[Ham-Mac] Digital Interface for PSK with PTT - more info.

[John Townend]

Hi,

Comments so far raise two points.  I have not been happy using the VOX 
control - muting or disconnecting the mike was a nuisance in my set up.

I use two Icom IC706Mk11Gs and a Yaesu FT817.  Control from the 
interface is via the ACC  or Data sockets both of which have the PTT 
line on one of the pins. It is just a question of pulling down this 
line to switch to TX.
K1QW's circuit of the interface takes the PSK/RTTY or whatever signal 
from the Mac (or PC) and feeds it into a band-pass amplifier (one 
section of quad op amp). The amplified signal passes to Comparator, 
Integrator and PTT delay circuitry (one section of the op amp plus 2 
transistors). From there it goes to a schmitt trigger (one section of 
the op amp) the output of which feeds the base of a 2N4401 NPN 
switching transistor across the PTT line.  The fourth section of the op 
amp is used for the meter amplifier

I am not sure Dick how unique the Auto-PTT feature on the SL-1 
interface is but this home brew interface does the same thing. The VOX 
is not enabled at any time.

0800 in the UK ----- sunny morning----- have a good day------73 John 
G3BBD / N3YZR