The underlying principles of the format result from a number of requirements. This was essentially a balance between efficient data storage and providing sufficient information about the data for potential users. We have arrange these data so that words are aligned over 80-byte boundaries, this simplifies inspection and printing of the files. The data should contain all information for the identification of the source and the observing circumstances useful for further analyses of the data by others. In addition, we have designed the format, so that it can be used for observations of pulsars outside the radio regime i.e. variable units for the observing frequency and bandwidth, as well as topocentric telescope coordinates which are time variable for satellite observatories.
Space is left for more descriptors and future adaptations and expansions.
The header fully describes the structure of the data, this structure is not changed within one file but can vary between files. That way it is possible to calculate the length of a data block within each file after reading its header. The file can then be opened for random access with fixed block length, faster than a sequential read. Many of the above mentioned requirements were already met by a format in use at Jodrell Bank to which we made suitable modifications and extensions to make it more flexible. The basic structure of an EPN file consists of a common fixed length header followed by a number of individual data streams of equal length.