Spectra Engineering MX800 - Receiver Module Testing; Front End Alignment; IF Alignment

Technical Manual Alignment and Testing
© SPECTRA ENGINEERING 2006 Revision 4.2.3
85
Procedure:
The test procedure for the Receiver is divided into the front-end alignment
and the IF alignment procedures.
Front End Alignment:
16. Switch DC power on. Check that the output voltage on pin 1 of IC8 is
5V +/- 0.2V, on pin 1 of IC2 is 8V +/-0.2V, on output of IC9 (on C66) is
8V +/- 0.2V and on pin 1 of IC3 is 9V +/- 0.2V.
17. Remove jumper E and D. Install jumper C. Connect tracking generator
output to CN1 and spectrum analyser input to CN4. Set tracking
generator to sweep the band. Adjust A4, A10 and A16 for a
symmetrical passband around the band centre frequency. Check that the
gain over the band is 12dB and that the ripple is <+/- 1.5dB. Check that
the attenuation at the first IF image is >50dB.
18. Remove jumper C and I. Install jumper E and H. Connect tracking
generator output to CN4 and spectrum analyser input to CN5. Set
tracking generator to sweep the band. Adjust B4, B10 and B16 for a
symmetrical passband around the band centre frequency. Check that the
maximum loss over the band is < 3dB and that the attenuation at the first
IF image is >50dB.
19. Remove jumper E. Install jumper D. Connect spectrum analyser input to
CN5 and tracking generator output to CN1. Set tracking generator to
sweep the band. Check for symmetrical passband around band centre
frequency. Check that the gain over the band is 10dB and that the ripple
is <1.5dB. Remove Jumper H. Install Jumper J.
IF Alignment:
20. Select the mid channel. Check that LD on SKD-16 goes high indicating
that the synthesiser is in lock. Remove S3 (0Ω local oscillator
connection to mixer) and solder a 50Ω coax test lead across C60
position (note C60 position is near a retaining screw and C60 is not
fitted). Connect a comms test set to this lead and check that RF local
oscillator power is +17dBm +/- 2dB. Measure local oscillator frequency,
this should be F
RX
-90MHz. Using a non-metallic trimmer tool carefully
adjust the TCXO (X2) frequency until the correct frequency is obtained.
Remove the test lead and solder S3 back in position.
21. Place the high frequency pick up loop in close proximity to IC1 in order
to pick up the second IF oscillator frequency (note do not probe directly
on the chip as test lead capacitance will affect oscillator frequency).
Adjust CT1 for 89.545MHz.
22. Inject an RF signal at -80dBm (unmodulated) at F
RX
into CN5 (Jumper I
out, Jumper J in). Measure DC voltage at VF output SKD-3, adjust L14
for 2.5VDC on this point.
23. Inject an RF signal at -80dBm with standard modulation at F
RX
into
CN5, monitor line RX out and adjust T1 and T2 for minimum distortion.
Reduce RF signal level and check that sensitivity is better than -112dBm
for 12dB SINAD.