DE
DANIELS
ELECTRONICS
2-8
VT-4B150 VHF Project 25 Digital Base Transmitter Instruction Manual
2.5.2
Amplifier Alignment
The RF power output of the amplifier is set to its rated value of 2.0 Watts or 8.0 Watts at the
factory. This should not require adjustment under normal circumstances. However, should it be
necessary to correct the output power, follow the procedure in the Amplifier Manual. Adjustment
may also be required when the transmitter's operating frequency is changed. When a large
frequency change has been programmed into the transmitter, the amplifier should be aligned at the
new frequency according to the Amplifier Manual.
2.5.3
Frequency Change
The transmitter is initially aligned at the factory for the frequency stamped on the 'Factory Set
Operating Frequency' label (see section 3.1). This label should list the frequency at which the last
complete transmitter alignment was performed. For a small frequency change, a simple channel
change (see section 2.2) may be all that is required. A larger frequency change may involve the
realignment of other modules. The frequency change in question is the accumulated frequency
change in relation to the frequency stamped on the label. For example, if the frequency were
changed by 0.5 MHz from that stamped on the label, then a second frequency change of 1 MHz in
the same direction would result in a total change of 1.5 MHz. The action taken would be on the
basis of the 1.5 MHz value. Failure to perform a realignment after a large frequency change could
result in unreliable transmitter operation or transmitter operation that does not conform to the
published specifications. The allowable frequency change is summarized below.
Note: It is advisable to confirm these frequency ranges with the Amplifier, as they are subject to
change with updated versions. The values in the module manuals take precedent over
those tabulated (following page).
Size of Frequency Change
Modules to be Aligned
less than ± 1 MHz
no alignment required, check output power
greater than ± 1 MHz
Transmitter Power Amplifier
2.6
Recommended Test Equipment List
Alignment of the transmitter requires the following test equipment or its equivalent.
Dual Power Supply:
Reg9.5 Vdc at 2 A.
Reg13.8 Vdc at 2 A - Topward TPS-4000
Oscilloscope / Multimeter:
Fluke 97 Scopemeter
Current Meter:
Fluke 75 multimeter
Radio communications test set :
Marconi
Instruments
2955R
(analog
only)
Motorola R2670 with Project 25 option
Alignment Tool:
Johanson 4192
It is recommended that the radio communications test set be frequency locked to an external
reference (WWVH, GPS, Loran C) so that the high stability oscillator may be accurately set to
within its ±1 ppm frequency tolerance.
