THE HP 8568B SPECTRUM ANALYZER WITH OPTION H96
With the release of the DC-100 extender card for HP8568B it has come to our attention that many 8568B's exist with option H96 installed. Its is also clear there is confusion about just what this option is and what changes to the 8568B were done. In short our opinion is that option H96 was done primarily to reduce the cost as compared to non H96 units. Every change we found is a reduction in capability, albeit small, of the instrument. That said it should be noted that most if not all these changes can be undone.
In the process of developing the DC-100 band extender for the HP8568B DKD Instruments obtained a HP8568B with option H96. We examined it and "opened it up" and discovered the following:
1) BNC Jack for primary RF input( N type removed), second RF input jack (BNC) removed
2) RF relay to select one of two RF inputs removed, as well as two front panel buttons that control it.
3) Oven controlled 10MHz internal reference is replaced with 10MHzTCXO plug in card.
4) 10Hz RBW is omitted. This change is done in two places, the software and hardware. It is the only change we could find that was not confined to the RF section. The display section has this change as a deletion of the 10Hz RBW in hardware. Our Display section with this change was also marked with H96 option. From what we can tell this is the only change to the display section with H96 option. In other words a H96 display section should work with non- H96 RF sections but 10Hz RBW will be found to be 30Hz. To install the 10Hz RBW the software in the RF section must be updated ( new prom set).
The removal of the 10Hz RBW indicates that perhaps the residual FM specification may have been relaxed. Or perhaps the omission of the oven reference prompted it. We cannot be sure. From our sample instrument we can say that once the 10Hz RBW was installed it seemed to work fine and as expected in terms of detected 60Hz spurious about a carrier and displayed phase noise of internal LO's.
5) DC probe power jack on front panel is omitted.
These are the changes we found. We successfully re-installed the 10Hz RBW( hardware and new prom set) , installed a RF relay for DC100 operation, two front panel buttons for RF relay control and changed the RF input connector to a type N. As for the 10MHz reference option H96 supports external reference , so it is no problem to drive the instrument with external reference form a higher quality reference. We do not claim these are all the changes to the H96 option. There may be others. If you know of any please let us know and we will post that information here.
INSTALLING THE DC100 BAND EXTENDER IN AN H96 OPTION MACHINE
Do to the extensive additional work involved we do not recommend this for users of the DC100. It can be done but installing the RF relay and moving the TCXO must be done to accommodate the DC100. This is not trivial and takes a fair amount of time.