Elecraft XV Transverter Owner's Manual - Manual (Page 26)

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Circuit Description
The circuits of the transverter for each band are similar. The signal flow is
described below at a block diagram level. This is followed by details of
the circuits based on the schematic diagrams.
Signal Flow
Refer to the block diagram on the following page. Many of the circuits in
the signal path are used for both receive and transmit. Switching between
receive and transmit is done by relays to preserve the low noise figure of
the receiver. The relays are shown in their de-energized state which puts
them in receive mode position.
In receive mode, signals from the antenna are routed by relay K1 to the
RF amplifiers and then through a band-pass filter to the mixer.
The local oscillator input to the mixer is 28 MHz below the signal
frequency, producing an intermediate frequency (I.F.) output from the
mixer in the 28 MHz range. Mixer responses outside of the 28 MHz I.F.
range are attenuated by the filter at the mixer output.
Relays K6 and K7 route the 28 MHz I.F. signal to the port selector circuit.
This circuit may be configured to work with an external rig that uses
either a single connection for both transmit and receive or separate
transmit and receive connections.
In transmit mode, the 28 MHz I.F. signal from the external rig is applied
to the TXin/IF1 connector. Relay K7 routes the 28 MHz I.F. signal
through the I.F. level control. The I.F. level control is adjustable to
provide the correct drive to the mixer from a wide range of I.F. transmit
levels from the 28 MHz rig.
Relay K6 routes the 28 MHz I.F. signal from the attenuator to the I,F,
filter and limiter. The limiter is part of a protective circuit described
below.
The mixer uses the local oscillator signal to convert the 28 MHz I.F.
signal to the transmit frequency. The RF band-pass filter selects this
frequency and attenuates the other mixing products.
Relay K2 routes the RF signal to the transmit driver. The transmit driver
raises the signal level as required to drive the RF power module. The RF
power module produces up to 20 watts output.
The output of the RF power module is routed through a low-pass filter
and relay K1 to the antenna connector.
The power monitor samples the output of the RF power module and
returns an analog signal to the controller. The controller illuminates the
power level LEDs on the front panel to indicate the RF output power.
A DB-9 connector is provided for connection to an Elecraft K2 or K3
transceivers. This connection includes the control signals needed by the
transverter.
When used with rigs other than an Elecraft K2 or K3, the KEY IN line
must be grounded by the external transmitter to switch the transverter
from receive mode to transmit mode. When the transverter is used with
an Elecraft K2 or K3, this command is furnished via the DB-9
CONTROL connector and the KEY IN line is not used.
When the controller switches the transverter from receive mode to
transmit mode, a transistor switch grounds the KEY OUT line to enable
an external power amplifier, if used.
The overload detector protects the transverter in the event a high-level
28-MHz I.F. signal is applied while the transverter is in receive mode.
The overload detector commands controller U1 to open relays in the I.F.
port selector to disconnect the transverter from the I.F. rig and blink the
front panel LEDs in unison to alert the operator. To reset the detector, the
transverter must be turned off, then on again. When used with an Elecraft
K2 or K3, the K2 or K3 must be turned off, then on again to reset the
detector.
Since the attenuator is switched out of the signal path in receive mode,
the mixer is vulnerable to damage from a high-level 28 MHz I.F. signal.
The limiter keeps the signal at a safe level while the controller reacts to
an overload condition.