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All true. I would check FM, DSB and what ever there is.
Modulation would be easier understand with a suitable SA.

?Use any web sdr.
Most have a waterfall option.

Can you recommend one/a few which can do that? I have not found a SDR which could do that.
Leif

Using a sharp tunable BPF after the LC LPF at the output of the generator I was able to measure the still present second order harmonics at -73dBc so third measurement ( at -24dB fundamental) is becoming limited by the 2rd harmonic still present but the first two measurements are only seeing internal generated second harmonic. 3rd harmonic remained invisible using the BPF so it must be much lower as was expected from the LPF.
Thanks for making me double check!

Or use a SDR receiver as a poor man SA. You can see modulation sidebands and splatter very well in the waterfall display. You can use really small BWs.

Regards,

Ignacio EB4APL

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El software de antivirus Avast ha analizado este correo electrónico en busca de virus.

To measure close in products you need a much narrower RBW typical is
30-100hz, maybe 300hz.? You also need to insure the carrier if any is
not overloading the input of the SA.

If true SSB source and no distortion there is only one signal that being the
sum or difference of the carrier and some carrier leakage which for any
competent system should be at least -40dbc or better.

Its easy to do but you need a suitably narrow bandwidth system.

Allison
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Your expectation on harmonics are dependent on the cause.

For example input overload can do that, often you get other products like 3/2s
as you have two signals generally the source and then the internal
signal with some offset.? Yes, third harmonic divided by 2, higher order is
possible as well.

it is also critical to know the generators harmonic level, hence the reason
for the setup I use with filters.? Most of the HP generators are very clean but
that is not absolute, there is always some.

Allison
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It slowly occurred to me that I am doing this still too complicated and there is an even simpler measurement approach. (if this is too much details for this group feel free to shut me up)

Using only one clean signal (harmonics really low) followed by a step attenuator it should be possible to observe the harmonics generated inside the tinySA and be able to predict everything what happens and calculate the IIP3 and SFDR
So I took a regular tinySA (no "special" this time) and started with a powerlevel calibrated signal at about -4dBm at about 9MHz.

This is how it looks with 0dB external attenuation



2nd harmonic at -54dBc and 3rd harmonic at -63dBc.
Calculating the IIP3 gives (-4 + (-4 - -63)/2) = +25dBm

Reducing the input with 10dB (using the external step attenuator) implies the 2nd harmonic should move to -64dBc and the 3rd to -83dBc and the IIP3 should stay the same



2nd order moves to -66dBc (seems ok) and 3rd order moves down 30dB so into the noise floor.?Let's pessimistically assume it is at -98dB so -84dBc. All looks good.
Calculating the IIP3 gives (-14 + ( -14 - -84)/2 ) = +21dBm which is a bit less so my assumption about the level of the 3rd harmonic may be too pessimistic.

Further reducing the input to -24dBm gives:



The RBW was reduced to 10kHz otherwise the 2nd harmonic would be invisible. Its now at -100dBm thus -76dBc which is indeed again 10dB better as it should be.
With the RBW at 30kHz this would have been invisible so the SFDR with an RBW of 30kHz seems to be 76dB.
In other words:?The internally generated intermodulation products of on or more tones at -24dBm or lower will no longer be visible at an RBW of 30kHz

So much to learn.

RBW means Resolution Bandwidth,e.g. the bandwidth of the narrowest filter before the power detector
This implies you can not see anything inside a good SSB transmission but you are able to see if there is a lot of over modulation

Thanks Allison for the advice.

As preparation for detailed performance measurements of a tinySA special using an high IIP3 mixer I?added two LC filters after the generators to remove the harmonics and did two measurements
One with both 9MH (f1) and 10MHZ(f2) at about 0dBm and another where I reduced f1 to -10dBm
If all is well all changes in harmonics should be completely predictable.

First with both at 0dBm



and the second with f1 at -10dBm



With the added filters all changes are now indeed as predicted
With f1 changing -10dB we get:
2 f1 changed -20dB (disappeared)
f1+f2 changed -10dB
3 f1 did not change
2f1+f2 changed -10dB
3f1 and 2f1+f2 boths disappeared.
2f1 - f2 and f1 - 3f2 also disappear
The calculated tinySA "special" IIP3 is about +27dBm

Now I think I have sufficient understanding and predictability to do some more detailed performance measurements.

AS the minimum RBW is 2.7kHz you can not "See" you modulation?
For that you best use a receiver and a PC with line in.

How close to a carrier I can get? Many Hams, educators and me would like to see and check their modulators. That is, can I see what does spectrum of? SSB with 1kHz modulation look like. Or 300Hz and closer.

Perfect, thanks.?

Minimum RBW is 2.7kHz

Clear, for the todo list if I have a spare moment....

On Thu, May 7, 2020 at 08:31 AM, <erik@...> wrote:

Would this line also induce some behavior?
Like a pass/fail message?
Or just a line?

==================================================
Eric, Just a line that you can set the value for and turn on and off.? Primarily used for quick visual indication of of how a measured signal compares against a set reference line.? I believe the line is usually labeled "ref" or "ref line" when it is displayed.? "limit line" might be another choice for a label to prevent confusion with reference level.

Some advanced analyzers do provide some type of pass/no pass or go/no go indication when the line is exceeded, but that seems a waste of memory space on the tinySA and might be better implemented in the software application if there was a user demand.

- Herb

Would this line also induce some behavior?
Like a pass/fail message?
Or just a line?

Me too.
Not now