About Us

May 3rd 06, 04:47 PM posted to rec.radio.amateur.antenna

On Mon, 1 May 2006 22:59:20 -0500, (Richard
Harrison) wrote:

Richard Fry wrote:
"Such networks don`t add or subtract electrical degrees, however. They
only reduce/cancel the natural reactance of the physical radiator in
use."

True if the only mismatch is reactance. A too-long antenna can be
electrically shortened for matching purposes by tuning it to resonance
with the proper series capacitance. A too-short antenna can be
electrically lengthened for matching purposes by tuning it to resonance
with the proper series inductance.

Reactance varies quickly near the resonant length. Radiation resistance
varies more slowly tending to increase at a steady rate as the antenna
is lengthened.

What radiates is current in a length of antenna. What gets current into
an antenna is a conjugate match. Reactance is zeroed out, and source and
load resistances are matched. That`s what`s needed for maximum power
transfer between generator and antenna.

Analysis may have been more abundant than needed for practical purposes.

The velocity of current through a coil has been disputed. Some said it
was almost instantaneous. That was new to me. The nature of inductance
is to produce counter emf which by Lenz`s law opposes current into an
inductance and temporarily delays current changes in an inductance. Only
in a pure resistance is there instantaneous correlation between voltage
and current.

Constraining the discussion to lumped circuit theory, the delay that
you speak of would seem to be relevant if one is measuring transient
response. However, for a steady-state a.c. current, is it not more
appropriate to describe the relationship as a phase lag between the
current through and the voltage across the inductor? Further, is it
not the case that such phase difference is nominally fixed at near 90
degrees (for a high Q inductor), and is it not true that the velocity
is nonetheless at the speed of light?

It is believed that the speed of light "c" is a speed limit on
electromagnetic waves. An action in one place must have a delayed
response elsewhere depending on distance.

I can imagine a wave launched at one of an inductor sweeping across its
length and ignoring the round and round path of the wire, but I don`t
know of any of the old authors in my collection who say that such a
short-cut happens. Conductors are the source of free electrons which
permit current flow and my experience is that electricity goes where it
is wired.

Best regards, Richard Harrison, KB5WZI

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search
Display Modes
Switch to Linear Mode Switch to Hybrid Mode Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Missing Degrees in Mobile Antennas?	Cecil Moore	Antenna	31	April 30th 06 02:45 PM
(OT) 83 Degrees	David	Shortwave	0	August 14th 05 05:32 PM
Walter Maxwell's Missing Posts	Richard Fry	Antenna	4	March 28th 05 08:58 PM
FT-80C missing buttons from FT-747GX	Sam Nelson	Equipment	0	November 10th 03 08:26 PM
FT-80C missing buttons from FT-747GX	Sam Nelson	Equipment	0	November 10th 03 08:26 PM

Menu

About Us