[TowerTalk] balanced line loss on a mismatched antenna

[Gary Slagel]

Thanks Paul,
 
I've attached the Source Data output below.  This, I believe, is showing me SWR and impedance at the feedpoint of each element.  I'm not sure if EZNEC gives me a way to see the SWR at the single feedpoint that I'll use to feed these two feedpoints but I assume it will be equally as bad.  
 
I'm using the standard ARRL W8JK model that comes with the demo version of EZNEC in the ARRL antenna book.  I modify that model to look like what I want to build and as long as I don't save it the software performs like the full version of EZNEC.  I'm over my head with antenna modeling as soon as I move past modeling a dipole but I forge ahead and try and get as much useful information as I can from it.
 
The question still is, if I get the antenna working properly how much loss will I see on the feedline.  Thanks much for your help.
 
 
 
                    EZNEC ARRL ver. 4.0
              2/28/2012     7:53:59 AM
         --------------- SOURCE DATA ---------------
Frequency = 7.05 MHz
Source 1      Voltage = 397.6 V. at -89.63 deg.
              Current = 1 A. at 0.0 deg.
              Impedance = 2.597 - J 397.6 ohms
              Power = 2.597 watts
              SWR (50 ohm system) > 100  (75 ohm system) > 100
Source 2      Voltage = 397.6 V. at 90.37 deg.
              Current = 1 A. at 180.0 deg.
              Impedance = 2.597 - J 397.6 ohms
              Power = 2.597 watts
              SWR (50 ohm system) > 100  (75 ohm system) > 100
              Total applied power = 5.193 watts



Gary Slagel
KT0A

 


________________________________
From: Paul Christensen <w9ac at arrl.net>
To: Gary Slagel <gdslagel at yahoo.com>; TowerTalk <towertalk at contesting.com> 
Sent: Monday, February 27, 2012 4:48 PM
Subject: Re: [TowerTalk] balanced line loss on a mismatched antenna

> "I think I can tune the antenna with the feedline and get it down to a more reasonable level, maybe 10 to 1, at the tuner end. Then the tuner will tune it to resonance so the xmttr can put its full load into.
> Question is, since the swr is 10 to 1 at the radio end of the feedline but 100 to 1 at the antenna end of the feedline, am I going to see the 3.5 db loss from a 100 to 1 swr or the .5 dbi that a 10 to 1 swr would give me."

Gary,  you can vary the impedance at the input end of the line, but not the SWR.  The SWR on the 450-ohm section will remain nearly constant over your 150 ft run, even with length trimming.

In EZNEC, what is the Z of the antenna you're modeling at the operating frequency in an R+j format?

Paul, W9AC