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Sunday, 11 February 2018

And here is a GREAT video on the Fourier Transformation!


Ever wondered about the math behind spectrum analisys?

I have and though I have the basic understanding, I did enjoy this video so much, I decided to share it on my blog:


Sunday, 14 January 2018

VMA Simple Spectrum Analyzer: New version that allows measurements on the selected trace!


This was for a long time on my todo list: being able to carry out all measurements on the selected trace, instead of the LIVE trace.

Up to now all measurements like the bandwidth measurement would always consider the LIVE trace only. This was limiting, since other traces could be more useful. For instance, the MATH trace could have been configured to consider a compensation. This made it difficult to read the desired value of traces other than the LIVE trace.

I added a new ComboBox on the trace section (lower rigth side of the window): select the trace you want to base all measurements on and off you go! The software will show dB value of the mouse or any other measurement based on the selected trace.

This works with the MATH trace, as well, which was the hardest part to implement.

Hope you like it.


Wednesday, 10 January 2018

Nova grelha NOS (TV Cabo) - 9 de Janeiro 2018


A NOS realizou ontem, conforme anunciado, a alteração da sua grelha. Isto significou para os clientes NOS uma nova sintoziação dos canais.

Esta medida tem aspetos positivos e negativos:

  • Finalmente, todos os canais digitais estão disponíveis sem encriptação, tornando possível a sua sintonia em todos os televisores da casa, desde que tenham um receptor DVB-C. Os receptores da NOS só são necessários para os canais premium.
  • Os canais foram "arrumados": temos no espetro de frequencias primeiro os 23 canais analógicos, depois temos os canais digitais. Isto evita problemas entre canais vizinhos, já que os canais analógicos e digitais são transmitidos com potência de sinal distintos.
  • Televisores mais antigos, que não conseguem sintonizar a híper-banda, conseguem agora sintonizar todos os canais analógicos - antes faltavam alguns.
  • Não entendo porque é que a NOS não é capaz de alinhar os canais analógicos por frequencia na mesma ordem como apresentado na grelha (RTP-1, RTP-2, SIC, TVI, etc.). Isto em televisores antigos (os que só têm sintonizador analógicos) dá um enorme trabalho!
  • So temos agora 23 canais analógicos...
Aqui o aspeto do espetro após a mudança:

E para ajudar a sintonizar os televisores com sintonizador analógico, eis a lista de canais ordenada por frequência e por grelha NOS:


Friday, 22 December 2017

Quick comparison: Agilent/Keysight E4403B - Siglent SSA3021X - Rohde & Schwarz CRTU


I have a loaned Keysight E4403B, so I used the opportunity to play a little with it.

Here are three Youtube videos, that show the same CATV signal on:
  • Keysight E4403B
  • Siglent SSA3021X
  • Rohde & Schwarz CRTU
The "test" was just to compare the refresh/sweep rate between the three devices. I fed my CATV signal and set all three devices as such:
  • Start Frequency = 50 MHz
  • End Frequency = 850 MHz
  • Span = 800 MHz
  • RBW = 1 MHz and 0.1 MHz
  • RBW/VBW = 0.1
The E4403B is labeled as "Keysight", but he same model has been previously produced by Agilent, which then comes historically from an HP design.

An intersting fact, at least to me: on the third video, if you increase volume, you will hear a chirping from the E4403B right in the beginning. Then I turn off the AUTO ALIGNMENT and the chirping is gone. Turns out that this is a normal behaviour and what you are hearing is the RF Frontend aligning itself at the end of each sweep, which results in relays clicking.

More info about this: Why is there a "chirping" noise coming out of my ESA Series Spectrum Analyzer?

I mention it, because it was driving me crazy - I feared that after repairing the PSU, there was some other fault...

Part 1

Part 2

Part 3

Well, nothing too spectacular to be seen, but I thought it might be interesting for some to see the live spectrum being rendered on the E4403B, SSA3021X and CRTU.


Tuesday, 12 December 2017

NOS (former TV Cabo) finally released their DVB-C bouquet in FTA!

Yesterday I received some good news for a change! I got an e-mail from NOS, who are better known as "TV Cabo", telling me that my TV could now render more than 110 channels.

After a quick reading, the issue was crystal clear: NOS has come to senses and removed their encryption on the base bouquet! This means that any TV equipped with a DVB-C tuner will be able to show all 110 channels of the base bouquet.

Before, you needed to rent an official NOS DVB-C receiver, but you could only have up to three and they cost extra money, of course. Well in a home like mine, we have 5+ permanent TV sets installed (not to mention my shack, which has at least another TV, if not more).

I always wondered why they would encrypt ALL their DVB-C channels (except a few international channels, which are FTA on satellite - I think for DRM reasons NOS had to keep them FTA when retransmitting them in their network).

Here are two pictures grabbed from my Emitor Megalook, which I managed to repair after studying the fault over 4 months... More info about that journey at EEV-Blog:

The complete CATV spectrum as used by NOS

Constellation diagram of transponder at 354MHz, using QAM256

Update on 10/01/2018:
Yesterday NOS changed the channel plan once again,
so the following list is not correct anymore!

Here is the channel list for PORTO area:
  • 121500 kHz QAM256 SR6.000 kBaud/s
  • 184500 kHz QAM128 SR6.000 kBaud/s
  • 170500 kHz QAM256 SR6.000 kBaud/s
  • 219500 kHz QAM256 SR6.000 kBaud/s
  • 240500 kHz QAM256 SR6.000 kBaud/s
  • 247500 kHz QAM128 SR6.000 kBaud/s
  • 254500 kHz QAM256 SR6.000 kBaud/s
  • 261500 kHz QAM256 SR6.000 kBaud/s
  • 306000 kHz QAM256 SR6.875 kBaud/s
  • 314000 kHz QAM256 SR6.875 kBaud/s
  • 322000 kHz QAM256 SR6.875 kBaud/s
  • 330000 kHz QAM256 SR6.875 kBaud/s
  • 354000 kHz QAM256 SR6.875 kBaud/s
  • 362000 kHz QAM256 SR6.875 kBaud/s
  • 386000 kHz QAM256 SR6.875 kBaud/s
  • 426000 kHz QAM256 SR6.875 kBaud/s
  • 474000 kHz QAM256 SR6.875 kBaud/s
  • 490000 kHz QAM256 SR6.875 kBaud/s
  • 562000 kHz QAM128 SR6.875 kBaud/s
  • 570000 kHz QAM128 SR6.875 kBaud/s
  • 602000 kHz QAM256 SR6.875 kBaud/s
  • 626000 kHz QAM128 SR6.875 kBaud/s
  • 634000 kHz QAM128 SR6.875 kBaud/s
  • 658000 kHz QAM256 SR6.875 kBaud/s
  • 674000 kHz QAM256 SR6.875 kBaud/s
  • 690000 kHz QAM256 SR6.875 kBaud/s
  • 714000 kHz QAM64  SR6.875 kBaud/s
It is now debatable if it wouldn't have been a better choice to distribute these channels with DVB-T modulation, instead, as the required DVB-T receivers are more common and cheaper (thanks to the TDT - "Terrestrial Digital Television"). But that would of course mean a significant investment for NOS, to change all equipment.

So at the end of the day, yes, I am happy. No more noisy analogue pictures, welcome to the digital TV on ALL screens of the house.

The final question is: Will NOS keep the analogue channels? Or will they be shut off after a given transition period? What would the free frequency ranges be used for?


Monday, 4 December 2017

Teaser: VMA Simple Spectrum Analyzer for HackRF One


As you know, I am a spectrum freak. There are two implementations already for the HackRF One:
  • qspectrumanalyzer - works well under Linux, but crashes right away under Windows
  • hackrf-spectrum-analyzer - works on Windows, but crasshes frequently when changing settings
Both are fairly limited in terms of functionality, but they show something impressive: the HackRF One is capabale to show a very high resolution spectrum over the whole supported frequency range (1MHz-6GHz). And the speed is incredible!

This motivated me to do a preliminary hack to see if the HackRF One could be used with my VMA Simple Spectrum Analyser software and the results are very promising:

Live spectrum (10MHz to 1000MHz)

Average Trace

Live, Min and Max Traces

Solid render of Live Trace

3D spectrum mode

The implementation is totally hacked and with errors:

  • I am not reading out the data correctly and there is some unfixed bug, which is why there is a blank on the right side of the spectrum in the above images
  • The frequency values are wrong
  • The frequency range cannot be set, nor can any other setting, as I have not implemented the protocol, yet

However, all other measurement functionality works and speed is fantastic! This could be a dream come true.

But there is a LOT of work required to get this to work and sadly I won't be able to manage it by myself.

First things first - the TODO list:
  • Better understand the hackrf_sweep protocol
  • Implement correct start/end frequency setting
  • Implement correct bin_width setting (FFT frequency resolution)
  • Implement num_samples setting (number of samples per frequency)
  • Implement interpretation of sweep output
  • Implement way to change current start/end frequency and other parameters (*)
(*) This is the crucial part: as it is, the hackrf_sweep.exe needs to be stopped with CTRL+C and restarted with new settings. This is not ideal, as it causes a significant pause.

Worse than that, under Windows, every CTRL+C crashes the HackRF One and a resume requires to press the physical RESET button.

Instead of having a hackrf_sweep.exe tool running in a shell outputting the sweep data to the console (from where I am reading it right now), I would prefer a TCP/IP communication to receive the sweep data and to send any new setting.

Unfortunately this requires to change the C++ sources of the hackrf_tools, something I am not literate to do.

If you know how to program VC++ and are interested in this project, please contact me!


Friday, 24 November 2017

Using HackRF One and GNU Radio on Windows 10


So finally I got my very own HackRF One!

While I was waiting for the order to arrive, I started to learn about how to use the HackRF One and all instructions I found online pointed to one basic fact: you need to have Linux to fully use the HackRF One.

The problem is that I currently have only Windows 10 installed on my computers, because most programs I use, are only available for this operating system.

For the casual Linux use, I droped having a dedicated Linux partition and instead started to use Ubuntu inside a virtual machine. Using the free VirtualBox has been a great experience, as it works really well.

However, I discovered that for HackRF One, the bandwidth of the virtual USB port is simply not enough. While you can in fact use the HackRF inside a virtual Linux box, performance is not ideal. It does work, but don't expect to TX/RX the full 20MHz.

I tried my luck with Pentoo, a Linux distribution on DVD that has everything radio related pre-installed. It does work, but again there was a slight annoyance: I am used to my SSD, which is really fast and I use three monitors to have plenty of desktop space. With Pengoo, everything loads from DVD and that is really slow! Also, all three monitors show the same content with a lower resolution that would be possible.

And so I ended up giving GNU Radio for Windows a shot and guess what: it works actually amazingly well!

How to set it up? Look here:

And yes, you get FULL HackRF One support, commands like "hackrf_transfer" are available and work.

I did a first test with my new HackRF One and this image shows the capture of a few seconds of just 2MHz:

Soon I ended up recording 20MHz bandwidth (basically the whole FM band in one go) and then transmitted it at 160MHz centre frequency... Why? Because I can!

The spectrum analyzer shows how it looks like...

...and my Uniden Bearcat UBC9000XLT could perfectly receive the relayed FM stations! Simply amazing!

Now I need to learn more about GNU Radio - it is an amazing piece of software!

So here is a prrof of concept that you can use the HackRF One with Windows, as opposed to basically all quick start instructions I have found.