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A multi-element directional antenna is essential for any serious
off-air pickup. “Turnstyle” or S-shaped, “all-directional” FM an-
tennas are all but useless in nearly any reception circumstance.
Professional FM-band receiving antennas are available from var-
ious manufacturers, and are recommended for long-term appli-
cations. With cost in mind, however, a consumer-grade alterna-
tive that has proven to work quite well is the Antennacraft
Model 70 Yagi, easily found at Amazon and other online sup-
pliers.
“Direct”
RF Input
High-level RF samples (from the transmitter’s directional cou-
pler, for example) may be fed to the 531N through a dedicated
rear-panel BNC connector. However, this
HI LEVEL RF IN
con-
nection does
not
bypass the tuner, the signal is simply padded-
down and applied to the tunable front-end. High-level inputs
should be restricted to a maximum of 7 volts r.m.s. to avoid
overloading the internal terminating resistor; and of course, the
receiver must still be tuned to the incoming frequency.
RF Input
Switching
The rear-panel
RF SOURCE SELECT
switch must be in the
proper position for
ANT
(antenna) or
DIR
(‘direct’ high-level) in-
puts.
COMPOSITE/MULTIPLEX CONNECTIONS
Composite
Output
The rear-panel
MPX OUT
connector is a direct output from the
FM demodulator. An internal buildout resistor sets the source
impedance at 100 ohms. This output is intended for oscillo-
scope monitoring or for feeding outboard analysis equipment
with high impedance ‘bridging’ inputs.
Observe good laboratory practice and avoid long connecting
cables, or otherwise highly capacitive or very low impedance
loads. Heavy loading of the
MPX OUT
connector may compro-
mise front-panel modulation readings.
Composite
Input
The
MPX IN
connector lets you monitor external baseband sig-
nals with the 531N, either from another off-air source or direct-
ly from a composite STL receiver or FM stereo encoder.
When the
MOD-MONITOR INPUT
switch is in the
EXT
position,
the RF tuner portion of the Model 531N is disconnected and the
MPX IN
baseband signal is routed to the level metering and ste-
reo decoding circuitry. This is a 100k-ohm, unbalanced/bridg-
ing input that can accommodate levels of 1V p-p (peak-to-peak)
or greater. The multi-turn
EXT MPX IN LEVEL ADJUST
control
affords adjustment over the external baseband input.
Composite
Signal Selection
The
MOD-MONITOR INPUT
switch selects between
AIR
(off-air)
and
EXT
(external baseband input).
Содержание 531N
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