content/eip545b_2.rst

Tue, 28 Aug 2018 15:05:01 +0200

author
David Douard <david.douard@logilab.fr>
date
Tue, 28 Aug 2018 15:05:01 +0200
changeset 104
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parent 82
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child 115
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permissions
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improve hgignore

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1 ========================================
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2 EIP 545B RF Frequency Counter - Part 2
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3 ========================================
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4
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5 :author: David Douard
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6 :Category: Electronics
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7 :Tags: test equipment, RF, EIP, 545B, counter
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8 :series: EIP545B Frequency Counter
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9 :series_index: 2
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10
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11 I've started a discussion_ on the `eevblog forum`_ to gather a bit help for my
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12 project. And I did well since a few fellows did help me a lot on some aspects.
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13
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14 I have now been able to run the power meter at full resolution (even if it's
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15 very out of calibration), and have been able to locate where these annoying
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16 default settings are set (tip: unfortunately not in the EEPROM, but in the
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17 firmware).
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18
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19 I've also digged a bit more for the sensitivity problem on band 3. I still
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20 haven't foudn yet the true culprit, but now I have a few tracks to follow.
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21
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22 I've been in the process of disassembling a part of the firware to look for
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23 these default settings as well as how to activate the power meter. This latter
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24 was in fact already activated (but with 3dB resolution, since A107 had no
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25 U12/CR3 populated).
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26
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27 .. _discussion: https://www.eevblog.com/forum/testgear/eip-545b-frenquency-counter
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28 .. _`eevblog forum`: https://www.eevblog.com/forum/
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30
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31 Power Meter
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32 ===========
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33
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34 While I was waiting for the parts I was missing to modify the A107 as an option
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35 02 enabled one, I was playing with the counter, and I discovered that the PM
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36 was in fact already activated.
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37
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38 Obviously, there was no need for the local EPROM (U20) on A107 (with its 2
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39 companions, U19 and U21) for the EIP454B. I already noticed the address range
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40 where this EPROM is located on the EIP545A (0x4000) is already filled with
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41 code/data in the main firmware on the CPU board (A105).
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42
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43 So I added an AD7524 (U12, 8-bit DAC), removed R39 and installed an FH1100
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44 equivalent (QSCH1245 ie. an HP5082-2835) diode as CR3.
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45
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46 After that, I could read (uncalibrated) power with the expected 0.1dBm
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47 resolution:
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48
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50 .. image:: {filename}images/eip545b/pm_full.jpg
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51 :alt: Power Meter at full resolution
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52
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53 *On avance !*
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54
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55 Now I still need to figure how to calibrate the damn stuff... A
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56 calibration procedure is quickly described in the service manual, but the
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57 procedure it imply writing the calibration table in the local EPROM on A107.
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58 Since this is not populated for the EIP545B, it must lay somewhere else.
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59
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60 That's where the magic of the wonderful eevblog comunity shine: HighPrecision_,
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61 who happens to have serviced these kind of test gears for years, `gave me the
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62 correct address`_ for the PM calibration table: 0x0810, in the EEPROM.
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63
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64 Much quicker than finding this in the firmware!
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65
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66 Now I need a decent power meter to be able to calibrate it, but one step at a
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67 time...
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70 .. _HighPrecision: https://www.eevblog.com/forum/profile/?u=116109
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71 .. _`gave me the correct address`: https://www.eevblog.com/forum/testgear/eip-545b-frenquency-counter/msg1400163/#msg1400163

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