RAT5 Manual version 1.2.0
RAT5 Information Manual version 1.2.0 © GW4GTE 2010
Page 14 of 29
4. Testing and Alignment
Having completed Section 3, the receiver can now be tested and aligned. No special test
equipment is needed although a frequency counter and signal generator would prove useful.
Instead of a counter an HF receiver can be used to measure the LO frequency. Instead of a
signal generator a transceiver set to CW or FM with the power turned to minimum can be
used together with a suitable attenuator. Do not connect a transmitter directly into the RAT5
antenna input – use a tapped attenuator or sniffer wire. Please contact the authors if unsure
how to proceed.
This looks difficult?
The procedure may at first glance seem involved. In actual fact it amounts to little more than
tuning the LO coil to the correct frequency and peaking three other coils for a maximum meter
reading.
If any tests fail, carefully repeat the procedure to confirm the problem then
refer to Section 6 : Troubleshooting.
4.1 Power-off Tests.
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Firstly and most importantly carry out a careful visual inspection of the track
using a magnifying aid.
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With no leads connected, using a multi-meter, measure the resistance across
the power input pins, PL3/1, 2. Connect the positive (red) meter lead to
PL3/2. A typical reading is 24k ohms after allowing the reading to settle. A
lower reading or a short circuit indicates a fault.
4.2 Power-on Tests.
Refer to Section 5, Interfacing for connection details. The Squelch / Mute connector PL3/5, 6
is unused in these tests.
Preparation.
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Do not switch on just yet
.
Connect an unpowered DC power supply of
between 9V and 15V to PL3/1, 2. (Pin 1 is 0V). Connect a milli-ammeter or
multi-meter set to DC mA in series with the supply.
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Connect LO-Out PL2/1, 2 to a frequency counter.
A resolution of 1 kHz is
sufficient. In the absence of a suitable counter, attach a length of wire such
that a suitable receiver can pick up the signal.
Do not
directly connect the
receiver – the LO output is too high a level.
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Loudspeaker (LS) PL3/9, 10
Connect an 8 ohm or higher impedance loudspeaker to PL3/9, 10.
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Set the potentiometers as follows:
RV1 (tuning) to centre travel. RV2 (squelch) fully CCW. RV3 (volume) fully
CCW.
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Pre-set T1, T2, L1 and L2 by adjusting the ferrite cores
.
Carefully unscrew each core CCW until the top of the core is flush with the
nylon thread. Now screw the core 3 turns (6 half-turns may be easier to
count) CW back down into the inductor.
