The cache is no longer located near the building in question as there have been a few issues in the past with cachers driving to the cache location or climbing fences. If you are interested in the building please walk
to waypoint "VORGRZ".Please bring your own pen!
It's not necessary to climb over
People who are just interested in a quick found-point can stop
I told you to stop reading!!
Anyway.. on a field a bit south of the main runway of the airport
you'll find a rather unimpressive
building. No high fences, no barbed wire.. just a white sign
bearing the logo of AustroControl - the company responsible for
managing Austrian air traffic - and a note that this building is
used for air traffic safety purposes.
But what's the purpose of this building and what makes it a bit
more interesting than the usual buildings found on nearby fields?
(Okay, maybe the antenna with the red lights.. but did I mention
the ammunition depots of the Austrian military northeast of this
location that aren't all that usual as well? - "Pulverturmstrasse",
nomen est omen)
The "code name" of this special building is "VOR-DME GRZ" - short
for "VHF Omni-directional Radio Range (with Distance measuring
equipment)", but just describing it as a "radio beacon" might make
things a bit more clear.
Still, what does this have to do with "birds in the sky"?
Well, contrary to geocachers airplane pilots are usually not
relying on GPS signals for determinating their position but on
measurements based on radio signals sent from ground stations.
These stations are commonly referred to as navigational aids, short
"navaids" (also in nautical travel). There are basically two
different types of ground stations used for this purpose,
non-directional beacons (NDB) and VOR.
is more or less an antenna that periodically sends a
radio signal together with a morse code. An automatic direction
finder (ADF) is then used on board of the plane to display the
bearing towards the NDB.VOR
s are much like NDBs, but also include a directional
amplitude-modulated signal that rotates 30 times per second. Older
systems really used a rotating antenna for this purpose while
current systems can do that electronically without any moving
parts. VORs are much more reliable and accurate that NDBs. When
receiving signals of two VOR it's possible to determine an exact
position (cross bearing). That's where the third acronym comes into
play - DME
, distance measuring equipment. An aircraft sends
a series of pulse-pairs towards the DME which replies after a short
delay. After locking in on the signal exact runtime measurements
are possible which can be used to calculate the distance between
the aircraft and the DME.
With VOR and DME a single ground station is enough for position
In Austria there are 17 NDB and 11 VOR-DME stations. Graz has both
a NDB (290kHz; at approx. N46°55.233 E015°27.533) and a VOR
(116.2MHz). The next NDB is at Gleichenberg (GBG; 426kHz).
Of course both VOR and NDB are marked on flight charts and also
used during approach together with several other interesting
Oh, and even if you're not interested in technology: Maybe you'll
also spot some deer (see header picture) or wild rabbits near the
location. It would be quite nice if the motorway wouldn't be that
Corrections are welcome.