I've been working on an Arduino based data logger to collect data from our CNC machining centers and dump it over WiFi to the office. I'm using the WizFi based module made by tinyosshop.com. I've got 2 prototypes installed in 2 machine centers that sit right next to each other (1 Toyoda, 1 Niigata). Both prototypes are identical and enclosed in grounded die-cast enlosures. The problem I'm having is that they work decently without any antenna connected. The time it takes before it drops out varies from a few minutes to sometimes a day or two. With an external antenna attached, they lose their connection and can't reconnect. As soon as I remove the external antenna, they have no problem re-establishing a connection. If I pull the RSSI readings directly out of the WiFi modules I get around -78db without an antenna, and right around -60db with either a rubber duck or the magnetic mount antenna I intended to use. So with an antenna I'm gaining almost 20db and it drops out.
I thought there might be an interference issue so I purchased a RF Explorer to look for any signs of interference in the band. Unfortunately, it doesn't show anything out of the ordinary. All WiFi signals are centered on channels 1,6, and 11, nothing inbetween. During the holidays we only had a couple of people in the shop and it still dropped so I've eliminated Bluetooth/Cell phone issues. In the area of the 2 machines with the rubber duck adapted to the RF Explorer I'm showing a peak of -64db on 11, -79db on 6 and -70db on 1. I played around with trying to force the modules to channel 11 but never could get them to accept the AT command for it. But something changed because the module installed in the Toyoda is now working most of the time. The Niigata still won't stay connected with an external antenna.
I swapped out the WiFi board in the Niigata with a different one and I still get the same result. I'm pretty much out of ideas so I'm hoping someone here might be able to offer some insight.
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