In article ,
Colin B. wrote:

So then if I read the original explanation correctly...

The fact that twinlead is used in a folded dipole is coincidental, and
each half of the wire pair is a different part of the whole single-wave
dipole path. In other words, there's a single loop path, and no propagation
velocity to correct for.

But each half of the antenna is in effect a twin-lead quarter-wave dipole,
and has the normal propagation of about 85%. Hence the shorting wire, to
shorten the quarter dipole and correct some SWR mismatch.

I'll check my reference books tonight, if I can, and see if I can
confirm or clarify that.

The next question then, is how much of a difference would this make for
FM reception? Is it noticable? Measureable? Worthwhile to do?

My guess is that the benefits are relatively minor, for several reasons:

[1] Most twinlead floppy dipoles are built without the shorting wires.

[2] The FM band is a relatively wide one - the width of the band is
roughly 20% of the center frequency. Any relatively thin
half-wave dipole cut for any frequency in this band is going to
be significantly mis-matched, and have a fairly high SWR
somewhere else in the band.

[3] In my experience, a twinlead dipole's ability to receive a clean
signal is usually limited more by the presence of multipath
reflections and nearby noise, than it is by the antenna's basic
signal sensitivity. Making small adjustments in the dipole's
location and orientation is probably going to make more of
a difference than tweaking with the dipole itself.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!