FM IF aligment with digital equipment

[daskorn]

Hi,

I’m an electronic hobbyist mostly interested in electronic repair. I recently started to work on a worthless AM/FM radio alarm from the 70ties. As I bought a bunch of test equipment over the last years I though abought doing a FM alignment.

I found some YT videos about that topic but in most cases an old school sweep generators combined with an analog scope is used. As I do not have the space to store these beauties I wasted my money in chines products. So, what I’ve got is a FeelTech FY6900 and a Siglent SDS1104X-E.
What I found out so far. I need to sweep over the 10.7MHz frequency. My first question is in that context: What is a recommended frequency rang to sweep over. Will 10.7MHz +/- 1MHz do the job?
 
Regarding the FY6900. What I found out already is that I can feed a ramp signal from channel 2 of the signal generator to its VPO input and use that as frequency-sweep trigger. I can use the same channel 2 as a trigger input for my DSO to do some XY magic. However, I wonder about two things here.

1. Can’t I just use the FM modulator feature of the FeelTech to generate the same sweep signal?
Set CH 1 to 10.7 MHz sine wave, CH 2 ramp let’s say 5kHz. Go to the modulation menu. FM mod, source CH 2. BIAS 2Mhz.
I can then use the CH 2 as before (but without T) to feed it as trigger to the DSO and do some XY magic.

2. As the XY mode of the DSO is not that great. Do I really need to use XY mode to do the alignment?
I played around with the FFT / Spectrum Analyzer feature of the DSO. I wonder whether it could be used for IF FM alignment. For my understanding in that case I do only need one channel of the DSO. By displaying the max values I was able to display frequency plot the sweep signal, as the sweep speed is limited. The FM modulation seems to be the better option to view in FFT mode. That way I do not need max mode.
But there seem to be so many settings having impact on the FFT function that I’m a little bit lost here. A recommendation on how to setup the FeelTech and DSO in that context would be highly appreciated.

That should be enough for now. Thanks in advance.
DK

[bob91343]

FM is too fast for sweep alignment.  You need to sweep slowly, perhaps below 100 Hz depending on the time constants.  XY mode is preferred.  You sweep about 200 kHz or a little more wide and look at the detector output.