W0EB's Dot Stabilizer

I was originally under the impression that this bounce was being caused by excess dot contact vibration as the contact "break" occurred, but after quite a bit of research and oscilloscope analysis by myself and one of my users (pictures of the traces later on this page), I have finally realized that it's caused mainly by improper contact alignment, minor imperfections in the contact surfaces of both the fixed and movable dot contacts that do not allow for near perfect mating of the two contacts as they come together and the fact that the movable contact is actually on the end of a spring that is really free to vibrate as the contacts come together during the forming of the dots.

In a perfect world, the factory would achieve perfectly smooth surfaces and perfectly square alignment of the two contacts, but we all know this is really asking too much of them, and the average individual either doesn't have the tools, expertise or patience to achieve this either. Mr. McElroy evidently figured this out and came up with the original "Dot Stabilizer" as he called it.

The DS stops the spring from bouncing too much as they come together at the beginning of the dot. It allows setting this "make" tension at an exact and adjustable point,and this comes very close to completely stopping that "contact wiping" bounce which appears to be the root cause of "Scratchy Dot Syndrome". It does not, however, correct bad CW caused by poor sending habits or failure to keep the bug's contacts clean.

T.R.'s original version required replacing the existing dot contact assembly with his stabilizer and fit only the McElroy manufactured keys. For some unknown reason, most information on the original Dot Stabilizer was either lost or ignored during the WW2 years and later except by a very few people. I'm quite happy that I was able to resurrect something from the past that does such a nice job of making a bug able to send better CW without having to severely modify a nice key.

Many people have used a bit of foam stuffed between the loop of the movable dot contact to stop the "scratchies" but it requires periodic replacing as the foam tends to crumble over time. I got a bug at a hamfest that had the foam solution a few years ago and after reasearching the reason for the foam, I found out about T.R. McElroy's original "Dot Stabilizer".

With advice from another bug user, I undertook a slight redesign of McElroy's original device to eliminate the necessity for replacing the vibrating dot contact assembly. This allows the device to be easily installed and removed quickly with simple tools. I also came up with a further variation on McElroy's design that can be used on even the "Flat Pendulum" bugs such as the Vibroplex Lightning Bug, Military J-36, Zephyr and Champion models as well as various copies of them.

Some additional images and information provided by a satisfied customer, Fred Schebor, K8NGW after he installed a Dot Stabilizer I made for his left handed Vibroplex Presentation. The following images are Copyright(C) Fred Schebor, K8NGW and are used here by permission.

Left Hand Dot Stabilizer mounted on K8NGW's late model Vibroplex "Gold Base" Original

Since I did not have a photo of a left handed bug with a left handed Dot Stabilizer properly mounted on it to use in the instruction sheet I provide with every dot stabilizer I make, Fred, K8NGW sent me pictures of the one he installed on his Vibroplex Original (Gold Bug) Presentation model. He also gave me permission to use the photo(s) as I needed and gave me a copyright release to do so.

Fred also hooked up a scope and ran before and after tests of the keying waveform using his bug. The first scope screen capture shows the contact bounce that causes the "Scratchy Dots" and the second trace shows the alleviation of the bounce that all but completely eliminates the "Scratchies". Many thanks to Fred for providing these pictures and for his kind permission to use them as I needed.

K8NGW Oscilloscope trace showing a "Scratchy Dot" before installation of the Dot Stabilizer.

And, finally, the last picture shows the effect of an installed Dot Stabilizer on the keyed dot, virtually eliminating the nasty bounce that caused the "Scratchy" dot. I hope these photos and the accompanying explanation helps illustrate the cause and one effective cure for a bug's nemesis, the "Scratchy Dot Syndrome".

K8NGW Oscilloscope trace of a keyed dot after installation and proper adjustment of the Dot Stabilizer.

Jim Sheldon - W0EB

Last updated by W0EB - 03/01/2023 @ 16:00 UTC