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Pls advise on the 4FSK spectral that I got

Question asked by luw on Dec 11, 2015
Hi,

I was using a commercial wireless development kit made by SiLabs that works @434MHz. I wanted to observe the received power using a N9010a Spectrum Analyzer. I programmed the dev kit with 2 example projects from SiLabs: 1) PN9 for a continuous transmission and 2) Standard Packet TX for a push-button triggered transmission (The packet structure is fixed as follows:  5-byte Preamble (1010 pattern) + 2-byte Sync Word (0x2DD4) + 7-byte Payload ('BUTTONx'), with no CRC.). Both modulation were 4FSK.

In the SXA, I observed that the spectral for Standard Packet TX seemed to be different in shape from that of the PN9. I do not know if it was due to the problem with configuring the SXA or it was simply because I did not understand these modulation technologies. For the Standard Packet TX, the 4 spikes were not equal in amplitude, #1 and #4 are much stronger than #2 and #3. Besides, #2 and #3 showed up later than #1 and #4 and had a noise spike in between them.

The parameters are:
Mkr1@433.9406 MHz, Mkr2@433.9805 MHz, Mkr3@434.0204 MHz and Mkr4@434.06 MHz.
RBW: 2 kHz. VBW: 2 kHz, IntegBW: 200 kHz, Sweeptime: 50 ms.

Please advise if you find anything that I didn't do properly. Thanks a lot!  

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