# HG changeset patch # User David Douard # Date 1457644680 -3600 # Node ID 518b499af7060f226e268ed7556e1365d8f62317 # Parent 5eb70985f6d8ff5df0376ced2e600bd1b9dc062a [10MHz] add a blog post about 10MHz reference diff -r 5eb70985f6d8 -r 518b499af706 content/10MHz_ref.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/10MHz_ref.rst Thu Mar 10 22:18:00 2016 +0100 @@ -0,0 +1,102 @@ +========================================== + Building a bench 10MHz reference: part 1 +========================================== + +:author: David Douard +:date: 2016-02-21 +:Category: Electronics +:Tags: test equipment, 10MHz, Rubidium + + +Many electronics test equipment need an accurate time base. Most +often, it's build on a 10MHz base. + +For quite a while now, I have a used rubidium frequency and time +reference (Efratom Model LPRO-101) waiting for a nice enclosure. I +also have a small Extron Electronics video signal amplifier I thought +I could use to make my freq reference able to provide its signal to +several test equipments at once. + +The Rubidium Frequency Reference +================================ + +The device is a small enclosure with only a 2x5 pins connector: + +.. image:: {filename}images/freq_ref/efratom.jpg + :alt: The Efratom LPRO-101 frequency standard. + +The exact model is an Efratom Rubidium Frequency Standard Model LPRO-101: + +.. image:: {filename}images/freq_ref/efratom_sticker.jpg + :alt: The Efratom LPRO-101 frequency standard. + +Inside the enclosure, there is a single PCB with SMD and trough hole +components. It's quite dense. + +.. image:: {filename}images/freq_ref/efratom_inside.jpg + :alt: The PCB of the Efratom LPRO-101 frequency standard. + +The rubidium lamp with the resonant cavity occupy almost 1/4 of the +total area. The cover of the enclosure is compartimented, mainly to +shield the lamp+cavity device from the remaining of the board: + +.. image:: {filename}images/freq_ref/efratom_enclosure.jpg + :alt: The enclosure of the Efratom LPRO-101 frequency standard. + + +The Rubidium Freq Ref seems to workjust fine. I've powered it a few +times, and it take a few minutes to lock the lamp and stabilize the +output frequency. I've made a quick measurement of the power +consumption; at startup time, the current goes up to 1.5A, but after a +while, it stabilize around 0.5 or 0.6A. According a voltage 24VDC, it +starts with 36W then goes down to 15 or 16W. + +Now, I have to embed it in a nice enclosure (preferably an aluminium +one so I can use is as a heatsink, since the frequency reference +produces a bit of heat.) + +The Extron Video Amplifier +========================== + +The video amplifer on the other hand has a bit of a trouble: + +.. image:: {filename}images/freq_ref/extron.jpg + :alt: the Extron Electronics video amplifier + +As you can see on the picture above, the inductor is broken, and there +is no visible mark on it. This inductor is used to produce the +symetric voltages required to poser the opamp used to dispatch the +signal. + +The switching power modules used on the board is a LT1616_ (marked as +LTNB on the S6 package). So I reversed engineered a bit the schematic +of the power to try to guess what kind of value this double inductor +could be, since the reference schematic in the datasheet does not use +such a dual inductor(/transformer). + +Fro the schematic I could extract, it appeared that the design is in +fact very close to the reference schematic proposed by LT in the +datasheet_, in the Bipolar Output DC/DC Converter configuration page +16: + +.. image:: {filename}images/freq_ref/lt1616_bipolar_output_DC2DC.svg + :alt: LT1616 Bipolr Output DC/DC converter. + +It produces +/-5V from the 12V input. But still, I did not know what +kind of inductor/xformer I should use. I did not notice at first sight +the two references for the inductor that are proposed in the reference +design. So I first searched using the nice faceted search tool of +digikey (reducing the selection according the informations I have on +the broken device and then looking at the pictures), I finally could +find the reference of the inductor. By the way, it's a Sumida CLS62 +Series inductor (as indicated in the datasheet). And according to the +reference design, it should be a 22µH one. So let's make a purchase +for this inductor as well as some 20k resistors for my HP8904A_. + +.. _HP8904A: {filename}hp8904a.rst + + + + +.. _LT1616: http://www.linear.com/product/LT1616 +.. _datasheet: http://cds.linear.com/docs/en/datasheet/lt1616fs.pdf diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/efratom.jpg Binary file content/images/freq_ref/efratom.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/efratom_enclosure.jpg Binary file content/images/freq_ref/efratom_enclosure.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/efratom_inside.jpg Binary file content/images/freq_ref/efratom_inside.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/efratom_lamp.jpg Binary file content/images/freq_ref/efratom_lamp.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/efratom_sticker.jpg Binary file content/images/freq_ref/efratom_sticker.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/extron.jpg Binary file content/images/freq_ref/extron.jpg has changed diff -r 5eb70985f6d8 -r 518b499af706 content/images/freq_ref/lt1616_bipolar_output_DC2DC.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/freq_ref/lt1616_bipolar_output_DC2DC.svg Thu Mar 10 22:18:00 2016 +0100 @@ -0,0 +1,976 @@ + + + + + + + + + + + + + + + + + image/svg+xml + + + + + + + + + + + V + + + IN + + + BOOST + GNDFB + SHDNSW + 5 + V + + + IN + + + 7.5V TO 25V + 4 + 1 + 6 + + + • + • + + + C3 + 0.01 + + + µ + + + F + D1 + L1A + 22 + + + µ + + + H + 23 + R2 + 10k + R1 + 30.1k + LT1616 + + + + + + D3 + + + + + + + + C5 + 1 + + + µ + + + F + 6.3V + + + + + C4 + 10 + + + µ + + + F + 6.3V + + + + + C2 + 10 + + + µ + + + F + 6.3V + + + 1616 TA06 + + + + + C1 + 1 + + + µ + + + F + 25V + + + + + + + L1B + 22 + + + µ + + + H + + + + + + + + + + + + + + 5V + 200mA + GND + –5V + 100mA + C1: TAIYO-YUDEN TMK316BJ105ML + C2, C4: TAIYO-YUDEN JMK316BJ106ML + C5: TAIYO-TUDEN JMK107BJ105MA + D1, D3: ON SEMICONDUCTOR MBR0530 + D2: 1N4148 + L1: 22 + + + µ + + + H 1:1 SUMIDA CLS62-220 OR + COILTRONICS CTX20-1 + –5V LOAD SHOULD BE LESS THAN + 1/2 5V LOAD, SEE DESIGN NOTE 100 + + + + + + + + + + + + + + + + + OFF ON + D2 + + + + + + + Bipolar Output DC/DC Converter + + +