Mikebits
Well-Known Member
One would think that since I use to work at a company that developed CDMA phones that I would completely understand how it works. Well, I actually worked on the backhaul end. That is, after the call signal left the cell site and was just a digital serial bit stream.
With that said, I find myself trying to get a better understanding of CDMA modulation. So I whipped up a digital bitstream and phase modulated it with a baseband carrier of 4.95 MHz, I even made a 4 pole passive BPF for it.
So below is BPF response.
Okay not pretty, but that what I got with parts on hand.
Using my Arbitrary waveform generator set to PSK, and externally modulated with a serial bit stream, I get a waveform somewhat like I expected except I wonder, how on earth do you suppress the carrier wave out of the bandpass, or do you filter to one of the lobes. I dunno, I really have myself perplexed.
The spread spectrum waveform should resemble something like below image:
My resulting waveform is as shown below:
Zoomed in it looks right, but I am not showing the carrier wave.
I am sure my thinking is just goofy, but I think I need a good head slap to set me right. Thanks
With that said, I find myself trying to get a better understanding of CDMA modulation. So I whipped up a digital bitstream and phase modulated it with a baseband carrier of 4.95 MHz, I even made a 4 pole passive BPF for it.
So below is BPF response.
![SA_170208151508.png SA_170208151508.png](https://www.electro-tech-online.com/data/attachments/93/93161-4064c62b392156c6044f8e50d80a1f06.jpg)
Okay not pretty, but that what I got with parts on hand.
Using my Arbitrary waveform generator set to PSK, and externally modulated with a serial bit stream, I get a waveform somewhat like I expected except I wonder, how on earth do you suppress the carrier wave out of the bandpass, or do you filter to one of the lobes. I dunno, I really have myself perplexed.
The spread spectrum waveform should resemble something like below image:
![cdma2k-12-1-12.gif cdma2k-12-1-12.gif](https://www.electro-tech-online.com/data/attachments/93/93164-5e108e9db9ac9dd543c5f4288d79dc07.jpg)
My resulting waveform is as shown below:
![SA_170207160659.png SA_170207160659.png](https://www.electro-tech-online.com/data/attachments/93/93165-951350be908621d46d4fda6f4bed035d.jpg)
Zoomed in it looks right, but I am not showing the carrier wave.
![SA_170207015904.png SA_170207015904.png](https://www.electro-tech-online.com/data/attachments/93/93166-e5fc8defeeb4565382ae2e30ab6354fb.jpg)
I am sure my thinking is just goofy, but I think I need a good head slap to set me right. Thanks