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About borjam

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    Bilbaina Jazz Club
  • Interested in Sound for Picture

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  1. borjam

    RF Interference

    Maybe I am asking a very silly question, my apologies in advance. How do you guys perform a RF Explorer scan? Some digital transmission systems work with very short bursts, so a regular spectrum analyzer has a limited detection probability unless you leave the analyzer running for some minutes and set up so that it holds the peak levels. Otherwise you might miss the offending transmissions.
  2. I cound't wait, first thing I did right after I arrived home was watching it. It's a really awesome documentary. I love how the story is told and how it can connect with you even emotionally. It's a pity that sound work is so invisible compared to camera/cinematography work that grabs so much more attention in the form of books and documentaries. Yet it is so powerful. Now wish me luck, I am going to try to convince my 18 year old nephew to watch it.He is studying 3D design and it seems he would like to work on video games.
  3. I preordered it on Amazon.co.uk in early Novemeber, the DVD just arrived today.
  4. I've just preordered it on Amazon.co.uk on DVD. The announced release date is November 25th.
  5. Good, it's available again for preorder on Amazon.co.uk. I just pulled the trigger.
  6. I saw it would be available for purchase on Amazon.co.uk but now it’s shown as “not available”. Does anyone have a clue? I would really like to watch it, no problem at all to purchase a copy.
  7. I own an NTG8 and I really like it for outdoors recording. There are two on sale here and the price is really a steal. Moreover, I tried a RF abuse test and it passed with flying colors. The main difference between the NTG5 and NTG3 seems to be, I would say, the NTG3 is supposed to have much better backwards rejection. I would say it is its strongest point. I own an NTG8 and I really like it for outdoors recording. There are two on sale here and the price is really a steal. Moreover, I tried a RF abuse test and it passed with flying colors. The main difference between the NTG5 and NTG3 seems to be, I would say, the NTG3 is supposed to have much better backwards rejection. I would say it is its strongest point.
  8. Indeed, and low frequencies tend to mask higher ones. I am sure of that. Moreover, "traditional" techniques to enhance bandwidth over very noisy channels deal with "natural" causes of signal degradation. Examples would be communications with space probes orbiting near the Sun or, for example, the work of Joe Taylor on low signal data transmission modes with bandwidths in the range of bits per second. Not even hundreds! Digital lossy compression on the other hand can butcher signal integrity in very curious ways. The modem example I mentioned is interesting because probably the designers of the compression system decided to allow 9600 bps modems to work. In the PPM vs MP3/AAC case, however, it's just completely opposite goals. Explaining it in a somewhat extreme way, lossy audio compression systems interpret the bit strem according to a psychoacoustic model and resynthesize them. I wonder wether someone has came up with a scheme robust enough to survive that. It sounds challenging and (intuitivelly) I am not really sure it would even be possible at all. Maybe playing with timing tweaks, but we are good at detecting that. Now, let's be careful. Imagine some crazy politician reading us and thinking about mandating a universal re-encoding of audio and video content over the Internet in order to avoid steganography
  9. That’s a difficult question, it would depend a lot on the details. There are data encoding methods that can withstand lots of abuse, but mostly “analog” abuse (ie, noise, multi path interference, etc). Of course at the cost of bandwidth, Information Theory is after all one of the hard limits in nature, like Thermodynamics. That said, if I was the designer of that thing I wouldn’t try to make it error tolerant. After all the rest of the protocol stack will take care of that and email or web page content are transmitted over lossless paths. I would include some error detection mechanism but that’s it. They are using the audio file just because it will be considered harmless. And using steganography they can avoid some detection mechanisms that can identify properties of computer code. But that’s it. I remember (old story) when some phone companies in Spain begun using audio compression in their trunk circuits. Suddenly 28800 bps modems were unable to link at a data rate above 9600. Of course those modems had the ability to negotiate a data encoding scheme. One of these steganography files would not make it. Moreover, error tolerance depends basically on redundancy. Redundancy undermines the security of encryption, they are two opposite goals. Any property invariant through several transformations will at the same time make cryptoanalysis much much easier.
  10. @simmiz Now that I remember, this guy in Greece sells PCBs with a proper coplanar transmission line that would help with signal integrity. You could mount a Minicircuits balun on them, they have several parts that would work. https://www.sv1afn.com/rf-experimenter-s-pcb-panel.html
  11. @Jay Rose It seems to be steganography. In this case it's not a WAV file exploiting vunlerabilities to run malicious code, but a mechanism to distribute new code to already compromised hosts. Why a WAV file? Because firewalls and other malware detection systems won't intercept them. So, no need to get paranoid about WAV files. The risk would be the same if it was kitten pictures. Anyway the potential risks in all this are mostly a Windows thing. I remember the latest twist I have seen recently. I am receiving email messages with attached malicious files in .tar.gz format (a Unix file format). Turns out that modern Windows systems can open them. But if I upload the malicious .tar.gz file to Google's Virustotal.com (where a farm of anti virus systems check it), most of the antivirus programs complain of an unsupported file format! Windows has always had a critical problem with consistency when dealing with the meaning of "opening" a file, which is not such a simple thing because a file can be data or executable code. And they have traditionally made a huge mess with it. Apple haven't been free of foolish decisions but they have done vastly better.
  12. Hmm I wonder wether the PCB layout might cause more losses than the balun itself would solve. The real expert on this is @LarryF. The only baluns I have built for UHF frequencies were narrow bandwidth ones based on transmission lines (ie, a piece of coax). I used them successfully for TV reception with a homebrew dipole array.
  13. Looking at the photo, it seems you can disconnect the preamplifier or even insert an attenuator depending on the gain you choose. Of course provided the block diagram really describes it. However, I guess the gain selection switch might need DC power in order to operate. I don´t see a photo of the switch itself. But in that case you can use a simple bias-tee like this one. https://www.amazon.com/Bias-Tee-10MHz-6GHz-Broadband-Frequency/dp/B07RZSPQD9/ref=sr_1_1?keywords=bias+tee&qid=1570475344&sr=8-1 Of course, this is just an educated guess. Beware active antennas without filtering in front of the preamplifier though. HTB1xeBlaojrK1RkHFNRq6ySvpXaF.jpg.jp2
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