I'm using this product at a co-located cluster of 2 FMs and 1 AM. The AM transmitter is at the studio site, so filters, grounding and wiring technique are considerations any time something gets moved, changed, rewired or looked at with anything but a loving gaze.
Granted, this interface is a little expensive (around $480), but if you need high output levels and/or good RF immunity, it does the job very well.
Before I went to this unit, I'd started with M-Audio Audiophile 192 cards, which I've used a lot. However, they don't provide the +10 output that most AM transmitters are designed to want, and they're very sensitive around AM RF. Replacing them with the outboard Henry product eliminated the problems and let me move to (physically) smaller computers.
Available in the 'States from BSW, B&H Photo & Amazon, among others.