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Back in the early 1940’s Jonathan Dickinson State
Park was a top secret RADAR base. It was only active for a
few years but the work done here significantly assisted in winning
the war. Now that JD is this great state park we can still
see remnants of the base in some very out of the way location as
well as right along the road. I was chided last year
for making the names of my caches a little too generic and promised
this year to do a better job.
The cache is located along the paved bike trail in
the western portion of the park. The paved trail runs for a
mile along side the main road and then continues to the east and
finishes along the power lines. These trails while not paved
are in pretty good shape this year and are
rideable.
So get ready for RADAR 101.
This series of caches will give you a brief
overview of the different types of RADAR systems that are still in
use today.
Search radars scan a wide area with pulses
of short radio waves. They usually scan the area two to four times
a minute. The waves are usually less than a meter long. Ships and
planes are metal, and reflect radio waves. The radar measures the
distance to the reflector by measuring the time from emission of a
pulse to reception, and dividing by the speed of light. To be
accepted, the received pulse has to lie within a period of time
called the range gate. The radar determines the direction because
the short radio waves behave like a search light when emitted from
the reflector of the radar set's antenna.
Navigational radars resemble search radar,
but use very short waves that reflect from earth and stone. They
are common on commercial ships and long-distance commercial
aircraft. Marine radars are used by ships for collision avoidance
and navigation purposes. The frequency band of radar used on most
ships is x-band (9 GHz/3 cm), but s-band (3 GHz/10 cm) radar is
also installed on most ocean going ships to provide better
detection of ships in rough sea and heavy rain condition. Vessel
Traffic Centre also use marine radars (x or s band) for tracking
ARPA and provides collision avoidance or traffic regulation of
ships in the surveillance area.
General purpose radars" are increasingly being substituted for
pure navigational radars. These generally use navigational radar
frequencies, but modulate the pulse so the receiver can determine
the type of surface of the reflector. The best general-purpose
radars distinguish the rain of heavy storms, as well as land and
vehicles. Some can superimpose sonar and map data from GPS
position.
Air Traffic Control and
navigation
Air traffic control uses Primary and Secondary Radars. Primary
radars are a "classical" radar which reflects all kind of echoes,
including aircraft and clouds. Secondary radar emits pulses and
listens for special answer of digital data emitted by an Aircraft
Transponder as an answer. Transponders emit different kind of data
like a 4 octal ID (mode A), the onboard calculated altitude (mode
C) or the Call Sign (not the flight number) (mode S). Military use
transponders to establish the nationality and intention of an
aircraft, so that air defenses can identify possibly hostile radar
returns. This military system is called IFF (Identification Friend
or Foe).
• Air Traffic Control (ATC) Radars
• Secondary Surveillance Radar (SSR) (Airport Surveillance
Radar)
• Ground Control Approach (GCA) Radars
• Precision Approach Radar (PAR) Systems
• Distance Measuring Equipment (DME)
• Radio Beacons
• Radar Altimeter (RA) Systems. Radar altimeters measure an
aircraft's true height above ground.
• Terrain-Following Radar (TFR) Systems
Space and range instrumentation radar
systems
• Space (SP) Tracking Systems
• Range Instrumentation (RI) Systems
• Video Relay/Downlink Systems
• Space-Based Radar
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