RTL-SDR.com reader Syed Ghazanfar Ali Shah Bukhari from the Frequency Allocation Board in Pakistan recently emailed us to let us know a trick he's found which lets you combine the bandwidths of two HackRF software defined radios in GNU Radio. Syed's program is based on Oliver's flowgraph that we posted previously, which was used to combine the bandwidth of two RTL-SDR dongles.
Syed also sent us the GRC file to share which we've uploaded here.
I have used grc flow graph of Oliver as mentioned in the link :-
https://www.rtl-sdr.com/combining-the-bandwidth-of-two-rtl-sdr-dongles-in-gnu-radio and modified it to be used with 2 HackRF Ones. I also shifted the two bandwidths inward by 1 MHz instead of 0.2 MHz to make a smooth continuation for a 38 MHz spectrum. Unfortunately one of my HackRF Ones has its RF Amp burnt up so I adjusted its IF and BB gain to have same noise floor as that of other HackRF One. It's really awesome. I am sending you the diagram and grc file. The attached image is showing complete GSM900 downlink spectrum (38 MHz) in my area with active 2G and 3G signals.
September 2018 Update:
An rtl-sdr user with nick JAAP had some query pertaining to calculation of center frequency of each HackRF. The values I used were a bit erroneous. If you the previous flow graph I sent you, the center frequencies for both HackRFs are same in the SDR source box. That should be different for both with a 20 MHz difference between the two. Some spectrums started repeating themselves on those values. I have improved the flowgraph using variables and equations to remove the logical bug. I have added a slider for bandwidth cropping that can be used for test pupose only to understand the concept behind the frequency shifting and cropping of spectrum of both HackRFs. I have attached the new grc file and the image. Gain values can be adjusted as per user requirement and sensitivity of your own SDRs. I am working on grc which will show a spectrum using 5 rtl-sdrs and two hackRFs thus combining BWs to give a span of 50 plus MHz.
Update GRC File available here.