This paper presents a new study of the spectral index distribution of the supernova remnant ( SNR ) Puppis A .
The nature of field compact sources is also investigated according to the measured spectral indices .
This work is based on new observations of Puppis A and its surroundings performed with the Australia Telescope Compact Array in two configurations using the Compact Array Broad-band Backend centred at 1.75 GHz .
We find that the global spectral index of Puppis A is \alpha = -0.563 \pm 0.013 .
Local variations have been detected , however this global index represents well the bulk of the SNR .
At the SE , we found a pattern of parallel strips with a flat spectrum compatible with small-scale filaments , although not correlated in detail .
The easternmost filament agrees with the idea that the SNR shock front is interacting with an external cloud .
There is no evidence of the previously suggested correlation between emissivity and spectral index .
A number of compact features are proposed to be evolved clumps of ejecta based on their spectral indices , although dynamic measurements are needed to confirm this hypothesis .
We estimate precise spectral indices for the five previously known field sources , two of which are found to be double ( one of them , probably triple ) , and catalogue 40 new sources .
In the light of these new determinations , the extragalactic nature previously accepted for some compact sources is now in doubt .