content/eip545b_2.rst@f4160af0485c (annotated)
content/eip545b_2.rst
Sat, 07 Nov 2020 15:49:10 +0100
- author
- David Douard <david.douard@sdf3.org>
- date
- Sat, 07 Nov 2020 15:49:10 +0100
- changeset 132
- f4160af0485c
- parent 128
- aba381b2bac9
- permissions
- -rw-r--r--
Add a new HP34970A blog post: new front panel PCB
| 74 | 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 | ||
| 82 | 19 | I've also digged a bit more for the sensitivity problem on band 3. I still |
| 74 | 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 | ||
|
128
aba381b2bac9
Fix several inter-document links
David Douard <david.douard@sdf3.org>
parents:
115
diff
changeset
|
50 | .. image:: {static}/images/eip545b/pm_full.jpg |
| 74 | 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 |
