Editing N900 FM radio transmitter
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==Hardware== | ==Hardware== | ||
- | The SI4713 chip is used to transmit FM radio | + | The SI4713 chip is used to transmit FM radio in the range 76-108MHz from a digital or analog audio input. |
- | + | It is short range only, see the section Inherent_Limitations. | |
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- | It is short range only, see the section | + | |
It can also receive the signal level on the tuned frequency. This enables transmitter application to scan all frequencies, checking for vacant ones, and suggesting empty frequencies to the user for selection as transmission frequencies. | It can also receive the signal level on the tuned frequency. This enables transmitter application to scan all frequencies, checking for vacant ones, and suggesting empty frequencies to the user for selection as transmission frequencies. | ||
- | The [[Nokia N900|N900]] controls the FM transmitter through the I2C | + | The [[Nokia N900|N900]] controls the FM transmitter through the I2C bus, and supplies analog audio to the transmitter. |
The FM signal is transmitted from a loop antenna built into the case, and connected to the PCB with clips. | The FM signal is transmitted from a loop antenna built into the case, and connected to the PCB with clips. | ||
- | product marketing sheet: | + | product marketing sheet: https://www.silabs.com/products/audiovideo/fmtransmitters/Pages/Si471213.aspx |
- | Full datasheet | + | Full datasheet available there immediately after registering. |
The documentation for the driver, along with some information on the chip is at | The documentation for the driver, along with some information on the chip is at | ||
http://www.mjmwired.net/kernel/Documentation/video4linux/si4713.txt | http://www.mjmwired.net/kernel/Documentation/video4linux/si4713.txt | ||
- | It is connected to the [[N900 Hardware Bus I2C|I2C]] bus | + | It is connected to the [[N900 Hardware Bus I2C|I2C]] bus. |
==Software== | ==Software== | ||
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There are several bugs open with regards the FM transmitter [https://bugs.maemo.org/show_bug.cgi?id=6792 this one] for example is regarding the policy to turn off the FM transmitter when the device is plugged into a computer using the USB cable. | There are several bugs open with regards the FM transmitter [https://bugs.maemo.org/show_bug.cgi?id=6792 this one] for example is regarding the policy to turn off the FM transmitter when the device is plugged into a computer using the USB cable. | ||
- | The | + | |
+ | The DBUS interface is documented in [http://maemo.org/api_refs/5.0/5.0-final/fmtx-middleware/fmtx_api.html this page] | ||
==Typical Range== | ==Typical Range== | ||
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Low power transmitters that are license compliant - do not exceed the regulations - are inherently short range devices and will have poor performance in many desired use-cases simply due to the regulatory limit on power usage. | Low power transmitters that are license compliant - do not exceed the regulations - are inherently short range devices and will have poor performance in many desired use-cases simply due to the regulatory limit on power usage. | ||
- | In the US - the limit is approximately | + | In the US - the limit is approximately 15nW, in the UK, 50nW. |
The below OFCOM document lists ranges to a good receiver with a fully extended antenna as 4m for 15nW and 8m for 50nW. (to achieve 'noiseless' reception) | The below OFCOM document lists ranges to a good receiver with a fully extended antenna as 4m for 15nW and 8m for 50nW. (to achieve 'noiseless' reception) |
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