Thanks very much for your kind assistance.
Yes you were right I was confusing audio sample rate with device sample rate.
I should have kicked the day off with a strong coffee :-)
Still I do wonder if device sample rate can be altered/accessed in some way as I also have some other much lower level spurs
on the FM band that I'm not sure of the origin of yet. Need to do a lot more testing, particularly on the RFI/EMI side of things.
Discovered my ethernet cable between router & modem was a source of interference, changed that from CAT5 to short length of shielded CAT6A
patch cable & that fixed that one source of EMI on the FM BCB. Purchased a heap of spit core ferrites yesterday as I suspect I'll need many of these when it comes to suppressing
EMR on HF from several PC cables etc.
Finally managed to install the IF Processor plug-in into SDR# and get it going (my first plug-in experience) after much reading & very happy with the performance
of the notch. Will have to wait for some DX on 98.3MHz to determine how much an effect the notched spur has on reception.
All a great deal of fun toying around with DSP. Thanks for the link, saved me a lot of time.