THE DUPLEXER:
This is a very nice project, especially for those Icom
706's that have an HF / 6m antenna connector as well
as a VHF / UHF connector. This duplexer allows you
to combine both outputs to a single all band antenna.
The project was found on Felix's HB9ABX site:

http://home.datacomm.ch/hb9abx/diplhf6m-vuhf.html

DUPLEXER SCHEMATIC

Component list:
all coils 1mm dia enameled copper wire
L1  = 1 turn 5 mm (id)
L2  = same as L1,  orientation 90 degr in respect to L1
L3  = 1 1/2 turn 6 mm (id)
L4  = same as L3 , orientation 90 degr in respect to L3
L5  = 7 turn 6 mm (id), 15 mm long
L6  = 11 turn 6 mm  (id), 19 mm long
L7  = same as L5
C1  = foil trimmer cap. 9 pf   (0.5-9 pf) see note in text
C2  = same as C1
C3  = same as C1
C4  = foil trimmer cap. 32 pf   (3-32 pf)
C5  = same as C4
C6  = same as C4
C7  = foil trimmer cap. 135 pf (5-135 pf)
C8  = same as C7
3  HF chassis plugs 50 Ohm 
1  metallic box (solderable)

dulexer3

duplexer


duplexer5

Adjustment procedure:

1.  Connect  50 Ohm dummyload to plug 0 - 440 MHZ .

2.  Connect SWR meter between 0 - 52 MHZ plug and TX  (51 Mc carrier low power).
    (If no 6m TX available adddjust on 10m band)
    Adjust C7 and C8 to obtain  SWR < 1.1 .

3.  Connect SWR meter between 2 m  plug and TX on 2 m (145 Mc carrier low power).
    Adjust C4, C5, and C6 to obtain SWR < 1.1 .
    C4 and C6 should reach the same value.

4.  SWR meter same as step 3, but TX on 70 cm (435 Mc carrier low power).
     Adjust C1, C2, and C3 to obtain SWR < 1.1 .
     C1 and C3 should reach the same value.

-   Repeat steps 2 - 4 , as adjustment of one band influences the other.
    You will need some patiance to reach proper adjustment on all bands!

Now your diplexer is ready for use.

I built the duplexer in an electrical box on copper board.
There is isolation between the sections and the SO-239
connectors are soldered to the box. Works great,
tested to 100w.