I know the article says it's not aliens, but... What happens to a very high power communication over intergalactic distances? Supposing you had a very high powe

I know the article says it's not aliens, but... What happens to a very high power communication over intergalactic distances? Supposing you had a very high power radio transmitter, and you modulated it somehow. Over how long a distance can it be demodulated? What would a signal look like after you can't discern the modulation?