UBS Axcera 835-3 Users Manual

3-kW UHF Transmitter Chapter 2, System Description

Chapter 2

System Description

The 834-3 is a complete 3-kW UHF solid-state, internally diplexe d television transmitter
that operates at a nominal visual output power of 3000 watts peak of sync and average
aural output power of 300 watts, at an A/V ratio of 10 dB.

2.1 System Ov er view

The 835-3 is made up of two cabinets: a UHF exciter cabinet (the left cabinet) and an
amplifier array cabinet (the right cabinet).

This 835-3 (1176-1527) is comprised of (A1) a UHF exciter assembly (1227-1200), (A2)
an amplifier array assem bly (1245-1700) , (A9) a bandpas s filter (2005-1064), (A10) a n
outp ut trap filter asse mbly, and (A11) an output coupler assembly (1020-1002).

The left cabinet contains (A1) the UHF exciter assembly (1227-1200) for the 3-kW
transmitter, mounted at the top of the cabinet.

The (A2) 3-kW amplifier array assembly (1176-1528) contains (A9-A1) an 8-way
splitter (ZFSC-8-43), (A9-A2) an ALC splitter board (1181-1002), six (A1 through A6)
600-watt amplifier trays (1227-1300), (A7) a 6-way combiner, (A12) a reject load
assembly (1278-1312), (A10) an AC distribut ion panel (1245-1300), and (A11) an
interface pa nel.

Switch S2 is an Automatic/Manual switch that controls the operation of the transmitter
by the presence of the video input signal. When the switch is in Automatic, the green
LED DS3 is lit and, if the video input signal to the transmitter is lost, the transmitter will
automatically switch to Standby. When the video input signal returns, the transmitter
will automatically switch back to Oper ate. In Manual, the amber LED DS4 is lit and the
operation of the transmitter is controlled by the front panel s witches. During normal
operation of the transmitter, switch S2 should be in the Automatic position. The front
panel of the UHF exciter also has LEDs that indicate an overtemperature fault, (red LED
DS6), an ALC fault, (red LED DS8), a video fault (loss) (red LED DS9), and a VSWR
cutback (amber LED DS7).

The (A1) UHF exciter (1227-1200) takes the baseband audio and video inputs and
produces a diplexed, modulated, and on-channel frequency visual + aural RF output.
The RF output of the UHF exciter at J15 is connected to (A2) the 3-kW amplifier
assembly (1245-1700), where it is split six ways in (A9-A1) the 8-way power splitter
assembly (ZFSC-8-43). The outputs of the splitter feed the six (A1, A2, A3, A4, A5, and
A6) 600-watt amplifier trays (1227-1300) that amplify the RF signa ls to approximately
600 watts each.

A forward power s ample from the 4-way combiner board inside the 600-watt amplifier
tray is connected to the dual peak detector board. This board provides a peak-detected
forward sample to the amplifier control board that supplies the sample to the front panel
meter of the 600-watt amplifier tray. Be fore exiting each 600-watt amplifier tray, the
RF is fed through a circulator for protection of the tray from high VSWR conditions. The
reject port of the circulator provides a reject sample to the 4-way combiner board that
supplies the reflected sample to the dual peak detector board. The peak-detected
reflected sample connects to the amplifier control board that provides the sample to the
front panel meter of the tray. The outputs of the six 600-watt amplifier trays are then

835-3, Rev. 0 2-4

3-kW UHF Transmitter Chapter 2, System Description

combined in (A7) a 6-way combiner that provides approximately 3400 watts peak of
sync output. The c ombined output of the amplifier assembly is connected to (A9) a
bandpass filter, (A10) an output trap filter, and then to (A11) the output coupler
assembly (1020-1002). The bandpass filter and trap filter are tuned to provide high out­of-band rejection of unwanted products. T he output of the trap filter is cabled to (A11)
an output coupler assembly that provides two forward and one reflected power samples
to the visual/aural metering board in the UHF exciter. The two forward samples are
processed to provide peak-detected Visual and aural power output samples to the
transmitter control board. The reflected power sample is also peak detected and wired to
the transmitter control board. The transmitter control board connects the visual, aural,
and reflected power output samples to the front panel meter for monitoring.

2.2 Transmitter Operation

The 835-3 transmitter needs two AC inputs of 220 VAC: one to the exciter cabinet at 80
amps and one to the amplifier as sem bly cabinet at 100 amps. In the exciter cabinet, the
220-VAC input connects to the AC input assembly in the upper, rig ht rear of the cabinet.
The assembly contains terminal block TB1 that connects to the 220 VAC. The 220 VAC is
wired from the AC input assembly to the TB1 in the AC distribution panel (1247-1100).
The AC distribution panel contains six circuit breakers that supply the AC to the two UHF
exciter trays, one for the 3-kW transmitter and one for the 1-kW transmitter. The input
AC is connected to CB1, the main AC circuit breaker (80 amps) that distributes the 220
VAC to TB2. TB2 has three metal-oxide varistors (MOVs), mounted to the terminal
block: one connected from each leg of the input AC to ground and one across the two
legs.

The input AC is wired from TB2 through five circuit breakers (CB2, CB3, CB4, CB5, and
CB6) to the exciters and the rest of the 1-kW transmitter. CB2 (10 amps) supplies the
AC voltage to the IEC outlet strip (A2-A1) into which the UHF exciter for the 3-kW
transmitter and the UHF exciter for the 1-kW transmitter are connected. A circuit
breaker mounted on the rear of each UHF exciter tray can be switched on and off to
control the AC to that individual UHF exciter Tray. CB3 (20 amps) supplies AC through
J5 to (A6) the 600-watt amplifier tray. CB4 (20 amps) supplies AC t hrough J6 to (A7)
the 600-watt amplifier tray. When the UHF exciter circuit breaker is switched on, +12
VDC f rom the bottom UHF exciter tray is supplied to the two 600-watt amplifier trays in
the 1-kW transmitter and +12 VDC from the top UHF exciter tray is supplied to the 3­kW amplifier array assembly for the operation of the LED status indicators in the tray.

The baseband video and audio inputs to the 3-kW transm itter co nnect to the rear of
(A1) the UHF exciter tray, the top exciter. The baseband video input connects to jack J1
and the baseband audio input connects to jack J5, balanced audio, or to J3, for
composite, stereo, audio. The back o f the UHF exciter also provides connections for
remote monitoring and operation of the transmitter at jack J11. Jack J11 should have a
dummy plug connected to it which has a jumper between pins 23 and 24 that provides
the interlock needed to operate the 3-kW transmitter. If remote connections are made
to the transmitter, they should be made through the plug in J11.

2.2.1 (A2) 3-kW Amplifier Assembly (1245-1700)

The (A2) 3-kW amplifier assembly contains (A9-A1) an 8-way splitter (ZFSC-8-43), (A9­A2) an ALC splitter board (1181-1002), six (A1 through A6) 600-watt amplifier trays
(1227-1300), (A7) a 6-way combiner, (A12) a reject load assembly (1278-1312), and
(A10) an AC distribution assembly, amplifier array (1245-1300).

835-3, Rev. 0 2-4