N8YX
05-28-2012, 07:31 PM
:soapbox:
I just spent the better part of the long weekend un-engineering something which Drake/Tono should have done right in the first place.
To wit:
Their Theta 7000 RTTY/ASCII/CW keyboard has a number of inputs and outputs...one pair is a TTL-level 'IN' and a TTL-level 'OUT'. This is provided so the unit can accept logic-level input from an external demodulator, or output transmitted data to a separate modulator/decoder. In this case, a Universal M-7000.
A bit of back story: The M-series digital communications gear used to be manufactured by Info-Tech, and they allowed for an external keyboard (such as their M-300) to be hooked to any of their equipment. This allowed full Baudot/ASCII/CW transceive operation, with transmitted characters being displayed on the decoder's attached monitor.
Now you would think that everyone else (Drake/Tono et al) would follow the established standards and only output TTL-level character data when the keyboard was in transmit mode, right?
WRONG.
The Theta's TTL-Out connection is a constant +5v, with the line being pulled to ground as space bits are transmitted. Of course, a logic high at the M-7000's "Aux RTTY" connection results in the unit not receiving any off-air signals, as its demodulator is logically overridden at this point.
What I ended up having to do is to build a small switching circuit on a piece of perfboard and mount it inside the Theta's case. It is triggered by the 'Remote' (PTT) logic circuit and uses a reed relay to route the TTL-Out signal to the appropriate connector, thus preserving logic "sense".
I cannot believe the designers of this equipment didn't anticipate such a configuration. There's even a chassis cutout for a deactivation switch for the circuit, though I didn't incorporate one.
This circuit, the associated research (no schematics for the Theta, natch) and the custom cable I needed to construct to interface the units killed two of three days this weekend. :wall:
I just spent the better part of the long weekend un-engineering something which Drake/Tono should have done right in the first place.
To wit:
Their Theta 7000 RTTY/ASCII/CW keyboard has a number of inputs and outputs...one pair is a TTL-level 'IN' and a TTL-level 'OUT'. This is provided so the unit can accept logic-level input from an external demodulator, or output transmitted data to a separate modulator/decoder. In this case, a Universal M-7000.
A bit of back story: The M-series digital communications gear used to be manufactured by Info-Tech, and they allowed for an external keyboard (such as their M-300) to be hooked to any of their equipment. This allowed full Baudot/ASCII/CW transceive operation, with transmitted characters being displayed on the decoder's attached monitor.
Now you would think that everyone else (Drake/Tono et al) would follow the established standards and only output TTL-level character data when the keyboard was in transmit mode, right?
WRONG.
The Theta's TTL-Out connection is a constant +5v, with the line being pulled to ground as space bits are transmitted. Of course, a logic high at the M-7000's "Aux RTTY" connection results in the unit not receiving any off-air signals, as its demodulator is logically overridden at this point.
What I ended up having to do is to build a small switching circuit on a piece of perfboard and mount it inside the Theta's case. It is triggered by the 'Remote' (PTT) logic circuit and uses a reed relay to route the TTL-Out signal to the appropriate connector, thus preserving logic "sense".
I cannot believe the designers of this equipment didn't anticipate such a configuration. There's even a chassis cutout for a deactivation switch for the circuit, though I didn't incorporate one.
This circuit, the associated research (no schematics for the Theta, natch) and the custom cable I needed to construct to interface the units killed two of three days this weekend. :wall: