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The HX751 has been carefully aligned at the factory for
the specified performance across the land mobile band.
Realignment should therefore not be necessary except in
the event of a component failure.
All component replacement and service should be per-
formed only by an authorized STANDARD HORIZON
representative, or the warranty policy may be voided.
The following procedures cover the sometimes critical and
tedious adjustments that are not normally required once
the transceiver has left the factory. However, if damage
occurs and some parts are replaced, realignment may be
required. If a sudden problem occurs during normal op-
eration, it is likely due to component failure; realignment
should not be done until after the faulty component has
been replaced.
We recommend that servicing be performed only by au-
thorized STANDARD HORIZON service technicians who
are experienced with the circuitry and fully equipped for
repair and alignment. Therefore, if a fault is suspected,
contact the dealer from whom the transceiver was pur-
chased for instructions regarding repair. Authorized
STANDARD HORIZON service technicians realign all
circuits and make complete performance checks to ensure
compliance with factory specifications after replacing any
faulty components. Those who do undertake any of the
following alignments are cautioned to proceed at their
own risk.
Problems caused by unauthorized attempts at realignment
are not covered by the warranty policy. Also, STANDARD
HORIZON must reserve the right to change circuits and
alignment procedures in the interest of improved perfor-
mance, without notifying owners. Under no circumstances
should any alignment be attempted unless the normal
function and operation of the transceiver are clearly un-
derstood, the cause of the malfunction has been clearly
pinpointed and any faulty components replaced, and the
need for realignment determined to be absolutely neces-
sary. The following test equipment (and thorough famil-
iarity with its correct use) is necessary for complete re-
alignment. Correction of problems caused by misalign-
ment resulting from use of improper test equipment is
not covered under the warranty policy. While most steps
do not require all of the equipment listed, the interactions
of some adjustments may require that more complex ad-
justments be performed afterwards. Do not attempt to
perform only a single step unless it is clearly isolated elec-
trically from all other steps. Have all test equipment ready
before beginning, and follow all of the steps in a section
in the order presented.
Required Test Equipment
RF Signal Generator with calibrated output level at
200 MHz
Frequency Counter: >0.1 ppm accuracy at 200 MHz
AF Signal Generator
Deviation Meter (linear detector)
VHF Sampling Coupler
Inline Wattmeter with 5% accuracy at 200 MHz
50-ohm Non-reactive Dummy Load: 10W at 200 MHz
7.4 VDC, 2A Regulated DC Power Supply
Standard Horizon HX751 Alignment Jig.
Alignment Preparation & Precautions
A dummy load and inline wattmeter must be connected
to the main antenna jack in all procedures that call for
transmission, except where specified otherwise. Correct
alignment is not possible with an antenna. After complet-
ing one step, read the following step to determine wheth-
er the same test equipment will be required. If not, re-
move the test equipment (except dummy load and watt-
meter, if connected) before proceeding.
Correct alignment requires that the ambient temperature
be the same as that of the transceiver and test equipment,
and that this temperature be held constant between 20
and 30 °C (68 ~ 86 °F). When the transceiver is brought
into the shop from hot or cold air it should be allowed
some time for thermal equalization with the environment
before alignment. If possible, alignments should be made
with oscillator shields and circuit boards firmly affixed in
place. Also, the test equipment must be thoroughly
warmed up before beginning.
Note: Signal levels in dB referred to in this procedure are
based on 0 dBμ = 0.5 μV(closed circuit).
Alignment
9
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