TESTS: Siglent SDG5082 Function/Arbitrary waveform generator. (+Inside images.)

[Siri]

I asked the local seller to see other instances SDG5162 mode sinusoidal signal. I do not have a defective version, all 5162 the same pattern with the noises in the nearest band.. So this question to a member Siglent is removed. But it seems to me, he's not soon reply to this topic

[rf-loop]

Note for signal amplitude when using AM modulation.
For avoid confusion this is good to know and understand how this works and what it means in practice.
This is how it is made and how it works. Also may help SDG1000 series users.

When you turn MOD (AM) on, independent of modulation depth (0 - 120%) signal carrier level drops to half of what is indicated on the screen level.  If Modulation depth is now 0% you just see that signal level is half from displayed level value and there is only carrier alone. No sidebands.

There are perhaps many peoples who are not so familiar with dBm, dB, dBc so I use also voltage in example.
Also this equipment dBm is only usable if system impedance is 50 ohm.

In start point lets think you set sinewave, say example 1MHz and level 1Vpp, impedance 50 ohm and MODulation function is OFF.  Offset level 0V.

Your load is 50 ohm.  This sinewave  is now 1Vpp (+0.5Vpk and -0.5Vpk)
(if your load is not 50 ohm - if load is very high impedance you get double voltage level)
You can look it with oscilloscope (50 ohm input) and it is nice sinewave 1Vpp (0.5Vpk)    If you look with Spectrum analyzer you can see around 4dBm peak.

Now, push MOD and select Modulation ON, set modulation example 1kHz and depth 0% (no modulation)
Just when you turn modulation on and % is 0 your signal (carrier) level is now  500mVpp.
Also look oscilloscope and it is true, nice unmodulated sinewave 500mVp-p (0.25Vpk.  If you look with Spectrum analyzer you can see around -2dBm peak. (as you see it drop 6dB from start)

What happen when you use other than 0% modulation depth. Let's try. Set 100%.
Now if you look this with oscilloscope. You can see 1kHz sinewave modulated carrier (if your scope is now example 2ms/div speed)  where minimum is zero level and maximum is 1Vp-p --- yes it is right. (also this max is now same what we have before we turn MOD function on!  So, modulation envelope peaks max are now same as your original level set.

Now if we look this with spectrum analyzer. What.....  carrier is still this same -2dBm level
(and if we can look with oscilloscope just alone this carrier (we can not easy do it) its is.....    500mV peak to peak continuous sinewave.)
What other we see with spectrum now. We see two peaks, 1kHz down and 1kHz up from this carrier.
We see three peaks. Center peak is carrier, level -2dBm and then we see upper and lower side peaks but level of these peaks are 6dB below carrier level. In this case -8dBm.

What now if you half this modulation depth. Set 50% depth.
If you are now  looking  with spectrum carrier do not change at all.   But if you look this signal normally with scope and this modulation envelope. Then peak to peak max value is not anymore 1V. But also it do not go anymore to zero.
With spectrum analyzer there is still -2dBm carrier and then both sideband peaks are now dropped 6dB more. They are now both -14dBm. (and if you now drop modulation again half, 25%... carrier stay same, sidebands drop again 6dB and they are now -20dBm level (-12dBc   (-12dB from carrier level)). And now with scope this modulated signal envelope peaks less.

Remember.
When you turn Modulation function AM  on, your signal level is half if it is only carrier (mod depth 0%).
So, if you want your carrier is 1Vpp then set sinewave level 2Vpp.
But now remember also that when modulation depth is more your signal peaks are more than 1Vpp. And with 100% MOD it is 2V peak to peak.

I do not say this is good or bad, right or wrong,  they have made it like this. Least one positive thing there still is. You can not easy make damage if you set signal level and then turn mod on and 100%. It do not exceed what you have set.

Most of real RF generators works different. There if you select signal level example +3dBm and then you turn modulation on, your carrier is still +3dBm and what ever modulation depth you select or turn MOD off... your carrier stay rock solid +3dBm.  (RF world it is very common to use power level dBm and usually in 50 ohm system.


Siglent Function generator SDG5000 is not any kind of exception. There is many kind of variations how different manufacturers have done these.

Before serious use: "Know your equipment features"

There is not enough information in user manual or data sheet about  this kind of things and details and this lack of information is not nice - even when  peoples do not today deep study manuals. ("why read manual if there is only trivial things and nearly total lack of important details" )

Here starting from this message there is some messages and images what may explain more this equipment behavior.
https://www.eevblog.com/forum/testgear/siglent-sdg1025-arbitraryfunction-generator-under-some-tests/msg1160671/#msg1160671


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And this is why:  RTFM

SDG models manuals tell it exactly:
* In the 0% modulation, the output amplitude is the half of the set one. 
* In the 100? modulation, the output amplitude is the same with the set one.

(exept that in some models some manual version may tell wrong that 120% mod amplitude is same with set one. This is error, there need read 100%)