Tonight I made an interface between my PC and the FT757.
It consists of a potentiometer in the TX audio line between the line out on the sound card, an opto-coupler to control the PTT via the RS232 port and a direct connection from the AF out port into the line in on the sound card.
With all this in place PSK31 should be a breeze.
I made a few CQ calls on 20m and tried answering a couple of calls but I had no success.
I am not sure if the FT757 has the TX and RX frequencies correctly aligned. I guess any misalignment between these would see me receiving at a different place to where I am transmitting. Given the very narrow bandwidth of PSK31 this may also be causing me a problem.
At least I have sorted out the audio levels, or so I thought. It turns out when I input audio through the PATCH connector it is paralleled with the microphone socket on front and, with the microphone connected to the FT-757 the transmit signal is less than with the microphone disconnected. The microphone is also ‘live’ when the rear panel PTT is closed.
I will try making some more contacts tomorrow night.