| Products > Test Equipment |
| Video Teardown, Analysis and Repair of an Agilent E4407B ESA-E Spectrum Analyzer |
| << < (4/9) > >> |
| Hugoneus:
--- Quote from: Lukas on October 03, 2014, 08:49:23 pm ---I watched the video from the beginning to the end, was really informative. Keep it up! You asked why the LO sweeps at varying speeds, my take on it: (Select text to see it) On the first ramp, it uses the fundamental of the LO, on the second the first harmonic and so on. Since the sweep speed is constant the LO sweep speed has to be halved when using the first harmonic to maintain the sweep speed. --- End quote --- Yes, you are right! Thanks for posting the answer! :-+ |
| G0HZU:
It's interesting to see inside one of these analysers. We have several of these at work for doing simple system work etc. I only skimmed the video to look at the schematics and the PCB layout bits but a few things in the video confused me a lot. eg there were several references to an IF at 312.4MHz I can't see how the IF can be 312.4MHz because most oldschool HP uW analysers have an IF at 321.4MHz. This allows easy generation of the 300MHz LO (from 10MHz) to mix 321.4MHz down to the common 21.4MHz IF. The 5.5GHz filter looks like a simple LPF using radial stubs and I can't initially see how this can provide a BRF notch at 5.5GHz whilst passing about 3.92GHz with low loss. This is despite the block diagram showing a 5.5GHz BRF symbol. Very confusing. The filter is too simple to allow this (unless some tradeoff against highish insertion loss at 3.92GHz is tolerated?). At a guess those radial stubs will give notches up around 6.5GHz or higher. Normally an analyser will have a steep LPF here in order to provide some isolation between the first two mixers across as much of the LO1 range as possible. My guess is that they have cascaded two LPFs here in order to try and get some steep rolloff to get LO isolation to minimise spurious terms in the two mixers. eg ABS(nLO1 - mLO2) = 321.4MHz. There's lots of smaller radial stubs littered along the IF path and I think these will be there for similar reasons. i.e. to notch out harmonics of the LOs to provide mixer to mixer isolation at many, many GHz. But that is just a guess. At 1:16:58 the prescaler output is to the left rather than on the right as the bit pointed to by the finger looks like a control line used to select different division ratios in the device? |
| apelly:
Thanks for the video. I could watch quality content like that for hours. If anything, I thought the end felt a bit rushed. I'm sure you were getting a bit sick of it by then though! I certainly wasn't. You make great videos, and I appreciate the effort you put in. Thanks again. |
| Noise Floor:
Woot woot. Thanks for doing that. |
| Hugoneus:
Thanks everyone for your contribution. Don't forget about the Twitter account (@TheSignalPath)! |
| Navigation |
| Message Index |
| Next page |
| Previous page |