comparison: content/10MHz_ref.rst
content/10MHz_ref.rst
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| 1 ========================================== | |
| 2 Building a bench 10MHz reference: part 1 | |
| 3 ========================================== | |
| 4 | |
| 5 :author: David Douard | |
| 6 :date: 2016-02-21 | |
| 7 :Category: Electronics | |
| 8 :Tags: test equipment, 10MHz, Rubidium | |
| 9 | |
| 10 | |
| 11 Many electronics test equipment need an accurate time base. Most | |
| 12 often, it's build on a 10MHz base. | |
| 13 | |
| 14 For quite a while now, I have a used rubidium frequency and time | |
| 15 reference (Efratom Model LPRO-101) waiting for a nice enclosure. I | |
| 16 also have a small Extron Electronics video signal amplifier I thought | |
| 17 I could use to make my freq reference able to provide its signal to | |
| 18 several test equipments at once. | |
| 19 | |
| 20 The Rubidium Frequency Reference | |
| 21 ================================ | |
| 22 | |
| 23 The device is a small enclosure with only a 2x5 pins connector: | |
| 24 | |
| 25 .. image:: {filename}images/freq_ref/efratom.jpg | |
| 26 :alt: The Efratom LPRO-101 frequency standard. | |
| 27 | |
| 28 The exact model is an Efratom Rubidium Frequency Standard Model LPRO-101: | |
| 29 | |
| 30 .. image:: {filename}images/freq_ref/efratom_sticker.jpg | |
| 31 :alt: The Efratom LPRO-101 frequency standard. | |
| 32 | |
| 33 Inside the enclosure, there is a single PCB with SMD and trough hole | |
| 34 components. It's quite dense. | |
| 35 | |
| 36 .. image:: {filename}images/freq_ref/efratom_inside.jpg | |
| 37 :alt: The PCB of the Efratom LPRO-101 frequency standard. | |
| 38 | |
| 39 The rubidium lamp with the resonant cavity occupy almost 1/4 of the | |
| 40 total area. The cover of the enclosure is compartimented, mainly to | |
| 41 shield the lamp+cavity device from the remaining of the board: | |
| 42 | |
| 43 .. image:: {filename}images/freq_ref/efratom_enclosure.jpg | |
| 44 :alt: The enclosure of the Efratom LPRO-101 frequency standard. | |
| 45 | |
| 46 | |
| 47 The Rubidium Freq Ref seems to workjust fine. I've powered it a few | |
| 48 times, and it take a few minutes to lock the lamp and stabilize the | |
| 49 output frequency. I've made a quick measurement of the power | |
| 50 consumption; at startup time, the current goes up to 1.5A, but after a | |
| 51 while, it stabilize around 0.5 or 0.6A. According a voltage 24VDC, it | |
| 52 starts with 36W then goes down to 15 or 16W. | |
| 53 | |
| 54 Now, I have to embed it in a nice enclosure (preferably an aluminium | |
| 55 one so I can use is as a heatsink, since the frequency reference | |
| 56 produces a bit of heat.) | |
| 57 | |
| 58 The Extron Video Amplifier | |
| 59 ========================== | |
| 60 | |
| 61 The video amplifer on the other hand has a bit of a trouble: | |
| 62 | |
| 63 .. image:: {filename}images/freq_ref/extron.jpg | |
| 64 :alt: the Extron Electronics video amplifier | |
| 65 | |
| 66 As you can see on the picture above, the inductor is broken, and there | |
| 67 is no visible mark on it. This inductor is used to produce the | |
| 68 symetric voltages required to poser the opamp used to dispatch the | |
| 69 signal. | |
| 70 | |
| 71 The switching power modules used on the board is a LT1616_ (marked as | |
| 72 LTNB on the S6 package). So I reversed engineered a bit the schematic | |
| 73 of the power to try to guess what kind of value this double inductor | |
| 74 could be, since the reference schematic in the datasheet does not use | |
| 75 such a dual inductor(/transformer). | |
| 76 | |
| 77 Fro the schematic I could extract, it appeared that the design is in | |
| 78 fact very close to the reference schematic proposed by LT in the | |
| 79 datasheet_, in the Bipolar Output DC/DC Converter configuration page | |
| 80 16: | |
| 81 | |
| 82 .. image:: {filename}images/freq_ref/lt1616_bipolar_output_DC2DC.svg | |
| 83 :alt: LT1616 Bipolr Output DC/DC converter. | |
| 84 | |
| 85 It produces +/-5V from the 12V input. But still, I did not know what | |
| 86 kind of inductor/xformer I should use. I did not notice at first sight | |
| 87 the two references for the inductor that are proposed in the reference | |
| 88 design. So I first searched using the nice faceted search tool of | |
| 89 digikey (reducing the selection according the informations I have on | |
| 90 the broken device and then looking at the pictures), I finally could | |
| 91 find the reference of the inductor. By the way, it's a Sumida CLS62 | |
| 92 Series inductor (as indicated in the datasheet). And according to the | |
| 93 reference design, it should be a 22µH one. So let's make a purchase | |
| 94 for this inductor as well as some 20k resistors for my HP8904A_. | |
| 95 | |
| 96 .. _HP8904A: {filename}hp8904a.rst | |
| 97 | |
| 98 | |
| 99 | |
| 100 | |
| 101 .. _LT1616: http://www.linear.com/product/LT1616 | |
| 102 .. _datasheet: http://cds.linear.com/docs/en/datasheet/lt1616fs.pdf |
