Question Color me a cheapskate but looking for a solution of using my recent cable modem as a wifi router for fibre ONT Ethernet

[cartaphilus]

I have fibre ONT from my ISP. I also have a recent purchase cable modem/router combo (nighthawk). The ONT has an Ethernet out but the cable modem doesn't have a WAN Ethernet port just WAN via COAX. Is there a way to convert Ethernet to coax so I can connect the ONT to COAX and use my nighthawk as a WiFi router?

 

[Sorrento]

There are several 'ethernet to coax' adapters around including Amazon, though I have no experience in using them? My old Virgin Media used router used coax which was a bit of a pain at times as quite clumsy, now I'm using a different ISP that uses ethernet.