Nautel XL12, Technical Instructions

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 2-1
01 January 2002
SECTION 2
INSTALLATION
PLANNING AND SITE PREPARATION
2.1
Transmitter sites for Nautel's XL12 - 12 000
watt AM broadcast transmitters should be prepared
to receive the transmitter prior to its delivery and/or
installation. The following must be taken into
consideration when preparing new sites. They
should be used as the evaluating criteria at existing
sites. It is recommended that all requirements be
incorporated to ensure optimum reliability and
performance is obtained.
NOTE
Frequent reference is made to terminal boards on
the remote interface PWB, which is located on the
rear of the control/monitor panel. Refer to figure
MD-3 as an aid in locating the remote interface
PWB and then, if necessary, to figure MD-5 for
its assembly detail.
2.1.1 TRANSMITTER ROOM
REQUIREMENTS:
The following transmitter
room requirements must be addressed when the
transmitter site is being finalized.
2.1.1.1 Transmitter Dimensions :
Refer to figure
MD-28 for transmitter dimensions. These
dimensions identify floor space requirements and will
assist in determining cable lengths and routing.
2.1.1.2 Transmitter Clearances:
A clearance of
at least 1.3 metres (4.0 feet) should be maintained at
the front and rear of the transmitter.
2.1.1.3 Air Flushing:
Four fan trays pull cooling
air through the cabinet's rear door, circulate it
through the RF power modules and exhaust it as a
low velocity stream through openings in the top of
the cabinet.
2.1.1.4 Cooling:
The transmitter room's ambient
air temperature must not exceed 50
°
C. A room air
exchange rate of 1000 CFM should achieve an
acceptable intake/exhaust temperature rise. For air
conditioning requirements, it can be assumed 16% of
the power being consumed, from the AC power
source, is converted to waste heat.
NOTE
A simple method of determining the number of
British thermal units (BTUs) per hour being
generated as waste heat is to multiply the average
RF output power (in watts) by 0.1905 (waste heat
factor) and then multiply the product by 3.413
(watts/BTU factor).
As an example: At 12 000 watts carrier power
with 50% modulation, the average power output
is 13 500 watts. This represents an average
long-term output power based on typical
processed program material. At 84% overall
efficiency, the waste heat generated (13 500 x
0.1905) is 2570 watts which equals (2570 x
3.413) 8776 BTU's per hour.
Since 12 000 BTU's per hour requires one ton of
air conditioning in a closed system, if the example
was in a closed system, it would require a 0.75
ton air conditioner to remove the waste heat.
2.1.1.5 Heating:
The transmitter room must
contain a heating system that will ensure its ambient
air temperature does not go below 0
°
C.
2.1.1.6 Work Area:
It is recommended that a
suitable work area with an adequate table surface be
provided adjacent to the transmitter to permit bench
adjustment/repair of modules.
2.1.2 LIGHTNING PROTECTION:
Extremely high voltage/current transients are
produced when a lightning strike occurs. These
transients, which are probably the most significant
hazard to any solid state transmitter, may be passed
to the transmitter through the wiring connecting it to
its power source and its antenna system. It is
imperative that all practical precautions be taken to
protect the transmitter from this phenomenon. Refer
to Nautel's
Lightning Protection for Radio
Transmitter Stations
booklet for recommendations
and for specific protection techniques. The following
requirements are considered to be essential.