Print Date 31/08/11 Page 6 of 22 E2136-00MA-02
over the heatsink fins with only a small ‘bleed’ of air over components mounted on the heatsink
surface itself.
1.1.4 : Two Way Combiner, Low Pass Filter and Directional Coupler
These interface between the two amplifier outputs and the antenna. The combiner section is a two
way Wilkinson utilising standard 70.7
Ω
or 75
Ω
coaxial cable and two 50
Ω
load resistors. The
following low pass filter is nine section Tchebycheff, giving a very high level of attenuation at harmonic
frequencies. The filter capacitors utilise PTFE boards in a screened ‘sandwich’. The output directional
coupler utilises microstrip lines on PTFE board with a dielectric overlay to optimise directivity. The
coupler board also contains the forward and reverse diode detectors and thus provides dc levels, to
the Control board, representing the forward and reverse power levels present. The final RF output
connector is either a 7/8in. (E2136-01, 03, 05 and 07) or 7-16 (E2136-02, 04, 06 and 08).
1.1.5 : Control/DisplayInterface Boards
The front Control Board contains circuitry to measure the Amplifier’s final output forward and reverse
powers via the output directional coupler, the temperature of the heatsink, via a precision temperature
sensor mounted on the heatsink, and the current drawn from the power supply via Hall effect current
sensors fitted on the Power Supply Board. These levels, as well as the analogue level representing
the required set output power, are converted to digital form by a microprocessor. This microprocessor
also receives direct information about the status of the Amplifier and any external inputs. All this
information, along with any fault messages, are fed to the Front Panel Display Board to be displayed,
the analogue levels in digital form, on a two line, sixteen character display and two red/green LEDs.
Individual levels and fault indications are selected by a push-button switch on the front panel Display
Board. A ‘watchdog’ circuit on the Control Board checks the microprocessor operation and sets an
additional red/green ‘CPU’ LED accordingly on the Display Board.
Equivalent information about levels and status is also fed to the Interface Board (see section 1.1.6)
and, when fitted, the optional Serial Remote Control and Monitoring Board (see section 1.1.7)
The Control Board itself also has outputs to control the power level of each amplifier ‘pallet’. A multi-
turn preset potentiometer, adjacent to the LCD on the Display Board, is accessible via the front panel
to enable setting of the power level. This setting will be over-ridden and the power level reduced
automatically (’folded-back’) if excessive temperature, or excessive reverse power is detected or if the
external mute/interlock circuit is activated (output muted in this case). The front panel power level
control can also be disabled if required (using a link on the rear panel Status connector) and power
level then set by an external DC voltage applied via the Status connector. This is the normal
arrangement when two XA500s are combined using an XC2000 which provides the overall power
level setting.
1.1.6 Interface Board
The rear Interface Board contains circuitry to provide filtered, protected status outputs, via open
collector transistors, equivalent to the status information provided on the front panel. Analogue outputs
representing the forward and reverse powers are also provided as is a fused +50V dc output, diode-
OR’d from the one or two E2322 Power Supply Units, for operation or control of external circuits
(including the XC2000 Combiner)
Inputs are provided to enable remote power level setting (‘select internal/external control’ and external
control voltage). Two inputs are also provided for connection to an external interlock circuit. When the
connection between these two pins is broken, the Amplifier will automatically mute. Slave relay output
contacts are provided which sense this condition and which can be used to simultaneously mute the
drive(s).
The Interface Board also contains a DC-DC converter to ge12V dc from the diode OR’d 50V
dc supply. This lower voltage supplies the Control and Display Boards (see section 1.1.5) where it is
used directly and also converted to +5V and –12V dc levels.
