class_docstr: Thread which runs rtl_power_fftw process
docstr: Get start and stop frequency for particular hop
code: def get_hop_freq(self, hop):
      """Get start and stop frequency for particular hop"""
      start_freq = (
          self.params["start_freq"] * 1e6
          + (self.params["sample_rate"] - self.params["overhang"]) * hop
      )
      stop_freq = (
          start_freq
          + self.params["sample_rate"]
          - (self.params["sample_rate"] / self.params["bins"])
      )
      return (start_freq, stop_freq)
  
file_path: qspectrumanalyzer/qspectrumanalyzer/backends/rtl_power_fftw.py
imports: import math, shlex
  from Qt import QtCore
  from qspectrumanalyzer import subprocess
  from qspectrumanalyzer.backends import BaseInfo, BasePowerThread
label_desc: Use image node_id 2 for calling the PowerThread obj's underlying member method code with example usage: obj.get_hop_freq(hop) and returns: start_freq,  stop_freq