I+jQ Span and Frequency Information

This topic provides span and frequency information that is unique to 2-channel I+jQ(Ch1+j*Ch2) measurements. The information applies to two different measurement configurations; the first uses only the baseband analyzer and the second uses the baseband analyzer with an external quadrature downconverter. See About Frequency for more information about the frequency and span parameters.

Two-Channel I+jQ Measurement Span and Frequency Information

The following frequency and span information applies to 2-channel I+jQ(Ch1+j*Ch2) measurements for the baseband analyzer.

The following figure shows the span and frequency interrelationships for a zoomed measurement in the negative frequency side of the analyzer's full span.

$image\Ch1Ch2_FullSpan_wmf.jpg$

Span

The span can be adjusted arbitrarily to the maximum span which is equal to double the maximum span of a single channel measurement. For the 89610A VSA using two E1438 ADCs, the maximum span is equal to 78.125 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. (twice the single channel span).

Max Span = 2 ´ (Single Channel Bandwidth)

Center Frequency (Fc)

The center frequency can be adjusted arbitrarily within the analyzer's maximum span (Max Span) limits. Trace data will be blanked for measurement spans that exceed the analyzer's Max Span limits. The center frequency (Fc) may be adjusted within the following limits.

Fc Range = ± (Max Span/2)

Two-Channel I+jQ Measurement Span and Frequency Information with External downconverter

The following frequency and span information applies to two-channel I+jQ(Ch1+j*Ch2) measurements using the baseband analyzer with an external quadrature downconverter. The external quadrature downconverter extends the baseband analyzer I/Q measurement capabilities to include RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). signals.

The analyzer's external downconverter interface is through the User Correction tab. Input data is provided for these external downconverter parameters: the external center frequency, the Intermediate Frequency (IF), and the External Bandwidth. The Frequency Converter checkbox must be selected to apply the settings to the measurement. If Frequency Converter is not enabled, the displayed frequency axis represents frequencies relative to the center frequency at the downconverter and not the absolute center frequency.

The External downconverter IF must be set to 0 Hz.

The following figure shows the span and frequency interrelationships using the 89610 baseband analyzer with external downconverter making a zoomed measurement at F_c(zoomed). In this example the external downconverter bandwidth is greater than the analyzer's maximum span.

$image\Ch1Ch2_ExtBWgrtrFullSpan_wmf.jpg$

Span

The span can be adjusted arbitrarily within the maximum measurement span which is analyzer hardware and external downconverter dependent. The maximum measurement span is the smaller bandwidth of the analyzer's full span and the external downconverter bandwidth. Trace data is blanked for any frequencies outside the maximum measurement span. For example, if an external downconverter with an external bandwidth (ExtBW) of 100 MHz is used with the 89610A baseband analyzer (with an Max Span of 78.125 MHz), the maximum span for a 2-channel I+jQ measurement would be 78.125 MHz.

Max Span = 2 ´ (89600 VSA Single Channel Bandwidth) or External Converter bandwidth, whichever is smaller

Center Frequency (Fc)

The center frequency (Fc) can be arbitrarily adjusted within the maximum measurement span, which is analyzer hardware and external downconverter dependent. To show the absolute center frequency, the downconverter center frequency must be entered and Frequency Converter enabled. Otherwise the displayed frequency axis represents frequencies relative to the center frequency at the downconverter and not the absolute measurement frequency.

Center frequency (Fc) range when the External downconverter bandwidth (Ext BW) is greater than or equal to analyzer full span

(ExtFc - Full Span/2) £ Fc Range £ (ExtFc + Full Span/2)
Center frequency (Fc) range when the analyzer full span is greater than or equal to External downconverter bandwidth (ExtBW)

(ExtFc - ExtBW/2) £ Fc Range £ (ExtFc + ExtBW/2)