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| 1 ======================================== | |
| 2 EIP 545B RF Frequency Counter - Part 2 | |
| 3 ======================================== | |
| 4 | |
| 5 :author: David Douard | |
| 6 :Category: Electronics | |
| 7 :Tags: test equipment, RF, EIP, 545B, counter | |
| 8 :series: EIP545B Frequency Counter | |
| 9 :series_index: 2 | |
| 10 | |
| 11 I've started a discussion_ on the `eevblog forum`_ to gather a bit help for my | |
| 12 project. And I did well since a few fellows did help me a lot on some aspects. | |
| 13 | |
| 14 I have now been able to run the power meter at full resolution (even if it's | |
| 15 very out of calibration), and have been able to locate where these annoying | |
| 16 default settings are set (tip: unfortunately not in the EEPROM, but in the | |
| 17 firmware). | |
| 18 | |
| 19 I've also digged a bit more for the sensibility problem on band 3. I still | |
| 20 haven't foudn yet the true culprit, but now I have a few tracks to follow. | |
| 21 | |
| 22 I've been in the process of disassembling a part of the firware to look for | |
| 23 these default settings as well as how to activate the power meter. This latter | |
| 24 was in fact already activated (but with 3dB resolution, since A107 had no | |
| 25 U12/CR3 populated). | |
| 26 | |
| 27 .. _discussion: https://www.eevblog.com/forum/testgear/eip-545b-frenquency-counter | |
| 28 .. _`eevblog forum`: https://www.eevblog.com/forum/ | |
| 29 | |
| 30 | |
| 31 Power Meter | |
| 32 =========== | |
| 33 | |
| 34 While I was waiting for the parts I was missing to modify the A107 as an option | |
| 35 02 enabled one, I was playing with the counter, and I discovered that the PM | |
| 36 was in fact already activated. | |
| 37 | |
| 38 Obviously, there was no need for the local EPROM (U20) on A107 (with its 2 | |
| 39 companions, U19 and U21) for the EIP454B. I already noticed the address range | |
| 40 where this EPROM is located on the EIP545A (0x4000) is already filled with | |
| 41 code/data in the main firmware on the CPU board (A105). | |
| 42 | |
| 43 So I added an AD7524 (U12, 8-bit DAC), removed R39 and installed an FH1100 | |
| 44 equivalent (QSCH1245 ie. an HP5082-2835) diode as CR3. | |
| 45 | |
| 46 After that, I could read (uncalibrated) power with the expected 0.1dBm | |
| 47 resolution: | |
| 48 | |
| 49 | |
| 50 .. image:: {filename}images/eip545b/pm_full.jpg | |
| 51 :alt: Power Meter at full resolution | |
| 52 | |
| 53 *On avance !* | |
| 54 | |
| 55 Now I still need to figure how to calibrate the damn stuff... A | |
| 56 calibration procedure is quickly described in the service manual, but the | |
| 57 procedure it imply writing the calibration table in the local EPROM on A107. | |
| 58 Since this is not populated for the EIP545B, it must lay somewhere else. | |
| 59 | |
| 60 That's where the magic of the wonderful eevblog comunity shine: HighPrecision_, | |
| 61 who happens to have serviced these kind of test gears for years, `gave me the | |
| 62 correct address`_ for the PM calibration table: 0x0810, in the EEPROM. | |
| 63 | |
| 64 Much quicker than finding this in the firmware! | |
| 65 | |
| 66 Now I need a decent power meter to be able to calibrate it, but one step at a | |
| 67 time... | |
| 68 | |
| 69 | |
| 70 .. _HighPrecision: https://www.eevblog.com/forum/profile/?u=116109 | |
| 71 .. _`gave me the correct address`: https://www.eevblog.com/forum/testgear/eip-545b-frenquency-counter/msg1400163/#msg1400163 |
