S2-LPQTR - Huge decrease in range when using wider channel band

[kienicholas]

We are a data company based out of the UK who use a data collection device which utilises RF transmission. The device transmits accelerometer data collected on it using the S2-LPQTR component. 

This set up is certified for FCC and CE, with the caveat that during compliance testing, the frequency band had to be made wider for the FCC regulations:

	CE	FCC
Base Frequency	868.2 MHz	921.4 MHz
Frequency Deviation	20 kHz	228.516 kHz
Channel Bandwidth	100 kHz	541 kHz

The end result of these changes is that the range of transmission has dropped from around 100 metres to around 5 metres.

I have attached some pictures of some investigation I did with a spectrum analyser to see the difference between the two settings. It's clear that some drop in range is going to occur, but is it expected for it to be so drastic?

We use 2-FSK modulation. Turning up the power doesn't seem to do anything as I think we are bottlenecked by the fact our device is small and the transmission is bottlenecked by a tiny copper antenna.

Is there any approach we can use to extend the range while staying within the FCC regulations?

[Peter BENSCH]

Welcome @kienicholas, to the community!

Could it be that, in addition to the 10dB drop, your antenna is also optimised for 868MHz and has even lower gain at 921MHz?

Regards
/Peter

[kienicholas]

Thanks a lot for the response, this may be very helpful. The antenna we use on our receiver is the FLEXI-SMA90-868, optimised for 868Mhz so will look into that.

[Peter BENSCH]

However, it is not only the antenna that is decisive, but also the balun used, which can have an even greater influence.