Aircraft's X Band weather detected a large stationary airborne object. FAA airtraffic radar did not detect the object.

Around 1983, I was flying as First Officer on a DC-9 aircraft approaching the Utica, NY airport from the Southwest. Weather was mostly clear. I was practicing with the high quality Collins X Band weather radar while the Captain was flying. I pointed out to him a large solid airborne target over the Air Force's Rome Air Development Center, just East of the Griffiss Air Force Base. It appeared to be stationary at that time. The size of the object had to be over a mile to create such a large return. The Captain called this out to the Air Traffic Controller who said he did not see it on his Radar. At that point, the target began moving to the West. I was able to follow it on our Radar by expanding the range out to the maximum of 180 nautical miles as the target moved rapidly westward.
This object appeared to be listening to our radio conversation and was escaping at a hypersonic speed westward past the cities of Syracuse, Rochester and Buffalo. An ordinary object that large and travelling at that speed would have created a spectacular sonic boom. It went off the 180 mile maximum scale of our Radar as fast as I could increase the range scale and recapture the target. We never had a visual sighting of the object.
At that time, the Rome Air Development Center had a large Restricted Area of land the Air Force used for electronic research..