Topband: Impedance of inv l?

[Wes Stewart]

To the first order, the feedpoint Z (at resonance) will depend on the height of 
the vertical portion, which affects the radiation resistance. and the resistive 
loss of the ground connection which appears in series with it.  A full height 
(1/4 wavelength) vertical over perfect (zero ohm) ground will be about 35 ohm.  
A shortened vertical, toploaded (the "L" portion) will be lower than this, again 
over perfect ground. Sixty ohm seems way too high and since you have a 
respectable, but not outstanding radial system, suggests to me measurement 
error. How are you measuring this?

My inverted L, 55 feet vertical, the rest horizontal measures ~24 ohm at 
resonance, with a very marginal (work in progress) radial field of twenty, 55' 
long insulated radials on the ground.  I've used three different instruments, 
all vector analyzers, to confirm this.  (DG8SQQ, FA-VA5 and AA-55)   I have a 
50KW BC station on 1550 kHz that measures -3 dBm on this antenna.  Only a vector 
analyzer, used with care, will handle this.

Wes  N7WS

On 11/18/2018 9:48 AM, Jamie WW3S wrote:
> well, I THOUGHT I had a good ground.....16 radials I think, 1/4 long.....so I thought I'd see around 30-35 ohms impedance.....not sure what to think now.....I was going to get either a balun and unun at the feed point, was going be someone else's statement that there inv l was around 22 ohms, glad I measured mine before I ordered one....
>
> ----- Original Message -----
>
> From: "F Z_Bruce" <k1fz at myfairpoint.net>
> To: ww3s at zoominternet.net, "Topband" <topband at contesting.com>
> Sent: Sunday, November 18, 2018 10:55:47 AM
> Subject: Re: Topband: Impedance of inv l?
>
>
> That sounds about right. As you put a good ground system under it, that value will come down, and the efficiency will come up.
>
> Many add extra antenna wire that pushes the current up the wire, this also raises the impedance, hopefully to near 50 ohms with the right length.
> A capacitor (variable, then fixed) in series at the feed point can cancel the added inductance.
>
> 73
> Bruce-k1fz
> https://www.qsl.net/k1fz/beverage_antenna.html
>
> On Sun, 18 Nov 2018 10:41:36 -0500, WW3S wrote:
>
> What should the Z be for a 1/4 wave inv l, with the radials attached to a radial plate? Mine seems to be 60 ohms or so....
>
> Sent from my iPad
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