{"id":4782,"date":"2013-04-26T09:38:03","date_gmt":"2013-04-26T07:38:03","guid":{"rendered":"http:\/\/www.gsm-modem.de\/M2M\/?p=4782"},"modified":"2013-07-19T22:02:27","modified_gmt":"2013-07-19T20:02:27","slug":"how-to-switch-between-an-internal-and-external-antenna","status":"publish","type":"post","link":"http:\/\/www.gsm-modem.de\/M2M\/uncategorized\/how-to-switch-between-an-internal-and-external-antenna\/","title":{"rendered":"How to switch between an internal and external cellular or GNSS antenna cheap? EA#"},"content":{"rendered":"

M2M devices in cars and trucks have sometimes a need for two antennas. If the external antenna will be demounted or damaged then the M2M device will switch to the internal antennas. Other reason for two antennas could be that the internal antennas on dashboard works fine, but the M2M device will be mounted on a place in a car, where the signal strength is less. The mobile control rooms for police or fire-fighters are a good example for M2M devices in a bus with decreasing the signal field strength by metal roof and metallised windows. Metallised windows we often find in new cars as protection against solar radiation as well.<\/p>\n

\"Heavy<\/a>

Heavy machine on railway<\/p><\/div>\n

Be careful by switching the GNSS signal. In year 1999 I ago had to detect where is to front and the back of a heavy machines (20 to 800 meter long) working on railways. Such machines has can work in one direction only. Worst case the machine has to be moved on a long distance to a turntable at railways station. Moving machines on railway costs money. You have to pay per kilometre. The way out was one GPS module with two antennas. The GPS Selective Availability of the US was in this time active. The front and the back were jumping +\/- 30 degree on the screen. Railways are long straight lines on a map. Even with the +\/- 30 degree fault it was possible to detect the direction of the machine. The only drawback was that the GPS module was completely lost by switching the antenna. It started with downloading the almanac again and made a complete new calculation of the position. If you want two GPS positions in close the same time, then you will run in trouble.
\nTest your M2M device at laboratory detailed before you move it to the field test.<\/p>\n

GaAS switch<\/h3>\n

If you search on Google for GaAS switch, then you will find a lot of examples for such RF switches.<\/p>\n

By selection of the GaAS switch just take care on<\/h3>\n