请问下行波天线的匹配电阻怎么计算呢？ [复制链接]

是不是用 9:1 balun 及 450 欧电阻的天线

termination value
having precise termination values isn't necessary, but get as close as you reasonably can. there are some impedance measurement suggestions circulating that absolutely do not work. one is to just use a tuner to match the terminated (or unterminated) antenna, and work backwards with loads to measure tuner impedance ratio after matching. this won't tell you a thing about proper termination, unless you repeat the measurements on dozens of frequencies spread over a wide range!
there are three fast, simple ways to test for proper termination:
with an antenna swr analyzer
connect the antenna analyzer at the beverage feedpoint through a good matching transformer
sweep the analyzer frequency from 1.8 to 7 mhz (or over a ~4:1 frequency range near the frequency intended for antenna) while watching swr
adjust termination for minimum swr variation (not minimum swr, minimum swr variation!)
when installation (including grounds) and termination is proper, swr value will remain nearly the same regardless of frequency
with an antenna impedance meter
measure the feedpoint impedance (right at the feedpoint) of a roughly terminated antenna at the frequencies of highest and lowest resistive impedance. you can do this through a known good transformer by correcting impedance for use of the transformer
multiply the lowest measured impedance by the highest, and then find the square root of that number. this will be the correct termination impedance of the antenna
with a clamp-on rf current meter
(this does not work well with voltage, because of measurement method error problems)  
apply a small amount of power from a transmitter, do not exceed antenna system component ratings!
measure current at the termination, and several points up to a distance of at least 1/2 wl from the termination
adjust termination resistance so current shows a smooth current decline as you move the meter towards the termination
                            note:
in about 500-800 feet of distance, power loss in a beverage is around 3db. this corresponds to a 1/3 reduction in current. if you attempt to adjust for equal currents (or voltages) over any distance, the antenna will be mis-terminated!