Specifications

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the application to the FCC. In addition you may wish to use a consultant to handle the details and type the
forms. We used Josie Lynch, of Professional Licensing Consultants, Inc. (see page 9).
Before seeking a license you will need to know the emissions characteristic of your transmitter (see data
section, page 8) and the latitude, longitude, elevation, and planned antenna height of your base station.
VHF. Frequency bands of 129 to 174 MHz and 220 to 222 MHz are often used for data transmission. These
lower frequencies do not require line-of-sight paths, but the antennas are larger and more expensive.
UHF. The frequency band of 450 to 470 MHz is often used for agricultural and industrial data transmission.
Older radio types use a crystal to set the carrier frequency, so the frequency must be known at the time the
radio is ordered. Newer radios often use a synthesized frequency, so radios can be shipped off-the-shelf and
frequencies can be set through the data I/O port by a computer at any time.
The radio modem/transceiver recommended by Davis is the RF Neulink 9600 operating in the 450 to 470
MHz band. Davis supplies two Antenna Kits, each of which includes an antenna and all necessary cables,
connectors, and mounting hardware, plus a power supply and a programming disk for setting the frequency
and other characteristics. One Kit includes a 2 dB omni antenna and one a 10 dB directional antenna.
The range of the Neulink 9600 is typically up to 25 miles, depending on terrain and antenna height and type.
The range can be extended by installing a Neulink 9600 in repeater mode. It should be ordered in this
configuration from RF Neulink; Davis software does not support configuring of repeaters.
In some circumstances RF radiation from the Neulink’s omni-directional antenna can affect the weather
station’s measurement of temperature and barometric pressure. If data are being averaged over an interval
that is long with respect to the duration of radio transmission from the station, the effects will be negligible.
If radio transmission is continuous (as in the case of displaying the Bulletin), the data may be affected. In
this case it may be necessary to raise the antenna to a height of three feet (1m) or so above the console or 1.5
feet (0,5m) above the Sensor Mounting arm (mast-mount hardware is included in the Antenna Kit), or in
some other way place it at a distance from the station (see Site and System Configuration section). An
Industrial weather station has better immunity to such RF noise than does a Standard station.
ANTENNAS
In selecting antennas the principal considerations are transmission distance (range) and whether an omni-
directional or directional type is needed.
ANTENNA GAIN
An antenna’s “gain” is a measure of its ability to focus its transmitting energy and its receiving sensitivity.
Gain is measured in terms of decibels (dB), the logarithm of the factor of increase; every 6 dB added to the
total of antenna gains at both ends doubles the transmission distance (if factors such as antenna height and
propagation path characteristics permit).
OMNI-DIRECTIONAL ANTENNAS
As the name implies, an omni-directional antenna transmits and receives signals in all directions (in the
horizontal plane). Its usual form is essentially a vertical wire. If the station is a Base Station which must
communicate with Remote or Field Stations located in different directions, its antenna probably should be
omni-directional.
Omni (or “whip”) antennas tend to be lower in cost, have lower gain (lower range), and be more compact --
less subject to damage by vandalism, ice, and wind. They do not need to be aimed.
DIRECTIONAL ANTENNAS
Directional antennas focus their transmitting energy and receiving sensitivity in one direction. This can have
two benefits: the effective range is longer, and the receiving antenna is less sensitive to interference coming