Wildlife Radio Direction Finding   using VHF or UHF CW / SSB receiver.

 

many of Wildlife study use Radio Beacon transmitter which send out pulse of 25 to 50 mS  every 500 to 1500 mS.  

at the receiver it sound like  Beep, Beep, Beep  ( click here to listen to how it sound like )

 

typical radio frequency used are 150 to 160 MHz, 216 to 220 MHz, 433 to 434 MHz.

in USA  FCC rule permit use of  40 MHz and 216 MHz band, but  216 MHz band is more practical for wildlife radio directional finding due to size of smaller directional antenna.

 

 

Typical Wildlife Crystal Oscillator radio transmitter weight 1 to 3 gram with battery  ( 150 to 433 MHz ), self Pulsing Crystal Oscillator circuit, frequency doubler circuit, frequency tripler circuit.

 ( click on figure for larger pictures )

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Another method of making less than 2 gram, 10 mm X 10 mm, wildlife tracking transmitter is to use Inverted Mesa Crystal rather than normal 3rd or 5th overtone crystal.

Over tone Crystal can oscillate up to 70 MHz for 3rd O.T. , 130 MHz for 5th O.T.

 

however, they still need to go through doubler or tripler stage to reach desired Frequency of 150 MHz, 216 MHz, 433 MHz

Inverted Mesa crystal can oscillate up to  315 MHz in fundamental mode. Therefore no need to use Frequency multiplier circuit. 

 

Which make it possible to use single stage Oscillator alone and can directly take RF output from oscillator circuit.

 

Inverted Mesa Crystal is available from  KYUSHU DENTSU CO LTD. (KDK) Nagasaki JAPAN

http://www.kdk-group.co.jp/01english/e_product.html#unit

 

Price of Crystal are around  $20 for QTY 500 , $10 for QTY 5000
This Oscillator produce

1mW ( RF output ) at 2.0V at 2.0mA ( 4.0 mW Input )
4mW ( RF output ) at 3.0V at 3.4mA ( 10.2 mW input )

Crystal size are small as  2.0 x 1.6 x 0.5 mm

 

This is Inverted Mesa Schematic used in this test.  ( click on figure for larger pictures )

 

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PCB Layout with parts value.  ( click on figure for larger pictures )

 

 

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Temperature Frequency variation chart.    ( click on figure for larger pictures )

Temperature test was done with 2.0 V DC input

Temperature characteristic of Inverted Mesa Oscillator can be compensated by using Negative Coefficient Capacitor, or Thermistor, or Microprocessor controlled.

 

 

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PC Board and actual Test Circuit used.

 

 ( click on figure for larger pictures )

 

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Difference between  Normal communication CW / SSB receiver  and Directional Finding CW /  SSB receivers.

 

normal CW / SSB receiver  are made to produce constant output audio , while input radio signal changes, using Automatic Gain Control circuit.

 

Directional Finding Receiver are similar construction CW/SSB receiver, except Gain are manually controlled, and by changing Manually gain of receiver ( mostly IF gain ) , User can adjust strong signal will not over load receiver and gain is sufficient to listen to weak signal to determine directionality of beacon transmitter by varying received signal strength by changing direction of directional receiver antenna.

 

Some of the Radio made for Amateur Radio can cover typical Wildlife Telemetry frequency, and can be used for tracking animals.

 

 

Yaesu FT-817 ND  --  cover 108.0-154.0 MHz, 420.0-470.0 MHz with CW/SSB mode.  It has RF Gain control , which is very useful for Radio Directional Finding.  Price is around US$ 680  ( should purchase optional CW filter YF-122C 500 Hz to avoid interference and noise. )

 

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Kenwood TH-D74A   --   cover 136.0-174.0 MHz, 216.0 to 260.0 MHz, 410.0-470.0 MHz with CW/SSB mode,  Unlike many other Amateur Radio Band Receiver cover 216 MHz band as general wide band scanner, this radio has dedicated receiver circuit to cover 216-260MHz band since it has transmitting capability from 222 to 225 MHz.  However, this radio do not have RF gain control, so it may be a little difficult to do radio directional finding when signal are very strong.  Price is around US$ 650

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If you have questions, or want me to design Wildlife Transmitter circuit, you can e-mail to me at :

 ( Please place in subject line , something like wildlife radio receiver or transmitter , so you help me  distinguish your good e-mail  from junk e-mail. )

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