Support our mission

YOKOSUKA NAVAL BASE, Japan — Navy and Japanese authorities pinpointed the cause of another communication breakdown in Sasebo city on Wednesday: an American-made baby monitor.

This is the second time this month that baby monitors interfered with local cellular phone communications. Both occurred at Hario Housing Area near Sasebo Naval Base and are an example of “If it’s cordless and it’s not Japanese, don’t use it,” said Brian Hurdlow, Sasebo’s IT manager.

“If you turn it off, the problem goes away,” Hurdlow said. “If not, you could be operating on the disaster-prevention frequency or cellular phone network.”

The problem is frequency. American cordless products — such as phones, monitors, walkie-talkies and ham radios — operate in the 900 megahertz range. This is illegal in Japan as that frequency is reserved for disaster prevention and cellular phone operation. Japanese cordless products operate on a different frequency.

According to Sasebo’s base newspaper, both U.S. Forces Japan and Commander, Naval Forces Japan received a complaint on the matter from the Japanese government. This is not the first time U.S. frequencies interfered with Japanese communications, said CNFJ Information Systems and Networks deputy Mike Dawson.

“There have been past incidents of harmful radio frequency interference that have been believed to have been emanating from U.S. Navy vessels both in port at Yokosuka and in the sea near the Japan coastlines,” Dawson said.

The Japanese Ministry of Internal Affairs and Communications fingered U.S. military communications in several interferences at Haneda Airport last October, one of which grounded 195 planes and delayed flights for more than an hour.

While not pinpointing the military, the ministry said the signal came from the area of Yokosuka Naval Base and gave USFJ a list of frequencies to avoid.

Currently, USFJ has a policy that prohibits the use of wireless and cordless devices not intended for Japan, Dawson said, but they are looking to draft the policy into a general order, he said.

CNFJ is also mounting an “aggressive” awareness campaign, he said.

“We are doing this via the base newspapers, Commander’s Channel rollers/banners, area orientation briefs, newcomer’s briefs, housing briefs and others,” Dawson said. “If you did not buy a cordless device from a Japanese vendor in Japan, don’t use it!”

Although the baby monitors that caused trouble in Sasebo were not purchased at a Navy Exchange store, 900 MHz baby monitors are being pulled off NEX shelves, said Rusti Rausch, district NEX operations manager.

“We pulled the ones we had off the floor and are putting up signage that says ‘If you purchased one of these, please bring it back for a full refund,’” Rausch said. “We’re also studying how many we’ve sold so we can get an idea of the problem.”

AAFES Pacific spokesman Master Sgt. Donovan Potter said the exchanges on other bases sell two baby monitors that are not made by Japanese manufacturers, but he didn’t know Wednesday afternoon if the frequencies were a problem. The exchanges sell only one brand of cordless phone — a Japanese version, he said.

Unless it’s a computer wireless device, such as Wi-Fi cards, adaptors or routers operating on a universally approved frequency, Hurdlow advised Americans to take a second look at their cordless gadgets.

“If it’s Japanese, you’re good to go,” Hurdlow said.

How do they track down wireless signals?

This month, two American-made baby monitors (called “Summer Infant”) interfered with NTT cellular phone communications in Sasebo Naval Base’s Hario Housing Area, according to base officials.

Working with the Japanese Ministry of Internal Affairs and Communications, Sasebo officials found the source of the signals — one on July 14 and one Wednesday.

Here’s how they did it, as explained by Commander, Naval Forces Japan Information Systems and Networks deputy Mike Dawson:

“Harmful radio frequency interference is a result of the unintended transmission of radio frequency emanations that cause interference on a frequency designated for another use such as emergency services, cellular telephone, taxi dispatch, etc. The severity and impact can vary widely.

“MIC uses a process called radio direction finding — typically simplified to direction finding or DF — to isolate the source of RFI. This is done by using two or more geographically displaced radio receivers equipped with directional antennas.

“The directional antennas are rotated until a peak is achieved on the receiver signal strength meter.

“For example, if MIC has one receiver in Tokyo and another in Izu, they can get bearing lines from each receiver and overlay them on a map. They triangulate the bearing lines by pinpointing the exact geographic spot at which the bearing lines cross each other. Obviously, the greater the number of geographically displaced receivers used, the greater the accuracy of the triangulation or pinpointing of the source.”

— Stars and Stripes


Stripes in 7



around the web


Sign Up for Daily Headlines

Sign-up to receive a daily email of today’s top military news stories from Stars and Stripes and top news outlets from around the world.

Sign up