66 OCEAN ELECTRONIC NAVIGATIONAL AIDS 



Puhe Repetition Rates. — Basic 20 (S), 25 (L) , and SSVs (H) pulses per second. 

 Associated with each basic rate are to be eight specific rates of which the 

 basic rate is one. The seven other specific rates are to be obtained by reduc- 

 ing the recurrence interval in steps of 100 microseconds. The specific rates 

 are to be labeled "0" to "7", starting with the one having the longest interval 

 (the basic rate). Example — ^Basic rate 25: 



Rate Cycles Microseconds 



25 40,000 



1 25Vi6 39,900 



2 251/8 39,800 



3 25%6 39,700 



Time Difference /Measuring Ronges. — Overlap the following limiting Values: 

 For basic rate: Microseconds 



20 500 to 17,000 



25 500 to 15,000 



331/3 500 to 11,000 



Time-Difference Accorocy. — With Signals Of equal strength over a temperature 

 range of —15° to +50° C. the accuracy of the time-difference measurement 

 shall be within plus or minus 1 microsecond. With a signal input up to 10 

 volts (peak) and signals differing in strength as much as 1,000 to 1, the time- 

 difference reading shall not vary more than 1 microsecond from the reading 

 with equal signals. 



Time Difference Presentation. — Direct reading by mechanical numerical meter. 

 The mechanical electrical coupling between the meter and time delay circuits 

 must be stable and simple to adjust for accurate prealignment. 



Cathode Ray Oscilloscope. — Three inch or larger screen. 



Timer Oscillator. — The timer oscillator shall have sufficient short-time sta- 

 bility to permit satisfactory use of the receiver indicator. Frequency varia- 

 tion for temperature excursion of — 15° to plus 50° C. and variation in relative 

 humidity of 15 to 95 percent shall not exceed 500 parts per million; and for 

 correction of such variation a control whose range slightly exceeds the amount 

 of variation shall be provided. 



Framing {Left-Right) Switch. — The framing switch for positioning the received 

 pulses on the indicator CRT screen shall provide suitable drift. 



If fixed drift speeds are employed a satisfactory speed for the slow sweep 

 is that equivalent to twice the difference beween two specific recurrence rates 

 (4,000, 5,000, and 6,666% microseconds corresponding to 20, 25, and 33^/3 

 pulses per second), while a drift speed of the order of 100 microseconds per 

 second is suitable for the faster sweep speeds. 



Pulse Height and Saturation. — The standard pulse height for the pulse matching 

 operation (fast sweep) shall be approximately 1^2 inches for a 5-inch CRT 

 screen and approximately 1 inch on a 3-inch CRT screen. It is desirable that 

 suflBcient additional output shall be available from the video-amplifier to show 

 a small degree of amplifier saturation on the screen on fast sweep. 



Horizontal Sweep. — The horizontal sweep shall be reasonably linear. The 

 approximate time lengths shall be as follows: 



Slow sweep V2 recurrence rate period. 



Intermediate sweep 1,000 to 1500 microseconds. 



Fast sweep 120 to 200 microseconds. 



Power Supply. — Power-input for 50/60 cycles, 115 volts plus or minus 10 per- 

 cent, consumption not to exceed 400 watts. 



Note. — Aircraft Loran receiving equipment should meet the minimum re- 

 quirements specified for marine Loran receiving equipment. The aircraft 

 gear differs in package size, weight, and power supply. It is important that 

 such equipment be designed in accordance with standard practice for elec- 

 tronic equipment intended for aircraft installation. 



