[Lowfer] modeling coils

Sat, 8 Mar 2003 11:20:17 -0600

Hey Mitch,
I assume that was 50 turns on the variometer instead of "%0 turns".

Mike>WE0H
http://www.we0h.us/lf

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Mitch Powell
Sent: Saturday, March 08, 2003 11:15 AM
To: [email protected]
Subject: [Lowfer] modeling coils

>
> Unless this is not a good idea, I'll wind the coil to 2.5 millihenries but
> add a few extra turns with taps.  Also, I'm including a variometer.

Coil pictures
http://technology.fanshawec.on.ca/tele354/digcoil.htm

Eric:
Information on my coil, which was based on "the coil of Dex".
Top/bottom plywood = 20 " square.
Height = 18".
Spacers = (11 of them ) 1/2" pvc pipe ( from Home Depot, of course)

#12 gauge "household" plastic covered wire.
Total turns = 70
Diameter of 16 inches. Vertical length of coil = 8 inches.
The link is (black wire in pictures) 2 turns at the bottom, to ground.

This coil measures out as 2 mH, with a Q > 400.

VARIOMETER is 250 uH.  Wound with #12 plastic on white 6" dia
PVC pipe ( sewer pipe I believe ). Length was 6 inches.
%o turns came out at 250 uH, with a Q>350.

I used a 3 foot piece of the 1/2 inch pvc pipe, drilled a hole through the
variometer coil form, and used this to rotate the coil.

End result was an inductor that could be varied between 1.5 to 2.5 mH,
which gave me plenty of range at 185 kHz.

TAPPING:
I tapped the top ten turns, by scraping a small area of plastic insulation,
and tinning. This allowed me to make significant changes as I modified the
tophat or vertical portion.

WIRING: I used small lengths of RG59/U coax shield for connections, so
example from the ends of the moving variometer, and to the taps. I was
worried about using the solid #12, bending and finally breaking.

I include a note by Andy G4JNT - which proved very useful, and very accurate
in planning coils. The coils were well within 5% for all coils I made.

quote:
Both my 73 and 137kHz loading coils were within 5% of design value (that is
actual real inductance, not the effective value after taking distributed
capacitance into account)

Initial design of multi layer coils is not too far out with this formula
either.

L (uH) = (N.D)^2 / (0.46 D + 1.02 G)

All dimensions in mm, D is coil diameter, G is length, N number of turns.

Andy  G4JNT

endquote"

Try that one on the variometer ! !  25.4 mm = 1 inch

Remember - being experimenters, anything goes, so try something
yourself. But glad to share this experience with you ! !

Another great article, and works out very well..... Bill Bowers article in
Lowdown.
http://technology.fanshawec.on.ca/tele354/bowers.htm

Mitch