W&G SPM6 Selective Voltmeter

[Alberto di Bene]

I have just bought a second (third?, fourth?) hand Wandel & Goltermann SPM6 selective
voltmeter, which ranges from 6 kHz to 18.6 MHz, with a -100dBm sensitivity. I understand
it has an IF output on the back panel, where I would like to connect a DSP processor to.
The  problem is that this unit came without any form of manual or documentation, so I
don't know the value of the last IF, nor which connector it exits from. Their Web site
doesn't list this model, obsolete by now.
Does anybody have any kind of info on this unit ? Thanks.

73,
Alberto di Bene,     I2PHD