[hpsdr] Munin - L4, and Spacers - some tips

[Tom McDermott]

Here's some tips on assembling Munin.
 
I had a difficult time assembling L4. The braid in the kit was too sparse to even get
the teflon wire to go through it, and braid from RG58 too dense. I damaged
the insulation on the teflon-insulated wire trying to get the fourth turn through
the last braid - it just would not go.
 
I bought some hardware-store brass tubing:  1/4-inch OD  0.014 inch wall,
and some 0.015 thick shim stock. I cut the tubing into two pieces, each 1.160 inches
long (with a band saw), and used tin snips to shape some of the stock to fit over
the end of the ferrite, and two more smaller pieces to serve as connecting tabs. I
drilled drill size H (0.266 inch dia.) holes in the shim stock, and assembled a
primary by soldering the tubing and shim. After this, inserting 4 turns of the
remaining tefloine coasted wire was a piece of cake. Don't know if this is
recommended or not, but it sure made assembly easier.
 
Brass tubing and shim stock:
http://www.tapr.org/~n5eg/index_files/Tubing_Shim.jpg
 
Photos of L4: 
http://www.tapr.org/~n5eg/index_files/L4_Left.jpg
http://www.tapr.org/~n5eg/index_files/L4_Right.jpg
 
I found that my stock of 6-32 nuts are 0.106 inch thick. This is close to perfect for
use as the PCB spacer. It was easiest to place the 6-32 nut over the 4-40 binding
post on the heatsink side (the 6-32 clears the 4-40 threaded post on the spacer).
This elevated the PCB to the correct height to install the two flange mount
transistors. Putting it on the heatsink side means that it doesn't fall off when
mounting/unmounting the PCB from the heatsink.
 
Spacer photo:
http://www.tapr.org/~n5eg/index_files/Spacer.jpg
 
-- Tom, N5EG