Many years ago I bought a Tigertronics Signalink USB, principally for measurements using FSM and NFM.
A nuisance with the device is the lack of a simple means of disabling PTT. This is particularly important if the system is being used for noise figure measurement with an expensive calibrated noise source which will not withstand transmitter output.
This note describes the fitting of a front panel PTT disable switch.
Tigertronics do not / will not publish a circuit diagram, so one is left trying to discover a mod to overcome their short sighted design.
Above, the track is cut between the relay and DIP jumper socket, and a hole drilled to pass the new switch wires through to the underside.
The switch wires are taken through the drilled hole, and connected to the PTT pads as shown.