We suggest and demonstrate a scheme to reconstruct the symmetric two-mode squeezed thermal states of spectral sideband modes from an optical parametric oscillator. The method is based on a single homodyne detector and active stabilization of the cavity. The measurement scheme have been successfully tested on different two-mode squeezed thermal states, ranging from uncorrelated coherent states to entangled states.PACS numbers: 03.65. Wj, 42.50.Lc, 42.50.Dv Introduction -Homodyne detection (HD) is an effective tool to characterize the quantum state of light in either the time [1][2][3][4][5][6][7][8] or the frequency [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] domain. In a spectral homodyne detector, the signal under investigation interferes at a balanced beam splitter with a local oscillator (LO) with frequency ω 0 . The two outputs undergo a photodetection process and their photocurrents are combined leading to a photocurrent continuously varying in time. The information about the spectral field modes at frequencies ω 0 ± Ω (sidebands) is then retrieved by electronically mixing the photocurrent with a reference signal with frequency Ω and phase Ψ. Upon varying the phase θ of the LO, we may access different field quadratures, whereas the phase Ψ can be adjusted to select the symmetric S or antisymmetric A balanced combinations of the upper and lower sideband modes.