In electrical power systems there must always be a balance between supply and demand of power. Any imbalance will result in a frequency deviation. To reduce the imbalance to zero, ancillary services for balance management are in use. Ancillary services for balance management are characterized by their deployment time and their capacity. These ancillary services as well as the requirements for balance management can be characterized in the frequency domain. Actors, that are responsible for maintaining the balance in the system, can use the characterization in the frequency domain to define their needs for reserve capacity. This paper describes a method for spectral analysis of the required and available reserve capacity.