With two unique features, the Z1203A goes well beyond
being a simple DC power injector:
- Isolated receiver output;
- Flexible remote DC power control and
- Active pull down.
The receiver output is isolated, i.e., it is not
connected to the Z1203A's ground. This helps reduce power line conducted noise
from being picked up on the remote active antenna.
Clifton Laboratories products, such as the Z10040B Norton
amplifier (as well as the older Z10040A) and the forthcoming Z1501C Active
Antenna may be powered with a separate DC power connector or over the output
coaxial cable. Remote power simplifies outdoor installation and saves the
expense of running a separate power feed.
Input connections in both the Z10040B and Z1501C are
routed through relays. When the device is not powered, the input circuit
switches to a "safe" position, disconnecting the input. This has two purposes:
- First, to reduce the risk of damage from lightning or
static build up when the device is not being used.
- Second, it provides a way to prevent strong signals
from nearby transmitting antennas from damaging the devices, which is of
obvious concern to radio amateurs.
Making use of the automatic input protection feature of
the Z10040B and Z1501C when transmitting requires switching the DC power supply
off and on. The Z1203A makes this easy by providing a control input to enable
and disable the DC output. For maximum flexibility, the control signal
functionality is configurable by moving a jumper shunt to enable DC power when
the control signal is taken low or when the control signal is taken high. The
Z1203A's power remain connected to the station's DC supply at all times, with
the remote device power being energized or un-energized depending on the state
of the control signal.
Although a remote control simple switch provides a great
deal of benefit, the Z1203A adds a second feature, active pull down. When power
is removed from a remote device, it takes some milliseconds for the filter and
bypass capacitors to discharge and drop to a level where the input
protection relay releases to the safe mode. Of course, during the time between
control signal assertion and relay operation, the input is not in safe mode. The
Z1203A adds circuitry to discharge the remote device's capacitive storage
through a low value resistor, switched into place when the control signal is in
voltage disable mode.
The two oscilloscope captures below show the benefit of
the Z1203A's active pull down feature, reducing the time it takes for a Z10040B
to go to safe mode by simply removing DC power.