LBI-33057
22
Network Analyzer Method
1. Remove the solder mask on the solder side of the
RF Board at the thin run between the output of
FL4 and the input of A6 (A6 pin 1). Cut this run.
2. Solder the center conductor of a small 50-ohm
coax cable to FL4's output at the cut run. Solder
the coax shield near FL4.
3. Terminate the radio's antenna with a 50-ohm
load.
4. Connect the other end of the coax to the network
analyzer and tune FL4 (all three sections) for best
return loss over the desired receive frequency
range.
5. Unsolder the coax cable from the output of FL4
and solder it to the input of A6. Ground the
shield near A6.
6. With the network analyzer's output at -30 dBm or
lower, adjust FL1 (all three sections) for best re-
turn loss over the desired
receive frequency
range. The receiver must be powered-up during
this adjustment.
7. With a small jumper, reconnect the output of FL4
to the input of A6. Test the radio over the new
frequency range.
Spectrum Analyzer And Best Quieting Methods
This procedure involves retuning the receiver's heli-
cal filters at the low, middle and high-side frequencies.
The same frequencies used to retune the VCO can be
used.
The preferred method is to connect a small 50-ohm
coax to the output of IF crystal filter FL2, ground, and
connect this cable to a spectrum analyzer tuned to 45
MHz and set to 2 dB/division.
A less desirable alternative using the same tuning
sequence can be achieved by varying the signal genera-
tor's level and tuning for best quieting (SINAD). No coax
cable connections are required using this procedure.
1. Remove the input and output (outer) tuning cores
from both FL1 and FL4 (four cores total).
2. Set the radio and signal generator to the low-side
receive frequency.
3. Set the signal generator's level to -30 dBm. If
tuning by quieting, set the generator's level for a
high receiver noise level.
4. Alternately tune the center cores of FL1 and FL4
for maximum IF signal. If tuning by quieting,
tune for best sensitivity and reduce the generator's
level as the receiver becomes more sensitive.
5. Set the radio and signal generator to the high-
side receive frequency.
6. Reinstall the input tuning cores into FL1 and
FL4. Alternately adjust these cores for maximum
signal or best quieting.
7. Set the radio and signal generator to the middle
receive frequency.
8. Reinstall the output tuning cores into FL1 and
FL4. Alternately adjust these cores for maximum
signal or best quieting. Under certain circum-
stances, best tuning may be achieved when cer-
tain tuning cores are not reinstalled. This is ac-
ceptable. Also, any excessively loose core should
be secured with a drop of adhesive.
