Tn Tx Dc Offset Reference Power - Nokia NPD-4 Series Technical Documentation Manual

CCS Technical Documentation
according to Table 2.
4 If the carrier can be centered but the PDM is out of range, check the control volt-
age on pin 1 of G501. If it is about 2.2v, (and pin 4 is at 2.7v, and pin 2 at 0v),
then the VCTCXO (G501) is working correctly but the circuit that delivers the
control voltage is not. Check soldering of all G501 terminals; also check R510,
R511, C503, and D200. If the control voltage on pin 1 of G501 is not about 2.2v,
but the carrier is centered, then there is a problem with the VCTCXO G501. If
there is 2.7v on pin 4 and the soldering is correct, then replace G501.
5 If the carrier cannot be centered, check to see if you can adjust to 2.2v on pin 1
of G501. If you can, within the PDM range of +/- 150, then the circuitry that
delivers the voltage is working correctly, and the VCTCXO has a problem. Trouble-
shoot it as described in the previous section. If you cannot adjust to 2.2v within
the accepted range, then the AFC circuitry has a problem. Troubleshoot it as
described in the previous section.
6 In cases where there is a fault with both the AFC circuitry and the VCTCXO, sev-
eral combinations of the previously described conditions are possible. Start by
ensuring 2.2v on pin 1 of G501 using a PDM within the range +/- 150, then cen-
ter the tone.

TN TX DC Offset Reference Power

The DC offset voltages on the I and Q inputs to the modulator are adjusted for minimal
carrier feedthrough (maximum carrier suppression). Initially the DC offsets are set to a
nominal value, and the power of a tone offset in frequency 20 kHz from the carrier is
measured in dBm and recorded as a reference (in this tuning). Then in the next tuning,
the carrier suppression (delta between center tone and tone that is offset 20 kHz) is
measured. If it passes, it is reported in that tuning. If not, the DC offsets are adjusted
until it passes, and the passing value is reported.
The reported result is the power in dBm of the tone that is offset 20 kHz from the carrier,
as measured on the antenna connector, with the nominal DC offsets applied.
Manual Verification:
In Phoenix, use the RF Main Mode window to set the AMPS transmitter to channel 384.
Using the RF Tuning window, set the I and Q DC offsets to 0,0 by entering 0,0 in the "val-
ues" edit box.
Center the transmit signal on the spectrum analyzer, set the span to 100 kHz. Lower the
bandwidth so that the two sidetones can be differentiated from the carrier. Measure the
amplitude of the sidetone at 20 kHz above the carrier. The amplitude of the sidetone will
probably be higher than that of the carrier; amplitude should be within the test limits.
Troubleshooting: If the carrier is not present, troubleshoot the cell TX chain using the
"things to check" list and probing tables/diagrams. If the two tones offset at 20 kHz are
Issue 1 02/2003
Nokia Corporation
Troubleshooting — RF
Confidential
NPD-4
Page 15