Hi Gerard - that looks like a good trace to me - well done!? The peak at 0Hz is a good indication and confirms that the LO is working and that the SI4432 is receiving signals.
You are right, this is a homebrew project that is not well documented.? Sorry for that.
Regarding the SMA connectors:
J12 Ref generator out.? This is a nominally -30dBm square wave output at the frequency selected in the reference drop down (15Mhz on your screen shot).? This can be used for calibration and some tests.
J13 is the tracking generator output (low range only), also a signal generator output (low range only) and potentially if I ever get round to writing the software for it a second input channel for the spectrum analyser.? At the moment it is only used as an output.? The tracking generator is a useful feature.? As the analyser does its sweep across the? selected frequency range the tracking generator frequency also changes. When the analyser is reading the values at say 30MHz the tracking generator is outputting a signal at 30Mhz, when reading 35mHz the tracking generator outs 35mhz and so on.? This can be used to measure the response of filters, amplifiers and so on.? the tracking generator can also be set to a fixed frequency, and then becomes a signal generator output.? The output is a fairly clean sine wave.
J14 is the low frequency input/output.? It is used as an input when used as a spectrum analyser, and as an output when in signal generator mode.? you can have both this and the tracking generator as signal generators at the same time.? The signal generator output is a fairly clean sine wave.
J15 is the high frequency range input/output.? If used as a signal generator output then the signal is not clean, filtering may be needed and there is less control of the output level than on the low range.
A good test is to connect the ref generator output to the low frequency input and set the ef gen output frequency to say 30MHz.? You should then see signal peaks at 30mHz and it harmonics (60, 90, 120 etc), with a level not far off -30dBm.
To see FM broadcast radio then connect your antenna to the low freq input and adjust the range accordingly.
To see say DAB TV signals then connect your antenna to the high freq input, select high range and adjust the frequency range as needed.
Warning- Do not apply strong signals from say a radio or other signal generator without checking the signal level is ideally below -30dBm, max 0dBm.? The analyser works best if the signals presented to the SI4432 are below -30dBm.? External attenuators can be used in addition to the up to 30dB internal attenuator.
If your results from applying the reference generator output to the input look good then we can look at some other calibration steps, probably best done once you have the display working.
Good work
Dave
