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Inexpensive Scaler Measurement

Fri, 04/06/2001 - 7:06am
By Hal Crittenden, Krytar

Krytar Model 9000B Power Meter is capable of measuring CW or Swept Power over the entire frequency range of 100 kHz to 40 GHz when used with 9540A Power Head.

The Power Meter is Auto-ranging in 2 ranges and has a linearity of ± 0.05 dB @ 25`C.

The unit measures CW Power of – 30 to 20 dBm which is displayed on a digital readout. The Power Meter is useable to - 39 dBm.

A DC output voltage of – 3.9 to 2.0 volts is generated which equates to an RF or Microwave Power input of – 30 to 20 dBm. The input to the Power Meter may be swept at a 100 millisecond rate. The resulting DC output may be displayed on an oscilloscope or low cost scalar measurements.


RF and power meter

The Krytar Power Meter is completely portable operating on internal rechargeable batteries that offer greater than 12 hours of operation and includes an internal fast battery charger. The battery is charged using 115 VAC, or from a car battery using an optional automobile cigarette lighter plug with cord.

An RS-232 port for connection to an external personal computer (PC) for data logging is available as an option. An IEEE-488 capability is also available for use in automatic test equipment (ATE) systems.

Krytar believes the accuracy of this power meter is equal to or perhaps better than many or all the more expensive power meters available.

The low price, accuracy and many other features of the Krytar Power Meter allows many uses. One such use is for low cost scaler measurement of a Band Pass Filter. See the block diagram (Figure 1) showing typical instruments and components used to measure performance of the Band Pass Filter.

What Does It Measure
• CW and Swept Power from the output of the Band Pass Filter.
• Minimum pass band insertion loss of the Band Pass Filter
• Frequency at which minimum insertion loss is measured
• Frequency Bandwidth of the Band Pass Filter
• Both lower and upper stop band attenuation of the Band Pass Filter
• Frequency point at which "Return Band" or "Spurious Bands" occur as well as the attenuation value of the Band Pass Filter at these frequencies.

Figure 1

The Measurement
Set the leveled output power from the sweep signal generator to its maximum (usually between 12 to 20 dBm. Maximum dynamic range for the Krytar Power Meter is – 39 to 20 dBm). Note that if 20 dBm is supplied to the band pass filter, stopband attenuation of 59 dB can be measured.

Many test setups have one or more components (isolators, connectors, cable assemblies, etc.) connected between the output connector of the sweep signal generator and the Unit Under Test. These components introduce insertion loss.

Remember, the power output from the sweep signal generator is leveled at the output connector. Any components added between the output connector of the sweep signal generator and the Unit Under Test will attenuate the power to the unit under test. This results in an unknown power being applied to the Band Pass Filter.

The output from the "Test String of Components" is connected to the input of a Krytar Directional Detector. The output from the Krytar Directional Detector is connected to the Band Pass Filter being tested.

The DC voltage from the Directional Detector is connected to the External Leveling connector of the sweep signal generator. This will level the power at the output of the Krytar Directional Detector (Note that the detected output is referenced to the output of the directional detector).

If the sweep signal generator is unable to furnish adequate leveled output power to the band pass filter, an amplifier will need to be added to the "test string of components." A Krytar Power Meter is connected to the output connector of the Directional Detector to assure adequate power is furnished to the Band Pass Filter.

The Power Meter is then removed and the Band Pass Filter is connected to the output connector of the Directional Detector. The system is now calibrated.

The output from the Band Pass Filter is connected to the Krytar Power Meter. CW Power is measured and displayed on the output Power Meter.

The Krytar Power Meter supplies a DC Voltage of – 3.9 Volts to 2.0 Volts which is equivalent to – 39 to 20 dBM.

The DC voltage from the Krytar Power Meter is connected to an Oscilloscope. This DC Voltage is shown on the oscilloscope as a calibrated attenuation (0 to – 59 dB).

The horizontal output connector from the sweep signal generator is connected to the horizontal input of the oscilloscope. The oscilloscope may then be calibrated to show frequency as generated by the sweep signal generator and will then display attenuation versus frequency of the Band Pass Filter being tested. (See Figure 2)

Figure 2

The Krytar Power Meter may be ordered with an IEEE-488 or RS232C interface. All readings from the Power Meter are stored on a computer. A report is generated using a spread sheet program like Microsoft Excel or equivalent. The report then is printed on a printer.

The setup may also be used to measure other passive devices such as Band Reject, High Pass, Low Pass and Stop Band Filters as well as fixed attenuators, pads, step attenuators, insertion loss of cable assemblies, etc.

Unit price of this power measuring combination is approximately $2000 which includes both the Display Unit and the Power Head. This same combination which covers a frequency range of 100 kHz to 4 GHz is only $1650.00.

For additional information on all Krytar Components and Test Instrumentation, visit www.krytar.com, email sales@krytar.com or phone (408) 877-5999.

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