Using a simple analytic model based on seed superposition we obtain the spectrum of microwave background perturbations induced by cosmic strings on all angular scales larger than about 2 armin .
We assume standard recombination in an Einstein de Sitter universe with h = 1 / 2 and study the fluctuation spectrum along a great circle in the sky .
Doppler and potential perturbations on the last scattering surface ( Sachs-Wolfe effect ) are shown to dominate over post-recombination perturbations on scales smaller than about 2 degrees .
Using a filter function corresponding to the COBE experiment we obtain an effective power spectrum index n _ { eff } \simeq 1.35 in good agreement with the recently announced second year COBE data showing n _ { eff } \simeq 1.5 .
The only free parameter ( G \mu ) of the string model is fixed by normalizing on the COBE detection leading to G \mu = 1.6 .
Other parameters ( e.g .
the rms string velocity ) are fixed by comparing with string simulations .
Using these parameter values we compare the rms temperature fluctuations ( { { \Delta T } \over T } ) _ { \it rms } predicted for ongoing experiments ( Tenerife , SP91 , MAX , OVRO etc ) with detections and with the corresponding predictions of inflationary models .