def dm_one_delay(freq_lo_mhz, freq_hi_mhz):
    """Compute the dispersion delay of a DM = 1 signal.

    :param freq_lo_mhz: Lowest frequency in the observation range.
    :type freq_lo_mhz: float
    :param freq_hi_mhz: Highest frequency in the observation range.
    :type freq_hi_mhz: float
    :return: The expected delay (in seconds) between the highest and lowest frequency of a DM=1 signal.
    :rtype: float
    """
    return 4150.0 * (freq_lo_mhz ** -2 - freq_hi_mhz ** -2)
