On Thu, 04 Mar 2004 21:36:22 GMT, "aunwin"
wrote:
What is it about parallel circuits that make them unsuitable?

They are used every day to load up halfwave verticals, which in turn
are also parallel equivalent circuits.

Did you mean that? A halfwave vertical is a parallel circuit!

That is the longstanding convention. Same thing applies to a one
wavelength dipole. All such are the basis of the J-Pole and the Zepp
(when you strip away their matching sections).

The input to the parallel
interface is performed through divider action (usually a tapped coil,
but could be through a capacitor divider).

Yes I know that but the question did say antennas didn't it?

Antennas don't find much application without some method of driving
them. Very few successful halfwave designs exist without matching.
This is because the halfwave vertical, looking like a parallel
circuit, has a considerable amount of Z that rejects power (unless
your rig is a van-de-graff generator). Adding the radiation
resistance to a high Z hardly allows any current into the radiation
resistance. On the other hand, a quarterwave looks like a series
resonant circuit with very low Z, and thus the radiation resistance
absorbs all the power applied. Very simple electronics.

One solution to feeding the halfwave tall vertical is to break it in
half and feed it half way up (where the two sections look like series
resonant, low Z elements feeding the radiation resistance without much
impediment). This is simplified, of course, but it illustrates how
the same circuit can support either a series resonant or parallel
resonant description determined only by the topology of connection.

You gave an answer to a question that was not asked. What you are refering
to is not for its radiation attributes is it? I hope we are not going into a
multi heading thread mode in less than 12 hours.

Matching sections to the J-Pole and the Zepp are contributors to
radiation due to the unbalanced nature of those antennas designs. How
much they contribute is perhaps arguable, but when they are built in
without care, their contribution cannot be denied. The matching
circuits contain both circulating currents and common mode currents.
The common mode currents, as a function of the physical length
compared to wavelength, offer radiation. The radiation may aid, or it
may hinder, but it is there none the less.

Is stagger tuning a parallel circuit ?

No, but it could be. Stagger tuning, by convention is a chain of
separately tuned circuits, be they RC, RL, or LC (or, of course RLC).

You mentioned the all important word of "tuned" so all of the above are
parallel circuits....right?

No, but they could be. The application of drive and loads determine
the topology:

One RC or RL circuit exhibits a 6dB/Octave or 10dB/Decade roll-off.
One LC circuit exhibits twice that or a 12dB/Octave or 20dB/Decade
roll-off. Again, it is all a matter of connections for the identical
components (which will show a slight shift in parallel to series
resonance frequency - which is to say it is application
dependent).

I totally miss this point and probably the blame is mine. I think you are
saying that yes, they are parallel circuits, but you have an exception that
you want to point out i.e.slight shift in parallel to series...........

No, they are NOT parallel - they could be, but there is nothing
inherently parallel and it all depends on the drive and load applied.

Not sure if you are saying 'yes'. I personaly think it is a parallel
circuit to which I would answer 'yes'.

No, they are NOT parallel - they could be, but there is nothing
inherently parallel and it all depends on the drive and load applied.

Force
12 has stagger tuning, if it is series devised then it gives more ammo to
the 'do not use parallel circuits for antennas' argument which seems to be
prevalent with antenna experts.

Force 12 makes many antennas, I will presume you are speaking of some
beam array. Stagger tuning, in that sense, is much akin to the
reflector, radiator, director relationship of the yagi. That design
is stagger tuned, but such stagger tuning is to accomplish various
delays that aid gain in one direction, and negate it in another. Such
stagger tuning is not directly engaged upon for the purpose of
bandwidth, although it may have indirect consequences. I have a beam
array for 440 that employs an LPDA radiator tied into the conventional
reflector and directors. As such it performs stagger tuning for the
purpose of beam forming AND bandwidth.

The elements in the Fan Dipole or the Log Periodic Dipole Array more
closely align to the conventional meaning of stagger tuning. The Fan
Dipole is the most obvious case. It's metaphor would be as many
parallel, series resonant circuits as there are elements, each
slightly tuned off from the other, all feeding in series and combining
in parallel to average a wider bandwidth response than any single
series resonant element.

73's
Richard Clark, KB7QHC