Antennas - Carver TX-11b Manual

switched in, and left in. This can give you music and programming
that's unbelivably clean and quiet, without a hint of annoying distortion
and noise. With the noise reduction features of the Asymmetrical
Charge-Coupled FM Detector, FM stereo listening on cable feed, in
many cases, will rival or exceed the noise performance of your tapes
(cassettes, reel-to-reel, etc.), in terms of audio quality.
Muting Time
When either the NOISE REDUCTION or MULT1PATH REDUCTION
switches are engaged, a logic system analyzes the signal for
multipath and/or noise content. This process requires about
3
/4 of a
second. Whenever a new station selection is made, the mute time is
about
1
/2 second. If a new station is selected AND either the NOISE
REDUCTION or MULTIPATH REDUCTION switch is simultaneously
engaged OR has already been engaged, the muting times are
additive:
3
A +
1
/2 = 1
1
/4 seconds.
Antennas
Sending information through the air, as part of basic radio
broadcasting, is a relatively simple process. At the broadcaster's end,
the set-up includes a studio, transmitter, and transmitting antenna.
The studio supplies program materials (music, drama, news, etc.) to
the transmitter. Acting as a giant amplifier of sorts, the transmitter
sends the signal at high power and a specific frequency on to the
transmitting antenna in the form of alternating current. This creates
an electromagentic field that propagates through the air. At your end,
the listener's end, a length of wire is set up for use as a receiving
antenna. When the electromagnetic fieid generated by the
transmitter/transmitting antenna combination reaches the wire, a
small AC current is induced in it. A tuner connected to this wire, or
receiving antenna, translates this small current back into a "usable"
form. In short, back into music, drama, and other programs for your
enjoyment.
Of course, this description of what goes on in the transmission part
of radio broadcasting has been greatly over-simplified. There's a lot
going on in the actual transmission of stereo signals, and you'll soon
discover there's a lot going on at your end when it comes to that
"length of wire" or receiving antenna. This chapter is an in-depth
discussion of how you can obtain the best signal possible for the TX-
11 b through selection and installation of an antenna system. At the
same time, we offer some alternatives and ideas, so you can choose
a system that's not only right for the TX-11 b, but right for you and your
locale.
We'll be looking at the three major topics that concern receiving
antennas: antenna configurations, installing the antenna, and the
feedline from the antenna to the TX-11 b. Of course, if you've decided
to have a company distribute TV and FM programming to your home
via cable, the following information may be of passing interest only.
Skip ahead to the CABLE section at the end of this chapter. If you'd
like to know more about antennas, the benefits of a quality antenna,
and some of the causes and cures for multipath, please read on!
FM Antennas
Configurations
To begin this look at receiving antennas, we must first establish a
reference for comparing different antennas. Our reference antenna
will be a half-wave dipole, just like the one that came with the TX-11 b.
Antenna A is an illustration of this type of ribbon dipole antenna.
Notice the length of the "arm" or element. This is important because
antennas are resonant (electrically sensitive) when their length is one-
half the wavelength of the transmitted signal. Here's the formula: 5616
divided by the frequency in megahertz (MHz) = half a wavelength.
The middle of the FM band is 98 MHz, so 57.3" is half a wavelength.
As you can guess, this is why it's called a half-wave dipole.
Another antenna characteristic is its gain. This results from a focusing
of the electromagnetic energy of a transmitted signal. The half-wave
dipole that came with the TX-11 b is bi-directional. If you were looking
down on the dipole from above, the reception pattern would appear
as it does in the diagram of Antenna A.
reception
pattern
52" to 63.7"
configuration
Now that you know the important characteristics of the reference
dipole antenna, let's look at a common derivative, the Yagi (or Yagi-
Uda, more correctly. It's named for the folks who invented it). The
Yagi-type antenna is Antenna B in the diagram. These are
multielement antennas where the driven element, the part that's
connected to the feedline, is surrounded by reflectors behind it,
directors in front. Look at the reception pattern in our diagram. Note
the dramatic change in directionality from that of the dipole. The gain
of a Yagi-type antenna depends on the number of elements, their
lengths, and spacings. But compared to the reference half-wave
dipole (where the gain equals "0 dB",) Antenna B has a greater gain:
from 6 dB to 20 dB — all other things being equal.
reception pattern
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