I want to make a very small transmitter with Si4012, and the problem is the PCB antennas are too big for my project. Is it possible to use a 433MHz ceramic chip antenna? I suppose yes, because such atennas have 50 ohm impedance, but I'm not an RF expert and had bad experiences using chip antennas with a GSM/GPRS modem. Do somebody has any experience?
Note that the RF amplifier is two sided, so the 4012 may not be your best choice. Can you pick a single-ended transmitter?
Also, I would think that your range will be greatly reduced with a chip antenna, but I'm not sure about that. Is that OK for your application?
As Dan has mentioned, the Si4010 / Si4012 chips are designed to drive a differential antenna structure (i.e., loop antenna) and works best with a differential load impedance of approximately 500 ohms.
It is possible (although somewhat component intensive) to construct a balun circuit out of discrete L-C components that matches the differential Si4012 output to a single-ended 50 ohm load. If you constructed such a balun match, then you could bolt on any 50 ohm antenna of your choice.
See our app note AN369 for a discussion of the balun match concept.
Thank you, I'll try the matching circuit described in the appnote.
With all the extra discrete components, how much power is typically lost in using a dipole chip antenna with the Si4010?
In our experience, we typically lose about 0.5 to 1.0 dB in the discrete matched solution, due to finite Q-factor of the inductors.
However, please note that the antenna efficiency / gain of a typical printed differential loop antenna is often no better than about -5 to -10 dBi. Printed antennas are cheap, but they are not awesome performance. So you *might* actually come out ahead by implementing the discrete L-C balun match to a single-ended chip antenna and suffering the loss of the discrete components, depending upon how efficient your chip antenna is.
Will this chip work at all without any antenna ?
I've programmed it via a MCU, no errors read back; however nothing gets registered by the SDR sniffer (less than half a meter away from the transmitter Si4012 chip; the SDR has an antenna and it works fine for other transmitters). I have used the excel spreadsheet to get all my values, power has been set to the maximum for PA. The only thing I can think of is the missing differential antenna.