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

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.

"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

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.

On Aug 10, 6:38*pm, ken scharf wrote:
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.- Hide quoted text -

- Show quoted text -

Dale got it, Pretty clear to me he is talking about a coil 1 turn long
by X turns deep similar to an inductor etched on a PC board. Seems Ive
seen a 6m coil like this. 2 or 3 turn of copper capilary tubing.

Jimmie

On Aug 10, 10:40 am, 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

Well we all know what an roller inductor is?
Here is a pix of one: http://www.palstar.com/ri20.php

So here is a link to a java program to calculate a
flat spiral pancake coil:
http://www.classictesla.com/java/calculat.html

I might have confused people with pi wound coils I'ma
not talking about pi wound coils such as the 3 pi
coil found he
http://www.oselectronics.com/ose_p91.htm

I want to use a flat spiral wound coil to replace a roller inductor.
Like the one in the above mentioned roller inductor link.
Any pro's and con's on this topic?

To calculate the coil I want to replace this is the link:

http://www.qsl.net/in3otd/indcalc.html

here is a link to a image of a flat spiral coil: aka pancake coil

http://pulsedpower.de/inductances/img_spiral.gif

73
n8zu

I guess what I really wanted to do is make a PA
for all bands with a plug in PCB. That would have
the right size coils etched into it for each band.
So when I change bands I would just unplug one
band PCB and plug in another PCB for the band
I want. Rather than a band switch that would arc
out. Or a roller inductor that I would have to turn
to the right number of turns to get to the band I
want. Alot cheaper to plug in PCB's than the
price of a band switch with lots of wires
or roller inductor.
This would eliminate trouble switching to 10
meters with a band switch I suspect.

I'd use an edge card connector to plug the coils/PCB
into and out of an edge connector.

On Sun, 10 Aug 2008, raypsi wrote:

I guess what I really wanted to do is make a PA
for all bands with a plug in PCB. That would have
the right size coils etched into it for each band.
So when I change bands I would just unplug one
band PCB and plug in another PCB for the band
I want. Rather than a band switch that would arc
out. Or a roller inductor that I would have to turn
to the right number of turns to get to the band I
want. Alot cheaper to plug in PCB's than the
price of a band switch with lots of wires
or roller inductor.
This would eliminate trouble switching to 10
meters with a band switch I suspect.

I'd use an edge card connector to plug the coils/PCB
into and out of an edge connector.

Well you wouldn't be changing bands with the transmitter
going. So in that regard, plug-in coils, bandswitch or
jumpers are about the same.

People like switches so they don't have to turn off their
transmitter (to ensure not dangerous voltages) reach into their
transmitter and plug in coils. If you have to reach in,
at least some of the other possibilities are viable.

Your edge connector may introduce problems of bad contacts.
If you have to run current through them, bad contacts will
not be a good thing.

And I'd add that a large inductor may not be feasible etched
on a circuit board. The only times I've seen coils etched
into circuit board have been when the coils are low inductance,
the sort of values you'd see at VHF and UHF. Making a coil
large enough may result in way too big a plugin board.

You haven't really specified, I don't think, whether this
is a tube or transistor transmitter. In the days of tubes,
the transmitters were narrow band. With transistors, they've
generally been broad band. So with transistor transmitters,
the bandwitching has been about switching in bandpass or low
pass filters for each band, and since the broadband transmitter
has 50ohm output impedance, the switching is relatively easy.

Michael VE2BVW

I guess what I really wanted to do is make a PA
for all bands with a plug in PCB. That would have
the right size coils etched into it for each band.
So when I change bands I would just unplug one
band PCB and plug in another PCB for the band
I want. Rather than a band switch that would arc
out. Or a roller inductor that I would have to turn
to the right number of turns to get to the band I
want. Alot cheaper to plug in PCB's than the
price of a band switch with lots of wires
or roller inductor.
This would eliminate trouble switching to 10
meters with a band switch I suspect.

I'd use an edge card connector to plug the coils/PCB
into and out of an edge connector.

That sounds rather like the Norcal Sierra design. The pluggable band
modules on the Sierra use toroidal coils for the band-specific lowpass
and bandpass filters. The PA itself appears to be a broadband design.

--
Dave Platt AE6EO
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