Setting different frequencies for RX1 and RX2

Having issues with the site, hardware, source code, or any other issues?

Moderator: robert.ghilduta

Post Reply
tslonaker
Posts: 3
Joined: Mon Jan 07, 2019 11:45 am

Setting different frequencies for RX1 and RX2

Post by tslonaker » Mon Jan 07, 2019 11:49 am

I'm trying to set RX1 and RX2 to different frequencies, so that I can receive both Uplink and Downlink I/Q data for different LTE bands. For now I'm just using BladeRF-cli.

However, when I go to set RX2, it sets both RX1 and RX2 to that frequency. Any ideas about what I'm doing wrong?

bglod
Posts: 196
Joined: Thu Jun 18, 2015 6:10 pm

Re: Setting different frequencies for RX1 and RX2

Post by bglod » Tue Jan 08, 2019 2:54 pm

This is not possible. The two RX ports share a common LO. Likewise for the two TX ports.

One might then wonder what is the purpose of that. There are many applications that use multiple "spigots" (MIMO) tuned to the same frequency. Because there are multiple, sometimes smaller, antennas, they can work together to provide significant improvements to gain, interference reduction, and data throughput. MIMO also lets you do some unique things like beamforming, which cannot be done with a single antenna. There's a decent introductory Wikipedia page on the topic if you are interested in learning more about it.
Electrical Engineer
Nuand, LLC.

tslonaker
Posts: 3
Joined: Mon Jan 07, 2019 11:45 am

Re: Setting different frequencies for RX1 and RX2

Post by tslonaker » Wed Jan 09, 2019 9:01 am

Thanks for your response!

So is there a way to make a setup like this work with the BladeRF 2.0? https://github.com/Nuand/bladeRF/tree/m ... i/sync_trx

I had it working previously with two x40s. Thanks

bglod
Posts: 196
Joined: Thu Jun 18, 2015 6:10 pm

Re: Setting different frequencies for RX1 and RX2

Post by bglod » Thu Jan 10, 2019 4:12 pm

The bladeRF2 supports trigger inputs/outputs and should work the same as bladeRF1. I believe you would still need two bladeRFs. You might be able to get away with pairing the bladeRF2 with one of your existing bladeRF x40s.
Electrical Engineer
Nuand, LLC.

tslonaker
Posts: 3
Joined: Mon Jan 07, 2019 11:45 am

Re: Setting different frequencies for RX1 and RX2

Post by tslonaker » Mon Jan 21, 2019 9:55 am

Thanks for the response, that's good to hear. I do have two xA4s so that's fine. I'm guessing I have to modify the trigger pin commands, and the clock commands in the scripts from that github link. So j71-4 should be j51-1 for the 2.0 boards. Just need to figure out how to set the clocks as out/in - what's the equivalent for "smb_mode" with the xA4s?

bglod
Posts: 196
Joined: Thu Jun 18, 2015 6:10 pm

Re: Setting different frequencies for RX1 and RX2

Post by bglod » Mon Jan 21, 2019 1:34 pm

If you're using the bladeRF-cli, then to enable/disable the UFL clock output (J92):

Code: Select all

set clock_out enable|disable
and to change the 38.4 MHz source (onboard VCTCXO or external via U.FL (J93)):

Code: Select all

set clock_sel external|onboard
If using an external clock, it should be within 10 kHz (or 100 kHz? I forget..) of 38.4 MHz, otherwise the FX3's PLL may unlock and you'll drop the USB connection. The PLLs on the FPGA may also unlock, causing it to reset itself.
Electrical Engineer
Nuand, LLC.

Post Reply