[email protected] kirjoitti:
I have another question about test equipment. When using a spectrum analyzer to examine the output of a frequency standard, what are the minimum specification needed? Bandwidth, resolution, sensitivity, etc?
It depends what you want to measure from there. In general, analysis of this kind of strong signals are not very difficult but if you want to find weak spuriouses there then the dynamic range of the SA may become a problem.
Looking at spectrum analyzers on eBay, I see quite a bit of difference between various models. Some have a resolution of 10Hz but others are 30Hz or even 100Hz.
This usually means resolution bandwith (RBW) and it has nothingh to do with actual frequency resolution. RBW means the bandwith of the adjustable IF filter in the SA signal path. With low bandwith you can see signals which are very close to each other but the sweeping will be slow. With high bandwith you can sweep large frequency areas in milliseconds but any sinals closer than RBW will be shown as one signal peak only. That's why it's very important to select correct RBW depending of what we are measuring. Usually the RBW selection is done auotmatically based on frequency span setting.
What comes to actual frequency resoltion you can usually set the center frequency with few decimals, it's not very accurate and it even doesn't have to be. When you sweep, you can analyze the peaks found in the trace with marker, but this is not accurate unless your spectrum analyzer is equipped with frequency counter function.
With counter function you can select the peak to be analyzed with marker and then use marker count function to see the actual frequency with that peak with the resolution of the counter (can be 1 Hz or 0.1 Hz for example -not as precise as with universal couner). But the difference with universal counter here is that you can count very faint signals also (for example less than -100 dBm) and you can select the signal to be counted even when there's multiple signals mixed. You may have some strong signal where your universal counter locks but then there's some faint signal mixed with it. If you want to count this faint signal you can do this with spectrum analyzer's counter easily.
With the counter function you will also need option to feed external 10 MHz reference to the SA. Without external ref the counter is mostly useless because it may have serious frequency error. This error is also stongly dependent of the frequnecy what you count. For example if you want to count something around 10 GHz, only 1 Hz error in the 10 MHz refernce means 1000 Hz error in the counted value at 10 GHz.
Some have a minimum frequency of 0.01Hz, 100Hz or even in the kHz range. Some are only sensitive to 60dBm, but others over 100dBm.
It's -60dBm or -100dBm. Both are quite poor values for spectrum analyzer but may be adequate if you only analyze strongs signals like oscillators.
Are any of the cheaper USB spectrum analyzers worth getting?
If you want to analyze only "easy" signals like oscillators etc. then yes. For anything more precise or very faint signals, I'd say no.
Most of these are appallingly expensive, so knowing what is needed can certainly help guide a purchase or to minimize cost. And if a "deal" is found, knowing that it is or is not adequate can help.
Yes, good specrum analyzers usually costs more than 2000 USD even as used. Also, a "high end" used 2000 USD specrtum analyzer can be much better than brand new "entry level" 10000 USD specrum analyer. And if you need any kind of vectored signal analysis, demodulation capability of modern communications etc. then the price will be very high.
Hope this helps... -- 73s! Esa OH4KJU _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
