diff --git a/applications/lofar2/model/pfb_os/dsp_study_erko.txt b/applications/lofar2/model/pfb_os/dsp_study_erko.txt
index 1e56353c154c77b925f21fddf910c2c871abd78a..e3756e2303ba6eca1a05778a6368ea6f37411af1 100644
--- a/applications/lofar2/model/pfb_os/dsp_study_erko.txt
+++ b/applications/lofar2/model/pfb_os/dsp_study_erko.txt
@@ -175,13 +175,20 @@ b) z-transform [LYONS 6.3, MATLAB]
 - Causal systems are 0 for n < 0, so sum from n = 0 yields one sided z-transform
 - For r = 1 the z-transform yields the DTFT, so DTFT evaluates the
   z-transform on the unit circle.
+- Properties [PROAKIS 3.3]:
+  . shift property: x[n - k] <--> X(z) z^-k
+  . time reversal: x[-n] <--> X(z^-1]
+  . convolution: x[n] * y[n] <--> X(z) Y(z)
+  . conjugation: x*[n] <--> X*(z*)
+  . real part: Re{x[n]} <--> 1/2 [X(z) + X*(z*)]
+  . imag part: Im{x[n]} <--> 1/2 [X(z) - X*(z*)]
 - Examples:
   . wire: H(z) = 1
   . delay: H(z) = z^-1, so x[n - 1] <--> X(z) z^-1 (shift property)
   . integrator: d[n] pulse at n = 0 --> u[n] step,
                 Y(z) = 1 + z^-1 + z^-2 + ..., multiply by (z - 1) / (z - 1)
                      = z / (z - 1) = 1 / (1 - z^-1)
-  . difference equation
+  . difference equation <--> rational z-transform
       y[n] + 0.5 y[n-1] = u[n] --> Y(z) + 0.5 z^-1 Y(z) = U(z)
                                    H(z) = Y(z) / U(Z) = 1 / (1 + 0.5 z^-1)