Originally written by Dave Austin
- What is DX?
- "DX" is radio jargon
for "distant reception." If you receive a signal
from an unusually long distance, it is DX.
- Where did the term
"DX" come from?
- Telegraphers over a century ago
invented many abbreviations for common words or phrases. If
one didn't have to tap out all the Morse characters in a word or
phrase, messages could be transmitted faster. Amateur radio
operators (hams) to this day frequently use such abbreviations. Many ham abbreviations have
become standard radio parlance; their definitions are widely
understood and even transcend different languages. Some other common ham abbreviations
are: QRM (interference), QSL (verification of reception), QTH
(location), and QRP (reduced power).
- How does DX happen?
- Broadly speaking, TV and FM DX
takes place when normal atmospheric conditions change to permit
distant reception. Disturbances in layers of the upper atmosphere
allow TV and FM band signals to travel through "ducts" for
several hundred miles. Sunrise, sunset, and some weather
patterns can set up temperature inversions that bend signals back to
earth 100-200 miles beyond their source. On rare occasions the
ionospheric layers hundreds of miles up become dense enough to
reflect TV and FM signals back to earth--500 to several thousand
miles away from their source. This last kind of DX mechanism
is commonplace at lower frequencies: it makes worldwide shortwave
broadcasts possible, and causes AM stations to come in farther at
night. But that's not "DX" because it's not unusual.
- So is this what they're
talking about when local stations sometimes announce that
atmospheric conditions are interfering with their signal?
- Very likely. The lower
VHF channels (2 through 6) are more susceptible to sporadic
interference from distant stations. When I used to live near a
TV station on channel 3, every summer when the "skip"
kicked in they would run a crawler along the bottom of the screen
explaining that the interference was due to atmospheric conditions
beyond their control.
- It means a signal-- that ordinarily would
just go off into space and be forgotten--has bounced off the
ionosphere (a layer of charged particles several hundred miles above
the earth) and back to earth several hundreds or thousands of miles
- Is TV DX the same as
getting out-of-town TV stations?
- No. Typically, a TV signal is
viewed throughout an area in a 25-100 mile radius of the
station. That means that every day you can count on watching
your favorite programs on a certain group of stations in your
antenna's range. TV DX, on the other hand, is unusual. You can tell it's a distant station by
commercials, news, and of course the station identification (ID).
- But don't you need
- Not always. Skip can be
received adequately with rabbit ears. For some DX it is helpful to
have the most sensitive antenna possible and to amplify the signal
using a preamp. Sometimes DX can only be received with
sophisticated equipment, but your ordinary TV antenna and set are
sufficient for at least some DX'ing.
- Does it require a
special TV set?
- Not necessarily. Generally
speaking, the newer "electronic" tuners (the ones with
digital channel display that automatically fine-tune and block out
weak signals) are not as desirable for DX as the old-fashioned
click-in-place dials with a manual fine-tuning knob. Serious DXers
can buy ultra-sensitive tuners that detect DX invisible to those
with more typical equipment.
- What about antennas?
- Generally speaking, the more
sophisticated antenna you have, the more DX you will see. Also, an outdoor antenna is almost always
preferable to an indoor antenna. (A rotor is essential so you can
point your antenna in the direction of the DX or minimize a local
signal that is "interfering" with the DX!) However, it is
entirely possible to see decent skip with rabbit ears in a basement!
This is because the signal is coming down to you from the atmosphere
rather than across the terrain.
- Is TV DX predictable?
- Only in the broadest sense, and
even then there's no guarantees. Generally, summer is the best
time for TV DX. DXers have also been able to chart activity
over many years and find most probable times for DX based on past
performance. Important variables include weather systems,
stable temperatures, sunspot activity, time of year, time of day,
latitude, and path geometry.
- How long does it last?
- Generally, it lasts as long as
the conditions creating it last. This can be anywhere from a few
seconds to several days. Some kinds of "tropo"
(tropospheric bending/ducting) can last a few days near coastal
areas. I once saw channel 9 from Orlando in Myrtle Beach, South
Carolina for a week. My wife's girlfriend from Tunisia used to watch
Sicilian TV from Palermo all summer, but only in the summer.
- Does it help if you're
near water? What about mountains?
- If water is between you and the
signal, then water can be helpful, whether the reception is DX or
normal, everyday reception. Large bodies of water can refract (bend)
signals, making long-haul DX possible. Mountains have the opposite
effect and tend to block out or reduce normal reception and do make
some kinds of DX more difficult. However, skip is entirely possible
even if you are completely surrounded by mountains. (Remember skip
comes from high angles off the ionosphere several hundred miles in
altitude.) I once saw skip in Green Bank, West Virginia, where the
National Radio Astronomy Observatory deep-space dishes are located.
- What's the point of
watching distant TV when you can just get cable or a satellite dish?
- If you are relying on DX for
your daily TV reception, you're far better off getting cable or a
dish. DX is an abnormal and temporary occurrence, not a source of
regular TV or FM. That's right, you can't count on DX
modes to watch a non-blocked football game from another city.
However, your interest in DX may motivate you to acquire such
superlative equipment that a distant TV market becomes commonplace
reception for you. For example, it would be reasonable for a
person in Washington, DC or New York to set up a system optimal for
DX'ing that would also allow daily, fair/good-quality reception of
TV stations in Philadelphia. DXers are fascinated by what and
how far they can pick up.
- Is the picture clear?
- Some DX comes in as clearly as
a local station. Often, though, the DX signal is weak, laden with
interference, fades in and out, is only video or audio, or all of
the above. The harder the DX is to pin down, the more it becomes a
- Can I get these
stations on satellite? Cable?
- Satellite TV operates on a
completely different set of frequencies and is not affected by the
same kind of atmospheric conditions that create TV DX. Your cable
company's master antenna ("head end") may receive DX just
like your rooftop antenna, especially if the regular station on that
channel is quite far away or isn't on the air yet. This can make for
some fascinating and unusual DX! Stronger local stations are rarely
affected by DX interference on cable. (And sometimes a local station
feeds its signal directly to the cable company, which wouldn't be
susceptible to DX at all.)
- Are all those antennas
on your house going to interfere with my TV reception?
- No. TV antennas are for
receiving only, not for transmitting. Interference is only possible
if you're transmitting something, not receiving signals.
- Does cable ever
interfere with TV DX?
- It can. Improperly installed
and maintained cable lines can radiate signals
unintentionally. It can even behave like a DX signal. If your
regular TV stations are being interfered with by cable leakage,
contact your local cable company. (I don't think cable companies are
under any obligation to eliminate your interference so you can
- Can you pick up
stations from other countries?
- In North America, DX signals
from the United States, Canada and Mexico can cross the border and
be received hundreds of miles inside the country, depending on what
kind of DX it is. Of course, people living near the border can often
receive foreign stations on a daily basis anyway. TV technical
standards are the same throughout North America, so everyday
reception as well as DX is possible using your present TV set.
"F2 skip" makes trans-oceanic reception conceivable,
though it is rare. Also, TV technical specifications are different
in many countries outside North America. The fundamental theory of
TV reception is the same all over the world, but there are
differences in frequencies, picture resolution, audio transmission,
and electrical cycles, so you would need a TV set compatible with
those specifications. (There is such a thing as a worldwide TV set,
but they are quite expensive and usually purchased only by people
who foresee moving back and forth, such as military and diplomatic
- Can I also DX FM radio?
- Yes! The FM band is affected by
the same kinds of atmospheric phenomena as TV. The FM band (88 - 108
MHz) is situated just above TV channel 6 on the spectrum. In fact,
if you tune your radio to the very low end of the FM band you can hear the audio portion
of channel 6 if you have a nearby station on that channel. I once
heard WPVI-6 in Philadelphia while in Shenandoah National Park, a
distance of over 200 miles, using my car radio.
- How can I find out more
about TV and FM DX?
- This FAQ is intended to be a
quick introduction to the subject. For more
technical information, check out our Treasury of
Of course, the best way
is to join our club! Click
here to send e-mail to the WTFDA staff. Mike Bugaj will
personally answer your questions or forward them to the right