FM-250 FM BROADCASTING EXCITER
Issue Date: 21 Jan 2003
IC2/a
provides the detection for a Forward RF Alarm,
with
R10 (FWD Alarm cal)
setting the
required threshold when the level is low. The output is used to give an Alarm signal via
TR1/RL1
.
d)
Reflected RF detection and Alarm
The Reflected RF monitoring input is via
SK2
(SMB), which provides a RF signal (nominally
0dBm), proportional to the RF reflected power of the Exciter. A dc output proportional to
the input power is achieved via
D5, D6 and IC1/b
(The diodes provide temperature
compensation). Adjustments are provided for
Level (R21)
and
Offset (R19).
The Offset
voltage is adjusted for
0.8V
nominal with no input signal at SK2. This is done to allow the
use of linear metering of the RF Reflected power in the Display module. The nominal
adjusted dc level is then
+5V/OdBm.
IC2/b
provides the detection for a Reflected RF Alarm,
with
R24 (REFL Alarm cal)
setting
the
required threshold when the level is high. The output is used to give an Alarm signal via
TR2/RL2
.
The detected dc output from
IC1/b
is routed via
IC2/c
and
R32 (REFL Alarm trip)
, which
sets a threshold to activate the
Timing circuit at IC2/d.
This provides a
10 second
re-cycle
time in the Exciter if the High reflected power persists. When the output of
IC2/d
is low the
Reflected Alarm is held on via D7
, which latches the Alarm indication during re-cycling via
IC2/b.
e)
Temperature detection and Alarms
The temperature sensing
Thermistor
, which is mounted in the RF PA module is input at
PL1
(pins 1 and 2). The nominal resistance of the Thermistor is 4700 ohms at 25
°
C.
R41 (Temp
cal)
, is adjusted to obtain a voltage output at
IC3/a
of
2.5V
for
25
°°
C
. The circuit sensitivity
is
10
°°
C per Volt
.
The Temperature detected output voltage is now routed via
IC3/b
,
TR3
and
RL3c
. to give an
Alarm indication, and
R45 (TEMP Alarm cal)
is provided to set the alarm level (normally
50
°
C). The voltage is also routed via
IC3/c
to provide a fixed
trip level
at
65
°°
C
. This
output switches off the RF PA Power supply.
f)
ALC (Automatic level control)
The ALC output at PL3 pin 2 is derived from
IC3/d
, which has the following inputs.
•
ALC CONT.
This dc input is derived from the Display module via PL6 pin 19.
•
FWD-V.
This dc input is derived from
IC1/a
(Forward power detected dc).
•
REFL-V.
This dc input is derived from
IC1/b
(Reflected power detected dc).
•
TEMP-V.
This dc input is derived from
IC3/a
(Temperature detected dc).
•
CURR-V.
This dc input is derived from
IC4/b
(RF PA current detected dc)
The circuit operates by
comparing
the set voltage from the
ALC Control
to the
FWD-V
voltage derived from the RF Forward power. This is done to correct any change in the
Summary of Contents for FM-250
Page 4: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 7: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 10: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 Figure 1 FM 250 Front Panel Controls ...
Page 12: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 27: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 32: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 48: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 49: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 50: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 51: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 52: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 53: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 54: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 55: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 56: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 57: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 58: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 59: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 60: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 61: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 62: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 63: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 64: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 65: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 66: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 67: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 68: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 69: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 70: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 71: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 72: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 73: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 74: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 75: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 76: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 77: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 78: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 79: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 80: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 81: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 82: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 83: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 84: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 85: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...
Page 86: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...