Nautel NX5 AM, Preinstallation Manual

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NX5 PRE-INSTALLATION MANUAL RF OUTPUT REQUIREMENTS
PAGE 1.6.4 VERSION 0.1 2015-08-01
Antenna System
Ensure that the antenna system meets or exceeds the standards specified in EIA Standard TR-101-A,
paragraph 8(b) (see below for the specific requirement), with a normal impedance of 50 ohms at the
carrier frequency.
 The impedance (resistance and reactance) characteristics of the normal load shall be such that
when the operating carrier frequency changes by ± 5 kHz, the resistance will be within 5% of the
resistance at the carrier frequency, and the reactance (adjusted to zero at the carrier frequency),
will be within ± 18% of the resistance at the carrier frequency. When the carrier frequency changes
by ± 10 kHz, the corresponding limits of permissible variation for resistance and reactance are
10% and 35% respectively.
The transmitter will operate with a maximum VSWR of 1.5:1, or with sideband VSWRs of up to 2:1
when the carrier frequency impedance is 50 ohms. However, overall system performance degrades as
the VSWR increases.
Advances in digital modulation schemes like IBOC and DRM systems require better performance from
antenna systems. To ensure the proper operation during digital broadcasting, ensure that the VSWR
does not exceed the values recommended by each standard.
In order to achieve the proper sideband symmetry (Hermitian symmetry) at the output of the
transmitter’s power amplifiers needed for IBOC or DRM operation, you may need to adjust the tuning of
the antenna system to balance the impedances at the sidebands. You must perform a full impedance
sweep of the antenna system before broadcasting IBOC or DRM. This also requires information about
the transmitter’s phase versus frequency charcteristic for Hermitian symmetry at the power amplifier.
This information is provided with the transmitter at time of shipment. For assistance relating to IBOC or
DRM transmitter requirements, contact Nautel Customer Support.
NOTE
: Hermitian symmetry may not be required for DRM if the VSWR across the bandwidth of the
transmitted signal is very low. Contact Nautel for recommendations.