8922 Timing Advance Problem

When a phone is connected and a call is set-up in the normal operating mode the 8922 uses the protocol to determine the correct triggering time. The default setting for timing advance is Auto, the function of this is to advance the timing of the mobile to compensate for any delays caused by test fixtures, filters etc. The 8922 does this by looking at where the midamble is, comparing that to where it knows it should be and adjusts it as it requires.

When using RF Rise to trigger on, certain problems occur causing the 8922 to tell the mobile to advance its timing. Ideally you want to trigger then capture the relevant data exactly at the right time thus your first bit that is captured is bit 0. If this happens then your pulse will fall in the middle of your power mask and the midamble will appear at the correct time. However with RF Rise triggering the 8922 triggers a fraction too late and fails to capture the start of the timeslot thus causing the midamble to appear late. If the Timing Advance is set to Auto the 8922 will try to compensate for this and advance the mobile's timing. The same thing will happen again as the RF Rise triggers slightly too late again and so the mobile is progressively commanded to advance its timing until it reaches its maximum.

This, therefore, is why Timing Advance should be set to Manual and zero.