Rebel regions of the splintered former Soviet republic have only been receiving Russian channels aired from Moscow throughout much of their 31-month war with the pro-Western government in Kiev.
The main transmission tower that showed Ukrainian television in the eastern conflict zone was destroyed by the insurgents in July 2014.
Many analysts in Kiev believe the rebels would get much less local support if people were not fed constant Kremlin propaganda that appears on Russian TV that they now receive.
Most of these have been civilians and Western efforts have failed to end one of Europe's bloodiest conflicts since the 1990s wars in the Balkans.
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Poroshenko today visited a Kiev-controlled town near the war zone called Gorlivka that lies near the spot where the new transmitter has been erected.
The original was situated in Slovyansk - the rebels' de facto capital for the first few months of the war that they fled after a major government onslaught.
But the militias did so only after blowing up the tower and making sure the regions they controlled were provided only with Moscow news.
Kiev and its Western allies accuse Russia of plotting and backing the war in retaliation for the February 2014 ouster of Ukraine's Moscow-backed president.
Russia denies the charges but admits that some "volunteer" or off-duty soldiers may have joined militia ranks on their own free will.
Poroshenko said the "super-powerful transmitters" were provided to Ukraine by its Western ally Poland.
Yet he also failed to specify when they will actually start working or how far east they will reach.
"Also, it is a very important element in the hybrid war being waged against Ukraine," the Interfax-Ukraine news agency separately quoted the president as saying.
Poroshenko added that he hoped to install another transmitter near the Crimea peninsula that Russia annexed from Ukraine in March 2014.