ESTeem 195C, Руководство пользователя, Страница: 41 / 75

CHAPTER 7
ANTENNA SETUPS
Revised: 15 Feb 2017 7-1 ESTeem Models 195MHC
ESTeem offers different types of antennas ranging from ¼ wave to 5/8 wave in physical size. The user choice is dependent on
the application.
Communications in the VHF and UHF bands are normally over "Line of Sight (LOS)" . Looking from the antenna of one wireless
modem you must be able to see the antenna of the wireless modem you wish to communicate with. If a large object obstructs
the line of sight view it is unlikely that satisfactory communications will result. This means you must relocate the antennas or use
the repeating freature and a second modem to go over or around the object.
The Model 195C, 195M and 195H products are allowed by the FCC to use high gain directional antennas.
It is noted that a ¼ wave antenna that does not have ground plane radials requires a ground plane to operate at maximum
efficiency. This can simply be a conducting surface under the antenna that is a ¼ wavelength in diameter. For the Model 195C
(450 ‐ 470 MHz) this is approximately 6.5 inches. A conducting surface can be anything from the rooftop of an automobile to a
file cabinet.
Coax Cables
To minimize signal loss, the overall length of the coaxial cable should be as short as possible. To avoid corrosion select coaxial
cable manufacturers with tinned copper braid, where possible. Listed below are representative cable losses in db/100ft at the
VHF and UHF frequencies:
Frequency
(MHz) RG ‐ 58u LMR 195
RG ‐ 8
(solid)
LMR600 1/2" Heliax
150 ‐ 174 ‐ 3.8 ‐ 4.4 ‐ 1.2 ‐ 0.964 ‐ 0.88
217 ‐ 220 ‐ 5.4 ‐ 5.4 ‐ 1.7 ‐ 1.4 ‐ 0.95
402 ‐ 420 ‐ 7.9 ‐ 7.8 ‐ 2.4 ‐ 1.72 ‐ 1.36
450 ‐ 470 ‐ 9 ‐ 7.8 ‐ 3 ‐ 1.72 ‐ 1.45
In a severe noise environment it may be desirable to use a double shield type of coax cable such as RG ‐ 214/U.
Note: Pre ‐ made coax cables can be purchased from the factory. A ‐ 3 dB loss means you have lost 1/2 of your signal. A +3 dB
gain means you have doubled (x2) your signal.
Keep the antenna feedline as short as possible to minimize losses.
Extreme care must be taken when attaching coax connectors to the antenna feedlines. If there is any error in
making this connection the output of the transmitter will be greatly reduced.