RAT5 Manual version 1.2.0
RAT5 Information Manual version 1.2.0 © GW4GTE 2010
Page 15 of 29
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Pre-set VC1 by adjusting to a centre position
. Set the VC1 screwdriver
slot perpendicular to the line of pins of U1.
Test Procedure
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Apply power.
Check the current drawn is in the region of 45mA. The milli-ammeter may
now be removed if preferred.
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Slowly advance the volume control
until a slight hiss is heard, then
advance the squelch control until the hiss stops. This tests the basic squelch
and audio circuitry functionality.
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Return the squelch control to the fully CCW position and set the volume
control to about 30%
4.3 LO Alignment
LO Alignment Overview
Using L1 and VC1 adjust the LO frequency so that tuning control RV1 gives the desired
coverage.
Alignment of the RAT5 is a straightforward procedure. Units tested so far have needed very
little coil adjustment from the preset settings detailed earlier. The procedure below basically
consists of setting the LO frequency, applying a strong signal, then tuning the RF and IF coils
for a maximum S-meter reading.
Detailed description:
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Set the LO frequency
.
Firstly establish the LO is running by connecting a frequency counter to the
LO output. If no counter is available use an oscilloscope. Failing that, assume
the LO is running and search for the signal on a receiver.
Decide on a receive centre frequency to use. 3615 kHz for 80m or 1950 kHz
for 160m is suggested. From this, the LO frequency required can be
calculated.
Subtract
455 kHz to the RX frequency to determine the LO
frequency on 80m.
Add
455 kHz from the RX frequency to determine the LO
frequency on 160m.
80m
RX: 3615kHz LO: 3160kHz
160m
RX:1950kHz LO: 2405kHz
For Medium Wave reception use an LO on the high side and use the same
calculation for LO frequency after deciding on a band centre. Capacitor
values are given in the RF/IF circuit diagrams and parts list.
Using a counter
If a frequency counter is used the LO frequency will be immediately
apparent. Adjust L1 to achieve the correct frequency.
Now rotate the tuning control to a fully CCW and fully CW position,
noting the band of frequencies covered. If the range is considered too
great or too small, adjust VC1. At any starting frequency, if a rotation
of VC1 causes the frequency to increase then VC1 is being reduced
in value, and the control range is being reduced. Adjust L1 to return
the centre frequency to the correct point. The adjustments may need
to be repeated until the correct range is achieved. Note there will be
a slight bandspread effect towards the lower end of the tuning range
due to characteristics of the varicap diode.
