orne set 
elapsed 
pulse is 
and the 
pulse is 
d to the 
)0 mega- 
fig. 2A) 
the air- 
)0 mega- 
magnetic 
quencies 
ig about 
: Shoran 
' interval 
n such a 
| interval 
ion of a 
s. There- 
93.1095 
h a pulse 
The tim- 
operates 
UE) 
ISLAND 
M 
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BAY 
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TAWA, ONT. 
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The pulse generators produce chains of 
short pulse signals, at a rate of 930 per 
second. One of the pulse generators sends 
its pulse directly to the radial deflexion 
electrode of the indicator tube. This pulse 
appears at a fixed position on the screen, 
since it remains in synchronization at a 
fixed phase relative to the sweep signal. 
This is the marker pip 'M' (fig. 2). The 
other pulse generator modulates the air- 
craft Shoran transmitter. This transmitted 
pulse triggers the ground Shoran station, 
and the returned pulse from the ground 
station 1s fed to the radial deflexion elec- 
trode. 
If the circuits feeding the pulse genera- 
tors are so arranged that the generators 
produce their pulses simultaneously, the 
marker pulse would arrive at the scope 
indicator some time earlier than the re- 
turned pulse. The pulses therefore would 
AIRBORNE SHORAN 
OSCILLATOR PULSE GENERATOR 
Y 
Y 
  
  
    
  
    
  
     
   
  
  
CALIBRATED 
VARIABLE PHASE 
ADVANCE 
  
  
Y 
  
  
PULSE GENERATOR 
  
INDICATOR 
GROUND SHORAN 
Figure 2: Basic Shoran equipment 
  
  
appear at different points along the indica- 
tor tube sweep. The distance between the 
two pulses on the screen is the distance the 
cathode ray spot was moved by its sweep 
voltage during the time that elapsed 
between the arrival of the marker and the 
returned pulses at the radial deflexion 
electrode. Therefore, it corresponds to the 
distance between the airborne and ground 
sets, plus certain fixed delays in the elec- 
tronic circuits. 
However, instead of thus measuring 
directly the distance between these pulses, 
a more accurate method is used. It consists 
of producing transmitted pulses sufficiently 
earlier than the corresponding marker 
pulses that a transmitted pulse returning 
from its ground station arrives in synchron- 
ization with the corresponding marker 
pulse at the indicator tube. The phase 
advancing is performed by the block label- 
led "Calibrated Variable Phase Advance" 
(fig. 2). It advances the phase of the sine 
wave signal fed to the generator of the 
transmitter pulse. À gearing ratio mech- 
anism coupled to the phase advance system 
  
  
Figure 2A: Shoran ground station