Well you don't have to buy a splitter to try it. If it works great if not you saved yourself from wasting money on a splitter. That said most likely the jack you used in the 80's was hooked up to an antenna not cable. The cable tv jack should not be acting as an antenna. Since you are using that jack for your cable internet we know it is not hooked up to an antenna. I have seen some older apts that have both cable and antenna jacks in the same room.
If somehow you can pickup fm on the cable jack be aware that installing a 2-way splitter will lower the signal to your modem by 3 db's. This may or may not be a good thing depending on how strong the signal is.
Sean
If somehow you can pickup fm on the cable jack be aware that installing a 2-way splitter will lower the signal to your modem by 3 db's. This may or may not be a good thing depending on how strong the signal is.
Sean