Multi Frequency balun.

The CC1101 868/915 MHz balun works fine for lower frequencies in RX (i.e no significant degradation in sensitivity). In TX, however, the 868/915 MHz balun will degrade output power and harmonics attenuation for the lower frequencies. Since SA430 is a "receiver" only I would assume they use the 868/915 MHz balun (that said, I do not know the finer details of this design).

I am sure you can make a tuneable balun by switching in and out components, but the performance will not be optimum and it will be a "messy" design. 

Debarjun, 

The balun we use on most of our designs is based on two filters connected in the middle forming a balun circuit. The filters are a low-pass filter and a high pass filter, at the cut-off frequency they each provide 90 degrees of phase shift in opposite direction and when connected they provide a total of 180 degree phase shift before combining the RF power. This creates the balun function needed.

This circuit works over a pretty large frequency range, a 1:2 type frequency range, but if you need more tuning range than 1:2 you need to enable some way of moving the filter cut-off frequency - this is where the adaptive balun comes in.

Sverre is, in the statement above, warning you of the difficulty in creating a variable cut-off frequency balun that will at the same time create enough attenuation during TX to pass regulatory requirements around the globe. But this could be achieved if you also implemented variable cut-off frequency low pass filtering in the final output stage. 

Regards,
/TA

We have measured 433 MHz sensitivity using the 868/915 MHz balun without seeing significant degradation in sensitivity vs 433 MHz balun. Not tested at 315 MHz though, but I believe 868/915 MHz balun will work fine also at this frequency in RX.