The oscillator frequency determining elements and the 

 bridge driver tank circuits are fixed-tuned and should 

 require no attention . Should the frequencies of a number 

 of these units be very different, it may not be possible to 

 synchronize the oscillators. Should this problem arise, 

 each of the oscillators should be set reasonably close to a 

 10-kc secondary frequency standard. 



Phasing of the unit is accomplished by a slight variation 

 in the tuning of the bridge output. This is a broad adjust- 

 ment and is not overly critical . The phasing adjustment should 

 be made for maximum output with a slight capacitive unbalance 

 in the bridge circuit. 



The bridge DRIVE (and injected carrier) is adjustable by 

 means of a deck-mounted potentiometer . This control is used 

 as a rough sensitivity control, with the front panel 

 PINE SENSITIVITY control being effective over a range of 

 about 10 percent of full scale. With the FINE SENSITIVITY 

 control at about midposition, the DRIVE control on the deck 

 should be adjusted until the full-scale deflection of the 

 recording stylus is satisfactory for the use intended. An 

 approximate full-scale signal may be secured by balancing the 

 bridge, setting the SENSITIVITY control to the 4-ineh-full- 

 scale step, then rotating the 0-0.001 ROUGH CAP. BALANCE 

 control one step in either direction. This adds or subtracts 

 100 u.uf in the gage arm, corresponding to approximately 

 2 inches change in the water level. 



The CAL„ ADJ. allows the calibration step to be adjusted 

 over a narrow range. It is intended that the calibration 

 step be full scale on the 4-inch full-scale SENSITIVITY 

 step. The CAL. ADJ. control should be adjusted until the 

 calibration step corresponds to a 2-inch change in submersion 

 of the gage while on the 4-inch full-scale SENSITIVITY step. 



In order to facilitate bench work on these units, the 

 bridge components are chosen so that the unit may be balanced 

 with no gage or cable connected. In operation, more than 

 100 feet of RG 62/u coaxial cable can be used, as the system 

 will balance with more than 4000 u.u.f of external capacity. 



BALANCING UNIT 



When it is desired to record wave heights from two 

 gages with the same wave-height recorder, a TMB Type 286-2A 

 Balancing Unit may be used to couple the two gages to the 

 single recording unit, and the recorder may then be switched 

 to either of the gages. The internal bridge balancing system 



