Flying the national flag usually signifies a display of pride or patriotism. But in Iran today, it may represent something much more sinister.

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.

“Ever since 2009, the telecommunications masts have increased 10- to 15-fold. It’s not clear where these masts are, but many in Tehran, including myself, believe that these tall flagpoles recently placed around the perimeter of the city are jammers,” said Shahin, a 32-year-old Tehran-based blogger. The flagpoles are present in other large Iranian cities but are most prevalent in the capital, Shahin said.

“The regime fears the Internet and satellites coming into the country more than they do the opposition forces living here,” he added. “That’s how we know they would do anything in their power, including risking our health, to protect their existence.”

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During the 2009 post-election uprisings, Iranian protesters who took to the streets turned to blogs and social networking sites like Facebook, Twitter and YouTube to voice and organize their opposition to the regime. Since then, the Iranian government has worked diligently to block access to such sites.

The jammer flagpole scheme “is very much in line with and fits the pattern they have been demonstrating since 2009,” said Austin Heap, executive director of the Censorship Research Center.

“The shape of the flagpole lends itself to house such a structure. If you notice the width of the pole decreasing as it gets taller, this is consistent with the design principles for good omni-directional broadcasting. … It’s a kill switch,” Heap explained.

“It’s just the next step in controlling what comes in and out of the country,” Heap said. “Iran is looking to become better at controlling the dialogue.”

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.

But foreign broadcast companies learned to work around that by switching signals, turning the censorship campaign into a cat-and-mouse game that requires more time and effort by the Iranian government to block each channel.

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.

“This new type of jamming is a catch-all,” Heap said.  “It is a one-size-fits-all solution.”

The increase in jamming has been noted by the United States and European Union, both of whom announced new communications sanctions and warnings against the Iranian regime in November.

Since the 2009 uprisings, roughly $76 million of the total $11.5 billion allocated to the Islamic Revolution Guard Corps has been spent on cyber warfare, the Iranian government once reported. Iran’s cyber police monitor the Internet, various websites, blogs and individuals suspected of using circumvention tools designed to evade the censors.

In early 2011, Iran unveiled plans for a “halal network,” or an “Islamically permissible” intranet that would disconnect the nation from the rest of the world. Such a service would automatically block popular global sites and search engines like Google, Facebook and Wikipedia.

Other experts are more concerned about the health side effects of these suspected flagpole jammers, and they cite a rise in cancer rates in Iran as a possible result of the increased jamming activity.

“A cancer tsunami is imminent,” Dr. Ali Mohagheghi, from Iran’s Ministry of Health, admitted earlier this year. Mohagheghi urged doctors to prepare for the coming “inundation” of cancer cases.

“I’m not a doctor, but I’ll tell you it’s a one-to-one correlation,” said Heap, who explained that the second type of jamming - the ground jamming - emits a much higher degree of cancer-causing radiation.

Those who have written about the flagpole jammers or hinted of their connection with cancer rates have been seriously criticized, even threatened with imprisonment.

Masoomeh Ebtekar, head of Iran’s Environmental Organization, echoed the idea of a “cancer tsunami” a few months later, to the semi-official Mehr News agency. But she went further and connected the increase in cancer cases to the jamming waves.

The government quickly responded by accusing Ebtekar of circulating rumors, and threatened to imprison her if she continued to speak about the subject, according to the Boltan News site.

Despite government pressure, the story has not disappeared, as doctors and others continue to research the possible jammer-cancer connection.

“New cases of pediatric cancer are growing at such an unbelievable rate that one can only connect this crisis to the increase in high-frequency waves,” said a pediatrician living and practicing in Tehran. “One only has to pay a visit to MAHAK (a pediatric cancer hospital) in northern Tehran to see how real this tragedy is,” she said.

“Of course the government doesn’t want these cases and these statistics to be announced. It might cost them the regime.”