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Radio Noise
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:
- DC shunt
elements on
feed lines
Improving ground
systems or
grounding
hits since created
April 2, 2009
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