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NerdyProjects / multichannel-hackrf-transmitter

MIT License
8 stars 4 forks source link

Implemented? #1

Open hakao32 opened 3 years ago

hakao32 commented 3 years ago

Hello, This is a nice project, thank you. Did you try this with hardware? Are you able to be on air at 3 frequency? And I need to ask one more question, how much CPU usage you are getting? Please let us know your hardware and CPU usage. Thanks a lot :)

NerdyProjects commented 3 years ago

Hey :-) Unfortunately, this is one of the projects I never finished. You can play a bit with number of filter taps etc. but on a raspberry Pi 4B, you will have no problems transmitting with 3 channels. E.g. I tested it with hardware, yep. I don't have a system by hand and cannot give you CPU information. I remember it not being close to full load, but for sure uses some CPU.

If you want to actually transmit with the setup, take care about all the spurious transmissions that get generated, especially if you reduce the filter taps.

hakao32 commented 3 years ago

Thank you for response I will test it when I have the hardware :)

image You mean this I guess. How can I filter them? Putting filter on single frequency at 200KHz bandwith should be tuff

NerdyProjects commented 3 years ago

You need to have enough "headroom" in the polyphase filterbank, e.g. enough taps and small enough bandwidths that there is no strong signal at the band edges (otherwise you need more taps). Also, you will want to check the output of your SDR and apply appropriate analog filters in the antenna path. If you are legally allowed to transmit, you should be aware of what's needed to make it work nicely :-)

hakao32 commented 3 years ago

I am going to use dummy load initially. I tried to put bandpass filter on 98-99 Mhz but difference between main signal and harmonic stays at around 80dB. How can I put desired frequencies in your design? As I see I can only step up.