|A simple system for locating satellite-received transmitters (PTTs) in the field|
The system was first used to directly monitor free-flying Houbara bustards (Chlamydotis undulata) in 1999 in Morocco (Peske 2000).
|Schema of the rotating antenna system &
Designed for a laptop with mono sound card input.
|PTT signal have rectangular envelope
This signal can be monitored by a SSB receiver and evaluated in CoolEdit2000
(signal length 0.36 sec, "sensor data" form slightly irregular edges in its second half)
|Flags are additional signals induced by the rotating antenna that:
- delimit each full rotation of the mast
- enable estimate true antenna orientation
Rotation starts few seconds before the expected PTT transmission and it ends just after it
PTT signal can be recognized, selected and analyzed even if it barely exceeds background noise.
|PTT signal is ideally recorded a period in which antenna rotates 2-3 times
above - low signal only slightly above backgound noise
below - good signal
(both showing clear maximum about 1/4 of a mast rotation after induction of the flag)
|An adequate level of PTT signal is
Strong signals must be attenuated because they are up-limited either in the receiver (above) or in the audio card (below).
|Excel radial graph of a signal recorded during one rotation of the antenna is identical to an antenna radiation pattern
Note good front-to-back ratio typical for H antennas, clear maximum and side minima.
Flags (always "up") enable geographical orientation.
|Rotating connector - crucial element ?HOW TO MAKE IT?
Commertially available connectors are difficult to find and expensive.
This combination of commonly available F-couplings is an effective substitution.
|Mixer of signals for a mono-input of laptop. ?HOW TO MAKE IT?
With this simple double-emplifier one can hear PTT messages and balance levels of flags (serial condensers) and PTT audio signals (pot).
This antenna has excellent operational parameters: small size, good gain and front-to-back ratio.
It is directional even if dimensions are far from theoretically ideal.
Dimensions (in cm) for 401 MHz: