Signal Preconditioning
If you can solder, follow a schematic, and drill holes in a metal box, then you can build this. What will you need? Time. That's the
big one. Take the time to lay out your project. You are the one who will have to live with it forever, so get it right the first time. Here's
layout (within the SR-III HR). Next, you will need some money, and/or a good junk box full of delightful treasurers. I buy a lot of
components from Mouser Electronics because of the convenience. They are nice people, ship fast, and are considerably less
expensive than their competition. No, I am not associated with them in any way! There is a link on the home SWL page with other
recommended vendors as well.
This combination of Input Protection, Impedance Matching, Signal Level Management, Preselection
Filtering, Superficial Noise Abatement, and ergonomic/intuitive layout is a product of several previous
I brought them all together in one project for the first time while assembling the
SR-III Hot Rod Project.
Some of this technology is used in my
Antenna Switcher project...and the Dynamic Noise Blanker
project. These circuits work and have been refined over several iterations. They are not perfect. That
statement is your challenge to refine their performance (please be a pal and advise me of your
findings - I'm always interested).
Note that all the signal manipulation is done in the analog domain - even though it can be
circumvented, I prefer to avoid any possibility of introducing digital noise - especially when working
with micro-volt signals.
The basic Broadcast Band Preconditioner. For the entire Broadcast Band, use the preselector filters
shown in the Type-3, type-4, or Type-5 units. Note the antenna matcher used here is a selectable tap
transformer rather than an LC tuner. The preselector filters are switchable for high, medium, and
moderate passband Q-factor. The attenuator is an L-pad configuration, not a T-pad or Pi-network. The
reason for this is simplicity. When measured against a true, lab-instrumentation attenuator, the
differences are minimal, and the cost and fuss is 10-times less. There is no undesirable signal loss
(loading) due to impedance mismatch between the transformer and any attenuator setting. The
transformer is designed to always look like a
constant voltage source to any subsequent stages.
The optional superficial noise abatement circuit. Compared to the preconditioner above, this circuit
is probably of less utility value. You may, or may not, want to consider it when starting. Of course it
can always be added later.
More to come as it develops. In the mean time, keep checking on the SR-III Hot Rod Project.
Contact me
Here is a plot of
coverage with
alternate circuit
components for
the preselector
Using a
switch, it is
possible to
have complete
coverage of
the BCB, plus
the ability of
selective "Q"
(bandpass filter