A simple system for locating satellite-received transmitters (PTTs) in the field
The system gradually emerged during the African odysey  project (launched 1995,  http://www.rozhlas.cz/odysea/angl ), which tracked black storks (Ciconia nigra) on their autumn migration from Europe and then on their wintering grounds in sub-Saharan Africa. 
The system was first used to directly monitor free-flying Houbara bustards  (Chlamydotis undulata) in 1999 in Morocco (Peske 2000). 

PTT locating system
PTT locating scheme Schema of the rotating antenna system & data evaluation

Designed for a laptop with mono sound card input.

SignalPTT 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 Flags are additional signals induced by the rotating antenna that:

- delimit each full rotation of the mast

- enable estimate true antenna orientation

Record Whole record

Rotation starts few seconds before the expected PTT transmission and it ends just after it
(in this case it lasted 12 sec when each rotation induced one vertical flag)

PTT signal can be recognized, selected and analyzed even if it barely exceeds background noise.

Signals 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)

Limited signals PTT An adequate level of PTT signal is important

Strong signals must be attenuated because they are up-limited either in the receiver (above) or in the audio card (below).

diagram 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.

Main elements used

rotating connector 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.
(Central spindle of the rotating part is toughen with a syringe needle.)

mixer 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).

H antenna Antenna HB9CV

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:
front element=34
rear element=37
distance between elements (boom length)=9