[time-nuts] DIY Frequency extension for 53131A - Need help on OPT 050 - OPT 124

Samuel DEMEULEMEESTER sam at canardpc.com
Wed Oct 14 21:44:14 UTC 2009

Hi timenuts,

Sorry to reply to my old thread, but I promised to let you know about that project. 10 months after, I successfully reproduced the OPT 030 option without any problem. Now, I want to build my own prescaler design in order to produce some kits without having to bother about potential HP/Agilent hardware copyright. My extension board will be built from scratch and will features higher frequency than the 3 GHz of the OPT030. The target is 8-12 GHz, but 18 GHz may be possible. Right now, my new design works but I have a big problem : according to the schematics available on Agilent website, the 53131A, 53132A and 53181A use two pins for EXTBOARD type detection (CH3CODE0/pin10 and CH3CODE1/pin9 on J2 connector). 

That's for theory. In practice, something goes wrong. If you ground CH3CODE0, the counter detect OPT 030 and applies a x128 multiplier on the channel 3 input. Just fine for that option which is basically a /128 divider, but not enough for higher frequencies (OPT 050 / OPT 124), which may use a /512 or /1024 divider. 

The problem is I tried every possible combinations with CH3CODE0/CH3CODE1 without being able to force the counter to detect an OPT 050 / OPT 124 extension board. This just doesn't work. Only OPT 030 seems possible the "easy" way. I'm now convinced there is an additional hardware or software trick to enable the higher multiplier. 

So, I need to find someone with a genuine OPT 050 / OPT 124 extension board, kind enough to give me some additional information.

If any of you can help me, that would be greatly appreciated :)


-----Message d'origine-----
De : time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] De la part de Samuel D. [x86/CPC]
Envoyé : samedi 14 février 2009 20:30
À : time-nuts at febo.com
Objet : [time-nuts] DIY Frequency extension for HP Agilent 53181A, 53131A or 53181A

Hi there,

First, let me introduce myself : I’m a 28-years-old electronic engineer working for a press magazine as Hardware & Test Chief Editor. I’m from France; so, please forget about my bad English. Since years, I’m obsessed with precision measurements and I spend the last 15 months finding the best way to accurately measure a couple of femtoamperes or nanovolts. For 2009, my new goal is to be able to measure the mHz part of a GHz signal so, I need ultra high accuracy frequency standard and other fancy things like that.

But here is the problem: I’m not rich and I don’t have enough money to build Agilent’s and Symmetricon’s stuff at MSRP. In the other hand, I love precision equipment and high quality, well-known hardware. After all, its 90% hobby and 10% professional, so, why spend thousands of dollars on a brand new Rubidium standard when you can build one with a Datum module found on eBay for a small fraction of that price? That’s what I will do in the upcoming weeks.
By the way, as you know, the two first equipments to own for precision time measurements are a high stability frequency reference and a good counter. Building the first one is quite easy but a good counter is something expensive. Fortunately, I just bought an Agilent 53131A for €350 on eBay and I’m really happy with it. As usual, I will now spend some time to see how I can improve it. 

HP/Agilent 53181A, 53131A & 53132A are probably the most used frequency counters in the world. They come with two kinds of options: three advanced time-bases (an OCXO with 2x10e-7, 1.5x10e-8 or 3x10e-9 monthly aging rate) and four frequency extensions. These counter’s max base frequency is 225 MHz and may go up to 1.5, 3.0, 5.0 or 12.4 GHz with an additional PCB linked to a BNC or type-N connector acting as Channel 2 (for 53131A) or Channel 3 (for 53131A and 53132A).

As often with Agilent, the price for those extensions is clearly and indecently overpriced: more than $2000 for the 3 GHz option, the price of the counter itself. Overpriced, Really? Yes! And if you still doubt, here is an anecdote from my experience: the Agilent 34420A Nanovolt Meter comes with a low-thermal input connector. Last year, I wanted to build a custom cable and I asked Agilent the price for a male connector. They quoted that small part more than €100. After lots or research I found the exact same connector, originally built by Lemo, and bought it new for less than $15.

Ok, come back to the 53131A frequency options. The extension sold by Agilent is nothing more than a prescaler (probably /16, /32, /64) mounted on a small PCB and connected to the counter with a standard ribbon cable. The PCB is really small and there is no more than 20 components built-in as you can see here : http://www.x86.fr/temp/003.jpg (3 GHz option) and http://www.x86.fr/temp/124.jpg (12.4 GHz option). 

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