[SEDXC] [SECC] Question about 30 meter halfwave vertical for the antennagurus

Tom W8JI w8ji at w8ji.com
Sat Oct 23 09:05:25 PDT 2010

I shunt-feed my 15m (50 foot) tower on 160m. I've got 160m WAS, and 25 
countries confirmed, all with 100 watts.

Apples and basketballs comparison.

I'd bet money your 50 foot tower is not a 1 or 2 inch dameter pole with 
nothing on the top.

More than likely you have some big antennas on the top, and the tower is 
pretty thick.

<<Of course, it helps to have lots of radials. I have about 30 totaling over 
1600 feet of wire. >>

With a fairly good ground on a 43-foot vertical you would have 5100 volts 
peak and 4.8 amperes RMS on the antenna base. That's a reactive power of 
17.3 kilowatts just to radiate about 24 watts of real power from the 

The difference between that and your tower is length, top loading by 
antennas, thickness, and feed system. They are not remotely similar in 
anything but length.

Even a sucky antenna can be made to work.>>

Nothing "sucky" about a 50 foot tower on 160 if it has some sort of loading 
on the top. It could be nearly as good as a 130 foot tower.

<<<But I agree about the 43 foot thing. It seems to be a cult-like 
condition, like the 88 foot dipole in QRP circles. Of course, LB modelled 
the 88 foot dipole at 100 feet and 70 feet. Most of the guys who put these 
up rarely get them over 35 feet.>>>

LB's error was not considering feedline loss and matching systems, not in 

Any dipole, even one a dozen feet long, will model with a good pattern and 
good gain if we ignore losses. The problem is getting power into it.

Same as the problem with a thin vertical stick with no loading.

73 Tom 

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