[GreenKeys] RTTY cassette interface storage circuit

[Bob Camp]

Hi

Those are both (RX and TX)  circuits for on / off keying to and from a tape. For RTTY, that may not be fast enough to give you 
good copy. The cassette stuff I was thinking about was  a duty cycle (PWM) on a fixed frequency tone.  The normal format was 
33% =  logic 0 and  66% - logic 1. You demodulated it with a one shot set to the 50% point. The one shot clocked a flip flop. If
the data was low, you got a zero. If it was high, you got a one.  Still a pretty simple circuit.  For modulation, a couple of one shots 
was a pretty simple way to go. One gave you the tone frequency, a pair could give you the modulation. Tricks to eliminate all those
expensive parts abounded. Today you could buy all the parts in the “expensive” design for < $1. 

Bob



> On Aug 29, 2015, at 1:14 PM, Doug via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> Someone mentioned cassette storage recently.  I know I had come across a simple RTTY cassette recorder interface circuit, but didn’t remember 
> where.  I just found out, it was in the September 1977 issue of 73 Magazine.  I wanted to try this out, but never got around to it.  In the link below, 
> about half way down the page, you will find the schematics for the recording and playback circuits.  Both are very simple, two transistor circuits.  
> The recorder uses the obsolete 2N2646 unijunction transistor.  They are still around, but will cost you a couple bucks or so.  You should be able to 
> use the readily available and inexpensive 2N6027 programmable unijunction transistor and an extra resistor.  Google 2N2646 substitute to find an 
> example of this.
> 
> http://www.seekic.com/circuit_diagram/Basic_Circuit/index144.html
> 
> Doug W.
> 
> 
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