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The RF4 Path in the RI7100 is unique tester resource due to its extremely low frequency range. Vector voltage measurements of sinusoids and noise down to 10kHz are possible. This makes the measurement path useful for measuring the IFs of direct conversion receivers and de-modulators, Low IF mixers, and Phase noise baseband measurements among others.

In looking at the RF4 path several things should be noted:

1.) There is no Receive attenuation. Fixture based signal conditioning may be necessary. Maximum input power is -20dBm
2.) There is no LNA, the noise figure of this port will be higher than RF3, RF6,or RF7. Approx 20dB vs 13dB.
3.) The dut looks directly at the RF mixer of the receiver. Because of this significant mismatch ripple is possible. A 6dB or greater attenuator should be implemented to reduce mismatch ripple. This will provide approximately 12dB return loss.
4.) The standard calibration of RF4 is from 10MHz to 1010MHz. To use the tester below 10 MHz an alternative calibration methodology must be implemented

Calibrating RF4 Below 10MHz
Two approaches can be used to calibrate RF4 for power below 10MHz. For testers that have Arbitrary Waveform Generators (ARB) and CF2 calibration plates. A testplan that will calibrate the port is attached. If running the testplan from the test plan window, remember: the .sym file is in the testsys directory, you must compile the testplan every time you run (to reset the calfactors) and you must save the tester after the calibration for it to stick. This cal plan can be implemented instead of the testers Standard RF4 Noise and Direct Gain Calibration
rf4tests.zip (Unzip for OS/2)
For testers with out the CF2 calibration plate but including an ARB can write a routine to calibrate the Fixture entity to "absorb" the error in the testers RF4 calibration. More on this topic can be found in AC calibrations.

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