We 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
average speed 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, some cause
local 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 term "coronal
mass ejection" (CME) is relatively new, have been first used in 1982, so it
is not mentioned
in this 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
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 content.
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.
As we 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.
Fig. 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 ionosphere.
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).
The 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 point.
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.
Although 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 midwest.
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.
Posted June 2, 2022
(updated from original
post on 11/25/2013)