This can be done with any EZNEC program type, including the demo:

1. Click Open.
2. Select BYDipole.EZ and click Open in the file selection dialog box.
3. Click SWR. Enter 14 for the start frequency, 15 for the stop
frequency, and .05 for the frequency step. Click Run.
4. Using the arrow keys or the mouse, move the cursor in the SWR display
to the points where SWR is about 2. These are about 14.1 and 14.75 MHz,
indicating a 2:1 SWR bandwidth of about 650 kHz.
5. Click Wires in the main window to open the Wires Window.
6. In the Diameter column, change the Diameter from #12 to 6 to
represent a 6 inch diameter cage. (Don't put a "#" in front of the 6.)
Press the Enter key to finalize the change.
7. Click SWR. Change the start frequency from 14 to 13 and click Run.
8. In the SWR display, move the cursor as before, and note that the 2:1
SWR bandwidth is now about 1.35 MHz, about twice what it was for the
original antenna made from #12 wire.

Now you're a Reg-certified expert, even if that took you a month of
Sundays to do.

You can also get a great deal of additional information from EZNEC, such
as the feedpoint impedance and SWR at any frequency, the pattern, and
effect of height and ground characteristics.

If that took you a month of Sundays, you might think a bit about what's
reduced your capabilities to that level.

Roy Lewallen, W7EL
-- Certified by Reg as both Old Wife and Expert!

Reg Edwards wrote:
It takes a month of Sundays for an expert to enter and interpret the
input/output data of a cage dipole using an Eznec-type program.
. . .