Iran
Lisa Daftari: "Sources and blog postings from inside Iran say that what seem to be simple flagpoles popping up all over Tehran and other large Iranian cities are actually clandestine electronic antennas, which use high-frequency waves to jam communications and block ordinary citizens from Internet, TV and radio signals. Some Iranians think the electronic emissions also may be hazardous to humans’ health. Tehran residents and communication experts report an increase in jamming has coincided with the strategic placement of the towering metal flagpoles, as the government continues its ongoing campaign to block some 500 TV channels and 200 radio stations from outside Iran deemed too Western-oriented. ... The Iranian government has relied on two jamming techniques, according to Heap. One is the more widely used 'satellite-to-satellite' method, in which waves are sent directly from one satellite to the other in an attempt to overwhelm the broadcast signal. ... The flagpole jammers represent a second method, referred to as on-the-ground or local jamming. That process involves sending high-frequency microwaves over a larger area, saturating signals that jam incoming signals." -- Shortwave radio, which travels well over long distances, but not so well over short distances, would have more immunity from flagpole jammers that would satellite or microwave signals.
(Fox News/Kim A Elliott /International Broadcasting)