HackRF sweep is a tool that

Usage

        [-h] # this help
        [-d serial_number] # Serial number of desired HackRF
        [-a amp_enable] # RX RF amplifier 1=Enable, 0=Disable
        [-f freq_min:freq_max] # minimum and maximum frequencies in MHz
        [-p antenna_enable] # Antenna port power, 1=Enable, 0=Disable
        [-l gain_db] # RX LNA (IF) gain, 0-40dB, 8dB steps
        [-g gain_db] # RX VGA (baseband) gain, 0-62dB, 2dB steps
        [-n num_samples] # Number of samples per frequency, 8192-4294967296
        [-w bin_width] # FFT bin width (frequency resolution) in Hz
        [-1] # one shot mode
        [-B] # binary output
        [-I] # binary inverse FFT output
        -r filename # output file

Output fields

date, time, hz_low, hz_high, hz_bin_width, num_samples, dB, dB, ...

Running hackrf_sweep -f 2400:2490 gives the following example results:

Date	Time	Hz Low	Hz High	Hz bin width	Num Samples	dB	dB	dB	dB	dB
2019-01-03	11:57:34.967805	2400000000	2405000000	1000000.00	20	-64.72	-63.36	-60.91	-61.74	-58.58
2019-01-03	11:57:34.967805	2410000000	2415000000	1000000.00	20	-69.22	-60.67	-59.50	-61.81	-58.16
2019-01-03	11:57:34.967805	2405000000	2410000000	1000000.00	20	-61.19	-70.14	-60.10	-57.91	-61.97
2019-01-03	11:57:34.967805	2415000000	2420000000	1000000.00	20	-72.93	-79.14	-68.79	-70.71	-82.78
2019-01-03	11:57:34.967805	2420000000	2425000000	1000000.00	20	-67.57	-61.61	-57.29	-61.90	-70.19
2019-01-03	11:57:34.967805	2430000000	2435000000	1000000.00	20	-56.04	-59.58	-66.24	-66.02	-62.12

Two ranges of 5 MHz are analyzed at once from the same set of samples, so a single timestamp applies to the whole range.

The fifth column tells you the width in Hz (1 MHz in this case) of each frequency bin, which you can set with -w. The sixth column is the number of samples analyzed to produce that row of data.

Each of the remaining columns shows the power detected in each of several frequency bins. In this case there are five bins, the first from 2400 to 2401 MHz, the second from 2401 to 2402 MHz, and so forth.