[Discuss-gnuradio] GMSK MOD question

[Vivian Paola Triana Galeano]

Hi Everyone,
My name is VIvian and I am working with GMSK modulation. I have a little doubt about it.

I am transmitting a cosine signal using UHD sink and source blocks, USRP1, daughter board RFX 2400. The spectrum that I transmit is the one that you can see in the attached files.

I use a network analyzer to see the real spectrum that I am sending and the spectrum that I obtain can be seen in the  other photo that I attach.

Finally I look the spectrum received in GNU Radio, which is attached to this email too.

I found that the spectrum that I send is the half of the size that I see in the network analyzer. I mean the spectrum that I send has a bandwidth of 200 KHz ( I see this in GNU Radio)  but the one that I obtain looking at the network analyzer is approx. 400 KHz. When i see the received signal in GNU Radio is perfect, its bandwidth is the same that I send ( 200 KHz). I dont know why I see a different bandwidth in the network analyzer. Anyone knows what is happening?

I would appreciate any help you can give me. Thanks in advance.

Vivian.
 

gmsk modulation_spectrum_rx.png
Description: PNG image

gmsk modulation_ spectrum_tx.png
Description: PNG image