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| I don't think you want to use that cable. The PL259 you reference is the connector type. My guess is that cable is a lesser-quality RG8 type cable (Belden RG8/U is common, RG-58 is the smaller style your mobile CB mounts use but not as thick as the RG8 style).
Belden RG8/U has a loss rate of 7.6dB per 100ft length at 900mHz. Every 3dB is 1/2 power loss, so you are already less than 1/4 power loss (1/4 = 6dB) at 900mHz.
A couple equations to use:
dBm to watt:
W = (10^(dBm/10))
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1000
Watt to dBm:
dBm = 10log (10*W)+20
Where:
W = Watt
dBm = decebels, power level
log = logorithmic (button on a scientific calculator)
Figure your 900mHz radio at 1 watt (sub whatever you are going to run here):
The power loss you will have through that cable that you have is as follows:
Convert your 1 watt to dBm:
10log (10*1)+20 = 30dBm
Figure your loss at 75ft:
75/100 = .75
.75*7.6 = 5.7 dB loss in 75ft of coax
Subtract 5.6 from 30 = 24.4 dBm left at the antenna.
Convert 24.4dBm back to watts =
(10^(24.4/10)) = .275 watts = 27.5 milliwatts (out of your 1 watt in from the radio).
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1000
Use better coax. Find you something that will be less than 3dB loss at 75ft would be good = expensive though at 900mHz. You're looking at something like Heliax LDF2-50A, about $2-3//ft (+ connectors), or better. Keep in mind, 3dB loss is still 1/2 your power gone in the cable. | |
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Repeater Coax
