I've just come back from a two-week trip to china, which I thought would be a great opportunity to test if the radio receiving ability of my g-shock is really as good as its manual says, so I broght my g with me.
According to the manual, it should have no problem adjusting itself within 1500 km to the transmitter.
The model I got was mrg-7100. To prevent possible confusion I switched to 60Hz only so that the other station in Japan wouldn't matter.
During this trip I spent several days in Beijing and Shenzhen (a city right next to Hong Kong), surprisingly it worked at both places eventhough Shenzhen is almost 2000km from the radio station.
I found most inteference seems to come from what's above my head. At both places my g never calibrate successfully if there's a metalic roof (say, on the bus, plane or airport lobby) or if I was on a lower floor of the building, it didn't matter whether I was close to a window or not. (meter always run between nothing and level-1)
Maybe that's because the radio signal has to be reflected from the atmosphere.
(My original plan was to test signal on the plane. But it didn't work.)
The best signal I got was between level-3 and 2, it took roughly 15 sec only to complete the adjustment. That was done in XingGuang restaurant (on the top of a hotel in Beijing)
night view from the restaurant
(Sorry but I've forgotten to take a picture until I had a bite... :P)
In Shenzhen I felt distance did have some effect. My g-shock took more than 2 minutes to complete the job and the meter showed that the strength of radio signal was level-1 only, nevertheless, it still worked.
That's it, apologize for the poor english and thank you for your patience.