Fractenna wrote:
Some care must be exercised to see that causality has not been violated: the
'July 9' date is a typo. The right date is, of course, 9 June.

I continue to get many e-mails asking for info about DLM designs. You will,
perhaps note, that the 7 June EE times article was AGAIN run--with
additions--on 14 June:

http://www.eet.com/showArticle.jhtml?articleID=21600147.

Mr. Vincent describes a design that, apparently, is well within the
description I discussed below on 11 June--at least that is my opinion.

As I have not seen Mr. Vincent's design, it would appear that said design is
either 'obvious to those skilled in the art', or not novel in some basic way,
again, an opinion. I will be most interested to see what true novelty is
ascribed and approved as the 'revolution' moves forward.

Incidentally, Mr. Vincent again ascribes his design as "wide in bandwidth" yet
describes substantial harmonic suppression. 'Wideband' designs are almost
always big enough in passband to cover the lowest end and its harmonics.

73,
Chip N1IR
---------------------------------------------------

Temat: DLM Antenna
Od: (Fractenna)
Grupa: rec.radio.amateur.antenna
Organizacja: AOL http://www.aol.com
Data: Jun 11 2004 12:29:42


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Hello--

I've received about 2 dozen e-mails on this subject. Prior to this, I
communicated with Mr. Vincent early on 9 July(SIC) and offered him the
opportunity
for scientific and objective independent testing. He declined due to a test
already ongoing at a facility that I feel is also capable of such testing (you
may ask Mr. Vincent if you wish).

My scientific interest in this topic is exhausted. I pose the following for
those interested in what is possible, and what has been done, along the lines
of distributed loading of helix monopoles. I invite you to investigate the
prior art for yourself.

I have not seen Mr. Vincent's design, but based upon his PR statements, it
appears to be a loaded helix monopole with a CCD-like arrangement for
neutralization. The design, of course, may be different and novel, although I
am not of that opinion, based upon the 3 reports published in the popular
press. In the absence of knowledge, it is impossible to fully assess. Still,
there is value in knowing what has been done and what is possible.

----------------------------------------

The prior art is rife with distributed loading of monopoles to extensively
shorten them.

Here is a prior art method that will gives a few percent bandwidth and about -2
dBd for less than 1/15 wave height. I invite you to experiment for values and
placements:

* Take a half wave of wire (approximately);
* Wind it into a helix of about 10^-3 waves diameter (or less);
* Place an inductive load half way up;
* Add at least 2 and up to 6 capacitors at distributed points along the helix
length;
* If you wish to truncate the current at the top, then add a small end cap hat;

Essentially this is a shrunken 1 wave dipole manifest as a 1/2 wave monopole,
using CCD (distributed capacitors) to neutralize the inductance. (remember:
not all cacapcitors need be discrete components ). Helical designs originated
with Harold Wheeler more than 50 years ago. CCD articles have predominantly
appeared in ham magazines in the 70's and 80's, although the original invention
is (I believe) British and over 40 years old. There are many relevant patents,
all expired to my knowledge.

This design approach will 'linearize' the current (slow he wave) and do a
pretty good job. A shrunken 1/2 wave monopole does better than a shrunken 1/4
monopole. When you compare it to a full-sized 1/4 wave monopole it will do well
at a specific frequency.

It is an interesting question whether the relevant comparison should be to a
1/4 wave monopole or a 1/2 wave monopole. Such shrunken designs are 1/2 wave
equivalents, not 1/4 wave equivalents. They will look much worse in performance
compared to full sized counterparts. A 1/4 wave monopole is not a counterpart,
although in a practical sense it is a much used antenna which one might seek to
replace and thus compare to.

HOWEVER for such a shrunken design--

* It will be moderate to narrow band;
* It will trade gain for efficiency and is NOT efficient;
* It will run hot in continuous-on applications with moderate to high power.

Gain is not efficiency. Sometimes efficiency doesn't matter, but gain does.
Other times the heating from inefficiency will kill an otherwise elegant design
option.

Mr. Vincent's original PR claims, to my recollection: high efficiency; good
(broad) bandwidth; very low height.

These are not mutually, physically, attainable. I, and many others, have spent
enough time to know. There is no reason to believe that Mr. Vincent has
attained these. What he has appeared to have attained, to my limited knowledge
based on published PR, is: moderate to low efficiency; modest bandwidth, and
very low height. To my knowledge, Mr. Vincent has neither done an efficiency
test nor a heating test.

In terms of applications, there are very few, besides some 'ham' and CB needs,
where a single band, somewhat inefficient whip is desired. Midland has a nice
compromise stick for CB'ers that's using some of these ideas and is two feet
high. I like their design.

--Using a heavily shortened CCD type helix monopole in a broadcast app will
lead to a fire. It is not highly efficient and the wasted power will manifest
as heat. As little as 30 watts of heat in a confined area will start a fire or
melt components if not properly dissipated. About a 1 dB loss to heat for 1000
watts power will produce well over 100 watts dissipated heat. Ergo, even a
reasonably efficient antenna is potentially dangerous if high power is used
and the heat is not properly dissipated. Mr. Vincent's design PR describes
melted components in some of his design efforts. This indicates inefficiency in
the design tested.

--Much of the world wants 'ground independent' antennas--not monopoles

-- Microwave applications are not single frequency, with few exceptions. Even
PIFA (inverted F) solutions--which are extremely low height, lower than Mr
Vincen'ts-- are multibanded.

--Much of the world wants multiband antennas, or wideband antennas, not modest
passbands.



What I have become stuck on is the claim of constant current along the
length of the antenna - or 80 percent as claimed. How does this work? I
don't profess to know much about these matters, but if the current stays
the same, then the voltage must too?

And i still can't figure out how such an efficient antenna "melts". 8^)

- Mike KB3EIA -