With Impedance selection and Gain
This magic box allows you to connect any of your antennas to any of your receivers. You can also better
match the incoming impedance either with the fixed selector, or through an outboard tuner. You can
also add a bit of gain or fixed attenuation in 10db steps. There is also the provision to protect (to some
degree) from DC static buildup and RF bursts from nearby strikes. Note that the input and output are
kept at 50 ohms. It also helps clean up your shack, keeping all the cables centralized, and ending the
task of constantly patching cables from one radio to another.
Below is the basic circuit which you should customize to suit your needs. I have built 3 of these in a
much simpler form (see below). One resides within the Type-1 Preselector, and the other two have been
out on loan ... for way too long.
Note how I break the line with switches, two times, between the input toroid (50 ohms input) and the
preamp (50 ohms output), so you can add two pair of additional connectors and have a "loop out/in" for
a preselector and tuner (transmatch).
In terms of construction, I'd recommend building the following modules in shielded sub-chassis:
preamp, attenuator, and toroid. Also, use RG174 coax, or similar to wire the inputs and outputs.
I'll be adding a preliminary sketch of how I invision the panel layout, but you should build yours the way
the most sense to you -- with logical and flowing control placement, and minimum of internal wiring
Build this box and switch between several antennas
and several radios. Insert a preselector and/or a tuner
at the jumper position and have convenient use of all
your facilities, controlled by one box
|Here's the basic circuit. It makes a neat, organized shack and allows for
any receiver to be connected to any antenna.
Customize the design to suit your needs, ideas, and tastes.
Left and right
full size views.