[digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s)
Robert: A DSP software engineer, smarter than you and me, can certainly write a diagnostic that will take the digitized audio, from a sound card A/D, and attempt to do what we do by ear. Typically such software, which does exist in other environments, relies on a number of human interventions, at the decision points, to classify the signal parameters. In the process of trying to determine what modulation and FEC scheme(s) are in use for a particular signal, knowing what the input pattern might be of limited value. The reason is that in any proper coding scheme, will, as one of its first steps, scramble or randomize the incoming data, in order to provide a uniformly random data stream to the subsequent steps in the process. These randomizers come in a few well defined forms, so it is not that hard to derandomize the result , once you have demodulated, and stripped off the FEC layers. If, as I note below, at this point the random, data does not appear the consequence of a known randomizing process, you may be looking at encrypted data. So in the end, what we are talking about is a software process that will try and look at the source encoding (in reverse, as a demod,decode, process), to see if the transmitted symbols are related to the input (user information data) by various types of FEC coding, (1) Frequency diversity, in the form of encoding the source to allow it to be transmitted (as adjacent multiple carriers) on multiple frequencies simultaneously, is needed to combat the frequency selective fading present on HF paths. This also can be used to lower the baud rate of the individual carrier. (2) FEC coding layers, to combat, with one type of FEC, the low signal to noise ratio (QRN) inherent in weak signal work, and additional layers of FEC, of a type appropriate to combat the time carrying interference environment typical of QRM and atmospheric QRN. (3) Time diversity coding, to combat the channels dispersive distortion in time over HF (short baud bad, long baud good), and frequency selective, but short duration, fading. Incidentally the short baud bad is one reason why spreading tends to underperform on real HF circuits compared to a flat white noise channel in a laboratory environment. However, in addition to the coding resulting from the input data that I have sumerized in the three steps above, there is an additional data steam added, at any step in the process, that is not derived from the input data, and hence, random with respect to the data, and is added at the same symbol rate as the user derived symbols, you will have a case for encryping coding. This certainly expressly forbidden by the FCC and most national ham rules and regs. If, at the addition of the random data, it is done at a symbol rate higher than the symbol rate of the user derived symbols, you have a case of spread spectrum. The end result, not obvious by the simple minded analysis allegadly done by the FCC endineering office, is a transmission wehere the symbol rate appears much higher that would be expected from the identified (steps 1-3) coding processes. The real anser to the acceptability of a modulation system is not the result of signal analytics, but an analysis of the coding specfifications, and hopefully source code examples, to see how you get from input data to modulated waveform. With is level of knowledge, the use of spread spectrum will be obvious. As an aside, the fact that a system uses m-ary FSK or multicarrier PSK, and the modulation keeps changing transmit symbols, when the input stream is all ones or all zeros, does not demonstate the presence of a spread spectrum process. This is not a sufficient test. On the other hand, if the sum of the transmit symbol rates is very much larger than the user data rate, much larger than could be rationally expected by the FEC expantion, then, spread spectrum could be suspected but not proven. In the end, systems like ROS, Clover, PACKTOR-XXX, etc, where there is not full published trasparency in the encoding process, are not suitable for legal amateur use, in my humble opinion. Thanks 73 Les Lester B Veenstra MØYCM K1YCM les...@veenstras.com m0...@veenstras.com k1...@veenstras.com US Postal Address: PSC 45 Box 781 APO AE 09468 USA UK Postal Address: Dawn Cottage Norwood, Harrogate HG3 1SD, UK Telephones: Office: +44-(0)1423-846-385 Home: +44-(0)1943-880-963 Guam Cell: +1-671-788-5654 UK Cell: +44-(0)7716-298-224 US Cell: +1-240-425-7335 Jamaica: +1-876-352-7504 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached
[digitalradio] Inquiry
I am quite new to digital modes and I often have trouble identifying what mode I'm hearing/seeing. Is there a website which has examples of the various modes which would help me? Wes W1LIC
Re: [digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s)
Many thanks, Les, for your comprehensive answer which has greatly increased my understanding of the issue. Not quite as straightforward as I imagined! 73 Robert
[digitalradio] Re: Bad sound card?
Are you sure it is not just an EMC issue? Have you tried listening on the PC speaker without the rig connected? Neil G7AQK --- In digitalradio@yahoogroups.com, Jeremy Cowgar jer...@... wrote: Hello, When purchasing a new radio this last week I decided to also set my computer up how it should have been long ago. I purchased a sound card to dedicate it to digital modes. The sound card purchased was: http://www.microcenter.com/single_product_results.phtml?product_id=0239854 It was $9.99... I wasn't asking for the world, but I didn't think I would get this. I am curious as to what you think? Here's the synario. I connect the line out to my rig blaster and when I transmit I get this: http://jeremy.cowgar.com/files/bad_sound_card.wav This was recorded from my mom's station that is 8 miles away. Obvious problem. I then simply moved the line out cable from my new sound card to my old sound card that is built into my mother board. No other changes. I do not have a recording of it, but it's beautiful, exactly how a feldhell signal should sound. Now, the most obvious thing would be is my sound settings wrong, i.e. way overdriving with the new sound card or something. I set them up the same. Looking at my ALC meter, I transmit into a dummy load, turn the line out volume up until I get ALC movement, then turn it back down until I cannot notice any ALC movement. Do you have any ideas? It's just $10, but I'd really like to have a dedicated sound card for the ham stuff, and please do not suggest a Signalink as I already have a nice setup, all wired and working, I just need to get this squared away. Until then, I'm working off my sound card built into the motherboard. Thanks for any help, Jeremy KB8LFA
Re: [digitalradio] Inquiry
This is a good place to start. http://www.w1hkj.com/FldigiHelp-3.12/Modes/ Andy K3UK On Sat, Jun 5, 2010 at 6:37 PM, Wes Linscott w1...@ymail.com wrote: I am quite new to digital modes and I often have trouble identifying what mode I'm hearing/seeing. Is there a website which has examples of the various modes which would help me? Wes W1LIC
Re: [digitalradio] Inquiry
Hi Wes Try this; http://www.youtube.com/watch?v=lOmrgJkFY40feature=related 73 Robert - Original Message - From: Wes Linscott To: digitalradio@yahoogroups.com Sent: Saturday, June 05, 2010 11:37 PM Subject: [digitalradio] Inquiry I am quite new to digital modes and I often have trouble identifying what mode I'm hearing/seeing. Is there a website which has examples of the various modes which would help me? Wes W1LIC
[digitalradio] The Roger Tory Peterson Guide to Digital Modes
Since the Roger Tory Peterson Guide Institute is in my local county, I guess I should adapt his famous birding field guide concept, and apply it to the often asked question about recognizing digital modes. Roger Tory Peterson laid out his guide in a logical manner , clustering similar specifies, and types of birds close together in his book. His illustrations emphasized obviously distinctive features that could be quickly used to I.D. the bird and then some of the less obvious features (like tail feathers). He also gave close up views , and in flight views. The same concepts could easily be employed for a digital mode guide, easier for hams versus SWL because hams do not use as many digital modes. Roger Tory Peterson also emphasized the song of the bird , the motion, and the habitat. Stealing all the ideas for digital mode recognition , the key facts would be Habitat -- where on the band is it ? Size? How wide on a waterfall is it ? 31 Hz? 500 Hz ? 2.7 Khz ? Song- Single or multi-tones ? High pitched, low pitched ? A constant tone or rhythmic pauses in tones? Markings: Two vertical lines spaced 170Hz apart? multi-layered markings in a complex 1000 Hz area ? Using the above principles, The Crows , Sparrows, and Robins of the digital modes (PSK31, RTTY, and JT65A) should be so common that you can generally recognize them at a quick glance or simply by hearing their song. Being able to do this, would take care of about 80% of the signals you are likely to hear. Becoming more of a habitat expert would easily add another 10% of the possible signals that you could recognize quickly. The remaining 10% will take some work , varying combinations of song and size, within the Thor, Olivia, Domino, families. I will put some illustrations together in RTP fashion in the near future. Andy K3Uk
Re: [digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s)
At 03:22 AM 6/6/2010, you wrote: (in part) In the end, systems like ROS, Clover, PACKTOR-XXX, etc, where there is not full published trasparency in the encoding process, are not suitable for legal amateur use, in my humble opinion. In other words, no one has the right to make money from their hard work and what could have been $$$ millions spent on research and development as would have been the case with Pactor 3. Or the right to protect it.
RE: [digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s)
You can of course protect your intellectual property. But such a commercial format belongs on commercial frequencies. That is, it has no place as a format used for amateur radio. Lester B Veenstra MØYCM K1YCM mailto:les...@veenstras.com les...@veenstras.com mailto:m0...@veenstras.com m0...@veenstras.com mailto:k1...@veenstras.com k1...@veenstras.com US Postal Address: PSC 45 Box 781 APO AE 09468 USA UK Postal Address: Dawn Cottage Norwood, Harrogate HG3 1SD, UK Telephones: Office: +44-(0)1423-846-385 Home: +44-(0)1943-880-963 Guam Cell: +1-671-788-5654 UK Cell: +44-(0)7716-298-224 US Cell: +1-240-425-7335 Jamaica: +1-876-352-7504 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. From: digitalradio@yahoogroups.com [mailto:digitalra...@yahoogroups.com] On Behalf Of John Becker, WØJAB Sent: Sunday, June 06, 2010 3:49 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s) At 03:22 AM 6/6/2010, you wrote: (in part) In the end, systems like ROS, Clover, PACKTOR-XXX, etc, where there is not full published transparency in the encoding process, are not suitable for legal amateur use, in my humble opinion. In other words, no one has the right to make money from their hard work and what could have been $$$ millions spent on research and development as would have been the case with Pactor 3. Or the right to protect it.
Re: [digitalradio] source coding, Randomizing, outer FEC, Inner FEC, coding to symbol, modulation of symbol(s)
On 06/06/2010 10:48 AM, John Becker, WØJAB wrote: At 03:22 AM 6/6/2010, you wrote: (in part) In the end, systems like ROS, Clover, PACKTOR-XXX, etc, where there is not full published trasparency in the encoding process, are not suitable for legal amateur use, in my humble opinion. In other words, no one has the right to make money from their hard work and what could have been $$$ millions spent on research and development as would have been the case with Pactor 3. Or the right to protect it. They can keep it secret all they want. I just do not believe amateur operators should use such protocols on the amateur bands. -- All rights reversed.
Re: [digitalradio] source coding,
I just do not believe amateur operators should use such protocols on the amateur bands. Such protocols ? What makes you say that?
RE: [digitalradio] source coding, Randomizing
By the same thinking (that being that a commercial company) is making any money should you not put kenwood and yaesu into the same? Or how about that mean money making company that made your sound card interface. or microsoft. John, W0JAB At 10:12 AM 6/6/2010, you wrote: You can of course protect your intellectual property. But such a commercial format belongs on commercial frequencies. That is, it has no place as a format used for amateur radio.
RE: [digitalradio] source coding, Randomizing
John: I am sorry that I did not make myself clear enough. My argument is directed to transmitted signal formats. That is, what is covered by §97.307 Emission standards. Les Lester B Veenstra MØYCM K1YCM mailto:les...@veenstras.com les...@veenstras.com mailto:m0...@veenstras.com m0...@veenstras.com mailto:k1...@veenstras.com k1...@veenstras.com US Postal Address: PSC 45 Box 781 APO AE 09468 USA UK Postal Address: Dawn Cottage Norwood, Harrogate HG3 1SD, UK Telephones: Office: +44-(0)1423-846-385 Home: +44-(0)1943-880-963 Guam Cell: +1-671-788-5654 UK Cell: +44-(0)7716-298-224 US Cell: +1-240-425-7335 Jamaica: +1-876-352-7504 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. From: digitalradio@yahoogroups.com [mailto:digitalra...@yahoogroups.com] On Behalf Of John Becker, WØJAB Sent: Sunday, June 06, 2010 6:44 PM To: digitalradio@yahoogroups.com Subject: RE: [digitalradio] source coding, Randomizing By the same thinking (that being that a commercial company) is making any money should you not put kenwood and yaesu into the same? Or how about that mean money making company that made your sound card interface. or microsoft. John, W0JAB At 10:12 AM 6/6/2010, you wrote: You can of course protect your intellectual property. But such a commercial format belongs on commercial frequencies. That is, it has no place as a format used for amateur radio.
Re: [digitalradio] Bad sound card?
On 06/05/2010 03:24 PM, Jeremy Cowgar wrote: Do you have any ideas? It's just $10, but I'd really like to have a dedicated sound card for the ham stuff, and please do not suggest a Signalink as I already have a nice setup, I know your problem - the sound card's too expensive :) I got a Cmedia Cm108 USB soundcard for $7 and it seems to do the trick here. The sockets for the connectors are not very good physically (I ended up soldering wires directly to the circuit board) but the audio quality is perfect for HF. -- All rights reversed.
Re: [digitalradio] source coding, Randomizing
Lester Veenstra wrote: I am sorry that I did not make myself clear enough. My argument is directed to transmitted signal formats. That is, what is covered by §97.307 Emission standards. All the FCC requires is that the protocol/algorithm be made available if required. Does not have to be published, and there is no requirement for every ham to be able to monitor. Just that if the FCC asks, it's made available. I know this first hand as my club worked directly with them in the mid-80's on a new modulation scheme developed by a member. We offered to provide the algorithm or keep source in escrow, and they basically said if they needed to monitor they had ways and would contact us as needed. IE: No need for source, etc. The modem was sold commercially, so the club wanted to have all above board. Even P3 is snoopable with commercial programs, so it's just a non-issue. Even hams could snoop P3 if they wanted to with the new capabilities SDR offers. Just record the data stream, and decode and work out the FEC over time. Not to defend SCS, but by providing the general description, tone frequencies, etc, for P3 there is more than enough information for the mode to be monitored by any agency who needs to. As a side note, the FCC also ruled on our new modulation scheme that randomization did not constitute encryption, nor was it considered spread spectrum. Randomization of data is both common and desired for modulation schemes as it keeps the average power up and minimizes the effect of sidebands in some schemes. (They are there, just less noticeable). If we dug very deeply I suspect we'd find P3 randomizes as well for the same reasons. To quote G3RUH who also used randomization in this modem: Secondly, since the data stream is now randomised, its spectral energy is evenly spread out at all times. Intense spectral lines do not suddenly appear and create sporadic splatter into nearby channels. A third reason is that since the data is guaranteed to have a regular supply of ones and zeros, the receiver's bit clock recovery and demodulation circuits work better. We had challenges from the nay-sayers on both points, so we had it in writing from the FCC engineers. So the idea that any mod scheme which does not send steady tones when sending zeros is spread spectrum is just flat out wrong. While SS can be thought of as an extreme form of randomization, randomization does not always equal SS. There are specific coding sequences used to improve decoding that are also pseudo random that are in common usage. Have fun, Alan km4ba
[digitalradio] Odd mode around 7057
While on 7056 CW today, I heard a loud digital signal that was unfamiliar to me. It was very wide, and sounded a little like across between JT65A and ROS. I wonder if it is some new ROS mode and they are trying it out in an odd part of the band. Andy K3UK
