#### Spurious Avoidance

The Spurious Avoidance submenu defines whether the analyzer measures with a local oscillator frequency LO below or above the RF input frequency.

This feature can be used to eliminate known spurious components in the input signal that can distort the measurement, especially in the low frequency range.

- In Auto mode, the analyzer auto-selects the local oscillator frequency, depending on the receiver (RF) frequency and the test port. This mode systematically avoids known spurious signals provided that no frequency conversion occurs in the test setup.

- LO > RF means that the LO frequency is always above the measured RF frequency. This mode is appropriate for avoiding single, known spurious signals.

- LO > RF means that the LO frequency is always below the measured RF frequency. This mode is appropriate for avoiding single, known spurious signals.

In the presence of several spurious signals, setting the Spurious Avoidance parameter globally may not be sufficient. To improve the result, perform a Segmented Frequency sweep and assign independent LO frequencies to the individual sweep segments
.

Application example

Consider the following test setup with strongly reflecting DUT (e.g. a bandpass in its stop band) that is measured in transmission. a1 is generated at a frequency RF.The reflected wave b1 falls into the receiver mixer of the analyzer port 1, where a small fraction of the mixer product RF + 2*IF can be reflected back towards the DUT. If this spurious wave a'1 passes the DUT, then it is received as b'2 at port 2, together with the wanted signal b2.

LO > RF implies that LO = RF + IF. The mixer at port 2 converts both the wanted signal b2 and the spurious signal b'2 which is at the frequency RF' = IF + LO, to the same IF frequency. The response of an ideal, infinitely steep bandpass filter with a pass band between B- and B+ looks as follows:

For a wide bandpass, the spurious response flattens the filter edges.

The spurious signal can be eliminated by dividing the sweep range into two segments with different LO settings:

- In the low-frequency segment, ranging up to the center frequency of the bandpass filter, the frequency of the local oscillator is set to LO < RF. This ensures that the spurious signal b'2 is not measured at port 2.

- In the high-frequency segment, starting at the center frequency of the bandpass filter, the frequency of the local oscillator is set to LO > RF. If the center frequency is larger than B+ – 2*IF, then there is no distortion from b'2.

Remote control: | [SENSe<Ch>:]FREQuency:SBANd POSitive | NEGative | AUTO

#### ALC (All Chans)

Enable or disables the Automatic Level Control (ALC) for all channels. ALC keeps the level of the a waves (source level) at a constant value, irrespective of the DUT's input impedance. The measurement speed is slightly reduced.

If the analyzer cannot reach the designated source level at a particular sweep point, it displays the message Ports n: Source level failure. Check the data sheet for an overview of the available source levels.

Remote control: | DIAGnostic:ALC:SETTings[:STATe] ON | OFF

#### Low Phase Noise

Reduces the phase noise of the source signals. The measurement speed is slightly reduced.

Remote control: | [SENSe<Ch>:]FREQuency<1>:LPNoise ON | OFF