[Antennaware] Model Contains Loss
Jim Miller
JimMiller at STL-OnLine.Net
Fri Dec 1 12:40:03 EST 2006
1. Eznec 4
2. 3D
3. Looking for "small" VHF attic antenna with some gain that can be rotated. Attic is a mess full of braces.
4. Height = 13 ft at bottom of antenna.
5. 4 Moxon rectangles
6. Vertical polarization for VHF simplex.
7. Stacked 2 side by side 24 inch separation
8. AND 2 more vertical above them by 22 inch for 4 total.
9. gives 27 inch turning diameter 83 inches tall.
10. Far Field gain shows 13.02 dBi
11. "Average Gain = 0.561 = -2.51 dBi Model contains loss"
What does "Average Gain = 0.561 = -2.51 dBi Model contains loss" mean? Is the Average Gain the actual total gain or is it to be subtracted from the 13.02 dBi or has that already been done. So, is the actual real gain -2.51, 13.02, or 11.51 dBi?
Is this amount of loss to be expected?
I don't remember seeing the loss statements on example models.
If I knew what causes it, I may be able to minimize it.
What can I do to eliminate it?
Thanks everybody,
73, Jim
----- Original Message -----
From: "Terry Conboy" <n6ry at arrl.net>
To: "Jim Miller" <JimMiller at STL-OnLine.Net>
Cc: "AntennaWare Reflector" <AntennaWare at contesting.com>
Sent: Thursday, November 30, 2006 12:05 PM
Subject: Re: [Antennaware] Model Contains Loss
> At 04:28 AM 2006-11-30, Jim Miller KG0KP wrote:
> >Just starting modeling.
> >
> >Why does a model say "Model contains Loss" in the control box when
> >it shows very good gain in the Far Field Plot?
> >What is causing this?
>
> Jim,
>
> I assume we're talking about EZNEC, when plotting 3D
> patterns. (Other programs may be similar.)
>
> In the real world, all antennas have loss (conductors, earth,
> resistive loads, etc.), so this is nothing to be especially concerned about.
>
> With copper wire dipoles well above "High Accuracy" ground (> 1/4
> wl), the Average Gain should be around -1 dB. For verticals, it's
> not unusual for them to exhibit an Average Gain of -5 dB or so, due
> to ground losses. Resistively terminated receiving antennas like
> Beverages, K9AYs, or Flags can have significant average losses, -20
> dB or more (thus the common need for preamps).
>
> As a point of interest, W8JI uses the difference between forward gain
> and average gain to obtain a figure of merit, which he calls RDF
> (receiving directivity factor). He lists the RDF and Average Gain
> for a number of receiving antennas at http://www.w8ji.com/receiving.htm.
>
> In free space, with zero loss conductors and lossless loading, the
> Average Gain should be very close to 0 dB.
>
> It usually indicates problems with your model construction or
> geometry if the Average Gain number is positive by more than a few
> tenths of a dB.
>
> 73, Terry N6RY
>
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