TX Dynamic Power Measurement Description

How is a TX Dynamic Power Measurement Made?

The TX dynamic power measurement provides a fast power calibration method for your AT. It is available in Active Cell and IS-856 Test operating modes ( Operating Mode ).

The measurement is not performed with a call established between the test set and AT. Rather, you must place your AT into a test mode which controls the AT to transmit a power sequence of successive down steps of fixed size and duration. An example AT output power sequence for TX Dynamic Power Measurement is shown in the figure below.

Before starting the TX dynamic power measurement, you must set the test set's receiver using manual control, with the power set to match the initial transmit power of the AT's power sequence, and with the frequency set to match the AT's transmit frequency (see Receiver Control ). This is required for the test set to tune its receiver properly for the initial measurement.

Typically, the dynamic power range of an AT is 90 dB, from -60dBm to +30 dBm. The TX dynamic power measurement can measure the AT's output power sequence ranging from -61 dBm to +37 dBm, in up to 99 steps. The Power Step Time may be 20, 40 or 80 ms in duration.

AT Output Power Profile for TX Dynamic Power Measurement

The TX dynamic power measurement is firstly triggered by an RF rise impulse from the AT (a positive change in power from 20 dB below the initial transmit power). To ensure successful triggering, it is recommended that you first command the AT to transmit continuously at the initial transmit power level, initiate the measurement, then command the AT to drop and then raise its output power by more than 20 dB to create the RF rise trigger.

Once triggered, the TX dynamic power measurement performs a series of channel power measurements in Very Fast speed (see Measurement Speed ), one at each step of the power sequence. The AT's initial transmit power (step 0) is measured at 6 ms, or 16 ms, or 36 ms (corresponding to the Power Step Time set to 20ms, 40ms or 80ms) after receiving the RF rise trigger. This is to ensure that the measurements always sample the stable portions of the data record. The test set then tunes its receiver to the proper level before performing each subsequent channel power measurement based on the measured power of the prior step and the Power Step Size setting. Each subsequent channel power measurement is automatically triggered at every 20, 40, or 80 ms (depending on the Power Step Time setting). The AT must step its power down and then hold its power constant at each step for Power Step Time duration. After completing the measurements at all of the requested power steps ( Number of Power Steps ), the test set returns power results for the initial AT transmit power (step 0) and each of the down steps.

So, the general procedure for making a TX dynamic power measurement is:

1. Set the test set's receiver in manual control with the power set to match the initial transmit power of the AT's power sequence, and with the frequency set to match the AT's transmit frequency (see Manual Operation: Manual Receiver Control ).
2. Set the Power Step Size , Number Of Power Steps and Power Step Time parameters (see TX Dynamic Power Measurement Parameters ) to match the power sequence to be transmitted by the AT.
3. Place your AT into the test mode required for performing TX dynamic power and command it to transmit continuously at the initial transmit power level (for example, the maximum power).
4. Arm the TX Dynamic Power measurement by the INIT command or by pressing the START SINGLE key.
5. Using the AT test mode interface, command the AT to generate an RF rise impulse (with a positive change in power from 20 dB below the initial transmit power) to trigger the measurement, and then transmit a power sequence of successive down steps of expected size and duration.
6. The test set measures the AT's initial transmit power and all of the requested power steps, then displays the measurement results in graphical "Bars" and numeric values. See TX Dynamic Power Measurement Results .

TX Dynamic Power Measurement Parameters

• Power Step Size

  Sets the power change (in dB) that the test set expects the AT to decrease between power steps. The test set re-ranges its receiver for each step power measurement based on the measured power of the prior step and this setting.

  GPIB command: SETup:CTDPower:STEP[:LEVel]

• Number of Power Steps

  Sets the number of power steps (steps down since its initial transmit power) that the test set expects the AT to transmit. The total number of power results returned will be the number of this setting plus one and can be queried using the FETCh:CTDPower:COUNt[:STEP]? .

  GPIB command: SETup:CTDPower:STEP:COUNt

• Power Step Time

  Sets the duration (20, 40 or 80 ms) of each power measurement. The test set expects the AT to hold its power constant during each power step. The test set triggers each channel power measurement relative to the first RF rise trigger based on this setting.

  GPIB command: SETup:CTDPower:STEP:TIME

• Measurement Timeout - see Measurement Timeouts . Ensure that you set the Measurement Timeout to a value great enough to allow you to command the AT to transmit its power sequence and for the test set to measure the power sequence.

TX Dynamic Power Measurement Results

• Integrity Indicator - (see Integrity Indicator ).
• Power Results - Power (dBm/1.23 MHz) are returned for the AT's initial transmit power (step 0) and each down step of the AT's transmit power sequence (see FETCh:CTDPower[:ALL]? ). The total number of power results returned is 1 + Number of Power Steps and can be queried using the FETCh:CTDPower:COUNt[:STEP]? command.

The TX dynamic power measurement result is displayed in both a tabular and a bar graph format. See TX Dynamic Power Measurement Display .

TX Dynamic Power Measurement Display

Graphical Display

The graphical display shows the measurement result for each step with a graphical "Bar". The x-axis graph represents the number of the power steps and y-axis represents the absolute power of the measurement step in units of dBm/1.23 MH. Up to 100 steps of the measurement results can be displayed on the graph. The view window can be adjusted to include a view of the entire 100 power step range, or reduced to include only the measurement steps of particular interest by the Graph Control softkeys (see Measuring TX Dynamic Power ).