Hi, (excuse me for my terrible English...). I have a system HP141T+HP8552B+HP8553B just buy , and I have a problem: signal calibration al 30 MHz instead of -30 dBm is on -49 dBm on the screen . I have this configuration on misuration : Bandwidth 300 KHz ; Scan Width per division 0.5 MHz; input attenuation 0 dB ; Scan time per division 2 mS; Log REf level 0 dB; (switch a 10 dB LOG) ; Linear sensitivity 0 dB; video filter 10 KHz; scan mode INT ; scan trigger auto. Why my signal is so low? I have put on parallel an oscilloscope (Philips 50 MHz bandwidth double trace) and level is go down to -55 dBm and on oscope signal is 28 mV peak to peak (i think that is -27 dB) with a bad sinusoid signal . Where is the problem? Can I make something ? Thanks for every reply and best regards. Roberto from Italy. 73 de IW0RAQ
The best way to troubleshoot the issue is with a functioning spectrum analyzer. Hopefully you have one of those or know someone who does. You should be able to verify the power levels throughout the system with a known input power level. The first thing to check is to make sure the calibration signal is indeed 30 MHz at -30 dBm; that way you have a known good starting point with a known signal amplitude. You can now use the schematics and measure the power level going directly into the first mixer. With 0 dB of input attenuation, you should see ~-30 dBm at 30 MHz coming out of the cable that attaches to the first mixer. If that signal level is OK, now is a good time to test the input attenuator by adjusting that from 0 dB to maximum attenuation and you should see the power level drop on the known good analyzer by the amount of input attenuation that you are changing. For example, with 0 dB of input attenuation the signal level measures -30 dBm, with 10 dB of input attenuation, the signal level measures
-40 dBm and so forth. Now reconnect the cable you took off the first mixer and measure the output of the mixer. Here is where it gets tricky. You’ll have to know what the first I.F. is since I don’t have schematics. That 30 MHz signal will be upconverted to some higher frequency like
2.6 GHz or something. It should be written on the RF block diagram. The first mixer will have ~7-10 dB of conversion loss. Just keep going down the RF front end chain until you find out where the excess loss is coming from. My guess is the input attenuator, a blown first mixer or something mis-adjusted.
I hope this helped -