Page 2: Mechanical Assembly SDM-1 Multi-Demodulator
location dimensions to the front panel prior to
Actual decal as printed with a clear laminate glued
to the front. Next it will be cutout in "module
sections" and thin double-sided tape applied to the
Screen shot of the decal being designed in a
graphics program. The (blue) guide lines allow for
perfect dimensional alignment and sizes.
The decal applied to the machined panel.
Panel rear with components mounted to test for fit
Front view showing how it all comes together.
Rear of panel while testing amber LEDs.
Knobs added. Note two pots missing, but
anticipating the FedEx truck.
I always have trouble photographing light-source
objects, but you get the idea.
This is the Detector Select mode switch. Since it
will be switching all five of the detectors' inputs,
455KHz (RF) and base band audio outputs, I had
to shield the front and back wafer sections. It is a
piece of copper that was drilled and inserted
between the wafer spacers. It will also serve as a
ground bonding point for all ten of the coax runs for
the inputs and outputs. That's gonna be a busy
The actual wiring will begin soon, but at the moment
some of the components are still on back order. I
hope to have this playing before the New England
snow flies...I hope to.
A few shots of the "quad-demod" (say that fast!). The fifth circuit, which is the Synchronous Detector, is on another sub-chassis, due to its size, and not shown here yet. Shown above
are the non-sync circuits, from left to right; full wave, ultra-linear, high dynamic range, and high-speed envelope detectors. Note the shields between each card - they are probably not
needed since the inputs and outputs are individually switched, but it never hurts to suspect the worst in crosstalk or oscillation ... also, the shields make for convenient PC board
Olympic sentence follows: I have beta tested these various modes of AM detection for many hours, and they really are an asset for clean, clear, crisp audio. Why they work differently for
various forms of fading, a la, selective, phase-shift, pseudo-multipath, and time delay QSB (fading) and the audio is demodulated either better or worse by these different circuits, at
different times, under different atmospheric conditions, is not well understood at the moment. But we are really going to try to figure it all out. I do know that there are many variables to
consider, and they are continuously parametric in the time, frequency, and amplitude domains - the permutations might seem to be almost infinite.
Amplitude Modulation Detector Circuit credits:
(Improved) Full Wave Detector; Rob, K2CU
Ultra Linear Detector; Dr. Ulrich L. Rohde, KA2WEU
High Dynamic Range Detector; Frank,WA1GFZ
High Speed (biased Schottky) Envelope Detector; Bob, N1KPR
Sync Detector; Ron, KK4PK
Here is the inside. I overlayed some labels that define the various modules.
Rear apron connectors:
4 IF Inputs
4 Audio Outputs
1 Audio Bus
1 IF Bus
1 Audio Loop
The audio loop allows the use of other
analog or A/D-D/A device, such as
Noise Filtering, Audio Equalizer,
Another shot of the front panel.
Special attention was given to making
the meters easy to read and in using a
pleasing amber lighting color and
intensity to avoid fatigue.