"Yuri Blanarovich" wrote in message
...
Another press write-up:
http://www.planetanalog.com/news/sho...cleID=21402311
Jim, K7JEB

[snip] "A helix
antenna is normally known to be a core radiator, because the current
profile
drops off rapidly; they are just an inductor, and inductance does not like
to
see changes in current, so it's going to buck that.

This sounds like false theory. He is implying that a distributed
inductor opposes a difference in current along its length, no?

The RF current in the distributed inductor can be different along its
length, modeling shows that, but this is AC and it is _always_ opposing the
changing AC (in this case RF) current at any point of the coil. That's what
inductors do. I can't get this to extend to opposing different AC currents
along the length of a long coil. If there is enough field from one end of
the coil coupling to the other end, then a falling field at the first end
tends to oppose a change in the current at that end as well as at the other,
but that's an opposition to a change in instantenous current, which will
increase inductance, not the AC current magnitude...


"What I found was that for any smaller antenna, if you place a
load coil in the middle you can normalize and make the current
through the helix unity; that is, you can maximize it and
linearize it," he added.

I can't get "Linearize" to work. Does he mean, "vary linearly along the
length"? "Normalize" and "unity" are pretty obsure as well.

Guess I'll wait for the movie to comeout.

--
Steve N, K,9;d, c. i My email has no u's.

This sounds like false theory. He is implying that a distributed
inductor opposes a difference in current along its length, no?

The RF current in the distributed inductor can be different along its
length, modeling shows that, but this is AC and it is _always_ opposing the
changing AC (in this case RF) current at any point of the coil. That's what
inductors do. I can't get this to extend to opposing different AC currents
along the length of a long coil. If there is enough field from one end of
the coil coupling to the other end, then a falling field at the first end
tends to oppose a change in the current at that end as well as at the other,
but that's an opposition to a change in instantenous current, which will
increase inductance, not the AC current magnitude...


"What I found was that for any smaller antenna, if you place a
load coil in the middle you can normalize and make the current
through the helix unity; that is, you can maximize it and
linearize it," he added.

I can't get "Linearize" to work. Does he mean, "vary linearly along the
length"? "Normalize" and "unity" are pretty obsure as well.


He means that a very electrically small monopole can be designed so it has no
current maximum: the current does not vary in magnitude with height. The
current value is the same along it's length.This is common for top hat
monopoles which are less than 1/30 wave in height.

The issue arises in the Vincent discussion because the electrical length of the
antenna is far in excess of the height, so the current changes--unless you
distribute additional inductance and capacitively truncate at the top.

Because the antenna is electrically long and physically short, it has a higher
feedpoint resistance, although the tradeoff of higher ohmic losses to higher
rad resistance gives, at best, a wash on gain.
It is, in effect, a short, slow wave antenna.

Monopole limits: At 1/30 wave height, the bandwidth can be on order of a few
percent or less, with -2 dBd or so. I have worked with such antennas for some
time. If you increase heights to 1/15 wave, the increase in bandwidth can be
dramatic.

The problem is that broadcast antennae need reduced height--but don't need the
many-percent bandwidth. They also have arcing issues from high voltage.

The problem is that commercial and military applications (such as cell
phones) need multiband or wideband--and not the modest bandwidth.

The problem is that RFID doesn't have a size and gain problem, but an impedance
problem.

Thus the 'revolution' is somewhat small in population....But hams need modest
bandwidth and low height. Hence a potential niche.--if you have room for a
ground plane.

Is there really a market for short , single band, ham monopoles? Understand
that for a few more feet in height, you can get an MFJ multiband
vertical--without a radial system.

73,
Chip N1IR

How do you put capacitors in? Is this a good slow wave solution?

CCD antenna use capacitors in a distributed way to cancel the inductance. They
are commonly used in 1 wave dipole configurations. They have higher feedpoint
impedances than 1/2 wave dipoles and they have 3 dB gain when fully stretched.
Their pattern is figure 8, like a 1/2 wave dipole.

The Vincent antenna could use such an arrangement to emulate a 1/2 wave
monopole CCD (that is, a 1 wave dipole) where the 1/2 wave electrical length is
wound into a helix along the height.. In any case, there are a number of ways
of doing this. In my opinion, this is not new, if that is the case.

I suspect that Vincent has a number of combinations of arrangements, depending
on the desired height above 1/30 waves.

Remember: these are not efficient antennas; they are slow wave antennas. Put
lots of power into them and they will heat up; arc; and melt. They trade gain
against efficiency. They are not multi or wideband.

I would be very interested to know how hot a Vincent antennas when running 1500
watts continuous for an hour....If it's hot it's not efficient.

73,
Chip N1IR.