On Tue, 24 Jun 2008 09:10:31 -0700 (PDT), Nick
wrote:

Hi Nick,

In response to the ad-copy, I would make some points:

When quarter-wave antennas are constructed over a good radial system,
they have a feedpoint impedance of about 36 ohms. When they are
constructed over less than a good radial-system there is a loss
introduced into the feed system that adds to the 36-ohm figure. This
improves the SWR but there is a loss in the efficiency of the antenna,
This is good, as far as it gets to this point, but...

signals transmitted and received have a higher take-off angle and
often there is current introduced on to the feedline.

Take-off angle is dictated to the quality of ground 5 to 10
wavelengths AWAY (and further) from the antenna.

You could, if you so choose, build 120 radials out 20 wavelengths to
achieve their implied claim of radials contributing to lower take-off
angles.

With a ground-mounted quarter-wave vertical, regardless of the radial
situation, but especially with poor radial systems, the feedline can
become part of the radial system, causing RFI and poor antenna
performance.

For a transmitter, it is unlikely that the listener could tell the
difference between operating into that "poor radial system" and adding
the a vfcc.

By using a VFCC at the feedpoint, the feedline is
effectively de-coupled from the antenna system, preventing interaction
with the radial system, improving antenna efficiency. You may notice
improved bandwidth as well.

This contains a contradiction when it gets to the "improved
bandwidth." Presuming that means wider, it then means more loss. More
loss would come from NOT using the vfcc (or why buy one?).

The Advantages of Using a VFCC:
Prevents unwanted RFI by eliminating feedline current and radiation
All power goes to the antenna, improving efficiency

Uh-huh. Again, will the listener be able to tell? A radiating
feedline might boost their gain - who knows?

Reduces noise or unwanted signals picked-up by the feedline
Overcome a less than optimal ground system
Bracket isolates the VFCC case from ground for best de-coupling"

The noise pickup is the more likely benefit (along with the remote
ground - tied into the service ground as required by code). House
noise can travel down the outer portion of the shield to then develop
across the load of the antenna, and then wrap around to travel back
inside the coax to the receiver. A choke will snub this path and the
remote ground will lower the resistance. The divider action
suppresses local noise.

The same benefit can be obtained from a $25 purchase of bulk ferrite
beads (about 50 of them) which are fitted over a one foot length of
RG-58 (or the distal end of your feedline).

73's
Richard Clark, KB7QHC