| Electronics > Repair |
| E4407B Tracking Generator Repair |
| << < (6/27) > >> |
| smgvbest:
I put the TG back together and hooked it back up. Setup for zero span starting at 10Mhz @ -10dB, enable the TG and all was good. went up to about 1.5Ghz in 100Mhz steps and at 1.5Ghz it went unlevel. I attached the U2000H to it and the actual reading at close, not perfect but close. the U2000H is way over due for a CAL. (see attached images) so yes, TG goes unlevel initially only above 1.5Ghz but longer it is on the frequency keeps getting lower. it's now unlevel at 1.29Ghz. |
| Jay_Diddy_B:
Hi, The U2000H Power meter will be very useful when tracking this problem down. The output amplitude of the TG is proportional to the product of the signal levels at A and B. The signal level at A should be fixed at +16dBm. The signal level at B should vary depending on the setting of the TG output level. It is the 'fine' control. The coarse steps come from the step attenuator. Can you use the U2000H and measure the signal levels at A and B? Jay_Diddy_B |
| analogRF:
--- Quote from: Jay_Diddy_B on September 25, 2020, 02:13:36 pm ---Hi, The U2000H Power meter will be very useful when tracking this problem down. (Attachment Link) The output amplitude of the TG is proportional to the product of the signal levels at A and B. The signal level at A should be fixed at +16dBm. The signal level at B should vary depending on the setting of the TG output level. It is the 'fine' control. The coarse steps come from the step attenuator. Can you use the U2000H and measure the signal levels at A and B? Jay_Diddy_B --- End quote --- looking at the circuit, I don't think the final amplitude is controlled by the amplitude of 600MHz. Rather I think it is controlled by the Hittite variable attenuator just before the main mixer. The 600MHz goes to a mixer directly and then through quite a bit of processing including what I think is a frequency doubler and then reaches the variable attenuator just before the mixer. Maybe -4.5 to -11dBm only indicates the acceptable range for 600MHz? or could it be that both the 600MHz amplitude and the Hittite chip together control the RF amplitude? What I still dont quite get is that what they are mixing with the 600MHz? It looks like a free running oscillator!? with no locking?! They need to create a 3.92GHz out of the 600MHz but it should be a very stable and locked signal...i cannot see how it is.... |
| analogRF:
I just traced back the 600MHz from A8A1A1 and as I expected there is no amplitude control/variability on this signal. -4 to -11dBm probably shows the acceptable range. Actually on the schematic where the 600MHz to BITG is generated only says -7dBm The fine tune is done by the Hittite variable attenuator as explained before. still I dont know what kind of signal they are mixing with the 600MHz and if it is not a locked signal then it makes little sense... so I may be still missing something in that regard |
| analogRF:
--- Quote from: smgvbest on September 25, 2020, 01:56:14 pm ---I put the TG back together and hooked it back up. Setup for zero span starting at 10Mhz @ -10dB, enable the TG and all was good. went up to about 1.5Ghz in 100Mhz steps and at 1.5Ghz it went unlevel. I attached the U2000H to it and the actual reading at close, not perfect but close. the U2000H is way over due for a CAL. (see attached images) so yes, TG goes unlevel initially only above 1.5Ghz but longer it is on the frequency keeps getting lower. it's now unlevel at 1.29Ghz. --- End quote --- mmm...so the unlevel is frequency dependent AND perhaps temperature dependent?? since it looks like having to do with temperature as well, see if you can locate any overheated component on the BITG board and also check the supply voltages on that board maybe... still my main suspicion is the output section of BITG including and specially that IGG5 hybrid. However, it would be helpful if you could check the LO input and 600MHz input to the BITG at a frequency that level fails (zero span) just to make sure those inputs are ok although most probably they are. power meter should be enough to do this. |
| Navigation |
| Message Index |
| Next page |
| Previous page |