OOPS! So sorry, I carelessly and mistakenly posted some GHz references. Thanks davenn for watching out for the integrity of our Forum’s posts!
There are astrophysical sources of this microwave 16.4 GHz frequency. Many new and planned radio telescopes are being built now will monitor it. Two sources are Galaxy ESO 149-3 and the Hubble image shows NGC 1566. A few other examples are:
Mon. Not. R. Astron. Soc. 386, 1729–1738 (2008) doi:10.1111/j.1365-2966.2008.13161.x
Multifrequency spectral analysis of extragalactic radio sources in the 33-GHz VSA catalogue: sources with flattening and upturn spectrum
http://authors.library.caltech.edu/14061/1/TUCmnras08.pdf
arXiv.org > astro-ph > arXiv:astro-ph/0102497v1
http://www.vlf.it/frequency/bands.html
http://en.wikipedia.org/wiki/Cassiopeia_A
AMIGPS16GH - AMI Galactic Plane Survey 16-GHz Source Catalog
http://heasarc.gsfc.nasa.gov/W3Browse/all/amigps16gh.html
Perrott, Y. C., A. M. Scaife, N. Hurley-Walker, and K. J. Grainge. 2013. “Investigating the Source of Planck-Detected AME: High-Resolution Observations at 15GHz.” Advances in Astronomy 2013: 1-9.
Perrott, Y. C., A. M. Scaife, D. A. Green, M. L. Davies, T. M. Franzen, K. J. Grainge, M. P. Hobson, N. Hurley-Walker, A. N. Lasenby, M. Olamaie et al. 2013. “AMI Galactic Plane Survey at 16 GHz – I. Observing, mapping and source extraction.” Monthly Notices of the Royal Astronomical Society 429: 3330-3340.