4
FM RECEPTION
HINTS
4.1 General
The FM
radio
band
covers the
frequency range from
87.50
to
108 00
MHz which corresponds
to wave lengths of approxima-
tely
3
meters. Radio waves of this
length
are
propagated
in
a
similar
manner as light.
This means that the best
reception
can
be
expected
if
there
is a direct
line
of sight to
the transmitter
an-
tenna. Of
course,
reception of adequate
quality
is also
possible
without a direct
line of sight,
however, only if a
high-quality
an-
tenna
and
possibly
also
an antenna
rotor is
used.
lf the synthesizer
tuner
8261 is connected to
a community
an-
tenna, the
reception
quality
is determined by the
quality
of the
antenna system
and especially
its
amplifiers.
Potential sources of
FM reception
problems;
M ultipath distortions:
Transmitted FM
waves are
reflected
by solid
objects such
as
walls, buildings, etc.
lf
direct
as
well
as
"detour"
waves
reach
the
antenna. unpleasant delay
distortions occur
in the receiv-
er
(analogous
to the
ghost
images
on
a television set).
Multi-
path
distortions
can be eliminated through
accurate
align-
ment of a directional antenna.
I nte rference
f rom
autom otive
i
g
n ition
systems:
The best
protection
agalnst radio interference
from automo-
tive ignition systems
is
a
wellscreened antenna cable
(coaxial
cable)
that
is
connected directly to the antenna
input of the
8261 tuner.
Cross
modulation:
The
8261 synthesizer tuner offers optimum
protection
agalnst
such
interference. Cross modulations that occur
in
poor
an-
tenna
systems/amplifiers cannot be
eliminated
by any tuner.
Radio noise:
The sensitivity
of the 8261 tuner
is
exceptionally
high. Even
if
the useful
signal
strength
of a mono station
is
just
barely
above
the
antenna noise,
satisfactory
reception is still
pos-
sible.
With
increasing
signal strength
the reception
quality
is
less affecled
by
inter[erence,
Stereo
reception
requires an antenna signal
that
is higher by
20
dB
(factor
of
10)
for the same SN
ratio as
in mono
recep-
tion.
lf the stereo
reception
over
a comrnunity
antenna system
is
poor
this
is
generally
caused by
weak or incorrectly
function-
ing antenna
amplifiers.
Maximum use
of all the features
provided
by a
high-quality unit
such
as the
8261
synthesizer
tuner
is
only
possible
in
conjunc-
tion
with
high-grade
peripheral
material
(antenna,
cable. etc.)
(tD)t
I
r
r
'',:-i?
,
4.2
Antennas
To obtain
maximum benefit from the exacting
quality
standard
to which the 8261 synthesizer
tuner has been built,
this unit
should be
connected to a
powerful
antenna system.
However, reception of surprisingly
high
quality
is frequently
pos-
sible
with
a simple
indoor antenna.
Preference should be
given
to an outdoor
(e.9.
roof) antenna
where installation
is
possible.
This can considerably
improve
the
reception
quality.
Since
this
may involve very long cables,
a
good
antenna booster should
be connected at
the base of
the
antenna. Only
unbalanced
(coaxial)
cables should
be used,
iJ
possible,
in order to
prevent
signal
losses by balance-to-unbal-
ance transformers
and to reduce
interference
pick-up
bythe
an-
tenna to
a minimum.
14
To Next Page
Loading...
Need help?
General
