IviSpecAnExternalMixer Extension Group

LabVIEW IVI Class Driver

IviSpecAnExternalMixer Extension Group

Many spectrum analyzers have outputs and inputs that allow external equipment to use the IF or mixer signal that the spectrum analyzer uses. In this case, external equipment can be used to mix signals to convert them to measurable frequencies. This allows the use of an analyzer to measure values that are outside of the normal frequency range of the equipment. When using an external mixer, many of the settings of the analyzer have to be carefully converted to allow you to know what is meant by the values read. Specifically, the frequency, the harmonic number, mixer configuration, and conversion loss must be configured carefully to be able to use the external mixing successfully. The frequency of the input signal can be expressed as a function of the local oscillator (LO) frequency and the selected harmonic of the 1st LO is as follows:


	fin = n * fLO +/- fIF
		Where: 	fin	frequency of input signal
			n	order of harmonic used for conversion
			fLO	frequency of 1st LO
			fIF	intermediate frequency

The Harmonic number defines the order n of the harmonic used for conversion. Both even and odd harmonics can be used. The selected harmonic, together with the setting range of the 1st LO, determines the limits of the settable frequency range. The following applies:

	Lower frequency limit: 	fmin = n * fLO,min - fIF
	Upper frequency limit: 	fmax = n * fLO,max + fIF
		Where:	fLO,min	lower frequency limit of LO
			fLO,max	upper frequency limit of LO

The following sections describe the mixer configuration and the conversion loss table configuration.

Mixer Configuration

The external mixers are typically configured either as two-port or three port mixers. Single-diode mixers generally require a DC voltage which is applied via the LO line. This DC voltage is to be tuned to the minimum conversion loss versus frequency. Some instruments can define a limit for the BIAS current. The two-port mixer connects the ’LO OUT / IF IN’ output of the analyzer to the LO/IF port of the external mixer. The diplexer is contained in the analyzer and the IF signal can be tapped from the line which is used to feed the LO signal to the mixer. The signal to be measured is fed to the RF input of the external mixer. On the other hand, the three-port mixer connects the ’LO OUT / IF IN’ output of the analyzer to the LO port of the external mixer. The ’IF IN’ input of the analyzer is connected to the IF port of the external mixer. The signal to be measured is fed to the RF input of the external mixer.

Conversion Loss

The maximum settable reference level depends on the external mixer’s conversion loss which is defined by average conversion loss or by using the conversion loss table. For example, if an IF signal with a level of -20 dBm is applied to the LO OUT / IF IN or IF IN input of the spectrum analyzer, full screen level is attained. Consequently, the maximum settable reference level is -20 dBm at a set conversion loss of 0 dB. If a conversion loss > 0 dB is entered, the maximum settable reference level increases in the same proportion. If the maximum possible reference level is set on the analyzer, this level is reduced if a smaller conversion loss is entered. In addition to the dynamic range of the spectrum analyzer the 1 dB compression point of the mixer has to be taken into account. The levels of the input signals lie well below this value to avoid generation of harmonics of these signals in the mixer. These are converted by the LO signals harmonics of higher order and appear in the displayed spectrum. Some instruments allow the definition of conversion loss tables. The Conversion loss table allows the conversion loss of the mixer in the selected band to be taken into account as a function of frequency. Correction values for frequencies between the individual reference values are obtained by interpolation (Linear interpolation). Outside the frequency range covered by the table the conversion loss is assumed to be the same as that for the reference value marking the table limit.

IviSpecAnExternalMixer VIs

IviSpecAn_ConfigureConversionLossTable

IviSpecAn_ConfigureConversionLossTableEnabled

IviSpecAn_ConfigureExternalMixer

IviSpecAn_ConfigureExternalMixerBias

IviSpecAn_ConfigureExternalMixerBiasEnabled

IviSpecAn_ConfigureExternalMixerEnabled

IviSpecAn_ConfigureExternalMixerNumberOfPorts

IviSpecAnExternalMixer Properties

IVISPECAN_ATTR_EXTERNAL_MIXER_AVERAGE_CONVERSION_LOSS

IVISPECAN_ATTR_EXTERNAL_MIXER_BIAS

IVISPECAN_ATTR_EXTERNAL_MIXER_BIAS_ENABLED

IVISPECAN_ATTR_EXTERNAL_MIXER_BIAS_LIMIT

IVISPECAN_ATTR_EXTERNAL_MIXER_CONVERSION_LOSS_TABLE_ENABLED

IVISPECAN_ATTR_EXTERNAL_MIXER_ENABLED

IVISPECAN_ATTR_EXTERNAL_MIXER_HARMONIC

IVISPECAN_ATTR_EXTERNAL_MIXER_NUMBER_OF_PORTS