[hpsdr] Fwd: Re: Munin - L4, and Spacers - some tips

[Kjell Karlsen]

------- Videresendt melding -------
Fra: "Kjell Karlsen" <la2ni at online.no>
Til: "Tom McDermott" <tom.mcdermott4 at yahoo.com>
Cc:
Emne: Re: [hpsdr] Munin - L4, and Spacers - some tips
Dato: Fri, 23 Aug 2013 21:16:51 +0200

Hi Tom.

Did you follow the advice on the Munin 2 (http://k9ivb.net/munin2/) and L4
construction description?

The reason I wind the transformer using a braid instead of the tubes is
that the transformer is much more efficient at 50 MHz. It is very
important that the 4 secondary turns are covered by the braid all the way
at the right hand side. In fact, the efficiency is around 10-15 % higher
at 50 MHz than a standard transformer.

This is a variant of the transformer used by ICOM, Kenwood and Yaesu in
all their modern transceivers. ICOM use 4 pieces of low impedance coax
with the braid connected in parallel for the primary and the inner wires
connected in series for the secondary. The result is the same.

This is also the reason why the output is near the primary to have as
short connecting ends as possible.

I think you can fix your transformer by cowering the turns on the right
side with braid and solder to get a complete shield. The Teflon insulated
wire is not damaged by the heat.

73, Kjell





På Fri, 23 Aug 2013 07:14:18 +0200, skrev Tom McDermott
<tom.mcdermott4 at yahoo.com>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> 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
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