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VSWR MeasurementWhen a transmission line (cable) is terminated by impedance that does not match the characteristic impedance of the transmission line, not all of the power is absorbed by the termination. Part of the power is reflected back down the transmission line. The forward (or incident) signal mixes with the reverse (or reflected) signal to cause a voltage standing wave pattern on the transmission line. The ratio of the maximum to minimum voltage is known as VSWR, or Voltage Standing Wave Ratio. Signal reflection occurs when the RF signal reflects back due to an impedance mismatch or change in impedance caused by excessive kinking or bending of the transmission line. The best possible value is 1:1 which means that all of the power generated by the transmitter is radiated from the Antenna.

Where to MeasureIt is important to know that for accurate VSWR measurements of devices, the VSWR should be measured at the input of the device in question (antenna etc). Any cable loss or attenuation, will make the VSWR at the input of the cable appear much better than at the load or termination. The reason is that the cable loss or attenuation increases the return loss.VSWR of the feeder cable is measured with the help of site master. Open/Short/Load 50 ohm is required for calibrating the site master for accurate result. At the BTS site RF cable (jumper cable connected to feeder cable) is removed from BTS and connected to site master RF Out/Reflection port. Other end of the RF cable is connected with sector Antenna. Site master is operated with 12.5 V dc. At tune on the site master runs through a series of quick checks to ensure the system is functioning properly. The Anritsu site Master is capable of up to 1.5 Hours of continuous operation from a fully charged, field replaceable battery. It can also be operated from an external DC source using AC-DC adapter. If the battery is low, or if the ambient temperature is not within the specified operational range, self test will fail. Site master must be re-calibrated whenever the setup frequency changes, the temperature exceeds the calibration temperature range or when the test port extension cable is removed or replaced. If the cal off message is displayed, or the test port cable has been changed, a new calibration is required.

How to Operate

Press the ON/OFF key on the Site Master. Press the MODE key. Use the Up/Down arrow key to select the Freq-SWR mode and press enter Press the Freq/Dist key. Press the F1 soft key as displayed on screen. Enter the desired start frequency using the key pad or the up/down arrow key. Press enter to set F1 to the desired frequency. Press the F2 soft key as displayed on screen. Enter the desired stop frequency using the keypad or the up/down arrow key. Press Enter to set F2 to the desired frequency Check that the start and stop frequencies displayed match the desired measurement range. Press the Start -Cal key The message Connect OPEN to RF out port will appear in the message box. Connect the calibrated OPEN and press the ENTER key. The messages Measuring OPEN and connect SHORT to RF Out will appear. Remove the OPEN, connect the calibrated SHORT and press the ENTER key. The message Measuring SHORT and Connect LOAD to RF Out will appear. Remove the SHORT and connect the LOAD. An audible tone will sound when the calibration is complete. Cal On message is now displayed Press Mode key, select Freq-SWR mode at display with up/down arrow key then press ENTER key. Press Amplitude key, select top and bottom amplitude of VSWR Press Meas/Disp key to display VSWR reading Connect the device (RF cable terminating at Duplexer or terminating at anteena port) under test to the site master. RF out port will be displayed on the screen. Press Marker key, press M1 and press On/Off to turn on Marker-1

Distance-To-Fault (DTF)The Distance to Fault transmission line test verifies the performance of the transmission line assembly and its components and identifies the fault locations in the transmission line system. After pressing the Freq/Dist press D1 to enter the start distance and press Enter, D2 to enter the stop distance and press Enter. Calibration is done again if the frequency (F1 and F2) of operation is changed. By pressing the DFT Aid soft key, select the appropriate cable type to set the correct propagation velocity and attenuation factor. Markers can be set as per requirement. The display will show distance and VSWR in front of M1 and M2 at the bottom of the screen. It can be saved and printout can be taken.

Procedure Connect one end of the RF cable terminating at Duplexer or terminating at anteena port to the RF Out/Reflection port in Site Master. Press the Mode key. Select the DTF-SWR using the Up/Down arrow key and press Enter. Press the Freq/Dist key, set the distance by pressing D1 and D2 soft key as per measurement distance. Press Meas/Disp key. Distance and VSWR with Marker will be display in the trace. Press Save Display, name the file and Enter.

Power MeasurementsThe Site Master can be used for making power measurements with broadband RF detectors, such as the 10 MHz to 20 GHz Anritsu 560-7N50B. The power monitor displays the measured power results in dBm or Watts.Note: Always make it sure while doing power measurement that all device under test should not be withdrawing supply while connecting it to Site MasterRequired Equipment Site Master model S331D with Power Monitor option Broadband RF detector, Anritsu P/N 5400-71N50B 30 dB, 50 Watt, bi-directional, DC 18 GHz, N(m) N(f), Attenuator, 42N50A-30

Procedure Press the ON/OFF key on the Site Master. Press the MODE key. Use the Up/Down arrow key to select the Power Monitor mode and press enter

Note: DO NOT connect Site Master directly to DUT as it can damage Site Master. Always remember to connect attenuater in between DUT and Site Master. Attenuater will be connected to sensor cord and sensor cord will be connected to RF port of Site Master.Zeroing the Power Moniter With no power applied to the DUT (Device under Test), press the Zero soft key. Wait for a few seconds while the Site Master accumulates data samples of the quiescent power. When complete, Zero Adj: On is displayed in the message area.

Measuring High Input Power Levels Insert an attenuator between the DUT and the RF detector to protect the Site Master so that the input power level is less than or equal to 20 dBm. Press the Offset dB soft key. Enter the attenuation in dB using the keypad. Press the ENTER key to complete the entry. The message area will show Relative: On along with the entered value in dB.

Note: Attenuation value that we insert while doing power measurement depands upon capacity of attanuater that we are using in between DUT and Site Master.(Output Power=Actual Power + Offset Power)

Displaying Power in dBm and Watts Press the Units soft key to display power in Watts.

Displaying Relative Power With the desired base power level input to the Site Master, press the REL soft key. The message area will show Relative: On and the power reading will indicate 100%. Press the Units soft key to display power in dBm. Since Relative is ON, the power reading will be in dBr relative to the base power level.

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