[GreenKeys] Navy Teletype Message Generator

[Stan Voynick]

Alf,

I was getting ready to type out an explanation, and I stumbled upon a nice article in this issue of Ham Radio, starting on page 99:

https://worldradiohistory.com/Archive-DX/Ham%20Radio/70s/Ham-Radio-197806.pdf

This takes us through the journey from blowing up an 8080 microprocessor, to deciding to opto-isolate the loop switcher, and ending up with the Darlington-connected pair.   Nice analysis, and it should answer your question.

73,
-Stan
WB7RPG

> On 01/29/2023 2:35 AM PST Alf Fisher <alffisher2 at gmail.com> wrote:
> 
>  
> 
> I was wondering if anyone had actually built this fox box from the 
> article in HR Nov 76?
> I've discovered a feature of the design that is not sensible.
> Looking at Fig 3 in the article, the power to the collector of output 
> transistor of the opto coupler Q6 is derived from the loop current but 
> only when the loop is open.
> When the run/stop switch stops all the counters from running, there will 
> be no power to keep the loop transistor Q5 on, so the loop will go open 
> - and...
> Maybe I'm missing something but has anyone got a work around for this 
> problem?
> 
> 73,
> Alf G3WSD
> 
> On 24/01/2023 15:55, Gillian Webb wrote:
> > Nifty! I found the original plans this appears to be built from, or at 
> > least a very similar "solid state fox box" circuit, on page 30 of the 
> > November 20, 1976 issue of Ham Radio Magazine:
> >
> > https://archive.org/download/hamradiomag/ham_radio_magazine/Ham%20Radio%20Magazine%201976/11%20November%201976.pdf
> >
> > What's the info printed on that white chip? I agree it looks like they 
> > "adapted" something in - thinking a comparison to this reference 
> > design could shed light on this.
> >
> > Cheers,
> > Gillian
> >