JDSU J745A spectrum analyser / VNA repair & mini review

[colorado.rob]

Can anyone confirm whether the JDSU 745A can do vector signal analysis (clock recovery and constellation diagrams) of FSK, PSK and QAM signals? Someone was trying to convince me that it could, but I saw little evidence that it would meet my needs.

[nctnico]

Can anyone confirm whether the JDSU 745A can do vector signal analysis (clock recovery and constellation diagrams) of FSK, PSK and QAM signals? Someone was trying to convince me that it could, but I saw little evidence that it would meet my needs.

You have to keep in mind that this is a cellular base station analyser. So as long as your signal kind of falls into a category that resembles a cellular communication signal, then you might get lucky. But you'll also need to find a unit which has the analysis options installed. Judging from the manual the J745A can't do much clock recovery as the manual says the J745A needs to be synchronised to the cell tower in order to get the best results.

[Gri]

C30 and R14 are some kind of feedback circuit. Likely to flatten the frequency characteristic. The bias resistor for Q1 is R8. Unfortunately I don't know the capacitor values. For C29 100nf will likely work fine.

Thank you for your correction on R8 being the bias resistor! that makes a lot more sense when looking over the board now. Are you able to confirm the number printed on R14 as being "551"? which would translate to 550 Ohms? Want to make sure i've got that right as it's something I'll have to order. Also just noticed I've got a cracked mlcc right at the input port, would a 100nF cap suffice for that too you think? I'm not well versed in RF circuit design


EDIT: removed some components and measured C17, and C18 at 36nF, C30 measured at 360pF. Do these values sound right? someone's clearly been in here before switching stuff around. Should C29 be matched in capacitance to C28?
Thanks

[colorado.rob]

Can anyone confirm whether the JDSU 745A can do vector signal analysis (clock recovery and constellation diagrams) of FSK, PSK and QAM signals? Someone was trying to convince me that it could, but I saw little evidence that it would meet my needs.

You have to keep in mind that this is a cellular base station analyser. So as long as your signal kind of falls into a category that resembles a cellular communication signal, then you might get lucky. But you'll also need to find a unit which has the analysis options installed. Judging from the manual the J745A can't do much clock recovery as the manual says the J745A needs to be synchronised to the cell tower in order to get the best results.

Thanks. I ended up getting an Agilent E4406A, which does exactly what I needed for quite a bit less than the J745A. I just had to find the hacks to get the Agilent 89600 software working with it. Sounds like I made the right choice. If I were to do it again, I'd probably opt for a Siglent SVA and hack in the vector signal analysis option. But that was not available at the time I made the purchase.

[zrq]

Maybe of interest of somebody. There is a 28G band downconverter JD780B28GDC for the JDSU units available on ebay these days for <$150. It is the same as the ThinkRF D2030, covering 27GHz to 30 GHz.