[Lowfer] The Dex VLF Loop

Tue, 29 Apr 2003 22:16:48 -0400

Peter Barick wrote:
> 
> Looking at the Web pics I see the two layered windings and wonder what
> holds the inner windings to the cross-pipes.

Peter I guess you are referring to this pic of the loop:

http://www.w4dex.com/newloop3.jpg

The inside windings are held in place by a "U" pin of the #14 wire.  Two
small holes were drilled though both sides of the pipe.  The holes are
spaced approximately one wire diameter apart.  The inside windings were
made first.  The U pin was pushed through the pipe and taped in place on
the winding side then bent at right angle on the other side.  The
outside windings then were laid between the two wires.  The ends of the
pin wires were then loosely twisted around the winding wire. 

> About how much C is used in tuning? Fixed of fixed and variable amounts
> of C?

The loop inductance is about 3.2 mH.  A few days ago while I was setting
it up for WWVB I found the loop to perform well from at least 8 kHz to
200 kHz.  I was just tacking fixed micas and compression micas in series
with the coil.  So to tune it takes whatever amount of capacitance it
takes to bring 3.2 mH to resonance at those frequencies.  At 60 kHz I
think I have a 2000 pf fixed SM and a small trimmer in parallel.  No
remote tuning.  So far I haven't really seen a need.  I don't claim this
loop to be practical but it's sure nice to see WWVB wave directly
displayed on a scope with no amp or filters in line.

Dex

> 
> Peter
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