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Monday, 30 April 2018

VMA Simple Spectrum Analyser - Put these harmonics into propper use!


It is no secret: when using the SMA/NWT device to generate a test signal, there will be a lot of harmonics, due to the absence of any filters. Of course, this is acceptable, considering the price of these devices.

This is what the spectrum looks like, when generating a test signal at 1GHz:


The picture was taken with help of my HackRF One, which allows to render a spectrum up to 6GHz.

One can clearly see:

  • Fundamental: 1GHz
  • 2nd Harmonic: 2GHz
  • 3rd Harmonic: 3GHz
  • 4th Harmonic: 4GHz
  • 5th Harmonic: 5GHz
So, what happens when the Fundamental is set to 4GHz, which is close to the maxium supported frequency of the ADF4350/ADF4351? You should have harmonics at 8GHz, 12GHz, 16GHz, 20GHz!

A quick test using an LNB connected to my Promax HD Ranger 50 SE showed that the harmonics can be used at much higher frequencies than the ones specified for the SMA/NWT devices!

Of course, to use the VMA Simple Spectrum Analyser to generate specific harmonic frequencies is a bit cumbersome, as you need to calculate the corresponding fundamental frequency - even if the math is just dividing by the order of the harmonics, it is a pain.

So I added some new functionality to my software:


The new Harmonics Signal Source allows to easily select the desired frequency, no matter if Fundamental or Harmonics. The graphics show were the harmonics will be located in the frequency space and with the scrollbar, the frequency can be set dynamically - if the generator is turned on, the signal will follow the scrollbar!


Of course I added a Harmonics selector to the Sweep Generator, too.

Need an application example? Here you go: use this in combination with the MAX HOLD function of your satellite field meter and you will be able to fully test your LNB's!


In this example I am trying out the Inverto White Ka LNB, which does 19.7GHz-20.2GHz. Unfortunately, the Promax HD Ranger 50 SE does not support negative LOF and this would be useful for this LNB, as it has a LO of 21.20GHz.

Notice how I just place the SMA/NWT in front of the LNB!


Activating the MAX HOLD and using the Sweep Generator, one can test the whole supported frequency band of the LNB. As expected, the SMA/NWT does not produce a really flat signal over the extended frequency range, but it is still OK to do GO/NO GO tests for LNB's and to figure out if there is something really wrong.


Head on to the download page and discover signal generation up to 22GHz with the SMA/NWT devices!

Do you have a different application for the "Harmonics Signal Generation" with the VMA Simple Spectrum Analyser software? Let me know about it!

Regards,
Vitor


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