have long known that activity on our sun affects electromagnetic
communications. Energetic particles, primarily electrons, explode
from the sun's surface (coronal mass ejections* and flares) and
are hurled at blazing speeds towards the earth at an
of around 424 km/s (263 mi/s). They begin
affecting our upper atmosphere about four days later by ionizing
atoms, thereby altering electrical conduction properties. This in
turn determines how and whether electromagnetic signals either pass
through the atmosphere into space or get refracted (bent) back down
toward Earth. Long distance communications in particular are effected,
but often even local communications are impacted as well. Some events
have little effect, some cause minor disruptions in communications,
communications blackouts, and some are significant enough to cause
entire power grids to fault and shut down. Frequency and intensity
of the CMEs and flares is correlated with the well-established 11-year
(approximately) cycle between solar maximums** and solar minimums.
This article discusses some of the ramifications of solar disturbances
using terms familiar to DX (long distance) Ham radio operators.
I wonder how many televisions were taken to the repair shop because
of these solar effects? * The
mass ejection" (CME) is relatively new, have been first used
in 1982, so it is not mentioned
1957 article even though CMEs certainly would have been occurring
at the time.
** We are currently experiencing one of the
weakest solar maximums in the last century.
Sunspots Mar TV Reception
By Sidney C. Silver, Service Editor, Radio & TV News
During peaks of sunspot activity, hundreds of spots of the
type shown at left may appear on the solar sphere. Graph
to the right shows the increase in number of spots from
January, 1955 (fewer than 10) to about 200 in January, 1957.
The cycle is still active.
Strange DX signals suddenly appear, taking over TV screens, plaguing
set owners and technicians.
A viewer who lives about 50
miles from the metropolitan area in which his favorite TV stations
are located, and who normally gets pretty good reception, is reclining
in his living-room chair one afternoon, completely relaxed, enjoying
his favorite program on, say, channel 4. He becomes aware of fine
horizontal lines faintly visible across the picture. Since he has
been enjoying reception on this channel for a number of years with
the same receiver and the same antenna, this entirely new phenomenon
puzzles him somewhat, but it is not sufficiently prominent to be
really annoying: he remains in his chair in the hope that the symptom
will go away of itself.
As he watches, the lines become
somewhat heavier and eventually mar his enjoyment. A somewhat darker
vertical bar is now noticeable, swinging back and forth across the
screen. Now he can barely make out his program at all; the lines
are practically dominating the screen. Then the picture goes completely
out of sync. Although he is bewildered, many a technician would
state at this point confidently - and correctly, to a degree - that
a serious case of adjacent - or co-channel interference is causing
all the fuss.
The harried viewer has left his chair and
is heading toward the set to apply the only remedial technique he
knows. He is preparing to twist every knob with which the receiver
manufacturer has supplied him in an attempt to exorcise the crazy
quilt on the screen. Before he can do this the receiver, as though
acting in self defense, suddenly permits an intelligible picture
to fill the screen again. As our viewer gets ready to relax again,
he realizes that the characters on the screen are completely unfamiliar.
The show itself is completely unfamiliar. It has nothing to do with
the program he was watching a short while ago and which should still
be on the air. While he is trying to make some sense of this odd
development, the program ends and a station break comes along. A
completely unheard-of station with call letters he never knew existed
identifies itself as "his" channel 4. Its location is given as some
metropolis in another part of the country, hundreds of miles away.
Before reaching into his pocket for a tranquillizing pill,
the victim just barely manages to reach the telephone and pour out
a garbled account of what has happened to his incredulous service
technician. While awaiting the technician's arrival, he stalks to
his window and stares out, puzzled, at his antenna, which is just
visible in one corner of his field of vision. He has to squint uncomfortably
because he is partially blinded by the bright light beyond his antenna
on this fine, clear day. The light comes from the sun. the unperturbed
culprit in our little drama.
Admittedly, the account just
given of interference resulting from so-called sunspot activity
is of a severe case; but it is based on an authenticated experience.
Nor will it be the last of its kind before we have drifted past
the current sunspot cycle maximum. Often, the effect does not become
as severe as in the unfortunate drama we have just presented; that
is, the interfering, distant transmission working on the same frequency
does not always become strong enough to ride over the desired local
program. In these less startling cases, the symptom will take the
form only of enough co-channel interference to ruin the program
being viewed or to mar it considerably, usually by introducing instability
or complete loss of sync, as well as by making a hash of picture
Uppermost in the minds of affected technicians
and set owners will be the question, "What can we do about it?"
Before we can start to supply answers - and there aren't many -
we have to have some picture of what is going on.
rise above the earth, penetrating its surrounding atmosphere, we
reach a region beginning about 50 or 60 miles up known as the ionosphere.
This consists of several layers in which free ions and electrons
occur with far greater frequency than they do in the more immediate
atmosphere that hugs the earth intimately. The highest of these
layers is about 200 miles straight up - quite a trip on the elevator.
1. Normally propagated TV transmissions travel in
straight lines, and cannot be picked up beyond the horizon.
When the sun acts up, they may bounce for great distance.
With all the free electrons an ionized particles in the upper layers
of the atmosphere, this ionospheric region is essentially a different
medium from the atmosphere we find immediately around us. It is,
in effect, a denser or less transparent medium, just as water or
glass, although still transparent, are denser media than air.
When a pencil is put in a glass of water, it appears to
be bent to the viewer standing away from the glass. What has happened
is this: the normally straight-beamed light rays (very super high-frequency
radiation) from that part of the pencil which has been submerged,
in travelling to our eyes, have been bent in going through the water
and glass, because they have been slowed up by the denser medium.
In like manner, radio signals are bent or refracted as they pass
through - or try to pass through - a "thicker" medium, like the
This phenomenon gives us our long-range or DX
short-wave transmission. As shown in Fig. 1, ordinary radio waves,
essentially unbent, travel line-of-sight and cannot be picked up
by receivers beyond the horizon. Other waves are refracted so severely
that they finally reflect downward and return to the earth at some
distant point beyond the horizon (receiver 2).
higher the frequency of either sound or electromagnetic waves, the
more resistant they are to refraction and reflection. The bass end
of the audio range, for example, seems to spread around the room
from a loudspeaker. The treble end of the range is more narrowly
beamed in front of the speaker and is not heard as clearly off the
speaker axis. With electromagnetic waves, the signals can bounce
around the world, between ionosphere and earth in the shortwave
bands; however, when we go up in frequency into the TV bands, the
signals tend to resist the bending effect of the ionosphere and
transmissions manage to fight their way through this medium without
being hurled back to earth. Thus, we ordinarily think of TV reception
as not being practical beyond the horizon from the transmission
The highest frequency that can be bounced back to
earth depends on the degree of ionization in the upper layers. This
m.u.f. (maximum usable frequency) seldom moves up as high as the
TV frequencies under ordinary conditions. However, along comes our
sun to shed a new, if somewhat confusing, light on the situation.
Alone in space, millions of miles from its nearest neighbor,
the solar orb gets bored now and then - about every eleven years
or so - and begins to amuse itself with what we have come to know
as sunspot activity. There is much speculation and less actual knowledge
about the whys and wherefores of this sunspot cycle. As to effects,
however, we do know that, during the period when the sun is riding
the peak of a sunspot cycle, disturbances also occur in the ionosphere.
Along with marked changes in the degree of ionization, the m.u.f.
soars upward, and may get well into the lower v.h.f. band. When
it does, TV transmissions at or below the m.u.f. can be thrown back
to earth hundreds and even more than a thousand miles from the point
of origin. The lensing action of the ionosphere may concentrate
the refracted energy sent back down into the distant area to the
degree that the returned signal will be strong enough to force its
way over local transmissions on the same channel, and take over
the screen completely.
We are going through a period of
heavy sunspot activity right now, and this condition is likely to
persist for half a year, or for more than a year; it is never easy
to predict its exact termination. This type of disturbance is a
new problem in the TV era: during the last sunspot peak, which occurred
in 1947, there were neither enough receivers nor enough operating
stations in the country to create much difficulty.
the disturbing effects already described may occur anywhere, areas
of primary reception will be less susceptible than others. The particular
instance with which this article begins occurred in a near-fringe
sector about 50 or 60 miles west of an eastern metropolis. Since
the locality is on high ground, many favored set owners are able
to get acceptable reception from the big city with nothing more
than indoor rabbit ears. The indoor antenna was beamed east, of
course, but antennas of this type are equally sensitive in the opposite
direction. The interfering station was identified as one from the
Most reports of DX TV reception at this time come
,from fringe areas, where the inherently weaker signals available
locally can put up less of a battle against intruders. Nevertheless,
the author, who resides in a near suburb of New York City where
there is signal strength to throwaway, has suffered some mild, occasional
co-channel effects - horizontal lines, windshield-wiper effect,
infrequent sync instability - on channel 2. This has occurred three
or four times over the last half year, and has lasted for two or
three hours on each occasion.
To the DX fan, these random
pick-ups are gifts from heaven - or from the sky, in any case -
especially when they fall on channels that are normally vacant in
the local area. To most viewers, these invading signals are unwelcome
obstacles to TV enjoyment, and these people can't understand what
is wrong with the idiotic technician who shrugs his shoulders helplessly
when he is asked to "fix the set."
The situation is a tough
one, because a sure, universal cure does not exist. In areas where
the victim has been getting by with an antenna that is largely nondirectional,
a narrowly beamed unit, aimed in the direction from which transmission
is desired, will cut down hobo signals that drop in uninvited from
random angles. However, the refracted intelligence may also swoop
down from the angle of optimum orientation. Even in these cases,
the fact that normal TV transmissions travel in the horizontal direction
gives us something to work on. The angle of incidence of radiation
bounced back from the ionosphere will be oblique (see Fig. 1). There
are many good antennas that not only discriminate against signals
arriving at the rear and sides, but also reject signals that do
not come in horizontally. A check of the vertical radiation patterns
supplied by most manufacturers of good antennas will be useful in
making a choice.
Recommending the expense of a new antenna
installation to a victim of the sun is a delicate problem, at best.
There is no assurance as to how effective it will be, and the unpredictable
sunspot cycle may come to an end before the cost of a new antenna
can be justified in terms of whatever relief it will provide from
the difficulty. The technician would do just as well to use the
opportunity for stressing the need for a better, newer antenna on
general principles, with possible reduction of sunspot interference
as an added inducement. Overstressing the possible protection against
interference from DX TV transmissions, even where this symptom has
been a fairly regular nuisance, leaves the technician open to recrimination
by the set owner where the results will not justify the expenditure
involved. Few technicians will want to take such a risk.
In any case - and especially in those where the condition exists
despite a good antenna installation - an important public-relations
problem confronts the TV service worker. Unless it is properly handled,
he may suffer loss of confidence with some customers. His best bet
is to make a rough sketch like the one shown in Fig. 1 and try to
explain what is going on. The simplified explanation given here
has been tried out on several nontechnical people with good success.
The technician is less likely to be looked upon as an idiot if he
can do this successfully; he is also giving his customer an honest
picture of the situation and expectations. In effect, the customer,
not the technician, is responsible for the decision as to whether
a gamble on a new antenna should be taken. Besides, while the explanation
is being given, the symptoms may very well disappear altogether.