  Studies of the pulsar B0823+26 have been carried out using the Large Phased
Array (LPA) radio telescope. At time span of 5.5 years, the amplitudes of the
main pulse (MP), postcursor (PC) and interpulse (IP) were evaluated in daily
sessions lasting 3.7 minutes. It is shown that the ratio of the average
amplitudes of MP in the bright (B) and quiet (Q) modes is 60. For B-mode, the
average ratio of MP amplitudes to IP amplitudes is 65, and the ratio of MP
amplitudes to PC amplitudes is 28. The number of sessions with a nulling is 4%
of the total number of sessions. Structure function (SF) and correlation
function analysis of MP, IP and PC amplitude variations of over a long-time
interval allowed us to detect typical time scales 37 \pm 5 days and one year.
The analysis of time variations shows that the time scale of 37 days is well
explained by refraction on inhomogeneities of interstellar plasma, which is
distributed mostly quasi-uniformly in the line-of-sight. This scintillation
makes the main contribution to the observed variability. Analysis of the
structure function showed that there may be a few days variability. This time
scale does not have an unambiguous interpretation but is apparently associated
with the refraction of radio waves on the interstellar medium. One-year
variability time scale has not been previously detected. We associate its
appearance with the presence of a scattering layer on a closely located screen
at a distance of about 50-100 pc from the Earth.
