Frequency Change Procedure; Test Equipment Required For Frequency Change; Frequency Determined Components; Frequency Determined Jumpers And Switches - Harris DX 25U Technical Manual

WARNING
ENSURE ALL PRIMARY AC VOLTAGE HAS BEEN REMOVED
FROM TRANSMITTER AND A GROUNDING STICK IS USED TO
GROUND ALL POINTS WHERE AC OR RF POWER HAS BEEN
APPLIED BEFORE PROCEEDING WITH THE FOLLOWING PRO-
CEDURE.
g. Remove the Driver Supply Regulator clear protective
cover and remove the external meter connections.
h. Replace the Driver Supply Regulator clear protective
cover.

Frequency Change Procedure

5.7
The following is a step by step procedure for changing the
frequency of the transmitter. If a complete frequency change is
desired this procedure can be followed in order. If only a specific
tuning procedure is desired (ex. Driver tuning) then only that
section needs to be looked at. In some cases, time is a considera-
tion in changing frequency of the transmitter. To allow a faster
frequency change, procedures which are performed to achieve
optimum transmitter performance, yet are not critical to the
reliable operation of the transmitter, are covered after the section
on "Basic Frequency Change."

Test Equipment Required for Frequency Change

5.7.1
The following is a list of the test equipment required to perform
a frequency change. A frequency change should not be attempted
unless the proper equipment is used.
•
Audio Generator and Distortion Analyzer
•
Oscilloscope
•
Frequency Counter
•
Modulation Monitor
•
Digital Multimeter (preferred)
•
Vector Impedance meter or Impedance Bridge
•
Frequency programmable RF Generator (must operate up
to 3 times carrier frequency)
•
RF Load, 125 kW average dissipation
•
Function Generator (optional)
NOTE
Output Network setup can be performed with a Vector Impedance
Meter or Impedance Bridge and RF Generator. A Vector Imped-
ance Meter is usually faster but can be sensitive to interference.
An Impedance Bridge can be more effective in an RF environ-
ment.

Frequency Determined Components

5.7.2
Refer to the FD Chart, 839-7855-137, in the Drawing Package.
Install all the proper parts listed for the new desired frequency.
Oscillator crystal frequencies and part numbers are on drawing
817-1280-025.
Note that the FD chart for the output network components is
organized in bands A through L. The mounting hardware, straps,
plates, etc. are all listed on the parts list. When installing these
components, make sure all connections are tight. Use special care
when handling vacuum capacitors.
Rev. Z1: 06-02-00 Additional info to ECN 46105 888-2297-002
WARNING: Disconnect primary power prior to servicing.
Table 5-7. Frequency Determined Jumpers and Switches
BOARD
ANALOG INPUT A35
OSCILLATOR A17
A TO D CONVERTER A34
OUTPUT MONITOR A27
DRIVER COMBINER A14
BINARY COMBINER A8
MAIN COMBINERS A5 thru A7 L1-L16
SWITCH/METER PANEL A31
LED BOARD A32
DC REGULATOR A30

Frequency Determined Jumpers and Switches

5.7.3
Refer to the Tuning Chart, 839-7855-140, in the Drawing Pack-
age. Many of the frequency determined components on the
transmitter are permanently installed and are changed by moving
the desired jumper, coil tap or switch position. The Frequency
Tuning chart lists all jumpers, taps, and switches that need to be
set per frequency. Some of these settings are considered presets
and may need to change during a specific procedure. A list of
boards with frequency determined jumpers, taps, preset adjust-
ments, and switches is shown in Table 5-7.

Output Network Dry Tune

5.7.4
Preset all output network taps according to the Frequency Tuning
chart with all FD capacitors in place. If a high power dummy load
is not available, a small terminating 50 Ohm resistor can be used.
WARNING
ENSURE ALL PRIMARY AC VOLTAGE HAS BEEN REMOVED
FROM TRANSMITTER AND A GROUNDING STICK IS USED TO
GROUND ALL POINTS WHERE AC OR RF POWER HAS BEEN
APPLIED BEFORE PROCEEDING WITH THE FOLLOWING PRO-
CEDURE.
Using a Vector Impedance meter or Impedance Bridge, adjust the
following output network sections to their appropriate X
values at the desired carrier frequency. The sections should be
isolated (disconnected) from the rest of the other components
and only the necessary connecting straps and hardware should
be used to make the measurements. See table below.
2C2
2C4
2L3
At frequencies where C5 is installed in series with 2L3:
•
Adjust 2L3 for A∠+90 or 0 + jA where A = 100,000/(1.257
x Fo) + 42.
Section V - Maintenance
FREQUENCY
DETERMINED
PRESETS
R85, R84, R43
P2, S1, J3
P10, S1
S1, S2, S6, S7, S9, P2
J14, J15, J16-J32
J30-J33, L1-L16
R1, R2
R41, R67
R51, R93
or X
C
13∠-90, 0 -j13 (2C2A and
2C2B capacitors only)
75∠-90, 0 -j75 (2C4A and
2C4B capacitors only)
42∠90, 0 + j42 (2L3 coil
only)
5-15
L