DESCRIPTION OF ORLANDO TEST STATION 



129 



to both the load impedance and the impedance to 

 ground. However, if no ground connection is made, 

 the meter will read the load dissipation independent 

 of the degree of unbalance. 



The 2 or the A signal, depending upon the posi- 

 tion of the reversing switch, will appear across i? 3 , 

 which consists of a pad plus coil. Voltage and current 

 components are obtained in the same manner as in 

 the unbalanced case by short-circuiting R.^ and dis- 

 connecting /{,, respectively. 



In the latest model of this wattmeter, the system 

 can be changed from a balanced to an unbalanced 

 condition by a switch on the front panel. In actual 

 operations, four records are obtained on the chart 

 paper, 2, A, c, and i. Since the levels are recorded in 

 db vs 10 — 16 watt, the subtraction of a proper constant 

 from the recorded 2 level will give 2-/4w!« in db vs 

 1 watt. The same procedure and the constant are used 

 to obtain A in the latter units. When these two read- 

 ings are so converted, the difference between them 

 will be the power delivered to the load. Similar pro- 

 cedures are used to convert the voltage signal to db 

 vs 1 volt and the current signal to db vs 1 ampere. 



It can be shown that the errors in the readings of 

 the wattmeter are functions of the ratio me/ni and 

 three ranges of impedance have been incorporated to 

 keep these errors at a minimum. If the records of cur- 

 rent and voltage differ by more than some 8 db in a 

 particular region, their product will be in error as 

 the above ratio indicates. An impedance range should 

 be selected which brings the two signals closer to- 

 gether and thereby improves the accuracy of the 

 power reading. These changes are readily made by 

 means of a switch on the instrument. 



The only element affecting the frequency charac- 

 teristic of the wattmeter is the loss on the insertion of 

 the coil replacing R s . This will appear as a variation 

 with frequency of the conversion constants but this 

 effect over the range of 50 c to 150 kc is less than 0.4 

 db. 



This wattmeter is used over a power range of 0.001 

 to 1,500 watts and an impedance range of 15 to 800 

 ohms. The accuracy is on the order of 1 to 4 per cent 

 for phase angles up to 85 degrees. The accuracy be- 

 yond this angle has not been completely investigated 

 experimentally. 



Miscellaneous Equipment 



General laboratory apparatus is available at all 

 times for use with the circuits that are being devel- 



oped and the construction that is in progress. This 

 equipment includes decade condenser and resistance 

 boxes, attenuators, storage batteries, and moderate 

 stocks of fixed resistors, condensers, and inductors. 

 Various switches and vacuum tubes are available in 

 addition to transformers for power, signal frequen- 

 cies, and variable voltage. 



A modified Hallicrafters short-wave receiving set 

 is used as a voltmeter and a harmonic analyzer for 

 low-level signals at the higher frequencies (15 mc). It 

 also provides an excellent means for detecting stray 

 radiation. 



6.3 



6.3.1 



DESCRIPTION OF ORLANDO TEST 

 STATION 



Site of Station 



The Orlando station of USRL is located on Lake 

 Gem Mary about 4 miles southeast from the center of 

 Orlando, Florida. The lake is almost circular with a 

 diameter of some 300 yards, which is ample for cali- 

 brations, yet it is not so large as to have high waves in 

 windy weather. Typical of the lakes in this region, it 

 is fed from subterranean sources and has no surface 

 inlet or outlet streams. The depth of the lake varies 

 with the amount of rainfall. This variation in lake 

 level so seriously affects the calibration work that 

 remedial measures are necessary. A pump is installed 

 which draws water from an adjoining lake and auto- 

 matically maintains the water level within ±0.25 

 inches. The depths range from 15 to 18 feet under the 

 test pier, which extends about 130 feet from shore, to 

 33 feet at the barge location in the center. These 

 depths are satisfactory for testing purposes. The lake 

 bottom consists of sandy loam, except for the central 

 deep portion of soft mud. The acoustic absorption 

 of the loam, as determined by tests, is high and in- 

 creases with frequency. The reflected sound is 10 db 

 below the incident at 20 kc. 15 db at 30 kc, and 20 db 

 at 60 kc. 



6.3.2 



Facilities 



The Orlando station provides facilities for the free 

 field calibration of underwater sound devices in the 

 frequency range from about 15 c to 150 kc. One ob- 

 ject in setting up this station was to have a place 

 where tests could be made when the water at Moun- 

 tain Lakes is frozen. For this reason, outdoor facilities 

 were of most importance, since the indoor facilities of 



