As well as studying the spatial variations of spectra, we may use observations at the lowest (< 100 MHz) frequencies to investigate SNRs and their interaction with the ISM via integrated spectrum studies. Nonlinear models of electron acceleration in shocks predict an electron spectrum flattening with increasing energy in the region 0.1-20 GeV appropriate for electrons emitting at radio wavelengths by the synchrotron mechanism. Some evidence for the corresponding flattening in the integrated radio spectrum has been found in Tycho, Kepler and SN1006, though with large errors.
When combined with higher frequency measurements, flux densities for SNRs that may only be marginally resolved at 74 MHz ( for the VLA, for the A+ configuration) may still give a sensitive measure of the integrated radio spectrum. A 74 MHz 27-antenna VLA system providing an rms <10 mJy in 12 hrs would give valuable low frequency flux density measurements for SNRs. Previous measurements below 100 MHz for all but the strongest SNRs have large uncertainties because almost all of them were obtained with single dishes and are strongly confused by nearby thermal sources and the Galactic background radiation.