HP 8494E Ref In/Out

[Ice-Tea]

Hello gents,

I have two 8594E's, one with ref in and out connected (picture) and one without the connection. And a 8595E without as well. They obviously need to be connected if you're not using an external reference but...

- What goes wrong if you don't?
- Is the connection crititical? I don't think so... Since you can use an external one of 'sufficient amplitude' cable losses don't matter and for the same reason delay/ fase difference probably don't matter either. So... A whatever piece of coax will do?

[pe1oxp]

My 8594E had also no cable, so I made one by myself.
Cable isn't critical, it's just 10MHz, so some short peace of RG58 or RG142/400 will do the job.

[Tony_G]

I used a 6" HP 50 ohm cable I had and it worked fine. I also tried it with a 36" one and didn't notice any difference.

Did you make a mod to that scope? The normal/typical connector is a HP 1250-1499 Reference Connector (can't find an image now but it looks like a little bar with 2 bnc connectors on one side).

TonyG

[Ice-Tea]

I bought it like this... So, not an original part? Good to know...

[Miti]

The HP8590 series of spectrum analyzers come with two reference oscillator options AFAIK, regular TCXO and high stability OCXO. You can also connect an external GPSDO, rubidium, atomic or whatever reference you have in your lab, hence the external connection.
All your internal frequencies are derived from the PLL oscillator that locks on the reference input. If you don't connect them, all your frequency measurements will be at the hand of a very inaccurate and unstable, approximately 600MHz oscillator.
The original BNC adaptor is on the left but I used the cable on the right with no problems. As long as it is 50 Ohm (or at that length probably even that doesn't matter) you are ok.

Edit: Looking at the block schematic, the reference PLL controls a 600MHz VCO so I adjusted my post accordingly.

[Tony_G]

[Interesting the image shows reversed between small and large on my machine - updated my text for the thumbnail image version]

The rectangular one on the left is the original one for the 8560 & 8590 series SAs. The BNC on the right is a common reference connector for many pieces of HP kit though.

TonyG

[Ice-Tea]

Well, got some regular BNC on the way. Doesn't seem very critical  even though I see the benefit of having a completely flat backend of the scope.