[GreenKeys] Distortion Testing of my AN/FGC-25

[Howard Weeks]

I agree that a probable cause is the keyboard contacts. Need to be 
carefully cleaned and adjusted. Another contributor to the problem could 
be the keyboard shaft clutch (lubrication, adjustment)etc.

Howard in GA

On 7/4/2015 11:39 AM, Chris Elmquist wrote:
> Don,
>
> What an awesome project and fabulous that you used an MEK6800D1 kit for
> the job!  When I am not collecting teletypes, I am collecting Motorola
> 6800 stuff and the place is full of them here.  My first computer, when
> I was 14, was an MEK6800D1 kit that my dad got for me, just before that
> processor had yet been released!  Still have it, still runs.
>
> I will study your data and certainly respond if I have any ideas but I
> will likely defer to the TTY experts on list since I'm probably better
> with the 6800 than the teletype :-)
>
> My initial impression is that the width of the glitches is changing
> a lot each time one occurs and so this suggests to me contact bounce
> rather than a speed or timing issue.  You mentioned in the notes that
> you had cleaned the contacts.  Have you revisted that since collecting
> this data or ??
>
> 73,
> Chris NØJCF
>
> On Friday (07/03/2015 at 10:08PM -0700), Don Sentz via GreenKeys wrote:
>> It was great to receive all the positive feedback regarding my teletype set, many thanks to all of you who wrote to me. I am very grateful to know so much more now, about the history of this set.
>>
>> After my last posting about my AN/FGC-25 teletype set, I developed a program for my microcomputer to sample the current loop at approximately 10 kilosamples per second. It starts storing samples upon detecting a mark-to-space transition. It then dumps the data buffer to the Win7 laptop PC, where I then port the data into MS Excel for plotting and analysis. The data buffer captures about 5 characters' worth of signal at 60wpm.
>>
>> I wrote a report that includes plots of some of the data I took a few days ago. I posted it for viewing and .pdf download at
>> https://www.scribd.com/doc/270450987/Distortion-Testing-of-My-AN-FGC-25-Teletypewriter-Set
>>
>> As evident in the report, both the keyboard and the tape reader appear to be suffering from frequent "glitches" in the mark signal that occur shortly after space-to-mark transitions. There were some data captures where no glitches occurred at all. It is quite puzzling to me. Adjusting the contact spacing did not seem to matter much (except for affecting the bias performance).
>>
>> Any feedback and advice regarding these glitches would be most appreciated.
>>                                                                     -------
>> I also posted a two-chart file that shows the result of adjusting the keyboard contact spacing slightly;
>>
>> https://www.scribd.com/doc/270451314/Keyboard-Results-Comparison
>>
>> To do the comparison, I recommend that you download the chart set and open it with your .pdf reader. Use your up/down or left/right arrow keys to flip back and forth quickly between the two charts, to get an animation effect.
>>
>> -73
>> Don
>