FW: 2.01.01.35R3B1
1. Changed the amplitude strategy of AM modulation: The carrier stays fixed at the amplitude, regardless of the modulation setting.
Finally, after many years, this small but important improvement.
No more confusion between using the conventional RF generator and sometimes using the SDG2000X for similar things with carrier alone (CW) or AM mod carrier.
Carrier level is now what you set and it keep this carrier level when user turn AM mod on/off and independent of modulation depth. Now it works just like conventional RF generator
(SDG1000X get this improvement around year ago)
Sorry, but I don't understand: AM means Amplitude Modulation, right? How can it be kept at a given level?
I've downloaded the new release and the output signal amplitude is varying as expected with the modulation depth, from the initial level up to 120% of this level (eg. from 1Vpp to 2.4Vpp). Can you please explain what is the difference between the previous strategy and the new one? Thanks
If you look AM in frequency domain, using example spectrum analyzer you see this meaning of course.
Lets take example.
We set generator to produce 1MHz carrier without AM modulation, just pure sine. We set this carrier level say example 0dBm (50ohm system) and we can see level is 0dBm if we look it with frequency domain - spectrum analyzer. (or time domain - oscilloscope we can see constant 0dBm level sinewave)
Then we turn AM modulation on without touching level:
Old FW, When turn AM on carrier drop 6dB (independent of modualtion depth)
Try with conventinal RF generator. Turn AM on and off. Carrier level stay constant.
New FirmWare (works now like conventional RF generator):
Turn AM on and off, carrier level stay constant and just as level was set..
Say example 1MHz carrier AM modulated with 1kHz sinewave and modulation depth 100%.
In real world there is now 0dBm 1MHz carrier and -6dBm 999kHz LSB tone and -6dBm 1001kHz USB tone.
If look with spectrum analyzer it is just what is show.
In old FW when select AM modulation, output peak level what was displayed/adjusted using SDG level setting. It was right only for signal peaks when mod depth was 100%. With all other modulation depths level setting was wrong. It was not peak level and not carrier level and not sidetones level (zero true).
In new FW level set have one true. It is always carrier level. As it is also when AM is on or off.Ok, now we drop modulation depth. Say example to 10%. Now we can see 1MHz carrier, level 0dBm and these sidetones levels dropped to -26dBm.
Then turn AM on and off. Spectrum analyzer show carrier stay always 0dBm and AM on there is sidetones and AM off, only carrier.
When look time domain, oscilloscope, AM on, there is bit over carrier peaks and bit under carrier lows and AM off, constant level carrier)
This may help for understand AM modulation (levels).
http://hpmemoryproject.org/an/pdf/an_150-1a.pdf and there chapter 2.