>>> 8230 VHF/UHF Directional Detector <<<

 

Figure 1, 8230S Front View

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Figure 2, 8230S Top View

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  The 8230 Directional Detector is intended for incident and reflected power measurement applications.  The Incident or reflected power level measurement is displayed in dBm on the 5130 VHF/UHF POWER METER front panel display or an Oscilloscope connected to the 5130 rear panel BNC connector for real-time broad-band measurements.

  To measure incident power, port 1 of the 8230 is connected to the VHF/UHF source, and port 2 is connected to the device under test (DUT).  The power level delivered to the load is displayed on the 5130 Power Meter or an Oscilloscope connected to the 5130 rear panel BNC connector for real-time broad-band measurements.

  To measure reflected power, port 2 of the 8230 is connected the VHF/UHF power source and port 1 is connected to the device under test (DUT).  The power level reflected back to the source from the DUT is displayed on the 5130 Power Meter or an Oscilloscope connected to the 5130 rear panel BNC connector for real-time broad-band measurements.

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8230 Application Note

  This application note describes the procedure used to evaluate the insertion and return loss of a band-pass filter.  A 591 MHz filter was selected for this evaluation, but any filter in the 10 to 900 MHz range can be evaluated with this equipment and procedure.

Filter Insertion Loss and Bandwidth Evaluation

  The equipment required for the insertion loss evaluation is shown in Figure 1.  The center frequency (CF) of the sweep generator is set to 591 MHz and the frequency deviation (Delta F) is set to 50 MHz. The sweep generator output power is set to 0 dBm, and the 6 dB attenuator lowers the VHF/UHF drive level to -6 dBm at port 1 of the 8230, Directional Detector Assembly. A few tenths of a dB increase to the generator output may be required to compensate for coupler and cable loss so that a -6.0 dBm reading is displayed on the 5130 Power Meter.

  Before the Oscilloscope vertical calibration is started, the Oscilloscope time base and trigger level, should to be setup. First, the Oscilloscope time base is set to 1/10 of the VHF/UHF sweep generator sweep time.  Because the VHF/UHF sweep generator used in this demonstration is set to a 10.0 mS sweep time, the Oscilloscope time base is set to 1.0 mS per horizontal division making the horizontal display range 50 MHz for 10 divisions. The Oscilloscope is set to trigger off the 10.2 volt P-P triangular waveform supplied by the VHF/UHF sweep generator sweep output connector. The trigger level of 5 +/- 0.2 volts is shown in Figure 2 on the right side of the Oscilloscope graticule.  In all figures containing an image of the Oscilloscope graticule, the CW Marker Generator is first set to 591 MHz, and the trigger level is adjusted so that the marker is centered horizontally on the Oscilloscope graticule.

 

Figure 1, Configuration for Insertion Loss and Bandwidth Evaluation

  Switch the Oscilloscope to the Channel 1 mode, and refer to Figure 2 for the following settings.  Since the 5130 Power Meter rear panel output calibration is 0.1 volt/dB, the Oscilloscope Probe setting needs to be set to 10X to produce 1.0/dB on the Oscilloscope graticule.  A suitable reproduction of the DUT response is achieved at Volts/Div = 5.00V (5dB/Div) making the vertical display range 40 dB for 8 vertical divisions. To display the complete DUT response on the graticule, set the Channel 1 trace to the top horizontal line of the Oscilloscope graticule to make it 0 dBm.

 

Figure 2, Oscilloscope Channel 1 Setup

 

  Switch the Oscilloscope to the cursor mode and refer to Figure 3 for the following settings.  Cursor 2 is set on the Oscilloscope trace that represents -6.0V (-6.0 dBm).

 

Figure 3, -6 dBm Calibration

  Refer to Figure 3A for the following settings.  With the Oscilloscope still in the Cursor mode, turn off the sweep generator VHF/UHF output and note the system noise floor on the Oscilloscope graticule.  Adjust Cursor 1 so that it is in the vertical center of the noise floor trace, and read Cursor 1 = -32.4V = -32.4 dBm and read Delta = 26.4V = 26.4 dB which is the system dynamic range.

 

Figure 3A, Noise Floor Evaluation

  Use the configuration of Figure 1 for the following evaluation. First connect the filter between the coupler (7) and port 1 of the 8230 (9).  On the Oscilloscope (11), move Cursor 1 to the point where the marker and filter response meet and read the filter loss, Delta = 2.2V (2.2 dB).

 

Figure 4, Filter Insertion Loss

Filter Bandwidth Evaluation

  The equipment configuration of Figure 1 is also used for the filter bandwidth evaluation.  Cursor 2 is positioned on the filter response to establish 0 dB and Cursor 1 is positioned below Cursor 2 so that Delta = 3.00V for the -3.00 dB point.  The Oscilloscope trigger control is adjusted to center the filter response on the Oscilloscope graticule, and then the frequency of the marker generator is adjusted so that the marker on the Oscilloscope graticule is on the center vertical line. The result of this calibration is shown in Figure 5.  The Counter (12) readout of the Marker Frequency set at this position is 590.701 MHz.

 

Figure 5, Calibration for Bandwidth Measurement

  Next the frequency of the marker generator is adjusted so that the marker on the Oscilloscope graticule intersects the point where the filter response and Cursor 1 meet on the left side of the graticule as shown in Figure 6.   The Counter (12) readout of the Marker set at this position is 581.09 MHz.

 

Figure 6, Filter F1 Measurement

  Finally, the frequency of the marker generator is adjusted so that the marker on the Oscilloscope graticule intersects the point where the filter response and Cursor 1 meet on the right side of the graticule as shown in Figure 7.  The Counter (12) readout of the Marker set at that position is 600.18 MHz.  From the preceding measurements, the Bandwidth can be calculated.  BW = F2-F1 = 19.09 MHz.

 

Figure 7, Filter F2 Measurement

 

Filter Return Loss Evaluation

  If external leveling of the sweep generator is available, a short circuit termination connected to port 1 of the 8230 can be used to calibrate the configuration of Figure 8, but to avoid adding external leveling to the sweep generator output, a high quality 6 dB attenuator with a short-circuit termination connected the unused port is used for calibration.  Both parts connected this way produce a load with a 12 dB Return Loss.  Additional information about attenuators, Return Loss, and Mismatch Loss is available by clicking on this hyperlink, Attenuator Application Note

  In the Figure 8 configuration, port 2 of the 8230 is connected to the source of VHF/UHF power, and Port 1 is connected to the 6 dB attenuator with short-circuit termination, (8A & 8B).  Refer to Figure 9 while performing calibration.  Calibration is accomplished by moving Cursor 1 to the center of the middle trace which makes Cursor 1 = -19.6V as shown on the right of the Oscilloscope graticule in Figure 9, and then move cursor 2 to the approximate center of second division from the top of the Oscilloscope graticule to make Delta = 12.0V = 12.0 dB.  This adjustment makes the position of Cursor 2 = -7.6V as shown to the right of the Oscilloscope graticule in Figure 9.

 

Figure 8, Calibration Configuration

 

Figure 9, Calibration Result

 

  The next four steps evaluate the calibration.  The Figure 10 configuration is used in all four steps. Connect a 10 dB attenuator having a short-circuit termination connected to the unused end to port 1 of the 8230.  This simulates a load having a 20 dB return loss.  Figure 11 shows the Oscilloscope display of the measurement result where Cursor 1 = -27.6V, Cursor 2 = -7.6V, and Delta = 20.0V.

  Next, connect a 3 dB attenuator with short-circuit termination to port 1 of the 8230.  This simulates a load having a 6 dB return loss.  Figure 12 shows the Oscilloscope display of the measurement result where Cursor 1 = -13.4V, Cursor 2 = -7.6V, and Delta = 5.8V.  Delta should be 6.0, but the calibration error has increased to 0.2 of a dB.

  Next, leave port 1 open to simulate an open circuit termination.  Figure 12 shows the Oscilloscope display of the measurement result where Cursor 1 = -8.00V, Cursor 2 = -7.6V, and Delta = .400V.  Delta should be 0, but the calibration error has increased to 0.4 of a dB.

  And finally, connect a short circuit termination to port 1.  Delta should be 0, but Figure 12 shows the Oscilloscope display of the measurement result where Cursor 1 = -6.00V, Cursor 2 = -7.6V, and Delta = 1.6V.  Delta should be 0, but the calibration error has increased to 1.6 dB.

 

Figure 10, Equipment Configuration for Calibration Evaluation

 

Figure 11, Oscilloscope Display for 20 dB Mismatch Termination

 

Figure 12, Oscilloscope Display for 6 dB Mismatch Termination

 

Figure 13, Oscilloscope Display for Open Circuit Termination

 

Figure 14, Oscilloscope Display for Short Circuit Termination

 

  The configuration of Figure 15 is used to evaluate the filter return loss.  Note that a 50-ohm termination is connected to the filter (8) output port.  Figures 16 through 18 show the results of the filter evaluation.

 

Figure 15, Equipment Configuration for Filter Return Loss Evaluation

 

Figure 16 shows the return loss at the filter center frequency, 590.57 MHz.

 

Figure 16, Return Loss at Filter Center Frequency = 590.57 MHz

  To evaluate the filter at the 10 dB Return Loss points (a level where the Mismatch Loss is small), move Oscilloscope Cursor 1 to -17.6V (-17.6 dB) so that Delta reads 10.0V (10 dB) and move the marker generator frequency to the point where the filter response and Cursor intersect (see Figure 17).   The Counter (12) display = 581.40 MHz.  The Oscilloscope display for the other point is shown in Figure 18 and the counter reading for that Marker is 599.71 MHz. The Bandwidth for the 10 dB Return Loss level is 18.31 MHz.

 

Figure 17, Marker = 581.40 MHz

 

Figure 18, Marker = 599.71 MHz

 

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