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Old December 25th 05, 12:25 PM posted to rec.radio.cb
Scott in Baltimore
 
Posts: n/a
Default questions about building CB antenna...

At 30 Ohms you will need some matching network to cancel the reactive
portion out and rasie the radiation resistance of the antenna up to
that of 50 Ohms. I would not reccomend direct coax attachment even to
a 1/4 lambda ground plane antenna.

james



LMAO!


Ok, I just ran my 40 meter vertical on a simulator...

R=35.87 jX=.354

SWR=1.39.. now why do I need a matchbax?

But of course a matchbox wont raise the radiation resistance of my
antenna... will it?


Nor will it fix the basic mismatch.

30 ohms. Oh ****! I better put a 20 ohm resistor is series
with my radio of it's gonna' burn up!

1.5:1 SWR can be 25 or 100 ohms.
25 ohms will draw more current and drop more voltage. (more current X less voltage)
100 ohms will draw less current and drop the voltage less. (less current X more voltage)
50 ohms will draw the most amount of POWER from the source. (equal voltage X equal current = MAX
POWER TRANSFER)

James, you need to learn the power transfer theorum and how
little is actually lost by a 1.5:1 or less SWR. You gain
more with a resonant antenna, then a bit of impedance mismatch.