A minor detail peculiar to Santa Fe locos and cabooses from the late 50's to 1972 is this unique antenna, known as a "top hat". Oddly, it's not because of the shape of the radome, but the guts under it, which are known in the technical radio field as a "top hat"-style antenna.
I rendered it in 3D to detail the handful of 1960's Santa Fe power and cabeese lounging about on my layout. The STL artwork can be downloaded here:
http://www.everywherewest.com/Top_Hat_Antenna_N_Scale.stl The stem below the plate is for drilled-hole mounting; some applications (check proto pictures!) you'll want to nip it off for flush mounting.
These antennas disappeared with the "yellow bonnet" scheme adopted in 1972, replaced as part of the repaint program with 2nd-generation Sinclair "skates". I worked briefly in the Santa Fe radio shop in Los Angeles, so have firsthand familiarity with the design and the unfortunate problem that if the radome was cracked or punctured, the aluminum guts would corrode quickly. I forget who the manufacturer was.
I have no idea if anybody besides Santa Fe used these.