S2C - Spectral issue

Hi there,

I bought 10 of the transceivers mentioned in the title. I want to record their spectral behaviour for research purposes.

Somewhat I don’t see the expected behavior with my spectrum analyzer (N9320B).

The datasheet mentions center freq around 2.4GHZ.

When i connect one of the transceivers directly to the spectrum analyzer i don’t see any signal but one that is about 200KHZ around 864MHZ center frequency, which I see whenever the transceiver is connected regarding its transmission (I thought that it’s the noise level of the device).

I should mention that the transceivers are connected to two different computers and passing messages between them effortlessly (even without antennas) using the XCTU program.

As I said, my goal is to record the spectrum of the communication between them but currently I don’t see anything that is relevant for recording. It may be that my device version is not on 2.4GHZ band as the datasheet says?

Does this device uses spread spectrum method by any chance?

All of my RF setup was verified good but the transceivers themselves.

I would very much appreciate your help and advice on what am I doing or thinking wrong and what should I do differently in order to see the desired communication signals on the spectrum analyzer.



The Zigbee/802.15.4 IEEE specification operates in different bands. The XBee product line uses the 2.4 GHZ ISM band for this protocol. The overall frequencies used is from 2.4 GHz - 2.49GHz. You can see a complete listing of the frequencies and channels used by going to 802.15.4 and ZigBee | Digi International and downloading the attached document. Page 2 shows the bands used. You will need to look at the CH or Channel command to know what channel the radio is operating on.

First, Thanks for your reply.
I am looking at the frequency band mentioned there and I can not observe any signal although the transceivers do communicate and pass messages effortlessly.
Therefore I asked if the device is using any sort of spread spectrum method?
Do you know about any case of the signals not showing on the spectrum (maybe power is too low for spectrum analyzer but still good for reception)?
And why am I observing this 864MHz signal whenever I plug in the transceiver directly to the spectrum analyzer? it does not seems to be proper behavior

The 802.15.4 versions do use a DSSS.

What is the part number for the XBee you are working with? I ask as Digi does offer XBee products that operate in either 868MHz, 900 MHz or 2.4GHz.

I use the Digi XBee S2C 802.15.4.
Is it enough or where can I look for the part number?

The part number would be on the back on the white label. It should be something like XB24C.

If it is the S2C, then it will not transmit unless you feed it data. Just understand that it is communicating at 250kbps over the air.

You will want to look at the CH command to determine which channel it is operating on. Then you can look up the Ch value telling you what Frequency it is operating at.

Hi, sorry for the delay and thanks again for your help.
the part number is : XB2CZ7SIT-004 and operating on CH 13.
As I mentioned, I cannot see any frequency behavior beside the one I detailed above.
Could it be that the transceivers operate in such low power while configuration is on maximal power? Any other suggestions?
Spectrum analyzer and RF cable are working good.

No I would not expect that to be the case. What I think is going on is that your spectrum analyzer is not set up correctly to catch the RF traffic when the module is transmitting.

I respect your opinion.
I am working with RBW and VBW of 30khz and ref lvl -60dBm on calibrated spectrum analyzer, I am looking for whatever it is I am doing wrong. Any suggestions?
Btw, the behavior in 864Mhz is still weird…

This is a 2.4 GHz product. Your total frequency band that you should be looking at is 2.40 - 2.48 or so GHz if I recall. I would also not have it set for a reference level of -60 but closer to 0. I could be off on the reference level just because it has been 3 years since the last time I used a Spectrum Analyzer. So I may be going off the wrong direction.