Specifications

Characteristic Impedance: 50 Si ±0.5%. Probe Travel: 50 cm. Scale in centimeters; each division is 1 mm. Scale Accuracy: ±(0.1 mm -+- 0.05%). Frequency Range: 300 MHz to 8.5 GHz (usable to 9 GHz). At 300 MHz, the slotted line coverB a half wavelength. Operation below 300 MHz is possible by use of lengths of Type 874 Air Lines.

Constancy of Probe Pickup: ±1.25%. Residual VSWR: Less than 1.01 + 0.0016 /»gh. to 7.5 GHz; less than 1.10 from 7.5 to 8.5 GHz; see also Figure 1.

Accessories Supplied: Storage box, rf probe, and 2 microwave diodes.

Accessories Required: Type 900-DP PrOL Tuner, recommended, or Adjustable Stub (Type 874-D20L) for tuning the crystal rectifier when audio-frequency detector or microammeter is used; suitable detector and generator; one each, Type 874-R22LA and Type 874-R22A Patch Cords, for generator and detector connections (patch cords are supplied with Type DXT Detector and GR Unit oscillators).

Dimensions: Width 26, height 4depth 3 H in (660, 115, 89 mm).

Catalog

Price

Number

Description

in USA

0874-9651

Type 874-LBB Slotted Line

$395.00

0874-9652

Type 874-LV Micrometer Vernier

41.00

0874-9511

Type 874-D20L Adjustable Stub

20.00

0900-9654

Type 900-DP Probe Tuner

75.00

"l'a- r

IMPEDANCE-MATCHING TUNERS FOR PRECISION COAXIAL-MEASURINC" SYSTEMS

The Type 900-TUB Tuner, for the 0.25- to 2.5-GIIz frequency range, complements the previously announced Type 900-TUA Tuner1, which covers the 1- to 8.5-GHz frequency range. The two tuners are similar in design and construction and, in addition to their wide bandwidths, have the following desirable features:

1. A unique neutral position, from which rapid convergence to match can always be achieved .

2. A fineness of control, so that vswr's as low as 1.0002 can be tuned out with ease

3. Stability — when a residual standing-wave ratio is tuned out, it stays tuned out; if the setting is changed, the original tuning is duplicated when the original setting is restored; if the connection between line and tuner is broken and then restored, the tuning is unchanged.

Each tuner has three tuning screws. In operation, two of the three screws are adjusted for match (which two depends on the frequency), while the unused screw is set to the neutral posi-^^

'"Coaxial Tuner with Neutral Setting," General Radio Experimenter, January 1965.

Figure 1. VSWR matching range oF the Types 900-TUB and -TUA Tuners. Specifications and data shown are under the most restrictive phase conditions of the reflection to be matched out.

tion. Each screw has a scale, with vernier, and can be locked at any setting.

The vswr matching ranges of the Types 900-TUB and -TUA Tuners (see Figure 1), while they are high enough for most applications, have been kept sufficiently low that extremely fine matches can be achieved with ease and speed.

APPLICATIONS Matching to a Standard of Impedance

With the G11900 Tuners one can reduce the residual reflections introduced into a coaxial system by terminations, measuring instruments (such as slotted lines, rf bridges and directional couplers), adaptors between line sizes, and connectors. These residual reflections must always be considered with respect to some standard of impedance. The standard may be part of a measuring instrument, it may be a termina

Figure 1. VSWR matching range oF the Types 900-TUB and -TUA Tuners. Specifications and data shown are under the most restrictive phase conditions of the reflection to be matched out.

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tion, or it may be a section of precision air line. The tuner is used, therefore, to match the impedance of the device in question to that of the standard.

The Measuring Instrument as an Impedance Standard

The Type 900-LB Precision Slotted Line is an excellent impedance standard. It covers the 0.3- to 8.5-GHz frequency range, and, at 2 GHz, for example, the residual impedance error (expressed in vswr) is less than 1.003. If a composite termination consisting of a Type 900-W50 Standard Termination and a Type 900-TUA or -TUB Tuner is assembled, as shown in Figure 2, and the tuner is adjusted^so that the amplitude of the standing-wave pattern observed on the slotted line is reduced to zero, then the residual vswr of the composite termination is made equal to the residual vswr of the slotted line. The improvement in vswr can be as

Figure 2. Composite termination consisting of a Type 900-TUB Tuner and a Type 900-W50 Termination, attached to a measuring instrument.

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Figure 2. Composite termination consisting of a Type 900-TUB Tuner and a Type 900-W50 Termination, attached to a measuring instrument.

COMPOSITE

MEASURING INSTRUMENT

COMPOSITE

MEASURING INSTRUMENT

MEASURING

STANDARD

I

TUNER

1

INSTRUMENT

I

1

TERMINATION

Figure. 3. Standard termination attached to a composite measuring instrument.

Figure. 3. Standard termination attached to a composite measuring instrument.

much as five-fold over the direct residual vswr of the termination alone.

Termination as an Impedance Standard

A well-matched termination, such as the Type 900-W.50 Standard Termination or, even better, the composite termination described above, can also be used as an impedance standard. For example, if the measuring instrument is a directional coupler or a hybrid junction, the instrument residual may be much greater than that of an available standard termination. In these cases a composite measuring instrument, consisting of the basic measuring instrument and a Type 900-TUA or -TUB Tuner, can be formed, as shown in Figure 3, and the tuner adjusted so that a null is observed with the measuring instrument. The residual vswr of the composite instrument is thus made equal to that of the standard termination.

Air Line as an Impedance Standard

The most accurate impedance standard is the characteristic impedance of a section of precision air-dielectric coaxial line, such as a Type 900-LZ Reference Air Line. The residual vswr of these air lines at 2 GHz is less than 1.0009. Both a composite measuring instrument and a composite termination, as shown in Figure 4, can be independently and simultaneously matched to the characteristic impedance of the air-line standard, at frequencies where the airline length is an odd multiple of a quarter wavelength2. The matching is accomplished by alternate adjustment of the tuners, I and II, until no reflection is observed by the measuring instrument (1) when the composite termination is connected through the air-line standard to the composite measuring instrument and (2) when the composite termination is connected directly to the composite measuring instrument (that is, with the air line out of the system).

Simplifying Substitution Measurements

Substitution techniques, such as those described by Sanderson3 and Zorzy4, are used to obtain accurate measurements of small reflections in the presence of comparable residual reflec-

1 MacKenzie, Thomaa K., "Some Techniques and Their Limitations as Related to the; Measurements of Small Reflections in Precision Coaxial Transmission Lines," presented at the 1966 Conference on Precision Klectro-rnagnetic Measurements, June 21—24, MRS, Boulder, Colorado. (Publication scheduled in the IEEE Transactions on Instrumentation and Measurement, December 1966.)

1 Sanderson, A. E., " A New High-Precision Method for the Measurement of the VSWR of Coaxial Connectors," IltE Transactions on Microirave Theori/ and Techniques, Vol MTT-9, No 6, November. 1961, p 521-528.

* Zorzy, J., "Precise Impedance Measurement» with Emphasis on Connector VSWR Measurements," 18th Annual ISA Conference and Exhibit, Chicago. Preprint No 47.4.63, 1963. (Available as General Radio Reprint No B20.)

COMPOSITE MEASURING INSTRUMENT

COMPOSITE TERMINATION

COMPOSITE MEASURING INSTRUMENT

COMPOSITE TERMINATION

Figure 4. Setup for matching composite measuring instrument and composite termination to the characteristic impedance of an air-line standard.

Figure 4. Setup for matching composite measuring instrument and composite termination to the characteristic impedance of an air-line standard.

.—¿ions in the measuring systems. In these ¿echniques, two measurements are required, and the desired quantity is dependent on the vector difference of the two measured quantities.

When an impedance-matching tuner is used to make one of the measured reflection coefficients equal to zero, the second measurement alone provides the answer2-®. This means that it is not necessary for one to perform the vector subtraction or to plot measurements on a Smith Chart and to make tedious constructions. Also, if only the magnitude of the answer is required, it can be obtained directly from just one magnitude measurement.

Quarter-Wavelength Substitution to Measure Termination

The simplification resulting from the --'•use of the tuner is illustrated by the example of the substitution technique that employs a quarter-wavelength reference air line to determine the reflection of a termination in the presence of the residual reflection of the measuring instrument.

Without the tuner, two measurements are required, one with and one without the reference air line in the

•Sanderson. A. E., "Calibration Techniques for One-and Two-Port Devices Using Coaxial Reference Air I.ines as Absolute Impedance Standards." 19th Annual ISA Conference and Exhibit. New York, Reprint No. 21, 6-8-64. (Available as Reprint No B21 from General Radio Company, West Concord. Massachusetts.)

Figure 5. a) Setup to measure '). b) Setup to measure

Figure 5. a) Setup to measure '). b) Setup to measure

system, as illustrated in Figure 5. (It is assumed that the reference air line is reflectionless and lossless and that the reflection coefficients of interest are small.) Thus

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