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Re: Analyzing Noise versus Leakage on CH1

 

Erik,

I re-ran it at 1.2GHz, which will correspond to 240MHz. I also changed the
offset to 4KHz. Here are the results:

[image: image.png]

The 1KHz peaks are still there (and unrelated to the IF frequency). It
would be preferable that they weren't there, but we're only interested in
the peak at the IF frequency, so can we just ignore them?

Rgds,
Dave

On Mon, 23 Sep 2019 at 10:57, <erik@...> wrote:

I tested windowing and that does not make a big difference as can be
expected in this case where the stimulus is fully controlled
What is worrying me are the multiple peaks you get 1kHz apart next to the
5kHz.
Some SI5351 have difficulty locking above 250MHz (the official maximum
output frequency) and your 1.29Ghz would use a 258MHz signal from one of
the SI5351 outputs.
The 1kHz pattern is identical to what I sometimes see, but for me its
closer to 300MHz and not always.
So the 1kHz peaks are not noise but an artefact of a SI5351 having
difficulty to output the required signal.
There is already a firmware that limits the maximum fundamental to 250MHz
to avoid this problem.



image.png

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