Alan, thankyou for your comments.
On the WIN7 box, I have discovered that the soundcard part is functioning but the com port still is'nt recognised .
When I look at the system device list I see the QDX listed under 'Other Devices' with a yellow triangled exclaimation mark, and 'QDX Tranciever' under the soundcard list. I guesss the triangle refers to the com port.
I've tried the reccomended drivers from the QDX manual and also your mentioned win8 drivers, but the com port is still hiding somewhere.
And, before anyone asks, Yes,I have tried numerous USB cables to eliminate that line of enquiry.
I suppose I had better describe the WIN7 PC, its a dual core 2.5Ghz, 8GB ram, running windows 7 64bit os.
As I previously said, everythig is working perfectly, afics, on my windows 10 PC and the Raspberry Pi 4 Buster OS.
Most confused...Mike G8NXD