| Products > Test Equipment |
| Video Teardown and Repair of an Agilent E4433B ESG-D Signal Generator |
| << < (8/11) > >> |
| G0HZU:
Yes, I'm not sure the GALI 84 is the right device to use because it has about 25dB gain down at 250MHz. By contrast, the original SHF0189 stage will probably be designed to only have something in the order of 12dB gain across 250-4000MHz using resistive feedback to flatten the gain to this level across this range of frequencies. Note that a feedback resistor with low self capacitance is needed in order to prevent issues with gain peaking up at several GHz. So if you refit the SHF 0189 then I think it's best to find and refit the original resistor parts if they have been removed as the stray feedback capacitance they introduce is fairly critical wrt gain stability up at several GHz. Alternative resistors may have higher self capacitance and this will cause unwanted gain peaking up at several GHz and will compromise the overall stability of the amp. So with 25dB gain at 250MHz in the GALI 84, the output of the vector modulator could be driving the GALI 84 output 13dB harder down at 250MHz. So that means the linearity may suffer and also it may cause issues with ALC control margins. |
| nctnico:
--- Quote from: G0HZU on October 15, 2015, 11:11:31 am ---Yes, I'm not sure the GALI 84 is the right device to use because it has about 25dB gain down at 250MHz. --- End quote --- I agree. When I looked for a replacement for a different HP RF generator I found the MMIC devices from Triquint had a much flatter gain/frequency response than those from Mini Circuits. With some tweaking I managed to get the frequency response to work reasonably over a wide range. However: if you can fix this generator using original parts then that is the best way to tackle this repair. |
| Mosaic:
Thx for the link, I ordered some of those transistors as I have an 'unleveled' E4432B, options 1E5, UN8, UN9, UND, UNA, 100 I took a risk on for $600 based on Shah's youtube video. I only have 1 active 4 Ghz P6217 tekprobe though for a 3Ghz TDS694C scope. Also, was that an SMA interface used to connect to the probes fed by PCB soldered RG316? --- Quote from: TSL on April 09, 2015, 05:26:23 am ---Hi Shahriar, Great video and very timely for me. I just picked up a 4432B ESG-D with opts 100,1E5,H99,UND for $700AU :) It has the same fault indicator. I'm just about to embark on a fault finding mission to see if its the same device that failed. FYI you can buy SIRENZA new parts from UTsource here... http://www.utsource.net/ic-datasheet/SHF-0189-1906844.html regards Tim --- End quote --- |
| G0HZU:
--- Quote ---Also, was that an SMA interface used to connect to the probes fed by PCB soldered RG316? --- End quote --- Be careful how you connect your test coax cables to the various locations along the RF signal path if you use a Hi Zscope. I haven't watched this video since the last time but I do recall that Shahriar had connected the Hi Z scope inputs to the signal path via lengths of coax. This isn't a very good (as in controlled/predictable) method because it will load the signal path differently for different frequencies and this can give confusing results. I guess one can argue that this method was fine because it helped find the dead part. However, this isn't how you are supposed to use RF test gear if you want to make reliable measurements because of the way the coax and scope will load the signal path 'differently' at different frequencies. At some frequencies it will load it a lot and it depends on the length of the coax and the test frequency. I recall that Shahriar seemed confused why the signal level had lots of ripple wrt frequency changes and this will be the reason. It appeared to me that he wasn't using the test gear correctly. |
| nctnico:
I agree. When I worked on the RF amplifier of my E4421B I set it to frequencies between 10MHz and 70MHz to be on the safe side when it comes to reflections while doing measurements to get some ball-park figures. |
| Navigation |
| Message Index |
| Next page |
| Previous page |