[Antennas] SWR Isn't Enough

Sun, 28 Apr 2002 20:35:42 -0500

Well, Dave, actually I started this thread. This isn't the LP thread but
another, new thread. As the subject states, I wanted to get into the other
issues of "antenna systems", specifically in how they show up in a modeling
exercise.

So how do I tell the efficiancy of an antenna from the numbers in a model?

One side question is the use of resistive loads and how they impact
efficiency. Clearly a resistive load uses power decreasing the antenna
radiation output. The tradeoff is increased bandwidth. I have a  model of a
15.5' folded monopole that has a great SWR from 80m to 6m. But it has a 1700
ohm resistive load going to ground. I expect it is highly inefficient but
don't know how to determine the actual efficiency.

Rud Merriam
K5RUD

----- Original Message -----
From: "Dave Shrader" <[email protected]>
To: "Rud Merriam" <[email protected]>
Cc: "antennas" <[email protected]>
Sent: Sunday, April 28, 2002 7:16 AM
Subject: Re: [Antennas] SWR Isn't Enough

>
>
> In Conclusion, an HF beam type antenna should meet your requirements for
> gain, efficiency, and bandwidth. Only then should you consider how to
> couple energy into that antenna.
>
> Dave, W1MCE
>
> Rud Merriam wrote:
> >
> > So we know that SWR isn't enough in determining a 'good' antenna. What
other
> > information is needed? Specifically, how do determine from a model if an
> > antenna is efficient, i.e. putting the most signal into the air? Neglect
the
> > radiation angles and directions. While they are important they are
readily
> > obvious from the model, it seems.
> >
> > I've been reading Cebik's web pages. There is an article -
> > http://www.cebik.com/aledz.html - about an 'one antenna' for upper HF
that
> > is 44' long. At one point he comments that the impedance across all the
> > bands is 'manageable'. I modeled the SWR across the bands and it seems
> > non-manageable to me. Any comments on what to consider manageable? One
> > criteria I'm looking at is the spec on my automatic antenna tuner which
says
> > it will handle an SWR up to 10:1 or impedances to 800 ohms.
> >
> > Start at the basics with me, please. I have the NEC4WIN evaluation
version
> > to see if antenna work is something I want to explore. Plus I'm trying
to
> > find a good HF antenna for my location. It has to be stealthy but not
> > terribly so. I do have areas where I could hid a vertical, say, or a
> > horizontal wire. Also could probably put a delta, say, on the side of
the
> > house.
> >
> > Rud Merriam
> > K5RUD
> >
> > - - -
> >
> > Your moderator for this list is:
> > Larry Wilson KE1HZ [email protected]
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