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Sunday, 4 December 2016

VMA Simple Spectrum Analyser - New name and new trigger function!


I am implementing the next item on my list and it is almost done: the trigger function.

A modern spectrum analyser has to feature a trigger function, which serves the purpose of alerting the operator whenever a given frequency exceeds a pre-defined treshold value.

Newer spectrum analysers, like the Siglent SSA3021X will actually allow the user to draw lines, which act as treshold values across the setup frequency range.

Naturally, I had to do something even better! The problem with defining a set of line segments to draw the power treshold for an alarm is that it takes ages to define a complex treshold mask.

Also, most spectrum analysers will only alarm if the signal power is greater than the defined treshold, not offering any alarm in case the signal power is lower than a second treshold.

I implemented something slightly different:
  1. The user saves a bitmap of the current spectrum (using the "SAVE PICTURE" button).
  2. The user opens said bitmap with Paint (or any other bitmap drawing tool) and draws the upper limit as a blue area and the lower limit as a red area.
  3. This new bitmap acts as a trigger map.
  4. Once loaded, the software will extract the exact upper/lower treshold contour and starts monitoring the live spectrum.
  5. Should any frequency have a higher or lower signal power than specified with the current trigger map, an alarm is issued.
  6. In the present state, the alarm is shown as a red or blue status message and the individual alarm is put with time stamp and description on a list box.
The following pictures show the process:

Picture 1: Just draw blue (MAX) and red (MIN) areas to define the trigger treshold mask. Don't worry about the remaining picture of the original spectrum screen shot, as the software will only extract the blue and red areas!

Picture 2: Once the trigger mask is loaded, it is rendered over the spectrum, so that the user can check the live spectrum agains the trigger mask. Note that the trigger mask is static: changing the spectrum amplitude or frequency range will NOT change the trigger mask!

Picture 3: Any alarm will be shown in the SPECTRUM TAB as a red/blue status alarm and listed in the TRIGGER LOG tab on a list box with further information, including time stamp and frequency value

This version will be made available, soon. I need to finish a few oddities.

Future functionality may include automatic e-mail with spectrum image upon alarm - stay tuned!

Regarding the name change: the software was initially called "SMA Simple Spectrum Analyser", since it was developed for the "138MHz-4.4GHz 35M-4.4G USB SMA Source/Signal Generator/Simple Spectrum Analyzer" device.

However, the software works with the NWT4000-1 and NWT4000-2, too (or at least I think so, but I did not test it, since I don't have such devices).

This made the "SMA" a bit silly, as it refers to the input connector format...

Because I do use my initials often enough, I just changed the name of the software to "VMA Simple Spectrum Analyser"...


Sometimes I excel myself (*cough*) and get actually surprised on what I did (joke):

I just tried out what happens if the trigger mask is drawn with just incomplete blue and red lines...

This picture says it all:

Note: The image in Paint is drawn at 50% scale, so that both screens fit the window.


I ended up implementing a simple "Trigger Mask Editor", but Paint can still be used:


The VMA Simple Spectrum Analyser is now sending TRIGGER ALARM e-mail messages with embedded picture of the offending signal:

Still needs a few polish up until the next release, but it is working!

Now you will never again miss that sporadic feed, the intermittent signal or the annoying random signal loss - even when away from your computer...



  1. , hola mi profesion esta relacionada con el mantenimiento de emisoras de radios, soy tecnico electronico, tambien radio aficionado, hace rato que estaba por comprar un simple analizador de sespectro chino , o con barredor , ahora que veo un software espectacular, una persona que le dedico mucho tiempo al mismo, y sigue en actualizandolo con mejoras, de 10 , mi inquietud es en señales de telefonia celulqar, como se comportaria el analizador ?, saludos

  2. Hola Luis.
    Si, es posible analisar señales de telefonia celular. En realidad, la función de mapeamento de la señal por GPS sirve exactamente para este tipo de aplicaciones.
    Envíame un correo que podemos hablar mejor sobre lo que quieres hacer - v m a @ n o r c a m . p t.