(SWR) Test Using the TEGAM 1830A RF Power Meter
Contents
1. No Error 10 TEGAM WAY e GENEVA OHIO 44041 440 466 6100 e FAX 440 466 6110 e www tegam com The following is an example of how to use the 1830A remotely to calculate output SWR This example can be used in any programming language that is capable of communicating with test and measurement equipment Equipment e TEGAM 1830A RF Power Meter e Thermistor Mount o TEGAM M1130A o Agilent 478A with options H85 or H76 e DUT Power Meter with 50 MHz 1 mW Reference Port For this example use Agilent E4418B Procedure The following procedure should be used for solving Output SWR 1 Power ON all equipment and allow proper warm up time for each If using a temperature compensated thermistor mount allow for proper temperature stabilization 2 Connect thermistor mount to 1830A a For M1130A use the following cables i TEGAM CA 7 48 Sensor Cable ii TEGAM CA 10 48 Heater Cable b For 478A use cable TEGAM CA 6 48 Sensor Cable 3 Use the following commands to configure 1830A for connection to M1130A or 478A a SET COMPENSATION_MODE CV 0 i 0 No Compensation TEGAM Mounts ii 2 432 Bias Comp Agilent Mounts b Make sure to read the return after the SET COMPENSATION_MODE CV 0 command to clear read buffer 4 Make sure the 50 MHz reference is turned off prior to connecting the thermistor mount a OUTP ROSC OFF 5 Connect thermistor mount to 50 MHz Reference Output Connection 6 Record RHO299 the S22 Magnitude of the therm2. OR BRIDGE BALANCER Figure 1 Thermistor Mount and Bridge Balancing with the 1830A Thermistor mounts like the TEGAM Model M1130A or the Agilent 478A with option H75 or H76 operate at a DC Resistance of 200 Q which has an RF impedance of 50 Q and a negligible Fzoaa zero With the ability to change the thermistor mount reference resistance to 100 Q the RF impedance becomes 25 Q giving a nominal Vroaq Of 0 33 The effective efficiency of the thermistor mount remains constant at both 200 2 and 100 2 so the power ratio can be measure accurately 1 The H75 and H76 are options for the 478A that represent optimized performance for VSWR Specifically from 1 MHz to 1 GHz maximum VSWR is less than 1 3 1 except at 50 MHz maximum VSWR of 1 05 1 10 TEGAM WAY e GENEVA OHIO 44041 e 440 466 6100 e FAX 440 466 6110 e www tegam com Calculating Output SWR Equipment TEGAM 1830A RF Power Meter Thermistor Mount o TEGAM M1i130A o Agilent 478A with options H85 or H76 DUT Power Meter with 50 MHz 1 mW Reference Port Procedure The following procedure should be used for solving Output SWR 1 8 9 Power ON all equipment and allow proper warm up time for each If using a temperature compensated thermistor mount allow for proper temperature stabilization Connect thermistor mount to 1830A a For M1130A use the following cables i TEGAM CA 7 48 Sensor Cable ii TEGAM CA 10 48 Heater Cable b For 478A use cabl
3. TEGAM Application Note 219 Output Standing Wave Ratio SWR Test Using the TEGAM 1830A RF Power Meter When using a power meter that references to a 50 MHz 1 mW output power reference it is important to know that the 50 MHz reference is within the specified performance limits The TEGAM Model 1830A RF Power Meter coupled with a thermistor power sensor also known as a thermistor mount can accurately measure the SWR of a 50 MHz reference By utilizing a unique function that most modern power meters do not offer the 1830A allows the user to change the value of the thermistor mounts terminating resistance Utilizing this method for measuring source match works well because it presents the source with two distinctly different values of loaa which allows accurate measurement of the power absorbed under two different conditions This application note will explain how we make this SWR measurement with the 1830A and a thermistor mount It is first important to understand how a thermistor mount operates and why by simply changing the resistance that the reference resistor balances at can accurately determine SWR Figure 1 shows how a DC bridge circuit maintains series resistance of two thermistors at the nominal bridge resistance typically 200 2 The thermistors T are matched so each thermistor is biased at 100 92 The thermistors are in parallel for the RF signal path since each are biased at 100 Q the pair make a good 50 Q termination SENS
4. am com a For an M1130A use the value of 33 as an estimated value b For a 478A us the value of 33 as an estimated value 8 Verify the 1830A reference resistor is configured for 200 Q a SET R_1 CV 200 b Make sure to read the return after the SET R_1 CV 200 command to clear read buffer 9 Zero the 1830A a Before issuing the rezero command wait minimum 5 seconds for mount to settle at 200 Q b SET REZERO_SYSTEM CV 1 c Make sure to read the return after the REZERO_SYSTEM CV 1icommand to clear read buffer NOTE A 49 will be returned after a rezero 49 is a system rezero warning 10 Turn on the 50 MHz 1mW reference on the DUT Power Meter a OUTP ROSC ON 11 Record the power level from the front panel of the 1830A a Before issuing the GET POWSUB_1 CV command wait minimum 5 seconds for mount to settle power measurement b GET POWSUB_1 CV c Read return buffer 12 Turn off the 50 MHz 1mW reference on the DUT power meter a OUTP ROSC OFF 13 Configure the 1830A reference resistor to 100 Q a SET R_1 CV 100 b Make sure to read the return after the SET R_1 CV 100 command to clear read buffer 14 Repeat steps 10 12 15 Calculate M using the following equation __ P20o 1 RH01001 P100 1 RH020012 16 Return 1830A to 200 Q a SET R_1 CV 200 b Make sure to read the return after the SET R_1 CV 200 command to clear read buffer Having confidence that your 50 MHz reference port SWR is within specifications is important By adhe
5. ase angles are within a reasonable range For this reason all calculations in this application note will only use RHO portion of Gamma 10 TEGAM WAY e GENEVA OHIO 44041 e 440 466 6100 e FAX 440 466 6110 e www tegam com 16 Using the Value for M calculate the output voltage coefficient using the following equation Ir 2 RHO200 M 2 RHO100 V 2 RHO100 2 RHO200 M 4 RHO200 M RH0100 2 M 1 s 2 RHO200 M RH010012 17 Calculate the output SWR using the following equation _ IPs awas 1 F 5 Worked Example of Output SWR For this example the DUT was an Agilent E4418B Power Meter Output SWR is required to be maximum 1 06 A TEGAM 1830A with a M1130A were also used for this example The output SWR is 1 029 Recorded Values Value Power mW 200 ohms Ref Resistor 0 9936 Power mW 100 ohms Ref Resistor 0 8939 Fixed Values From Thermistor Mount calibration data RHO 200 ohms Ref Resistor 0 0014 RHO 100 ohms Ref Resistor 0 33 Calculations Calculate Factor M 0 990485764 Calculate Output voltage reflective coefficient 0 01451123 Calculate Output voltage reflective coefficient 6 020735385 Output SWR 1 029449814 Output SWR 1 39834802 NOTE A downloadable spreadsheet with all formulas is located in TEGAM Forums http geneva tegam com forums 10 TEGAM WAY e GENEVA OHIO 44041 e 440 466 6100 e FAX 440 466 6110 e www tegam com Calculating Output SWR Programming Example The follow
6. e TEGAM CA 6 48 Sensor Cable Manually configure the 1830A for selected thermistor mount Make sure the 50 MHz reference is turned off prior to connecting the thermistor mount Connect thermistor mount to 50 MHz Reference Output Connection Record RHO200 the S22 Magnitude of the thermistor mount at 50 MHz at 200 Q a For an M1130A this value is available on the calibration report b For a 478A use the value of 0012 as an estimated value Record RHOjo0 the S22 Magnitude of the Thermistor Mount at 50 MHz at 100 Q a For an M1130A use the value of 33 as an estimated value b For a 478A us the value of 33 as an estimated value Verify the 1830A reference resistor is configured for 200 Q Zero the 1830A 10 Turn on the 50 MHz 1mW reference on the DUT Power Meter 11 Record the power level from the front panel of the 1830A 12 Turn off the 50 MHz 1mW reference on the DUT power meter 13 Configure the 1830A reference resistor to 100 Q 14 Repeat steps 10 12 15 Calculate M using the following equation P299 1 RHO1001 M Pi90 1 IRHO200 2 Verify on 1830A front panel that heating is complete and unit has a stable zero 3 Please refer to 1830A User Manual for configuring a Temperature Compensated Thermistor Mount vs an Agilent 478A Thermistor Mount 4 Please refer to the DUT Power Meter Manual for operating instructions 5 Gamma of the load is a complex value however we can give a sufficiently accurate answer providing the ph
7. ing is the exact procedure we just followed manually however in this procedure we have included all the command necessary to complete the procedure remotely with third party software such as VB or LabVIEW The necessary command will be BOLD Before communicating with the 1830A we must first understand how the 1830A can be communicated with and how to set up a proper command structure 1830A Remote Operation Remote control of the 1803A is available via two different methods A command structure that allows for the control and query of all operations is available through Universal Serial Bus USB and TCP IP Commands are text and not case sensitive Commands are made up of multiple words or values sent as a space delimited string NOTE Whether using SET or GET it is always necessary to read back after each command The 1830A returns back an error code after every SET and every GET If the buffer is not read after each command improper results will be returned 1830A Command Structure GET and SET variables by following the structure below GET VARIBLE NAME ITEM Retrieve a system variable value SET VARIBLE NAME CV VALUE Set the current value of the variable to the passed input value Example To retrieve the current loaded calibration factor we would use the following command structure GET K_1 CV 1830A Returns 00 1 0000 00 No Error 1 0000 is the calibration factor SET COMPENSATION_MODE CV 0 1830A Returns 00 00
8. istor mount at 50 MHz at 200 Q a For an M1130A this value is available on the calibration report b For a 478A use the value of 0012 as an estimated value 7 Record RHOjo9 the S22 Magnitude of the Thermistor Mount at 50 MHz at 100 Q 6 No Compensation To be used with TEGAM thermistor mounts such as the F1130A The TEGAM thermistor mount is a type of bolometer whose resistance decreases as a function of increasing heat associated with ambient temperature or applied power This system also features the Model 1830A temperature control circuitry that temperature stabilizes TEGAM and Weinschel thermistor mounts This eliminates changes in the thermistor element s resistance due to ambient temperature changes and thus isolates the causes of thermistor variation to the application of RF and DC power only Therefore compensation for ambient temperature is not needed 7 432 Bias Comp This mode assumes that a temperature compensated mount is attached The Bias Comp mode balances both channels just like the 432 Compatible mode the difference is the voltmeter readings from only Channel 1 are used in the simple power equation of P V OFF V ON R This method is recommended for standards lab use with 478 486 8478 series thermistor mounts because the errors from only one channel are transferred while in a lab the mount environment can be stabilized using insulation 10 TEGAM WAY e GENEVA OHIO 44041 e 440 466 6100 FAX 440 466 6110 e www teg
9. ring to the procedures while using the TEGAM Model 1830A RF Power Meter and a calibrated thermistor mount like the TEGAM Model M1130A you can be certain that your 50 MHz reference SWR is within the manufactures tolerance 10 TEGAM WAY GENEVA OHIO 44041 440 466 6100 e FAX 440 466 6110 e www tegam com
Download Pdf Manuals
Related Search