>>> SRC1K SWEPT FREQUENCY SETUP <<<
The following procedure is used to setup the configuration of Figure 1 for swept frequency (ΔF) response testing of filters, amplifiers, couplers and other devices.
Figure 1, SRC1K with Power Supply & VX Driver
First, set the SRC1K center frequency (CF) with R7 of Figure 1. The result of this step is displayed on the Spectrum analyzer screen image of Figure 2. The drive level (CV) from the VX Driver is displayed on the oscilloscope screen image of Figure 3.
Figure 2, Spectrum Analyzer Screen Image of SRC1K CF Operation
Figure 3, Oscilloscope Screen Image of the VCO Driver CV Output @ 8.4 VDC
In Figure 3, cursor 1 is set at the vertical center of the graticule , 0.00 VDC, and Cursor 2 is set at the level selected for this demonstration, 8.37 VDC which makes the CF equal to 525 MHz. The oscilloscope cursor adjustment resolution prevents a precise setting. The oscilloscope is set to trigger off of CH2 which is connected to the function generator sync output connector.
Figure 4, SRC1K Tuning Plot
The slope of the SRC1K tuning plot shown in Figure 4 is:
ΔV/ΔF = 12.5mV/MHz
To setup the SRC1K for an 80 MHz ΔF, first calculate the Peak – Peak amplitude of the triangle waveform required to drive the SRC1K which is .0125 X 80 = 1 VPP. Set a function generator to the following parameters: 1 KHz triangle waveform @ 1 VPP and connect its output to the BNC connector of the VX Driver. Figure 5 is an oscilloscope screen image of the CV output to the SRC1K VX terminal. This trace shows the 1 VPP waveform centered around the 8.37 VDC.
Figure 5, Oscilloscope Screen Image of the VCO Driver CV Output @ 8.37 VDC Plus 1 V P-P Triangle Waveform
In Figure 5, cursor 1 is set on the bottom of the triangle waveform, approximately 8.00V, and cursor 2 is set at the top of the waveform, approximately 9.00V. The P-P level of this waveform indicated by Delta V is 1.00V. The DC level is still 8.37 VDC, but the oscilloscope cursor adjustment resolution prevents a precise setting of Cursor 1 and 2. The oscilloscope in this case also is set to trigger off of CH2 which is connected to the function generator sync output connector.
Driving the SRC1K VX terminal with the waveform of Figure 5 produces the ΔF response shown in Figure 6.
Figure 6, Spectrum Analyzer Screen Image of SRC1K ΔF Operation
At the bottom of the Spectrum Analyzer Screen Image, Figure 6, the SPAN is shown at 100 MHz (bottom right). The span across 10 horizontal divisions makes the horizontal calibration 10 MHz/division. The SRC1K for this Figure 1 configuration produces a ΔF of 80 MHz.
This procedure can be used for a swept frequency measurement setup with a CF between 25 and 1025 MHz. The maximum ΔF of 1000 MHz is only available when the CF is set to 525 MHz and the minimum ΔF depends on how close the CF is to 25 or 1025 MHz.
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