Author:
Jeff Barnhill in Northeast Louisiana
|
[
Next Thread |
Previous Thread |
Next Message |
Previous Message
]
Date Posted: Tuesday, December 11, 09:10:25pm
In reply to:
Larry--l2volt clothing.com
's message, "What is SWR?" on Tuesday, December 11, 06:44:25pm
SWR (no S) stands for Standing Wave Ratio.
A transmitter matched to a 50ohm antenna in a perfect world will not have any RF or Radio Frequency reflected back to the transmitter. If you drop a rock into a small pond a wave will go out. If it encounters a resistance, the wave will reflect back. Antennas reflect waves much like the rock scenario. When the transmitter sends RF towards the antenna,
if the antenna is not tuned to the particular frequency, a portion is reflected back towards the transmitter on the coax. It's bad to have RF reflected back to the radio. The length of the antenna is directly connected to the frequency it is on.
CB channel 19 is 27.185mhz. Using the formula 300 divided by the frequency gives us a 11.035 meter wavelength.
11.035 x 39.36 (converts meters to inches)=434 rounded off. Usually a mobile CB antenna is a 1/4 wavelength 434x.25=108.5" Many antennas use a coil to compensate for a shortened physical antenna length. The antenna usually is cut or shortened to length with a SWR meter. The end of the antenna usually moves in or out as needed to match the exact frequency you want.
AN SWR meter shows both Forward (transmitted) and Reflected power. The watts reflected back to the radio. is the ratio of transmitted( forward) power
Jeff KB5SAR
[
Next Thread |
Previous Thread |
Next Message |
Previous Message
]
|
