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888-2587-001
4/18/11
WARNING: Disconnect primary power prior to servicing.
FM HD Radio System
Section 1 Introduction/Specifications
1.5.2
Boost Pro Amplifier
For multi-cabinet transmitter systems, such as ZD (dual cabinets), separate mode and
SLC systems, the Boost Pro is used to increase the gain of the ALT RF OUT output of
the HDx-FM exciter to appropriate levels for the IPA stage of a 2nd cabinet or 2nd
transmitter.
1.5.3
High Power Combiner With Reject Load
This will be a 10dB combiner when used for the Separate combining mode, or either a
3dB, 4.77dB, or 6dB combiner when used for Split-Level combining. The RF outputs
of analog and HD transmitters will be applied to the Input Ports of the combiner. The
combiner will mix these two inputs at the specified ratio, with the majority of this signal
being output to the Antenna Port. Any variation of the input ratio will cause an
imbalance which will appear at the Reject Port and may result in not meeting IBOC
specifications.
The reject load is typically a 50 Ohm resistive device connected to the Reject Port of a
high-power combiner. It must be appropriately sized and should be monitored at all
times, as it will be continuously utilized under the predicted normal conditions and
could be severely taxed upon an unbalanced condition such as:
•
No, or low RF output from one transmitter.
•
High antenna VSWR condition.
Since this device is continuously dissipating RF energy into its surrounding area in the
form of heat, it may be desirable to install it in a different location away from the
transmitter. Ideally it could be located in a specially air conditioned room for maximum
resistor life.
1.5.4
Test Load
Optional 50 Ohm resistive load, sized according to expected transmitter RF output.
Used for testing purposes when up-to full power output is necessary to test a transmitter
without radiating the signal. Depending upon system configuration, this load could be
sized for the entire IBOC system output, or switched into the output of an individual
transmitter.
1.5.5
Isolator (Circulator with Reject Load)
A circulator is a ferromagnetic device that steers an RF signal, in one direction only,
through a circular path. A typical use for a circulator is a 3-port device with the 1st port
