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Old 02-28-2008, 04:09 PM
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Groucho Groucho is offline
Rising Sun Ham Guru
Join Date: Aug 2005
Location: Arvada, Colorado
Posts: 1,679

Originally Posted by subzali View Post
But there are some people who run 1/4λ antennas, which would be around 19" tall. But also, as on CB, a 5/8λ antenna generally works better, thus the 4' 2m antenna. Can you wrap the conducting surface as they do with CB antennas? A 5/8λ CB antenna should be around 246 inches (20.5 feet) long, yet they shrink it into a 4' whip. I suppose you give up a lot of RF transfer by doing that...

Before the test I wanted to make sure you got the math correct for this idea. It is close, but off just enough.

From our example, the multiplier for 5/8λ is 585. The low end frequency in MhZ for CB (11 meter) is 26.965 MhZ, the high end is 27.405 MhZ.

Then, we find the length in feet = 585 / 27.405
which is 21.35 Feet.

For the other end, we find that the length in feet = 585 / 26.965
which is 21.69 Feet.

So for CB, the length of the whip of a 5/8λ vertical antenna needs to be between 256.2 inches and 260.3 inches long.

By my calculations, if you were using the 585 multiplier you were assuming that the CB frequency was in the middle of the 10 Meter HAM band (28.000-29.700 MhZ).

L = 585 / 28.53 MhZ.
L = 20.5 feet.

Did you use the 585 multiplier? Did you use 28.530 Mhz?
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