Dale Parfitt wrote:
"ken scharf" wrote in message
...
raypsi wrote:
All I ever see for Pi coils is cylindrically wound single layer. I
remember when I built my first 6146A output cw transmitter back 40 yrs
ago, I used a B&W pre made coil for the Pi.

Depending on the Q and plate resistance you see coils for multi band
use up to 33 uh, in transmitters.

The only place I see pancake coils used is in Tesla coils, one of
which I built with a pre made 18" tall secondary coil. I wound my own
primary pancake coil.

Done right a pancake coil takes up alot less room than a cylindrically
wound coil.

A six inch diameter pancake coil can have the same inductance as a
three inch diameter by six inch long coil with the same size wire.

Anybody know why I shouldn't use a pancake coil in my final? I just
bought a 4-1000A. from ebay.

73
n8zu
Pancake coils are usually wound with several sections, not one large
section. The problem with these chokes is that they may exhibit resonance
within a ham band, this would be bad as the coil would 'explode' as it
absorbed the power. When we had only 5 bands, 80,40,20,15 and 10 meters
it was easy to design such a choke keeping any self resonance out of the
ham bands. Now that we've added 60,30,17 and 12 meters the odd's that
those old chokes don't self resonate in a ham band is not the good
anymore. A single layer choke will have only one self resonate point, and
it can be made to be above 30mhz (if it falls at 40mhz the choke would
also work on 6 meters). A pancake coil may have several self resonance
points.

Are we talking about the same thing here?
My take was that the poster was asking about the output pi network coil not
a plate choke- but I could be wrong. I took the question to be suitability
of a 2 dimensional spiral vs. a classic solenoid coil.
And for clarification, when you say pancake- are you talking about a 2
dimensional spiral?

Dale W4OP


Did he mean a toroid coil then? They have been used in tank circuits.