The survey plates were taken with the Schmidt telescope located at the
German-Spanish Astronomical Center (DSAZ) on Calar Alto/Spain, using the
objective prism.
If the Milky Way region (
) is omitted,
the complete northern sky can be covered by 567 fields. For all fields
two objective prism plates are now available, with at least one plate having
a quality grade of A or B. For the definition of the grades we refer
to Paper I. Direct plates are available
for all fields, except in the region 
and
. For this region the digitized POSS (Jenkner et al.
1990) is presently used for comparison with the prism
plates. The complete plate archive now contains 1288 objective prism and
583 direct plates. A list of the plates is available from the
www-page of the observatory.
The objective prism plates were scanned with the Hamburg PDS1010G
microdensitometer in a "low-resolution" mode
(cf. Paper I). After on-line background
reduction and object recognition, the low-resolution density spectra
(
15 independent pixels per spectrum) were used to search for
QSO candidates. Different search techniques
were applied taking advantage of typical spectral properties of QSOs, such as
emission lines and blue continua. The selection technique currently
applied to search for bright quasars will be described in a following
paper (Hagen et al., in preparation).