This static takes the audible form of a sizzling noise that can elevate in intensity and pitch from a slow hissing, popping, noise to a whining musical noise that increases in pitch.

When lightning flashes, even in the distance, the noise often stops. The noise then restarts, rapidly building to high pitches or high levels.

On FM radio systems, it usually occurs with top mounted antennas in inclement weather. The effect is to create a white noise that masks signals, rendering receivers useless. This is very common in 2-way radio systems, and a good reason to not have the antenna mounted above a supporting structure.

Examples of System Problems

Case 1, multiple contest stations

A search of contesting archives will reveal consistent complaints about noise on high antennas.   Here's a sample of a typical post from a contest reflector. This one is from NQ4I on the 3830 contesting archives:

"Comments:

First of all we had storm after storm...nearly 36 hours of continuous Precip static...the stacked yagis were useless...we had to use the lowest antenna "

From N3UM
"Terrible P-static: S-5/6 on Beverage, S-7 on Inv.-L Tx ant. Fri./Sat.,
only ~1 S-unit better Sat./Sun. By Sat. 06 Z, NO QSOs in W5, 6, or 7
except one AZ.  Finally, ~06 Z Sun., TX, ID, NV, and IA in 30 min.
Fun to have a G and a VP9 answer my CQs.  Last 2 hr. (22-24 Z Sun.),
static down to S-3; picked up 43 QSOs and 3 multipliers: NF, NS, and EA8.

Ordinarily I emphasize CW contesting; only my second time doing CQ 160 SSB, but
the challenge of making QSOs on 160 SSB got me involved despite the P-static and
lightning crashes."

From AA5AU:

"If you look at the score you would think that my main problem was lack of
multipliers.  Yes, that was a problem but the main cause of the low score this
year was the weather.  The weather has been unkind me to in the past year and
it put the screws to me pretty good during the contest.  An hour into my low
band run, and with the rate running well over 100/hr since the start of the
contest, a train of thunderstorms started rolling over the area beginning at
0000Z that produced frequent lighting strikes and torrential rains which cause
rain static that blanketed 40 meters completely.  The static was very bad on 80
but I was able to copy signals; using my lower tribander for a receive antenna. 
But on 40, no matter what antenna I tried, the rain-static ruled the band.  The
only time the static would subside was after a lightning strike.  After a
lightning strike, the static would go away for about 30 seconds.  So I'd CQ and
work a couple of stations, them BAM, the static was back.  It's a hell of a way
to have to operate."
 
Clearly lower antennas are better, despite grounding and insulated or bare. 
 
Search the 3830 archives for "static" and see what you find.  

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.

Summary

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 and in a variety of systems. Antennas with grounded elements and antennas with insulated elements all behave in similar ways. 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:

  • Having something else much taller than the receiving antenna close to the receiving antenna or lowering antenna height.
  • Avoiding sharp points on or near the antenna. Sharp points increase voltage gradient and increase corona.
  • Avoiding protruding elements. Protruding elements increase corona.

As a general rule the following makes little difference:

  • Grounded elements
  • DC shunt elements on feedlines
  • Improving ground systems or grounding

 

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