RAT5 Manual version 1.2.0
RAT5 Information Manual version 1.2.0 © GW4GTE 2010
Page 16 of 29
Or:
Using a receiver
Tuning by means of a separate HF receiver is a little more involved
but the principle is the same. Set the HF receiver to 3160kHz or
2405kHz and attempt to tune through the channel by rotating the
RAT5 tuning control. If a signal is not heard, return the tuning control
to a central position then adjust L1 by several turns CW and antiCW
from the preset position. It should be possible to eventually find the
signal. Then determine the tuning range by following the signal on
the separate receiver as the tuning pot is rotated. Adjust VC1 and L1
as required in a similar way to alignment using a counter.
While the receiver is stable enough for normal use, stability can
nonetheless be improved by minimising the tuning range, as the
greatest source of drift is the temperature coefficient of the varicap
diode D1 and the trimmer capacitor VC1. The less contribution they
make (by minimising the tuning range) the better the stability.
Based on a centre frequency of 3615kHz, with VC1 set to minimum,
the tuning range is typ/-20kHz. With VC1 set to maximum and
L1 re-adjusted for 3615kHz the tuning range is typ/- 150kHz.
4.4 IF and RF Alignment
IF/RF Alignment Overview
Apply a signal on the correct receive frequency then tune T1, T2 and L2 for maximum reading
on PL4/2 (S-meter o/p)
If the ferrite cores of T1, T2 and L2 have been pre-set as described earlier, the chances are
that a medium/strong on-channel RF signal can now be received. Constructors lucky enough
to have a signal generator will need no instruction how to produce a suitable signal.
Detailed description:
4.4.1 IF Alignment.
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Power off the RAT5
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Make sure the squelch control is fully CCW. Advance the volume control
about 25% from its minimum position.
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Attach a multi-meter to the S-meter output PL4. Set it to display voltages of
up to 5V.
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Connect a signal source directly to the antenna input at a starting level of
around 100uV. If using a transmitter
do not
use a direct connection. A fly
lead from the RAT5 antenna input wrapped round the coax from the test
transmitter to a dummy load should suffice. Set the signal source to the
receive frequency based on the LO frequency established in the previous
procedure.
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Re-apply power.
