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I need to know the power output needed for transmitter if I want that receiver catch this signal? In details, there is a tunnel 4 by 4 meters and a cars in it, cars have a receiver inside and transmitter on the tunnel upper floor. So, when car rides under the transmitter, receiver catches a signal. Is 22 dBm enough on 2.4 GHz frequency to go through car's frame? Antenna is just simple PCB.

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  • \$\begingroup\$ The signal isn't going to go through the car's frame, it's going to go through the window openings and any nonmetallic body panels. \$\endgroup\$ – Dave Tweed Dec 1 '14 at 16:45
  • \$\begingroup\$ Of course, I just should be more specific \$\endgroup\$ – cy8g3n Dec 1 '14 at 16:54
  • \$\begingroup\$ What data is being sent and what data is responded? What data rate are you contemplating? \$\endgroup\$ – Andy aka Dec 1 '14 at 17:29
  • \$\begingroup\$ Very small amount of data, and it's only one way signal, from transmitter to receiver. \$\endgroup\$ – cy8g3n Dec 2 '14 at 9:38
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22 dBm is a pretty significant signal, which should be plenty at such close range. However, as Dave Tweed said, it's not going to go thru a metal roof or metal hood at all. You need to make sure this PCB has some kind of visibility to the roof of the tunnel, while considering any extended metal surface to be opaque. Your 22 dBm signal is strong enough that some will also bounce off the tunnel walls and come in sideways thru the windows of the car.

Still, you shouldn't expect reliable reception in a mostly enclosed metal space, like under the hood or in the trunk. A good place to put the receiving PCB would be on the dashboard or under the plastic of the dashboard. That way it will catch the transmitted signal directly thru the windshield. Another good place might be under the rear window if the car is a sedan, for the same reason that under the windshield will work.

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  • \$\begingroup\$ Thanks for your reply. I'm just experiencing an issue in estimating power needed for signal. How much wave power in 0 dBm, or 10? Plus a lot dependent from frequency, but how waves behave on different frequencies I understand, problem is actually in power evaluation. Any way, I just wanted to hear the second opinion that 22 dBm will be enough. The problem that receiver is a user's personal device and it can be located anywhere in the car. \$\endgroup\$ – cy8g3n Dec 2 '14 at 9:44

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