Rain Bird Gold LINK 900, Руководство пользователя, Страница: 5 / 35

4
September 2015
3. Radio Basics
LINK900 wireless communication works by broadcasting radio waves to communicate between the central
control and field controllers. The LINK900 system uses custom designed Frequency Hopping Spread
Spectrum radios (FHSS).
Key Advantages:
-
No FCC license required for operation in USA.
- No antenna height restriction in most areas (check local regulations)
- Capability to use field controller radios as repeaters to relay the signal
- FHSS is highly resistant to narrowband interference
- FHSS is difficult to intercept
- FHSS can coexist in a frequency band with other broadcasts with minimal interference
Signal strength is measured in decibels (dB). Radios transmit with a certain amount of power (Wattage) and
signal reception is subject to loss of strength due to attenuation caused by impedance in the antenna
cables, fittings, and the atmosphere itself.
Radio transmission power is related to signal strength in the following manner:
- Reducing the output wattage by half reduces the signal strength by 3dB
- Doubling the output wattage increases the signal strength by 3dB
In Rain Bird
®
LINK900 wireless communications, no true electronic signal boost is provided after the radios.
Antennas can be used to shape or focus more of the transmitted signal energy into the areas targeted. This
signal increase is termed as “Gain”. An antenna with a “dB gain” value does not provide more power, but
rather it modifies the shape of the transmitted signal. The higher the antenna gain, the narrower the useful
signal beam width.
a) Antennas:
Rain Bird
®
LINK900 wireless communications uses two distinct types of vertically polarized
antennas. Omnidirectional and Directional (also known as Yagi).
Omni-directional:
This is the most common antenna used. Each Rain Bird
®
Golf LINK900 radio/modem/antenna kit
(H49008 & H49004) comes with this type of antenna. Different types of Omni-directional
antennas can be used on a LINK900 system.
Here are two examples:
Standard PAR+ES Omni “shot glass style” antenna, 3dB (GSP-TRA9023N)
High Gain 48” Omni antenna, 5dB (GSP-ODA-48)