Fm Reception Hints; General; Antennas - Revox B261 Operating Instructions Manual

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