RadioBanter - Vincent antenna

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Loading Coils; was : Vincent antenna

On Sun, 02 Dec 2007 14:34:23 -0600, Cecil Moore
wrote:

I don't know about Art, Richard, but I detest your trying
to mind fornicate with me.

A contorted sentiment suitable for a schoolgirl's diary. :-0

I do believe we are discussing the delay characteristic of
current in a coil.

How does a Texas bumpkin manage to strain through two such heavily
mannered expressions?

Surprise us with a chorus of "Feelings" and maybe it will be you who
gets rolled out of the nest.

Loading Coils; was : Vincent antenna

Owen Duffy wrote in
:

A further issue is the accuracy of the estimate of the coil's
electrical length when represented as a transmission line. Using the
length of the wire in the coil (as is sometimes done) is too
simplistic. The Corum paper referenced at the calculator above
describes a method that appears to be more reliable.

I should have added... but what are you going to do with a more accurate
estimate of the equivalent electrical length of the coil anyway?

Owen

Loading Coils; was : Vincent antenna

Owen Duffy wrote:
One of the proponents posted on eham, the following solution to a loading
coil for 160m: "The VF of a 6" dia., 4 TPI coil on 160m would be about
0.02. Whatever number of degrees you want the coil to occupy, wind it
accordingly.", note the independence of coil size and location on the
monopole.

HUH???
THE LENGTH OF THE COIL IS NOT INDEPENDENT OF COIL SIZE!!!
THE LOCATION ON THE MONOPOLE IS NOT INDEPENDENT OF LOCATION!!!
The number of turns is dependent on coil size needed.
The number of degrees required is dependent upon location.
Please reread what I wrote until you understand those facts.

A greater number of degrees is obviously needed for center-
loading than for base-loading. This concept is extremely easy
to demonstrate in a an open-circuit stub.
************************************************** *************
When the Z0 at the impedance discontinuity *increases*,
electrical degrees are *lost*. When the Z0 at the impedance
discontinuity *decreases*, electrical degrees are *gained*.
************************************************** *************
For a base-loaded mobile antenna, electrical degrees are *gained*
at the coil to stinger junction.

For a center-loaded mobile antenna, electrical degrees are *lost*
at the base element to coil junction and *gained* at the coil to
stinger junction. Therefore, a center-loading coil has to be longer
than a base-loaded coil - all other dimensions being equal.

It is really simple transmission line analysis. Please perform
the following exercise to understand the concepts involved.

Example 1:

---600 ohm line---+---100 ohm line---open-circuit

The 100 ohm line is 10 degrees long. How many degrees does
the 600 ohm line have to occupy to be equivalent to a 1/4WL stub?

Example 2:

--100 ohm line--+--600 ohm line--+--100 ohm line--open-circuit

Each section of 100 ohm line is 5 degrees long, the same
10 degrees of total length as the 100 ohm line in the first
example. How many degrees does the 600 ohm line have to occupy
to be equivalent to a 1/4WL stub?

Hint: In the second example, the 600 ohm line will need to
be a lot longer because we have moved it from the base of
the stub to the center of the stub. Does this sound like
what happens when we move a coil from the base to the
center of a mobile antenna?

When one understands the above examples based on simple
transmission line stubs, one will understand what is
happening inside a loaded mobile antenna (but Richard,
this has nothing to do with radiation patterns).
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna

Earlier, I wrote:
AI4QJ wrote:
In an inductor, current lags voltage. If you connect a resitor and a
coil in parallel and apply AC, EE101 tells you that, although the
phase of the voltage across them stays the same, the current is
"delayed" by the phase angle in the inductor when compared to current
resistor.

No, it isn't - the phase of the current around the circuit has to
stay the same. Think of the simplest possible circuit: an AC voltage
source (of zero internal impedance) with one terminal wired to R,
lumped L in series, and directly back to the other terminal of the AC
source. If the phase of the current were delayed through L as you
suggest, there would then be a difference in phase between the two
terminals of the AC source... which is obviously not true.

It's the magnitude and phase of the voltage that varies at different
points around the circuit; but the magnitude and phase of the current
has to remain the same all the way around the loop. In more formal
terms, Kirchhoff's current law applies all around the circuit; and it
most certainly applies between the two terminals of a lumped inductance.

My apologies to AI4QJ. He was talking about a parallel R-L circuit, and
my reply was about a series R-L circuit. Each of our statements was
correct in its own context.

Thanks to Tom B for pointing this out.

--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Loading Coils; was : Vincent antenna

John Smith wrote:

[stuff]

Cecil Moore wrote:

[more stuff]

John Smith wrote:

[even more stuff]

Cecil:

When one is well armored and prepared to face the slings are arrows of
the religiously devout, one is able to contemplate and verbalize
personal visions/guess/questions of how the capacitive coupling and EM
coupling between turns in a humble-multi-turn coil might REALLY be
acting/interacting ... indeed, some may desire accurate formula to
describe this in finite detail, those I find are only "ball-park."

Perhaps an area for dreamers--I simply find it keeps me from bars and
loose women! :-P

Regards,
JS

Loading Coils; was : Vincent antenna

Owen Duffy wrote:
The key thing is that the transmission line solution passes to lumped
elements when the coil length is sufficiently short, so they are not
inconsistent. It is questionable whether the transmission line solution
is worth the trouble for short coils.

That's a Catch-22, Owen. All lumped coils are short.
Therefore, the transmission line solution is never
needed.

A 160m bugcatcher coil is *NOT* short!!!! It is an
appreciable percentage of the delay through the
10 foot long mobile antenna.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna

Ian White GM3SEK wrote:
- the phase of the current around the circuit has to stay
the same.

Only in a standing-wave environment. The phase of the
current does NOT stay the same in a traveling-wave
environment. That is the key technical fact that the
r.r.a.a gurus have been missing and it can be blamed
directly on the short-cut models which deviate from
reality, sometimes considerably.

In a traveling-wave environment, the phase changes
every inch around the circuit and I can calculate
that phase change for you if you are incapable of
doing it for yourself.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna

On Sun, 02 Dec 2007 21:58:34 GMT, Cecil Moore
wrote:

Some of the signal skips from
coil to coil reducing the phase shift through
the coil.

In what, about 2-4 ns?

Skips along, talk about technically rigorous. This is more schoolgirl
diary writing.

Loading Coils; was : Vincent antenna