[TowerTalk] Elevated vertical

[Ken]

A low SWR does not indicate resonance.   

Resonance does not necessarily provide a low SWR.

A true quarter wave resonant vertical over a perfect ground plane has a feed impedance of about 30 ohms and therefore a 1.6:1 SWR "at resonance" (assuming 50 ohm coax).  

Seems to me, IIRC, radials for a ground plane should be 5% longer than the radiator (check the Antenna Book to be sure.)

Ken WA8JXM

On Dec 22, 2011, at 5:23 PM, Tom Osborne wrote:

> Hi All
> 
> I just put up an elevated 40 meter vertical.  The feedpoint is around 15 
> feet or so up and I have 8 radials on it right now.  I cut the radials the 
> same length of the vertical section.  I have a coil of around 8 turns of 
> coax for a choke.
> 
> It works good, as the first day I put it up, I worked some Europeans from 
> here in Oregon.
> 
> The thing that seems strange is that at the low end of 40, the SWR is around 
> 1.3:1.  As I go up the band, it goes up to about 1.5:1, then when I get to 
> the top of the band, it goes back down to 1.2:1.
> Is that because some of the radials are resonating at different parts of the 
> band??  73