Linearity Measurement System (LMS)

Linearity Measurement System (LMS)

Unit Testing Procedure

Test RF input into Unit Under Test (UUT)

Use this procedure to check the actual RF power going into the UUT (which will be a bit less than the signal coming from the signal generator because of internal loss within the LMS chassis).

1)  Use coax cable to connect Signal Generator to the RF_IN connection on the front of the LMS chassis

2)  Use another coax cable to connect a measurement device (power meter or spectrum analyzer) to the UUT_IN connection on the front of the LMS chassis (see note on 4th page)

3)  Flip left hand switch on LMS chassis (labeled “ext - int”) to “int”

4)  Flip right hand switch on LMS chassis (labeled “input - output”) to “output”

5)  Allow RF to flow from the signal generator, and read the resulting power from the measurement device.

6)  This resulting power is the actual power going into the UUT

Testing RF input into UUT

Test Linearity of a device (UUT) using a computer interfaced data acquisition device (i.e. Lab VIEW)

1)  Use coax cable to connect the RF_IN connection on the front of the LMS chassis to the Signal Generator

2)  Use coax cable to connect the RF_OUT connection on the front of the LMS chassis to the data acquisition hardware

3)  Use coax cable to connect the UUT_IN connection on the front of the LMS chassis to the RF input of the UUT

4)  Use coax cable to connect the UUT_OUT connection on the front of the LMS chassis to the RF output of the UUT

5)  Flip the left hand switch labeled “ext - int” to “ext” on front of LMS chassis

6)  Connect an external logic control device (i.e. Function generator) to the connection labeled External Input

Note: * Logic 0 at External Input connection places the attenuator in

series with the output of the UUT

*Logic 1 at External Input connection places the attenuator in

series with the input to the UUT

7)  Turn on the RF power on the signal generator

8)  Turn on logic control device

9)  Turn on data acquisition device and begin taking data

Linearity Test Using Data Acquisition Device and a Logic Control Device

Test Linearity of a device (UUT) manually using supplied switch to control logic

1)  Use coax cable to connect Signal Generator to the RF_IN connection on the front of the LMS chassis

2)  Use coax cable to connect the RF_OUT connection on the front of the LMS chassis to a measurement device (see note on 4th page)

3)  Use coax cable to connect the UUT_IN connection on the front of the LMS chassis to the RF input of the UUT

4)  Use coax cable to connect the UUT_OUT connection on the front of the LMS chassis to the RF output of the UUT

5)  Flip the left hand switch labeled “ext - int” to “int” on front of the LMS chassis

6)  Flip the right hand switch labeled “Input – Output” to “Input” on the front of the LMS chassis

7)  Set amplitude and frequency of the Signal Generator to desired starting values

8)  Turn on the RF power on the Signal Generator

9)  Record value given on the measurement device

10)  Flip right hand switch labeled “Input – Output” to “Output”

11)  Record value given on the measurement device

12)  Repeat steps 6,7, 9 – 11 for desired testing range

Diagram of setup on following page

Manual testing of a device

Note: Power meters tend to be more accurate in testing than spectrum analyzers. The testing of the linearity of the LMS chassis itself was done using a Gigatronics 8541 power meter and an HP 8593E spectrum analyzer. The power meter showed linearity over a wider range of power input test values. However, the power meter was not able to test below 1 MHz. The spectrum analyzer was able to test the LMS chassis at 100 KHz, but showed linearity for a shorter range of power input test values. So, when possible, use a measuring device that is at least as accurate as a power meter when measuring the linearity of a device.

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