Welcome to rec.radio.shortwave (AM/FM DXing)

Welcome to rec.radio.shortwave (AM/FM DXing)

Post by Scott Fybu » Mon, 04 Jan 1993 03:34:04

INTRODUCTION TO REC.RADIO.SHORTWAVE
Am/FM DXing

By Scott Fybush

One of the easiest parts of the radio spectrum to explore is the
broadcast bands.  This posting will attempt to offer some hints to
make your exploration of the medium wave and VHF-FM bands more
enjoyable.

I. WHAT ARE THE AM/FM BROADCAST BANDS?

The medium wave (commonly referred to as AM) broadcast band currently
extends from 525 to 1605 kilohertz.  Channels are spaced in even 10
kHz increments; i.e.: 530, 540, 550, ... , 1600 kHz in the United
States and Canada.  Elsewhere, channels are generally spaced in 9 kHz
increments, i.e.: 531, 540, 549, etc.  In the United States, plans are
underway to expand the band to 1705 kHz.  Within a few years, stations
will begin appearing on the 1610-1700 kHz frequencies.

The FM broadcast band in the United States extends from 88 to 108
megahertz.  Channels are assigned at 200 kHz increments; i.e.: 88.1,
88.3, 88.5, ... , 107.9.  The channels from 88.1 to 91.9 are reserved
for noncommercial educational stations.  Outside the United States and
Canada, the boundaries and channel spacing vary.  In Japan, the band
starts at 76 MHz.  In Western Europe, the band runs from 88-108 MHz,
but channels can be irregularly spaced, i.e.: 101.25 MHz.

II. SIGNAL PROPAGATION

The distant stations you are able to receive will depend largely upon
signal propagation.  This varies depending upon the time of day, the
season, and other factors.  For medium-wave, the single most important
factor for good DX is the time of day.  Medium-wave signals pass
through the ionosphere during daylight hours and are lost to space.
As a result, all medium-wave signals received during daylight hours
will arrive by ground wave.  Reception of signals over a few hundred
miles away is generally impossible in daylight.  At night, however,
the ionosphere reflects medium-wave signals, making it possible for
signals to be heard at much greater distances, up to a few thousand
miles.  Reception also tends to be better in winter than in summer.
Many smaller medium-wave stations are required to sign off or reduce
power sharply at sunset so as to reduce interference to distant
stations.

For FM, daylight is unimportant.  FM signals generally carry no more
than 150-200 miles even under the best conditions.  Since the
ionosphere generally does not reflect VHF FM signals, such signals
must travel line-of-sight to reach the receiving antenna.  FM
transmitting antennas are thus usually located as high as possible.
Tall towers, high buildings, and mountaintops are common FM
transmission sites.  Under certain conditions, the E layer of the
ionosphere will reflect VHF FM signals, thus making it possible to
receive extremely long-distance FM reception.  This is almost
impossible to predict, however.

III. RECEIVERS

Almost any radio is capable of some broadcast-band DXing, especially
long-distance medium-wave reception.  However, most recent radios,
even those designed for quality shortwave reception, do not have
outstanding broadcast band reception.  One exception is the General
Electric SuperRadio II (Model No. 7-2885F.)  The SR II is designed for
optimum AM/FM broadcast performance, incorporating:

* RF amplifiers on both bands
* Ceramic filters and Automatic Frequency Control on FM
* An analog tuner with an IC-type receiver chip and air-variable
capacitors.
* No PLLs or digital displays for less electronic noise.
* A 2-way speaker system with 1 watt of audio power.

The SR II is a bulky (4" x 10" x 12") portable radio which can be run
off 120V AC or 6 "D" batteries, providinover 400 hours of battery
life.  The styling is cheap silver and black plastic, and has been
described as ugly.  Nevertheless, this radio has become popular among
the DX community for its exceptional performance.

It costs between thirty and sixty dollars in the US, and may be found
at many discount outlets.  It is generally back-ordered by mail, but
can be obtained from Bennett Brothers (Order #R8883) at 1-800-621-2626
or 1-800-631-3838, or from Best Products (Order # 140457) at
1-800-950-2398.

With the sale of GE's consumer electronics division to Thomson, this
product's future remains in the air.

If you don't have a SuperRadio, some important things to seek out in a
receiver are:

* External antenna connections.  These make it easier to use a better
antenna than the one supplied with the radio.

* High selectivity.  This refers to the receiver's ability to reject
strong signals on adjacent frequencies, and is more important to good
reception than is sensitivity, since a good antenna will provide
more-than-adequate signal strengths.

* Digital frequency display.  While the circuitry involved does add to
the level of internal electronic noise in the radio, digital display
makes it possible to more easily determine what station is being
heard.

IV. ANTENNAS

For medium-wave reception, most receivers have a short internal
ferrite rod.  This will provide acceptable signals for high-powered
distant stations.  The ferrite rod tends to be quite directional, and
the radio can thus be turned to null out strong interfering signals,
or to improve reception of the desired signal.

For more advanced DXing, an external antenna is a must.  The easiest
external antenna is a simple longwire, 50 feet or more run out the
window and then as high as possible (up in a tree, for example.)  The
wire can be connected to the external antenna terminal.  If none
exists, you can open up the radio and wrap the wire a few turns around
the ferrite rod inside.  It is also possible, although less desirable,
to simply wrap the wire around the entire radio.  If the radio has a
terminal marked "ground" or "GND," another wire can be run from this
terminal to a copper rod driven a few feet into the earth.

A more advanced antenna is the "beverage" antenna.  This is a length
of wire 1000 feet or more.  It is terminated at the far end with a 450
ohm resistor connected to a metal stake driven into the ground.  It
should be pointed in the direction of the desired station.  The
beverage antenna can, under good conditions, be used for transatlantic
and transpacific DX.  Another more advanced antenna is the loop, a
four-foot wooden frame with about 20 turns of wire run around it.  It
is connected to the radio with a 365 pF variable capacitor for tuning.
The loop is extremely directional.

For FM, the important factor is height.  The higher one can place an
antenna, the better reception will be.  A multielement Yagi antenna,
which can be found in Radio Shack or similar stores, will often
produce excellent reception.  Since a yagi is quite directional, the
use of a rotor is essential for reception of stations in different
directions.

V. WHAT'S OUT THERE TO LISTEN TO?

There are over 10,000 radio stations in the United States alone.  It's
important to have some idea of what to expect to hear.  A good
directory is important (see STATION LISTINGS below), but it's
essential to know what the station information means.

For medium-wave, US frequencies f