Products > Test Equipment
HP 5334A option 030 redesign
croma641:
Yes, I know. My replay was to note that the 5334A doesn't have any ROM that accepts :64 prescalers.
ekoloski:
Quick update for the community on this project. As with any first run of a board, there are some changes and some bodges. All things aside though, this looks promising. I have only tested from 60-990MHz, further testing to determine the upper limit will commence once I've cleared some bench space!
Some quick notes:
* I will need to look into improving the sensitivity. I believe the original HP version worked down to -23dBm without a preamp, I am seeing reliable input down to about -17, so some work needs to be done here. Perhaps another gain stage or an LNA on the frontend
* The pin diode attenuator is aggressive, only the top 1/4 of the range seems to work, with anything lower cutting the signal below detection. I'll adjust this
* The biasing on both clock lines between the two divider stages has been altered, I bodged in a voltage divider to provide about -2V and used that instead
* The biasing on the input to the first divider is now 50/150ohms
Update: After hooking up an SDR to test it, it appears the upper limit of stable readings is 2.1GHz. Not bad at all, considering this counter maxes out at 100MHz and this is a divide-by-20 frontend! I've also got it reliably working down past -23dBm on the input.
ekoloski:
As promised, attached is a revised schematic reflecting the changes I had bodged into the board. I will also update the PCB and upload the gerbers, in case this can help anyone else out there.
Regarding other counters like the 5328A. The general design could easily be adapted to fit other models. For those with a 64:1 requirement, different prescaler configurations could easily be fit as well. I believe the real magic here is in the signal conditioning section and the peak detection to prevent false readings due to background noise.
I have also passed the point of no return and have drilled some holes in my nice counter. The level control and a type-N connector now happily reside on the front panel of the instrument. Next, I'll need to find a suitable knob and figure out a way to label the panel. Beyond that I may add a connector to bring power out for a LNA/preamp. I'm eyeing up TSS-53LNB+ to fit the purpose. I had briefly considered using a bias-tee arrangement, but the thought of injecting DC into anything being measured if I forget to switch it off when used is unsettling.
I appreciate all of the feedback. To address some of the points raised:
Yes, I think I would have benefited from posting in the RF section as well. This has been a learning experience in the ways of 'magic plumbing' for signals greater than a few hundred MHz.
The components on the board are pretty small. The RF is mostly 402 sized smd, simply due to RF considerations. The remaining are 603, which is small but still workable for hobbyist assembly and repair. This was assembled using nothing more exotic than a solderpaste stencil, some fine tweezers, a hot plate, hot air station, and a cheap microscope to verify that I hadn't misplaced anything.
Swainster:
What input fuse did you use? I notice that you went with something on the board, rather than something built into the BNC jack - makes sense as the BNC type seem to be unobtanium. My HP 5335A is the older version, so should be compatible with this prescaler design... I shall have to put it on my future projects list, though it might get bumped up if another 5335A enthusiast provides a compatible layout.
ekoloski:
You're spot on about the fused connectors, I had to go with something on the board out of necessity.
Its probably a faux pas, but I went with a 1206 sized polyfuse, a 1206L012WR by Littlefuse specifically. It did add about 6 ohms of series resistance, and I am considering replacing it with a standard fuse instead. The intent with the polyfuse was to avoid ever having to replace it but now I am questioning my decision.
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