Re: NEC-LIST: Modeling short dipoles

Hi, Charley,

Let's forget the matching network and drive the antenna without one.
If you take the reflection loss associated with the antenna-generator
mismatch into account you will get the gain of the combination. For
example, if the antenna had an impedance of 5+j0 ohms, and the source
was a 50 ohm generator, the antenna's voltage reflection coefficient
(rho) would be (50-5)/(50+5) = .818 and 1-(rho)^2 = .331 = -4.81dB.
This -4.81dB is the amount of power delivered to the antenna
resistance relative to what is available at the source and has to be
factored into the overall path loss. Then you have to figure out how
much of the antenna resistance is radiation resistance (Rrad) or
copper loss (Rs) and how it effects the power to Rrad given the Rs you
have. It's more of a circuit theory problem than a radiation one.

--
Paul, AA1LL, Greenville, NH
paul.e.gili_at_lmco.com
______________________________ Reply Separator __________________________
Subject: NEC-LIST: Modeling short dipoles
Author:  Charley Rhodes <ctr_at_nis.lanl.gov> at INTERNET
Date:    11/14/97 11:11 AM
Folks:
I know that this topic was discussed back in September under the topic
.......
.
.
So, I as the group, is there a better way to calculate the gain of the 
short antenna not worrying about a matching network or trying to guess 
what the loss is? Or, is there a way to use NEC to get the real 
efficiency?  My use of the short antenna may in fact be a direct 
connection to a 50 ohm receiver with no matching. I want to be able to 
estimate the antenna's true (I will eventually measure it - but know 
early will save some time) gain.
c.rhodes