[time-nuts] Frequency Counter Choice

[Gregory Beat]

Giorgio -
You may find the Phillips models to be easier to acquire via European surplus.

In 2019, I acquired a surplus Agilent 53131A, at a significantly lower price than regularly seen, on eBay.  Mis-categorization by the reseller likely created this bargain.  
When received it had a NASA Glenn Center (Cleveland, OH) calibration sticker.
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As noted by other time-nuts members (and documented on Internet), the switch-mode power supply (SMPS) is an “Achilles heel” for these HP/Agilent counters.
I replaced the fan in the SMPS and a couple of large electrolytic capacitors with 105 degree Panasonic replacements.
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There are numerous YouTube videos by: EEVBlog, GerrySweeney, and others for this HP/Agilent 531xx counter series (as well as Phillips PM-series).  I cringe watching some of these YouTube videos (my curse of having a Motorola field/bench engineer for high school electronics classes).  While I understand Gerry Sweeney’s reasoning for changing the function of the 53131 power button — I would NOT perform that modification.
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My Agilent 53131 did not have the OCXO or third channel 3GHz (030) options installed.

For the OCXO option, I selected the OCXO board developed by 
Gerry Sweeney (UK) in 2013 and recently updated.
https://gerrysweeney.com/update-diy-hpagilent-53131a-010-high-stability-timebase-option-pcbs-available/

Gaurav Singh at Embedded Engineering (Circuit Valley) developed an open-source OCXO project in 2018.
https://www.circuitvalley.com/2018/07/agilent-53132a-53131a-ocxo-ultra-high-stability-oven-time-base-upgrade-option-open-source.html
Both individuals offer bare boards.  The OCXO selection (new or used) is important.
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I waited until 2020 to make a decision for the Third Channel option 030 (3 GHz range) with the HP/Agilent 531xx series.  Andrew Coulthurst at Synamedia (UK) stopped offering his 030 option board design (2013), but a number of Chinese clones of the design can be found on eBay.  Gerry Sweeney shows the 030 option board in his video.

Gaurav Singh (Circuit Valley) developed an open-source 3 GHz option (030) board.
https://www.circuitvalley.com/2018/08/agilent-53132a-53131a-diy-open-source-3ghz-channel-option-030-board-hp.html

I went in a different direction, and talked to Razvan Cojocariu at Cojotech in Bucharest, Romania.  He is a one-man owner/engineer, with an attention to details.
https://cojotech.com/

I selected the Cojotech HPO-080 8 GHz board with his custom SMA connector that fits the BNC “D” punch out on the HP 531xx series front panel.
BTW, for Phillips PM 668x counter owners, he offers an Input C option (3 and 8 GHz).
https://cojotech.com/pmo-080-8-ghz-replacement-kit-input-c
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Results?
I calibrated my Agilent 53131A OCXO against the Symmetricom 58503B and Trimble 36204-61 (Red labeled Thunderbolt) near the bench.
Still reading 10 MHz from both sources, months later.
I have not fully exercised the Cojotech board (third channel), yet.

greg
chicago
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Date: Thu, 22 Oct 2020 11:50:08 +0000
From: Giorgio Barinetti <giorgio at barinetti.it>
To: "time-nuts at lists.febo.com" <time-nuts at lists.febo.com>
Subject: [time-nuts] Frequency Counter Choice

Hi,
As a newbie in the field, I've collected, by chance, some frequency standards
Now is the time to measure them, and see how they perform.
I've inherited a 5371, but something tells me that is not the right instrument - and maybe is even faulty.

So, I'm in the need to buy a counter to use together with TimeLab.

Choices are many, but I'll try to avoid the "older" machines lile 5370 or 5335. 
The HP/Agilent 531xx series seems nice ( money apart )
But again : which one between the three (3) models? 53131, 53132 or 53181 ?

Can somebody shed some light, and maybe help even to found a baseline for us beginners ?

Regards,
IZ2JGB
Giorgio