On 27 Sep 2006 02:34:40 GMT, (John E. Davis)
wrote:

Does EZNEC report
the oscillations when the frequency increment is on the order of 0.01
MHz? What version of NEC does EZNEC use?

Hi John,

I've been using various flavors of E(L/Z)NEC for more than a decade
and I've never seen such dramatic cogging of the data that was not
attributable to construction (notably fractals). Your data is
stranger yet in having correlated noise on the left, and uncorrelated
noise on the right.

When I run the model at the resolution you suggest (0.01MHz), yes, I
do see some very fine cogging. It is on the order of 0.5 Ohm reactive
up tick which, for example, translates to a shift from 1.60:1 to
1.62:1 on a generally downward slope. When I run again with the
double precision math, this goes away. Both curves do not exhibit a
flat bottom, but rather an asymptote.

You can observe this quite readily on the download, free version of
EZNEC for yourself.

73's
Richard Clark, KB7QHC

On Tue, 26 Sep 2006 22:36:53 -0700, Richard Clark
wrote:
I've been using various flavors of E(L/Z)NEC for more than a decade
and I've never seen such dramatic cogging of the data that was not
attributable to construction (notably fractals). Your data is
stranger yet in having correlated noise on the left, and uncorrelated
noise on the right.

Please look at the ftp://space.mit.edu/pub/davis/misc/nec/swr.png
for a plot of the SWR using a spacing of 0.01 MHz. I suspect that the
noise that is showing up may be due to truncation error. I believe
that spacings of higher values, e.g., 0.2 MHz result in a different
sampling of the noise.

The version I am using (see
http://packages.debian.org/stable/hamradio/nec) contains this warning:

This version contains code which hasn't been extensively tested for
errors, which was input by hand from a report -- use with care. The
numerics are currently only SINGLE PRECISION.

If EZNEC were available for linux, I would look into it. Also, can it
be driven in "batch" mode without a GUI?

Thanks,
--John

On 27 Sep 2006 06:52:46 GMT, (John E. Davis)
wrote:

Please look at the ftp://space.mit.edu/pub/davis/misc/nec/swr.png
for a plot of the SWR using a spacing of 0.01 MHz. I suspect that the
noise that is showing up may be due to truncation error. I believe
that spacings of higher values, e.g., 0.2 MHz result in a different
sampling of the noise.

Yow! That is a lot of trash.


The version I am using (see
http://packages.debian.org/stable/hamradio/nec) contains this warning:

This version contains code which hasn't been extensively tested for
errors, which was input by hand from a report -- use with care. The
numerics are currently only SINGLE PRECISION.

Hi John,

Yes, this confirms the shift to double precision in EZNEC lowering
artifacts in the fine data.

However, I think it goes beyond simple matters of single or dual
precision math. When I was designing Fourier Analysis packages while
I was on contract to HP, I discovered there was a world of variability
in math library's transcendental functions.

Microsoft's product was abysmal, whereas Borland's was superlative. A
telling example is that for the transform of a sine wave into the
frequency domain under Microsoft math libraries, the noise floor was
at 60 to 80 dB below the fundamental peak with harmonics. When I
switched to Borland math libraries, there was a single bin response
and the noise floor plunged to 200dB down!

For others following this description, they may wonder at the
terminology of noise floor for a simple sine wave transform. Fourier
Analysis is done by parts through FFTs and this departs from classical
Fourier which is continuous. Because FFTs are discrete (bound by an
arbitrary start and stop), this injects spurious responses into the
transform. On top of that, rounding errors attributable to series
expansions of the transcendentals would give lower accuracy -
statistical (largely uncorrelated) noise. The sine wave transform was
a method of self-validation of the library used and Microsoft failed
big time (especially considering the 10:1 cost differential for the
more expensive M$).

If EZNEC were available for linux, I would look into it. Also, can it
be driven in "batch" mode without a GUI?

There have been various reports of success and failure when Windows
emulators have been used. I cannot report any personal experience
because my Linux machine is largely confined to Server development
(XAMMP/Wiki/MySQL/RubyOnRails).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On 27 Sep 2006 06:52:46 GMT, (John E. Davis)
wrote:

. . .

If EZNEC were available for linux, I would look into it. Also, can it
be driven in "batch" mode without a GUI?

There have been various reports of success and failure when Windows
emulators have been used. I cannot report any personal experience
because my Linux machine is largely confined to Server development
(XAMMP/Wiki/MySQL/RubyOnRails).

The last reports I've gotten are that Wine, the Linux Windows emulator,
isn't able to open the EZNEC manual, and has at least one other problem
with EZNEC. I've gotten several reports that the SoftWindows emulator
for the Mac runs even the professional versions of EZNEC flawlessly.
There isn't, and won't be in the foreseeable future, a native Linux or
Mac version of EZNEC; the market is simply too small.

EZNEC can be run in something resembling batch mode with MultiNec
(http://www.ac6la.com/).

The NEC-2 calculating engine in the demo and standard EZNEC program
types contains a mixture of single and double precision variables which
does considerably better than a fully single precision implementation
but with only a slightly greater memory requirement. EZNEC+ and the
professional programs also include a fully double-precision
implementation. None of these are identical to NEC-2 (of which there are
several slightly different versions in circulation); EZNEC has
consolidated scattered constant values, added protections against
numeric overflow, incorporates third-party math libraries for some
calculations, and has a few obscure bugs in the code fixed, among other
differences. Although EZNEC doesn't implement all the features of NEC-2
(patches, for example), it has features which NEC-2 doesn't, such as a
comprehensive geometry check and provision for wire insulation (and of
course the GUI). I've also found some optimizations done by various
compilers which cause errors or crashes in some cases, and of course
these are avoided when compiling EZNEC's calculating engines. In fact,
I'm just now working with a compiler manufacturer in tracking down what
looks like a bug I found in a new compiler I'm considering using for
future versions. NEC-2 is free, and people pay for EZNEC. They do get
something for it.

Roy Lewallen, W7EL

On Wed, 27 Sep 2006 04:40:51 -0000, (Dave Platt) wrote:

In article ,
John E. Davis wrote:

The elevation pattern of the antenna shows a hint of the high-angle
secondary lobes which characterize an EDZ.

This is definitely noticable on a log plot.

So, I'd conclude that you've developed a variant on the EDZ (or
something partway between an EDZ and a center-fed fullwave) which
yields slightly lower gain than an EDZ but has a simpler matching
section.

What sort of gain is expected from an EDZ? I tweaked the topology
of my design a bit in the hope of getting a broader bandwidth, but
instead got even more gain. For example, the version represented
below has a minimum gain of more than 4.7 dBi (at the side) and more
than 5.25 dBi in the forward direction. Previously I reported gain
values that ran from 4.2-4.7 dBi. So this one represents a bit of an
improvement.

For an EDZ in isolation (no mast) I believe it's around 3 dBd or 5
dBi, plus or minus a hair.

I modelled a copper-pipe EDZ, mounted at the top end of a conductive
mast. This one came out with 5.85 dBi in the favored direction, and a
2.5 dB front-to-back ratio.

Have I missed something here? As I understand the EDZ (is it not the Extended
Double Zepp?) it comprises a center-fed doublet with a 5/8 wl wire on each side
of the feed point. It's broadside gain is about 3.1 dBd, with a narrower lobe
than that of a dipole, from which the gain over a dipole is obtained. Am I
correct so far?

If so, then we have only a single radiator. How then can there be a
front-to-back ratio?

Walt,W2DU

On Wed, 27 Sep 2006 04:40:51 -0000, Dave Platt
wrote:
I modelled a copper-pipe EDZ, mounted at the top end of a conductive
mast. This one came out with 5.85 dBi in the favored direction, and a
2.5 dB front-to-back ratio.

Have you considered using the much simpler moxon? This one has a
forward gain of 5.6-6.4dBi (6.2@146MHz) and a front-to-back ratio of
18-31dBi (29@146MHz). It uses #12 AWG wire. Thanks, --John

CM Model: moxon for 2m
CM parms = [29.1337, 4.18345, 1.4995, 5.70003, ];
CM
CM A: 29-1/8 in.
CM B: 4-3/16 in.
CM C: 1-1/2 in.
CM D: 5-11/16 in.
CM Wire Diameter: 0.0808081
CE
GW 1 3 -0.10626 0 8.774 0 0 8.774 0.00102626
GW 2 15 0 0 8.774 0 0 9.514 0.00102626
GW 3 3 0 0 9.514 -0.10626 0 9.514 0.00102626
GW 4 3 -0.144347 0 9.514 -0.289128 0 9.514 0.00102626
GW 5 15 -0.289128 0 9.514 -0.289128 0 8.774 0.00102626
GW 6 3 -0.289128 0 8.774 -0.144347 0 8.774 0.00102626
GE 0
FR 0 401 0 0 144 0.01
EX 0 2 8 0 1
GN -1 0 0 0 0.0 0.0 0.0 0.0 0.0 0.0
RP 0 1 73 1001 90 0 1 5
EN

On Wed, 27 Sep 2006 00:19:53 -0700, Richard Clark
wrote:
Yow! That is a lot of trash.

For most uses, it is not so bad. For example, elsewhere in this
thread I posted the .nec file for a 2m-moxon. The corresponding plot
of the SWR may be seen at
ftp://space.mit.edu/pub/davis/misc/nec/moxon_swr.png. The noise is
still there, but the amplitude is much smaller and would not be
noticable on a coarser frequency grid.

Thanks,
--John

In article ,
Walter Maxwell wrote:

For an EDZ in isolation (no mast) I believe it's around 3 dBd or 5
dBi, plus or minus a hair.

I modelled a copper-pipe EDZ, mounted at the top end of a conductive
mast. This one came out with 5.85 dBi in the favored direction, and a
2.5 dB front-to-back ratio.

Have I missed something here? As I understand the EDZ (is it not the Extended
Double Zepp?) it comprises a center-fed doublet with a 5/8 wl wire on each side
of the feed point. It's broadside gain is about 3.1 dBd, with a narrower lobe
than that of a dipole, from which the gain over a dipole is obtained. Am I
correct so far?

Yup.

If so, then we have only a single radiator. How then can there be a
front-to-back ratio?

The model I developed/posted was for an EDZ, which is side-mounted at
the top of a conductive mast. One half of the doublet sticks up above
the mast "in the clear", but the other half runs down parallel to the
mast, perhaps a foot away.

As with any side- or tower-mounted antenna, there's some amount of
reflection from the mast, and this is enough to create a few dB of
"front to back" ratio.

If the antenna were modelled (or used) in isolation, with no mast and
with the feedline running out sideways, the "front to back" ratio
would be unity or very close to it. Just delete the mast pipe from
the model I posted and re-run NEC.

The design/installation data for Telewave's side-mounted folded-dipole
arrays show several different patterns, ranging from something very
close to a cardioid, to an "off-center circular" pattern, to a nearly
perfect circular pattern. All of these patterns can be achieved using
the same antenna array, by simply altering the length of the
side-mount arms which support the dipoles beside the mast or tower.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
John E. Davis wrote:

I modelled a copper-pipe EDZ, mounted at the top end of a conductive
mast. This one came out with 5.85 dBi in the favored direction, and a
2.5 dB front-to-back ratio.

Have you considered using the much simpler moxon? This one has a
forward gain of 5.6-6.4dBi (6.2@146MHz) and a front-to-back ratio of
18-31dBi (29@146MHz). It uses #12 AWG wire. Thanks, --John

If I were actually seeking a high front-to-back ratio, a Moxon would
be a good choice!

I actually developed the EDZ models for a different application... the
main antenna on a 2-meter repeater installation. We want a reasonable
amount of gain, and a near-omnidirectional pattern. The high
front-to-back ratio of a Moxon would not be appropriate in this case...
the 2.5 dB ratio of the side-mounted EDZ is probably as much as we'd
want to accept, given the shape and size of our service area.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Richard Clark wrote:

Hi John,

Yes, this confirms the shift to double precision in EZNEC lowering
artifacts in the fine data.

However, I think it goes beyond simple matters of single or dual
precision math. When I was designing Fourier Analysis packages while
I was on contract to HP, I discovered there was a world of variability
in math library's transcendental functions.

Microsoft's product was abysmal, whereas Borland's was superlative. A
telling example is that for the transform of a sine wave into the
frequency domain under Microsoft math libraries, the noise floor was
at 60 to 80 dB below the fundamental peak with harmonics. When I
switched to Borland math libraries, there was a single bin response
and the noise floor plunged to 200dB down!

snip
73's
Richard Clark, KB7QHC

Richard

I am not surprised with your result after having used various MS
compilers over the years. Do you have any idea what the real
differences were in the libraries? Borland C always seemed better, more
robust at error handling, and more accurate.

I noticed similar problems back in the late 80's with MS C, but never
really needed the precision, and work pressure being what it was....

tom
K0TAR