[TowerTalk] Question on Multiple Inverted L Antennas

[wa3afs at inav.net]

My coaxial inverted Ls can be thought of as 1/2 of a bazooka.  It is fed by coax.  At the antenna base the shield of 
the feeding coax goes to the center conductor of the RG8X coax of the antenna and the center conductor goes to 
the shield of the antenna.  Some percentage up the coax, the coax is shorted and the coax is also shorted again at 
the top.  My goal when putting this antennas up is to make them as vertical as possible (Darn--I do not seem to 
have any 135 foot trees for 160M, but my 80M, 40M, and 20M coaxial inverted Ls are just about vertical.  

I use ground mounted radials -- as many as possible, but the antennas usually start 'playing' at 3-4 radials.  My goal 
is to have greater than 40 radials on each within the next couple of months.  One way to determine if there are a 
decent amount of radials is to measure the SWR when the ground is dry and also when raining.  If the SWR does 
not change between the two, then you are probably getting close to the correct amount.

This antenna is a super DX antenna 

73 Bruce

On 13 Jul 2006 at 16:52, hasan schiers wrote:

> Hi Bruce,
> 
> The only way for the bandwidth of an inverted L to be broad is if there are 
> excessive losses.
> 
> If you measure the resonant impedance at the feedpoint and compare it to the 
> known radiation resistance of the antenna, you may see why yours is so 
> broad....unless we aren't talking about the same antenna. Any 1/4 wave 
> vertical that shows very broad VSWR is operating with very high 
> losses...there is no other way to get broad band performance out of a 
> standard 1/4 wave vertical, as far as I know.
> 
> You might provide the details of your "coaxial" inverted L's....if they 
> follow the pattern of the double bazooka dipoles, then we know that it is 
> losses that account for the broadbandedness...but in any case, it will be 
> interesting to hear what exactly you are doing. Please tell us more.
> 
> 73,
> 
> ..hasan, N0AN
> ----- Original Message ----- 
> From: <wa3afs at inav.net>
> To: <towertalk at contesting.com>
> Sent: Thursday, July 13, 2006 4:20 PM
> Subject: Re: [TowerTalk] Question on Multiple Inverted L Antennas
> 
> 
> > Please be aware that the bandwidth for a coaxial inverted L is very broad. 
> > My SWR at 1.800 is 1.3 and slowly rises
> > to 1.7 at 2.000Mhz.  (The antenna is cut for 1.8400MHz and is physically 
> > located about a foot away from the base
> > plate of one of my 80M coaxial inverted Ls).  Because of my phasing 
> > system, It is not easy for me to measure the
> > SWR curve from the shack for my 80M, 40M, or 20M coaxial inverted Ls, but 
> > I remember that the curves were
> > decent for all of them when I installed them.
> >
> > 73
> >
> >  Bruce, WA3AFS
> >
> 
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