Richard Harrison wrote:
Geoff Mendelson wrote:
"I think if I were to short both ends and center feed it, it would be an
equivalent to a wid(er) 1/4 wavelength end fed antenna and will still
need a counterpoise."

No counterpoise needed. Its called a "folded quarter wave dipole". Its
first resonance is due to its 1/2-wave circumference. Its input
resistance is not 300 ohms but 600 ohms. Its gain is 0,5 dB less than
the 1/2-wave dipole. This information is from "TV and Other Receiving
Antennas" by Arnold B. Bailey.

You might want to feed it with 450 ohm ladder line.

Best regards, Richard H. Harrison. KB5WZI

In my copy of Bailey (1950), he says (p. 415) that the feedpoint
resistance of this antenna at resonance is very high, its value
depending on the conductor diameter and spacing. He shows one example
having a resistance of 4160 ohms, and states (p. 416) that

"Thus we see that at first resonance the [quarter wavelength] folded
dipole exhibits the qualities of a shunt-tuned circuit and has a
terminal resistance value Ra of high magnitude. This precludes its
general use where a normal transmission line is employed, unless the
rods are made very thick."

Even if you did manage to reasonably match the antenna, the bandwidth
would be very narrow and the loss potentially high.

Sorry, as Robert Heinlein said, TANSTAAFL - There Ain't No Such Thing As
A Free Lunch.

Roy Lewallen, W7EL

Roy Lewallen wrote:
"Thus we see that the (quarter wavelength) folded dipole exhibits the
qualities of a shunt-tuned circuit and has a terminal resistance value
Ra of high magnitude."

Yes, my copy of Bailey says the same. I got the 6000 ohms from page 509
in the catalog section where large diameter rods were used for the 200
MHz antenna.

Looking at Bailey`s page 508, Fig. 8-14, it seems a 1/2-wavelength
perimeter can be opened into a loop instead of a folded dipole and iits
radiation resistannce drops to about 5 ohms. This is a mixed blessing
because as Roy says, "There`s no free lunch". A loop configuration does
not lower the loss resistance in the conductor and this will extract a
larger percentage of the energy fed to the conductor with a lower
radiation resistance.

A closed loop has an inductive reactance at frequencies below first
resonance (when the wire perimeter is almost 1/2-wavelength). This
reactance can be compensated with a simple low loss series capacitor. It
is unfortunate to not have room for a straight radiator.

Best regards, Richard Harrison, KB5WZI