Truetime 820 was made in the 80's and 90's and we have many at my day job fed with 1kHz AM modulated IRIG-B120. Schematic at http://www.trailing-edge.com/IRIG-B-DECODER.pdf Useful if you also have the theory of operation at http://www.arsitec.com.br/arquivos/produtos/man-820-210.pdf Tim N3QE