JOURNALTECHNICAL INFORMATION from the -Hp- LABORATORIES VOL

HEWLETT PACKARD

JOURNALTECHNICAL INFORMATION FROM THE -hp- LABORATORIES VOL. 2. No. 7-8

Power Measurements from 10 to 12,400 Megacycles

T HIGH frequencies, instruments for set-up for signal generator standardization is 0 A measuring power have wide usefulness. shown in Figure 1. The signal generator is This usefulness is based on the fact that meas- connected through a length of coaxial cable urements of h-f power can be made with to a bolometer mount where the output good accuracy and have more significance power from the generator is absorbed. With than measurements of h-f voltage or current. present-day signal generators that have a To provide more complete coverage in the source impedance reasonably well matched -hp- line of power-measuring equipment, a to the line impedance, this measurement can number of new devices have been added to be made on the basis of maximum available the basic group of power-measuring instru- power with an untuned bolometer mount. If ments described in the May, 1950 issue’. The the source impedance is unknown and a complete line now includes power-measur- measurement of maximum available power ing equipment for use over the range from 10 is desired, a stub tuner can -be used to trans- to 12,400 mc. form the load impedance to the conjugate of Power measurements have many practical the generator impedance. If the measure- h-f applications. For example, in the labora- ment is desired in terms of a “flat” load, a tory it is often necessary to standardize the slotted section can be inserted into the trans- output power from signal generators. By use mission line and the load tuned so that no of the power meter and suitable bolometer reflection occurs. mounts, such standardization becomes a sim- The basic range of power measurements ple and straightforward process. A typical with the -hp- Model 430 power meter is from il less than 50 microwatts to 10 milliwatts, a very useful range for most signal generator applications. However, this range can be easily extended upward for higher power measurements. For example, lossy type coaxial cables can be used as attenuators at frequencies up to the UHF region, where the losses of standard cables may be high enough for a given application. In waveguide systems, powers in the range from 1 to 2 watts can be attenuated to the range of the Figure 1. Set-up for standardizing signal generator outpiit pou,er nsirzg - new -hp- Model 476A broud-burid bolometer rnotittt ‘B. P. Hand, Direct Reading UHF Power Measuremenis, and new Model 430B power meter. Hewlett-Packard Journal, Vol. 1, No. 9, May, 1950.

WWW.HPARCHIVE.COM tance caused by this heating effect. mal variations in its characteristics H-f power can also be measured with do not introduce errors into the bridge substitution techniques, sev- measurements. Also, when using eral methods being in use. In general, thermistors with long thermal time the bolometer element is connected constants, the measurements are not into a bridge circuit and the h-f slowed by the necessity for waiting power to be measured is applied to for stabilization of the thermistor re- Figure 2. New -hp Model 476A 10-1000 mc udmed bolometer mount. the bolometer element. Enough d-c sistance when h-f power is applied power is then applied to the element or changed. power meter by the use of fixed pre- to bring its resistance to the value The -hp- Model 430A Power cision attenuators. A group of such that balances the bridge. Next, the Meter, introduced in 1948, was de- attenuators has been developed as h-f power is removed and low-fre- veloped on the self-balancing prin- part of the new equipments added to quency power is substituted in its ciple and was designed for the meas- the -hp- power-measuring line. The place and adjusted in magnitude urement of c-w power with the use frequency range and insertion loss of until the bridge is again balanced. of a fuse or barretter. Since the in- these attenuators, Model 370, is The low-frequency power is then troduction of the 430A, many custo- shown in the accompanying table. equal to the h-f power that was ap- mers have requested a similar instru- Powers above the 1 to 2 watt plied in the beginning. Since the ment that could be used to measure range can be measured by the power operating resistance of the bolometer pulsed power. Such an instrument meter in combination with direc- element is known, the applied low- has now been designed and assigned tional couplers. In this case the wave- frequency power can be measured the model number 430B. The new guide is terminated with a high- with a voltmeter or ammeter cali- Model 430B can measure either con- power termination such as the -hp brated in power units. tinuous or pulsed power and oper- Model 912A which is suitable for All of these hand-balancing meth- ates with fuses, barretters or ther- powers up to 250 watts in the larger ods are tedious and somewhat diffi- mistors of 100- or 200-ohm value. size waveguide and 100 watts in the cult. As a result, there has come into The power-measuring range of the smaller size. At power levels higher wide use a somewhat different meth- new 430B is the same as that of the than thia, water loads can be used for od,the self-balancing type of bridge. 430A, 0.1 milliwatt full scale to 10 terminations and a combination of In this circuit the measurements are milliwatts full scale in five ranges. directional couplers with attenuators made automatically and the tedious First production units of the 430B used to sample and reduce the power hand-substitution of power is not are expected to be. available some to the range of the power meter. necessary. The action of the circuit is time after mid-summer. For measurements of c-w power, such that the bridge is always auto- The d-c biasing power range avail- the power meter can be used with a matically balanced, a feature that of- able from the Model 430B provides platinum-wire type bolometer ele- fers several advantages in practical for operating barretters that have a ment, but for pulsed power applica- measurements. For example, no re- 200-ohm value at a nominal level of tions the thermal time constant of liance is placed on the characteristics 15.3 mw and for operating therm- this device is such as to prevent di- of the bolometer element so that nor- istors that have a 100-ohm value at rect-reading measurements. In pulse MENT Fop USE WJTH ~- appiiofttioas, tkre€ore, it is cwwin- 99&ulk~- ary to use the bead thermistor which Frequency 6,10,20 OB High has a time constant suitable for most Type of Detector Range Fixed Power Mount pulse rates. Systam Attenuator Terminotion The use of bolometer elements in 476A3 h-f power measurements is based 10-1OOo coaxial on coaxial 475B1 the assumed ability of such elements 2600-3950 waveguide S485A6 S370A, B, C5 S912A to absorb power equally well at both 3950-5850 waveguide G485B4 G370A, B, C? high and low frequencies. The power 5850-8200 waveguide J485B4 J370A, B, C5 absorbed by the elements is convert- 705 0- 10,OOO waveguide H485B4 H370A, B, c' X912A ed to heat, which changes the resis- 8200-12,400 waveguide X485B4 X370A, B, Cj tance of the element. I 'For use with ZOO-ohm fuse or barrener. The magnitude of the absorbed aFor u5e with 100- or ZOO-ohm fuse, barretter or thermistor. 850-ohm mount. uses 200-ohm fuses. h-f power can be determined by 'For use with 2d0-obm barretter or crystal. %&fixes A B C signify 6 10 20 DB, respectively. measuring the change in the resis- 6For use wh'ZOO-ohm b&r&er.

WWW. H PARCHIVE.COM The most practical sf these devices is the double-stub tuoer. By special 0

mamiy 50 ohms so

lOLOMETER MOUNTS coaxial transmi to make h-f power parallel circuit arranged to appear ent is connected as a termin- as 200 ohms to the

tl circuit. The match 0:

quired. iuad for 5hhm circuits. In coaxial systems several types of e device an be used as a load fa5&ohm a double-stub tuner. f

Such mounts can be

tion and shunt suseeptances in a &om exceed 0.2 db. If the source im- combination such that pedance is closely matched to 50 line is terminated ohm circuit. ohms, the err= int To aid La dngpower measure- Model 476A will -

M.HPARC H IVE.COM WAVEGUIDE MOUNTS megacycles. In this mount, a fixed losses. When barretters are used, the Waveguide mounts are usually de- quarter-wave matching section is lo- mounts provide a good match for signed so that the bolometer element cated behind the bolometer element. waveguide systems and in general extends between the wider surfaces By compensation of this section, it their VSWR is less than 1.5 over of the guide. One terminal of the has been possible to achieve a low their rated frequency range. If a element is brought out through the VSWR for the mount and dispose of completely “flat” line is desired in wall of the guide in such a manner the need for hand-tuning to achieve these applications, the mount can be that d-c or low-frequency biasing best match. The mount is designed preceded by a slide-screw or E-H power can be applied to the element. for use only with 200-ohm barretters tuner. A quarter-wave shorting section is and hasa VSWR of less than 1.3 over These waveguide mounts, as well located in back of the bolometer ele- its rated frequency range. as the coaxial mounts, can all be used ment to aid in achieving maximum The remaining four mounts in the with either the Model 430A or the absorption of the power flowing series are the Models G485B, J485B, new Model 430B power meter to down the guide. H485B, and X485B, corresponding make power measurements over the e As part of the -hp- waveguide pro- to the -hp- G, I, H and X sizes of range from less than 50 microwatts gram announced earlier this year, a waveguide. These mounts can be to 10 milliwatts, or to higher powers series of waveguide bolometer used with either barretters or silicon with attenuators and directional mounts has been designed for the crystals such as the 1N21B or 1N23. couplers. In addition to the above- frequency range from 2600 to 12,400 The mounts are tunable and consid- described waveguide bolometer megacycles. The first of the series, erable care has been taken in their mounts, a series of thermistor the Model S485A, is designed for use design and construction to prevent mounts will be available about mid- with 3” x lr waveguide over the “holes” or other undesirable operat- summer. -B. P. Had ad frequency range from 2600 to 3950 ing conditions due to tuning plunger N. B. Schrock

MODEL 370A, B, C MODEL 4908 MODEL S48SA 6, 10, 20 DB MICROWAVE POWER METER UNTUNED DETECTOR MOUNT FIXED ATTENUATORS POWER RANGEI Full xole rendings of 0.1, WAVEGUIDE SIZE: For use with 3” x 1%“ Models ore provided in fixed volues of 6, 10 0.3, 1, 3, and 10 milliwatts. Also cnlibroted woveguide. or 20 db; suffixes A, 8, C after model numbe; in db to give continuous rending from -20 signify units for 6, 10, or 20 db respectively. dbm to +IO dbm (0 dbm = 1 mw). Power RECOMMENDED FREQUENCY RANGE, 2600 to range con be extended with ottenuntors or WAVEGUIDE SIZES: directional couplers. 3950 mc. Model 5370: 3”x1%” (2.6-3.95 kmc) Model G370: 2”xl” (3.95-5.85 kmc) EXTERNAL BOLOMETER: Either barretters or DETECTOR ELEMENT: Designed for use with Model J370: 11/z”x%” (5.85-8.2 kmc) thermistors con be used. Suitable bnrretters 200-ohm borretter. (Borretter not included.) Model H370: 11/4”x%” (7.05-10.0 kmc) ore certoin l/lW-ampere instrument fuses Model X370: l”x2“ (8.2-12.4 kmc) pr Sperry 821 bnrretters suitable thermistor VSWR: Less than 1.3 over recommended fre- Model P370: .702”x.391” (12.4-18 kmc) is W.E. Dl66382 type. Bnrrettor should quency mnge. hove resistonce of 200 ohms at approx. ACCURACY: Attenuation set within 0.2 db ot 15 mw. Thermistors con be operated at INPUT FLANGE: Ploh cover tlonge’of UG- colibrotion frequency. Cnlibrotion frequen- either 100 or 200 ohms. Thermistor resis- 53/U type. cies ore 3, 4.5, 7, 8.6, 10 and 15 kmc (each tonce should be 100 ohms ot opprox. 14 model colibroted at approprinte frequency). mw or 200 ohms at npprox. 9 mw. Therm- OUTPUT CONNECTOR: Type BNC iock. VSWR: Approx. 1.15 moximum over fre- istors con not be operated ot 200-ohm level quency ronge shown following above on 10 mw ronge. PRICE: $125.00 f.0.b. Polo Alto, Cnlifornio woveguide sizes. FREQUENCY RANGE: Determined by bolo- MAXIMUM DISSIPATION: Approx. 1 wott meter mount. (Not supplied.) e overoge, 1 kw peok. ACCURACY: Within 5% of full scale value. PRICE: Model 5370: $75.00 DIMENSIONS: 12” wide, 9” deep, 9“ high. Model G370: $65.00 WEIGHT: 19 Ibs.; shipping weight, 32 Ibs. MODEL 0, 1, H, X485B Model J370: $65.00 POWER: Operotes from nominol 115-volt, TUNED DETECTOR MOUNTS Model H370: $60.00 50/60 cycle source. Requires 75 wotts. WAVEGUIDE SIZES: Model X370; $55.00 CABLES SUPPLIED: 7‘ 6” power coble per- Model P370: $60.00 monently attached; 3‘ input coble consist- Model G4853, 2”xl”; 3.95-5.85 kmc. Prices f.0.b. Polo Alto, Colifornio. ing of shielded coble with one end free; Model J4858, l1/2”x3/4”; 5.85-8.20 kmc. other end has type BNC plug (UG-88/U) to Model H4858, 11/4”x5/8”; 7.05-10.0 kmc. e mate with UG-lBJ/U input jock on 430 Model X4858, l”x1/2“; 8.20-12.4 kmc. ponel. MODEL 4761). Price upon request DETECTOR ELEMENT: 200-ohm Borretter or e silicon crystal of 1N21 type. (Element not UNTUNED BOLOMETER MOUNT MODEL 912A provided.) NOMINAL FREQUENCY RANGE: 10 - 1000 mc. HIGH POWER TERMINATIONS VSWR: Can be tuned to give less than 1.5 POWER RANGE: 10 mw mox. with -hp- WAVEGUIDE SIZES: VS‘NR with barretter over recommended Model 430. 80 mw moximum power input. Model 5912A: 3‘xlVz” (2.6-3.55 kmc) frequency ronge. VSWR: 1.15 maximum from 20 to 500 mc; Model X912A: 1”x’h” (8.2-12.4 kmc) INPUT FLANGE: Plaln cover tlonges ore pro- 1.25 maximum from 10 to 1000 mc. DISSIPATION: S912A. 250 watts overoge, vided. CONNECTORS: RF input, type N jock (UG- 100 kw peak; X912A. 100 watts overage 23/U); power meter input, type BNC iack 50 kw peak. Forced air cooling must b6 OUTPUT CONNECTOR: Type BNC iock. (UG-625N). used when units are being operoted obo\o 50% of rated power. BOLOMETER ELEMENTS: Four selected 1/lo0 PRICE: Model G485B: $95.00 VSWR: 1.1 Max;mum. 0 ampere instrument fuses. (included) Model J4B58: $90.00 DIMENSIONS: 5” Ig, 1%“ diom. PRICE: Model 5912A: $125.00 Model H485a: $85.00 Model X912A: $75.00 SHIPPING WEIGHT: 2 Ibs. Model X4858: $75.00 PRICE: $125.00 f.0.b. Polo Alto, Colifornio Doto subiect to chonge without notice All prices f.0.b. Palo Alto, Colifornio.