The RA1792
Page 4
The 2nd LO Synthesiser
Old style

Just as there are two possible versions of 1st LO, there are also two possible versions of 2nd LO. The newer version includes a pair of extra buffer amplifiers and a couple of extra test points. The 2nd LO board, as well as providing the reference frequency for the 1st LO, gets its own reference from one of three possible sources. The most common frequency source being an off-board but local 5MHz ovenised oscillator (see below). Alternatively there is provision for a local on-board 5MHz reference or and external source which can be either 1MHz, 5MHz or 10MHz. The two wire links in the centre of the board are used to select the input frequency of this external source. Since the 2nd IF in the RA1792 is 455KHz, the 2nd LO output is 40MHz. The 2nd LO synthesiser board also incorporates the BFO circuitry, the output of which is centred on 455KHz.

New style
Racal-Dana ovenised 5MHz frequency standard type 9442/12