"amdx" wrote in message
...
The gap in the ribbon would be 0.020", but note; in the pictures
a moon shaped piece has been cut from both ends.

This decreases what's otherwise taken as a lumped capacitor right at the
feed point; this is generally undesirable because it lowers the impedance
from the theoretical calcuations.

There are 4 toroids on the coax. These are under a piece of heat
shrink, so I have no idea what material they would be.

Those toroid are a simple but effective balun: Without them, current that's
supposed to return to the inner side of the coax's shield instead has a
choice between that inner side or the outer side. Currents that flow on the
outer side of the coax's shield significantly distory the radiation pattern.
The toroids "work" because they look like inductors (hopefully big
impedances) to single-ended currents (current trying to go down the coax)
while the fields of current going down the center conductor of the coax in
addition to those from the same current going down the inside of the shield
cancel out to (almost) nothing outside the coax and therefore the ferrite
toroids aren't "seen."

Driven element impedance

Well, if you're driving it with 50 ohm coax, it should be realtively close
to 50 ohms at resonance!

---Joel