3-8. TEST ADAPTER.
The test adapter provides a means of routing signals to, from, and between the reference fixture and a unit under
test (UUT). Signals may be routed, sampled, and changed for different test procedures.
The different functions of the test adapter can be divided into seven major areas. They are:
Test Equipment I/O
Reference Fixture I/O
RF Signal Routing
The interaction of these areas is shown in the block diagram of figure 3-3. A complete schematic of the test
adapter is shown in figure FO-19. The following paragraphs discuss the major functions of the test adapter.
a. Test Equipment I/O. The test equipment used with the maintenance group connects to BNC connectors
mounted on the test adapter front panel. The list below details the connections.
RF SIG GEN
HANDSET (six-pin audio connector)
Frequency counter input
Scope Channel 1 input
Scope Channel 2 input
RF Probe used with DMM
Output from modulation generator
section of function generator.
Output from function generator.
External trigger input of function generator.
RF output of signal generator.
Test probe supplied with scope.
H-250/U handset included with
b. Reference Fixture I/O. AUDIO REF and ANT REF connectors are connected to the AUD/DATA and ANT
connectors of the reference RT which is part of the reference fixture included in the maintenance group. Audio
signals, data signals and control signals are exchanged with the reference RT through the AUDIO REF connector.
Transmitted and received FM radio signals are exchanged with the reference RT through the ANT REF connector.
c. UUT I/O. The ANT and AUDIO UUT connectors are connected to the ANT and AUDIO/DATA connectors
of an RT UUT. As with the reference RT, audio, data, and control signals are exchanged through the AUDIO UUT
connector and FM radio signals are exchanged through the ANT connector.
The UUT connector is used to interface with the system connector of an RT UUT. It may be connected to several
other types of equipment with the use of different test cables. Power, control, and communication signals are
supplied to a UUT through this connector.
d. Power Supply. 27.5 V dc is input to the test adapter power supply through the POWER + and - inputs of
the front panel (J15 and J16). See figure 3-4 for a partial schematic diagram of this section.
Diode CR1 prevents test adapter damage from accidental reversal of the power supply inputs.
Voltage regulators U1, U2, and U3 convert the input voltage to the voltages used by the UUT. The 1.5 V supply is
provided by a voltage divider composed of RI 2 and R13 tapped into the 6.75 V supply line.