90 TECHNICAL SURVEY 
useful for: 
1. Indicating blind areas in a station’s coverage. 
2. Assigning the operating area of a station. 
3. Checking the range and azimuth accuracy. 
4. Checking the transmitter output and receiver 
sensitivity. 
5. Estimating nonstandard propagation. 
6. Planning test flights. 
While methods used in different theaters vary as 
to detail, the typical permanent echo diagram is 
prepared about as follows. The equipment should 
be in normal operating condition: that is, the trans- 
mitter output and receiver sensitivity should be as 
recommended by the instruction manual; the range 
and azimuth calibrations should be accurate; and 
the weather conditions that affect propagation should 
be average. The receiver gain should be set to some 
standard level, usually maximum, or to some definite 
noise height. The value of the data taken will depend 
to a considerable extent on the skill and judgment 
of the operator. The station would normally be taken 
out of operation for about an hour while data are 
taken, although it is possible to take observations 
during normal scanning by stopping momentarily. 
Where antenna switching is provided, the low-angle, 
long-distanee beam should receive the most atten- 
tion although the other combinations should be 
checked also. 
If the beam is highly directive and can be changed 
in elevation, a low angle such as would be used for 
distant search should be used for recording perma- 
nent echoes. In some situations several elevations 
should be used. On plan position indicator [PPI] 
scopes it may be more convenient to photograph the 
screen if proper equipment is available. Care should 
be taken not to confuse storm and fog echoes with 
permanent echoes on microwave sets. 
A more detailed procedure is required where A- 
scope presentation is used. After the initial adjust- 
ments have been made the next step is to decide on 
MOUNTAIN 
ECHO 
Figure 35. Permanent echo diagram. 
