@spec parse_df_strength(integer()) :: df_strength()

Decode the S digit of a DFS value into {strength, description}.

An unrecognised digit gives {nil, description}.

@spec parse_phg_directivity(integer()) :: phg_directivity()

Decode the D digit of a PHG value into {degrees, description}.

An unrecognised digit gives {nil, description}.

@spec parse_phg_gain(integer()) :: phg_gain()

Decode the G digit of a PHG value into {dB, description}.

An unrecognised digit gives {nil, description}.

@spec parse_phg_height(integer()) :: phg_height()

Decode the H digit of a PHG value into {feet, description}.

An unrecognised digit gives {nil, description}.

@spec parse_phg_power(integer()) :: phg_power()

Decode the P digit of a PHG value into {watts, description}.

An unrecognised digit gives {nil, description}.