I/Q Tuning Measurement Description

Last updated: December 3, 2008

How is an I/Q Tuning Measurement Made?

The I/Q Tuning measurement is used in the production process (normally at mobile pre-test) where the I/Q modulator of the mobile is being calibrated. The measurement is normally performed with the mobile station in test mode and transmitting a GMSK modulated sequence of all 0s or all 1s. The mobile can be transmitting either a bursted signal or a continuous wave signal. I/Q Tuning is not an ETSI specified measurement.

NOTE

When using the I/Q Tuning measurement with an EGPRS mobile, you must select a modulation coding scheme which uses GMSK modulation (MCS1 through MCS4). The I/Q Tuning measurement does not support 8PSK modulation coding schemes (MCS5 through MCS9).

The carrier frequency is shifted up or down 67.7083 kHz by transmitting a sequence of all 0s (+67.7083 kHz) or all 1s (-67.7083 kHz). The accuracy of the mobile's I/Q modulator is determined by measuring the level of spurious signals relative to the desired signal (the desired signal being the carrier frequency +/-67.7083 kHz). The signals the test set measures are: the carrier frequency (Fc); Fc+/-67.7083 kHz; Fc+/-135.417 kHz; Fc+/-203.125 kHz and Fc+/-270.833 kHz. These signals are measured at the RF IN/OUT port.

The figure below shows a typical spectrum generated by a mobile transmitting a sequence of all 0s. The peak at the +67.7083 kHz offset is the one used as the reference.

The I/Q Tuning measurement also allows you to make an additional relative power measurement at any frequency you want between -13.0 MHz to -1.0 MHz and +1.0 MHz to +13.0 MHz relative to the carrier frequency.

Spectrum of a mobile transmitting a sequence of all 0s

Single or Multi-Measurements

The I/Q Tuning measurement can return either single or averaged measurement results.

If you set the multi-measurement state OFF then only a single measurement is made at each offset.
If you set the multi-measurement state ON, and the multi-measurement count number to a value greater than one, then multiple measurements are made at each offset. The returned results are an average of these measurements.

Types of Signals I/Q Tuning can Measure

I/Q Tuning measurements can be made on these types of input signals.

Normal TCH or PDTCH burst without a midamble.
CW signal.

I/Q Tuning Input Signal Requirements

The I/Q Tuning measurement will complete and meet its measurement accuracy specifications under the following input signal conditions.

Input signal level is between -15 dBm and +43 dBm.
Input signal level is within +3 dB and -10 dB of the expected input level.
Signal must be within 500 kHz of expected frequency for RF Rise triggering to function.

Trigger Source

The trigger source depends on the type of input signal.

Recommended Trigger Source Settings
Input Signal Type	Recommended Trigger Source
Normal TCH or PDTCH burst without a midamble	RF Rise
CW signal	Immediate