  A modern Q-band low noise amplifier (LNA) front-end is being fitted to the
10.4 m millimeter-wave telescope at the Raman Research Institute (RRI) to
support observations in the 40-50 GHz frequency range. To assess the
suitability of the surface for this purpose, we measured the deviations of the
primary surface from an ideal paraboloid using radio holography. We used the
11.6996 GHz beacon signal from the GSAT3 satellite, a 1.2 m reference antenna,
commercial Ku-band Low Noise Block Convereters (LNBC) as the receiver
front-ends and a Stanford Research Systems (SRS) lock-in amplifier as the
backend. The LNBCs had independent free-running first local oscillators (LO).
Yet, we recovered the correlation by using a radiatively injected common tone
that served as the second local oscillator. With this setup, we mapped the
surface deviations on a 64 x 64 grid and measured an rms surface deviation of
~350 um with a measurement accuracy of ~50 um.
