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
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?
|August 1957 Radio & TV News
of Contents]These articles are scanned and OCRed from old editions of the Radio & Television
News magazine. Here is a list of the
Radio & Television News articles
I have already posted. All copyrights
(if any) are hereby acknowledged.
* 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
** We are currently experiencing one of the
weakest solar maximums in the last century.
available vintage Radio
Sunspots Mar TV Reception
By Sidney C. Silver, Service Editor, Radio & TV News
Strange DX signals suddenly appear, taking over TV screens, plaguing
set owners and technicians.
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.
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.
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.
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.
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.
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.
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 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
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."
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.
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.
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 November 25, 2013