From the USGS at http://www.npwrc.usgs.gov/resource/2002/radiotrk/convent.htm

Transmitters. — Each radio transmitter consists of electronic parts and circuitry, usually including a quartz crystal tuned to a specific frequency. Crystals come in different degrees of shock-resistance, and for animals such as wolves that lead aggressive lifestyles, high-shock resistant crystals are usually used.

Signals can be either continuous, which sounds through a speaker like a high-pitched whine, or pulsed, which sounds like a series of "beeps." Pulsed signals are usually used at rates of 30-120 per minute. Lower pulse rates yield longer transmitter life. Pulse widths can also vary, with 18 milliseconds being the minimum that is easily tracked. The narrower the pulse, the longer the life.

Transmitting Frequency. — Frequencies used in wildlife telemetry usually range from 27 MHz to 401 MHz. VHF transmitters typically give a ground-to-ground range of 5-10 km which is increased to 15-25 km when received aerially (Rodgers et al. 1996). Lower frequencies propagate farther than higher frequencies since they reflect less when traveling through dense vegetation or varying terrain (Cederlund et al.1979; Mech 1983). However, lower-frequency signals (e.g., 32 MHz) consist of longer wavelengths, which increase the size of the transmitting and receiving antennas necessary for detecting them. This has implications for feasibility and receiver portability (see below).

The commonest frequency ranges used for VHF tracking are 148-152 MHz, 163-165 MHz, and 216-220 MHz. The higher frequencies bounce more (e.g. off mountains) but have the advantage of requiring smaller antennas. Whatever frequency is selected, individual transmitters are usually tuned 10 KHz apart to allow distinctiveness despite signal drift (1-2 KHz) due to temperature and battery fluctuations (Mech 1983).

[Code of Federal Regulations]
[Title 47, Volume 1, Parts 0 to 19]
[Revised as of October 1, 1998]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR5.108]

[Page 599]
 
                       TITLE 47--TELECOMMUNICATION
 
            CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION
 
PART 5--EXPERIMENTAL RADIO SERVICES (OTHER THAN BROADCAST)--Table of Contents
 
                     Subpart C--Technical Standards
 
Sec. 5.108  Wildlife tracking and ocean buoy tracking operations.

    Except as provided in Secs. 5.101, 5.102, 5.103 and 5.106, the use 
of frequencies in the bands 40.66-40.70 MHz and 216-220 MHz for the 
tracking of and telemetry of scientific data from ocean buoys and animal 
wildlife are subject to the following conditions:
    (a) All transmitters used at stations first licensed after February 
18, 1975, shall comply with the technical requirements in paragraph (b) 
of this section and shall be verified as provided in Sec. 5.109.
    (b) Technical requirements for transmitters used for these 
operations are as follows:
    (1) In the 40.66-40.70 MHz frequency band, the bandwidth required 
for frequency tolerance plus the occupied bandwidth of any emissions 
must be adjusted so as to be confined within this band, except as 
permitted by paragraph (b)(6) of this section.
    (2) In the 216-220 MHz frequency band, the carrier frequency shall 
be maintained within 0.005 percent of the assigned frequency.
    (3) Classes of emission will be limited to A0, A1, A2, F1, F2 and/or 
F9.
    (4) Occupied bandwith shall not exceed 1 kHz.
    (5) The maximum carrier power shall not exceed 1 milliwatt for 
airborne wildlife applications, 10 milliwatts for terrestrial wildlife 
applications and 100 milliwatts for ocean buoys.
    (6) The mean power of emissions shall be attenuated below the mean 
output power of the transmitter in accordance with the schedule shown in 
Sec. 5.103(b) of this subpart.

[40 FR 2814, Jan. 16, 1975; 40 FR 6474, Feb. 12, 1975; 48 FR 52738, Nov. 
22, 1983; 63 FR 36602, July 7, 1998]

    Effective Date Note: At 63 FR 36602, July 7, 1998, in Sec. 5.108, 
paragraph (a) was amended by removing the term type accepted and adding 
in its place verified, effective Oct. 5, 1998.