[digitalradio] Re: digital voice within 100 Hz bandwidth
I would be plased to have a complete list of the phonemes and corresponding audio files from different speakers. I fear 44 phonemes will not be enough to do a context-free analisis. The data rate will be closer to 200pbs i think, since you will have to transfer a magnitude component along with the phoneme index, and maybe also a pitch component. Think of the pitch raise in a question, this feature is important for understanding. The main problem will be the fft to phoneme table correlation i think ... but to work on this there must be a phoneme table first.
[digitalradio] Re: A challenge to RTTY operators!
Rick, I used a CP-1 TU up to the day the WF1B RTTY contest program became unsupported. WF1B supported quite a few TU types but no sound cards. That was around 1996 or 7. Here's a tidbit of info. Score required to win 1997 USA CQ WW RTTY single op assisted in 1997 = 553k points. I still have the plaque for it. It was done with a CP-1 and WF1B software. This was TU, not sound card era for RTTY. I don't believe MTTY and was created until several years later. MTTY by itself was pretty much useless as a contesting program. It couldn't even export its logs. It only supported a few rigs. It wasn't until codes like Writelog and N1MMLOGGER integrated MTTY and such engines in contesting programs that contesting became practical. K6STI RTTY was in there too about the same time with perhaps the best decoder available and a contesting interface. Piracy issues essentially killed the K6STI program. The author stopped supporting it. The last few years about 1.5 million points is required to win the same award. I ammend my statement. It wasn't just sound card RTTY but sound card RTTY plus having it integrated into contesting programs that released the contesting flood of RTTY stations. P.S. despite the sound card revolution, I stick with my HAL DXP38 DSP TU. Sound card apps seem to have a nasty habit of refusing to work for unknown reasons. One day they work, the next they don't. One has to be a computer Geek to bring them back to life. This isn't just my experience. 73 de Brian/K3KO --- In digitalradio@yahoogroups.com, Rick [EMAIL PROTECTED] wrote: I have to concur with Jose on this. I was a very active HF and VHF digital ham starting around 1981 with a homebrew XR2206/XR2211 TU that was from QST magazine and called The State of the Art TU. It most assuredly was not, but being naive and new to RTTY found it to be a very poor performer. It was actually only detecting one of the tones with the tone decoder! This was before computers became popular and I was interfacing with a Model 15 TTY and a homebrew loop circuit. I was able to borrow an huge tube ST-6 design TU and that was much better. Then computers started to be available at more affordable prices and I moved to the Commodore 64 and a ROM based software package. Later I had the Kantronics UTU, and eventually an AEA CP-1 using the BMKMulty DOS software. This was before it could do Pactor, but the program already cost $100 for basic RTTY/AMTOR and then you had to buy the CP-1 or some kind of interface to key the rig. BMKMulty eventually had a Pactor upgrade for I think another $100, but I have heard it was not that good. In fact, none of the third party hardware for Pactor was as good as the SCS modems, probably because they did not duplicate the memory ARQ. 73, Rick, KV9U Jose A. Amador wrote: Allow me to disagree (slightly) on the beginnings of RTTY popularity. I would blame Baycom, and the old Mix DOS versions. I used them (as well as quite few hams I know) way before PSK31 and the sound card modes appeared. Actually, after using them, I built a hardware modem that improved a LOT their performance, using both as terminals. I would say that PSK31 started the popularity of sound card modes. This is what I remember. Maybe others may have a different perspective. 73, Jose, CO2JA Brian A wrote: The advance that made RTTY so popular was the advent of sound card RTTY. I can attest to that since I operated RTTY contests before and after sound cards happened. The number of stations exploded as did contesting activity.
Re: [digitalradio] Re: Proposed Digital Operating Questions to FCC
Howard is looking at this correctly and fairly. It is very unfortunate that instead of making suggestions to improve the questions to the FCC, Bonnie, KQ6XA, has again used personal attack, and does so only with absolutely no explanation of what she is criticizing. She did this recently on QRZ and made huge numbers of enemies, even from those who might otherwise be supportive of some of her ideas. It is not reasonable to tell other hams that they are less than zero, just because you don't agree with their views. I am hopful that the great majority of hams know instinctively that the person making such attacks, does so, precisely because they have nothing positive to add to the request for input and they innately known that their own position is flawed. That is why they can not make constructive suggestions as was asked for. Bonnie went further than that and for personal spite removed me from the HFlink yahoogroup, the very group that she asks people to join to find out information on ALE and her ideas. When I first joined some time back she blocked some of my posts as not meeting the guidelines which she could not explain when asked for specifics. So I have not posted again, and yet was still removed, not for posting on her group, but for speaking my mind here and other venues. My long term hope is that we can get some basic answers to questions that many, many hams have been asking and only the FCC can answer. 73, Rick, KV9U Howard Brown wrote: Bonnie, there are some of us out here who would like to operate some of the modes in question, but feel that they are prohibited by the rules. We are not willing to just 'get away with it'. This seems to be what you are willing to do. Please consider apologizing to Rick and deleting your post about maliciousness. He is trying to help us clarify the rules and maybe even get them changed to allow faster digital operation. Be a good sport and look for the honest intent. Howard K5HB --- In digitalradio@yahoogroups.com, expeditionradio [EMAIL PROTECTED] wrote: It is sad to see such maliciousness being perpetrated upon fellow amateur radio operators. Perhaps is is not to discover real answers to Operating Questions, but rather, a charade to stir up trouble. Are we to believe that the perpetrator neither has the ability to read and understand the FCC Rules, nor willingness to learn when others have explained very clearly? Perhaps there is a lack of acceptance of the fact that even though their rules are antiquated, they must be followed anyway by USA operators. Perhaps the ham operator who wrote that story is disgruntled by having been rejected from participation in other forums for similar conduct there. But that is no excuse for submitting such lies to the FCC, or to ARRL representatives, under the guise of questions. Bonnie VR2/KQ6XA
Re: [digitalradio] Re: A challenge to RTTY operators!
I have to concur with Jose on this. I was a very active HF and VHF digital ham starting around 1981 with a homebrew XR2206/XR2211 TU that was from QST magazine and called The State of the Art TU. It most assuredly was not, but being naive and new to RTTY found it to be a very poor performer. It was actually only detecting one of the tones with the tone decoder! This was before computers became popular and I was interfacing with a Model 15 TTY and a homebrew loop circuit. I was able to borrow an huge tube ST-6 design TU and that was much better. Then computers started to be available at more affordable prices and I moved to the Commodore 64 and a ROM based software package. Later I had the Kantronics UTU, and eventually an AEA CP-1 using the BMKMulty DOS software. This was before it could do Pactor, but the program already cost $100 for basic RTTY/AMTOR and then you had to buy the CP-1 or some kind of interface to key the rig. BMKMulty eventually had a Pactor upgrade for I think another $100, but I have heard it was not that good. In fact, none of the third party hardware for Pactor was as good as the SCS modems, probably because they did not duplicate the memory ARQ. 73, Rick, KV9U Jose A. Amador wrote: Allow me to disagree (slightly) on the beginnings of RTTY popularity. I would blame Baycom, and the old Mix DOS versions. I used them (as well as quite few hams I know) way before PSK31 and the sound card modes appeared. Actually, after using them, I built a hardware modem that improved a LOT their performance, using both as terminals. I would say that PSK31 started the popularity of sound card modes. This is what I remember. Maybe others may have a different perspective. 73, Jose, CO2JA Brian A wrote: The advance that made RTTY so popular was the advent of sound card RTTY. I can attest to that since I operated RTTY contests before and after sound cards happened. The number of stations exploded as did contesting activity.
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
Hello Cesco, For information, I have tried to see if it was possible to transmit a speech through a 500 Hz channel using a digital transmission. I have decomposed the audio spectrum (but not through a FFT, but by intercorrelation to choose the carriers I wanted) in several carriers and associate to each carrier a level. Then I have tried to decrease the number of carriers N, the number of levels L and increase to the maximum the duration of intercorrelation T (the duration of an element of a speech), up to to find a just comprehensible speech. It's a compression of the information, up to the maximum possible. Above this limit, the speech can't be understood. After that, I do the reverse operation (equivalent to a FFT-1) and have not much that listening to the result. At each 1/T it was necessary to send NxL elements of information, which gives the final rate. This way is disappointed because you need much more information that you can transmit through a 500 Hz channel (for example: 23 carriers, 128 levels and T=40 ms). With 23 carriers, 8 levels and T=40 ms (which can be send through a 500 Hz channel), it is very difficult to understand a (French) speech. 73 Patrick - Original Message - From: cesco12342000 To: digitalradio@yahoogroups.com Sent: Friday, November 16, 2007 4:26 PM Subject: [digitalradio] Re: digital voice within 100 Hz bandwidth I would be plased to have a complete list of the phonemes and corresponding audio files from different speakers. I fear 44 phonemes will not be enough to do a context-free analisis. The data rate will be closer to 200pbs i think, since you will have to transfer a magnitude component along with the phoneme index, and maybe also a pitch component. Think of the pitch raise in a question, this feature is important for understanding. The main problem will be the fft to phoneme table correlation i think ... but to work on this there must be a phoneme table first.
[digitalradio] Re: NIC issue
--- In digitalradio@yahoogroups.com, Jose A. Amador [EMAIL PROTECTED] wrote: Misko, Most likely the module for the old NIC is no longer adequate for the new NIC. Look for the proper module and install it. Jose, CO2JA Miroslav Skoric (YT7MPB) wrote: Recently I changed the network card to one based on 3c905-tx chip. It makes me wonder how to make it working with Linux Mandrake 9.1 ? It is a PCI card (before it I used an ISA card that worked fine, but I moved it to another comp). Misko YT7MPB __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu That is a pretty old (and unsupported) version of Mandrake. You might want to try a newer release. Your NIC might be better supported. Good luck! KD7OFV
Re: [digitalradio] Proposed Digital Operating Questions to FCC
I have waited a couple of days, but since few constructive comments other than Andy, will try and take this into consideration to form the best approach that I can come up with. Separate groups to discuss sub issues are not generally successful and are developed primarily to keep the trouble makers away from the primary group. This is counter productive in the long run because there are always new people coming into the main group and they are not aware of what is going on. In this case there is really no debate. We already had much of that in the form of (hopefully) an informed discussion. All I am doing is preparing comments that I personally have wondered about (some for years now) or others have asked me about. ARRL has helped a little bit, but not on all the issues, so there is only one other place we can go. 1. The reason that I preface some of my remarks to the FCC is to provide some background. If I just ask a question, without any preparatory comments, I question whether they will fully understand why I am asking the question. Asking them for a rationale for the 300 baud limit seems reasonable to me and I am surprised Andy finds it the opposite. If they suggest proposing the change, that would be excellent since it would suggest that they might be willing to do this. I have felt that ARRL should have done this a long time ago, but I realize that they got burned pretty bad by the over reaching bandwidth proposal they had submitted and they are probably very uncomfortable about it right now. 2. The reason for the introduction to #2, is to set the stage for the question, which is the use of single tone modems in the voice/image portions of the bands. At this time, I have not heard from anyone (and I have asked this many times) who is using the high speed single tone modems in the voice/image areas here in the U.S. It seems very odd to me that this is not happening, as this should be available on the PC-ALE and other software. I want to make sure that this is legal as this may be holding some back here in the U.S. I personally want to do this, even if you or others do not. And I do not understand why you would not want to confirm it. 5. Again my intent is to preface the question with some background. I will try and rephrase the question so that it is more in line with a person who wants to do something but wants to make sure it is OK to do. In other words, operate in a certain manner without breaking the law. This is NOT nit-picking at all! This is a huge issue with a majority of hams that I have talked with. Automatic operation is not like a net to me, but perhaps the FCC will see it that way. To suggest that groups that have listed frequencies for automatic operation in the automatic portions of the bands do not see these frequencies as as theirs seems to me to be naive. One only has to look at the actual statements by such groups. For operation outside the automatic sub bands, it would be difficult for them to argue that they have any special right to operate when they want to operate. But the reality is that automatic stations transmit no matter what other signals are on frequency if they are turned on by a human operator. Either way, any of us can either accept whatever the FCC interprets, or if we disagree, send in a proposal for change. To me that is better than being a scofflaw, or at least being perceived as a scofflaw. As a consultant who dealt for many years with government officials, once a government official interprets the rules, that is the rule until such time as there is either a change from that official or from a higher authority. I have had situations that seemed unreasonable to me with a rule interpretation, have challenged the interpretation, and have been able to get the interpretation changed ... sometimes. Then again sometimes you lose and a lot depends upon how important the issue is to you and in my case, how much time/money it would cost my clients. I plan to openly share any information that I receive. 73, Rick, KV9U Andrew O'Brien wrote: Since Rick has advanced some new issues on the topic that I had enforced an embargo on, his posting is within the rules of this group. However, in order to prevent the previously experienced endless debate, I will end the thread here by UTC 20/11/2007 BUT I do encourage that the topic be vigorously debated over on our sister site... http://groups.yahoo.com/group/digipolicy No limitations on that site. Rick, here are my comments Can you give us some rationale as to why there is the 300 baud limit today and whether this could be increased to at least 2400 baud at some future time as long as the mode operated within the passband of standard SSB transmitters? I do not think Can you give us some rationale is good language. I am not sure the FCC exists to give explanations after their initial rule-makings. Additionally, the
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
Very low bitrate algorithms exist now. There are a few that operate from 200 bps to 600 bps. The Navy has software called IVOX that gets in this range. So you could transmit 16 QAM and hit the 100 HZ goal. The bigger problem would be getting it to survive propagation and survive receiver filtering. One would probably need to use a very narrow band OFDM scheme. It would be an interesting but do-able experiment. If it worked well, it would be a very worthwhile mode. Patrick Lindecker wrote: Hello Cesco, For information, I have tried to see if it was possible to transmit a speech through a 500 Hz channel using a digital transmission. I have decomposed the audio spectrum (but not through a FFT, but by intercorrelation to choose the carriers I wanted) in several carriers and associate to each carrier a level. Then I have tried to decrease the number of carriers N, the number of levels L and increase to the maximum the duration of intercorrelation T (the duration of an element of a speech), up to to find a just comprehensible speech. It's a compression of the information, up to the maximum possible. Above this limit, the speech can't be understood. After that, I do the reverse operation (equivalent to a FFT-1) and have not much that listening to the result. At each 1/T it was necessary to send NxL elements of information, which gives the final rate. This way is disappointed because you need much more information that you can transmit through a 500 Hz channel (for example: 23 carriers, 128 levels and T=40 ms). With 23 carriers, 8 levels and T=40 ms (which can be send through a 500 Hz channel), it is very difficult to understand a (French) speech. 73 Patrick - Original Message - From: cesco12342000 To: digitalradio@yahoogroups.com Sent: Friday, November 16, 2007 4:26 PM Subject: [digitalradio] Re: digital voice within 100 Hz bandwidth I would be plased to have a complete list of the phonemes and corresponding audio files from different speakers. I fear 44 phonemes will not be enough to do a context-free analisis. The data rate will be closer to 200pbs i think, since you will have to transfer a magnitude component along with the phoneme index, and maybe also a pitch component. Think of the pitch raise in a question, this feature is important for understanding. The main problem will be the fft to phoneme table correlation i think ... but to work on this there must be a phoneme table first.
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
Is this the IVOX system:? http://downloads.pf.itd.nrl.navy.mil/ivox/ LA5VNA Steinar W2XJ skrev: Very low bitrate algorithms exist now. There are a few that operate from 200 bps to 600 bps. The Navy has software called IVOX that gets in this range. So you could transmit 16 QAM and hit the 100 HZ goal. The bigger problem would be getting it to survive propagation and survive receiver filtering. One would probably need to use a very narrow band OFDM scheme. It would be an interesting but do-able experiment. If it worked well, it would be a very worthwhile mode. Patrick Lindecker wrote: Hello Cesco, For information, I have tried to see if it was possible to transmit a speech through a 500 Hz channel using a digital transmission. I have decomposed the audio spectrum (but not through a FFT, but by intercorrelation to choose the carriers I wanted) in several carriers and associate to each carrier a level. Then I have tried to decrease the number of carriers N, the number of levels L and increase to the maximum the duration of intercorrelation T (the duration of an element of a speech), up to to find a just comprehensible speech. It's a compression of the information, up to the maximum possible. Above this limit, the speech can't be understood. After that, I do the reverse operation (equivalent to a FFT-1) and have not much that listening to the result. At each 1/T it was necessary to send NxL elements of information, which gives the final rate. This way is disappointed because you need much more information that you can transmit through a 500 Hz channel (for example: 23 carriers, 128 levels and T=40 ms). With 23 carriers, 8 levels and T=40 ms (which can be send through a 500 Hz channel), it is very difficult to understand a (French) speech. 73 Patrick - Original Message - From: cesco12342000 To: digitalradio@yahoogroups.com mailto:digitalradio%40yahoogroups.com Sent: Friday, November 16, 2007 4:26 PM Subject: [digitalradio] Re: digital voice within 100 Hz bandwidth I would be plased to have a complete list of the phonemes and corresponding audio files from different speakers. I fear 44 phonemes will not be enough to do a context-free analisis. The data rate will be closer to 200pbs i think, since you will have to transfer a magnitude component along with the phoneme index, and maybe also a pitch component. Think of the pitch raise in a question, this feature is important for understanding. The main problem will be the fft to phoneme table correlation i think ... but to work on this there must be a phoneme table first.
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
Yes it is Steinar Aanesland wrote: Is this the IVOX system:? http://downloads.pf.itd.nrl.navy.mil/ivox/ LA5VNA Steinar W2XJ skrev: Very low bitrate algorithms exist now. There are a few that operate from 200 bps to 600 bps. The Navy has software called IVOX that gets in this range. So you could transmit 16 QAM and hit the 100 HZ goal. The bigger problem would be getting it to survive propagation and survive receiver filtering. One would probably need to use a very narrow band OFDM scheme. It would be an interesting but do-able experiment. If it worked well, it would be a very worthwhile mode. Patrick Lindecker wrote: Hello Cesco, For information, I have tried to see if it was possible to transmit a speech through a 500 Hz channel using a digital transmission. I have decomposed the audio spectrum (but not through a FFT, but by intercorrelation to choose the carriers I wanted) in several carriers and associate to each carrier a level. Then I have tried to decrease the number of carriers N, the number of levels L and increase to the maximum the duration of intercorrelation T (the duration of an element of a speech), up to to find a just comprehensible speech. It's a compression of the information, up to the maximum possible. Above this limit, the speech can't be understood. After that, I do the reverse operation (equivalent to a FFT-1) and have not much that listening to the result. At each 1/T it was necessary to send NxL elements of information, which gives the final rate. This way is disappointed because you need much more information that you can transmit through a 500 Hz channel (for example: 23 carriers, 128 levels and T=40 ms). With 23 carriers, 8 levels and T=40 ms (which can be send through a 500 Hz channel), it is very difficult to understand a (French) speech. 73 Patrick - Original Message - From: cesco12342000 To: digitalradio@yahoogroups.com mailto:digitalradio%40yahoogroups.com Sent: Friday, November 16, 2007 4:26 PM Subject: [digitalradio] Re: digital voice within 100 Hz bandwidth I would be plased to have a complete list of the phonemes and corresponding audio files from different speakers. I fear 44 phonemes will not be enough to do a context-free analisis. The data rate will be closer to 200pbs i think, since you will have to transfer a magnitude component along with the phoneme index, and maybe also a pitch component. Think of the pitch raise in a question, this feature is important for understanding. The main problem will be the fft to phoneme table correlation i think ... but to work on this there must be a phoneme table first.
[digitalradio] Re: digital voice within 100 Hz bandwidth
Very low bitrate algorithms exist now. There are a few that operate from 200 bps to 600 bps. The Navy has software called IVOX that gets in this range. Can you somehow lay hands on such a 200 to 600 bps codec? Im VERY intrested. The IVOX thing is based on 2400 bps lpc. With silence detection they bring it down to 1200bps average. Thats not the 200 to 600 bps codec.
[digitalradio] Re: digital voice within 100 Hz bandwidth
My problem is that if I can't find someone to help me get started, the project will die with my tow papers. Miken6ief
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
Cesco, RR for all At each 1/T it was necessary to send NxL elements of information, which gives the final rate. This corresponds to your calculation: 23 * 3 bit = 69 bit per 40ms. 69*25=1725 bps. More than enough for the 1400bps codec. I can help you with this codec if needed. Yes 1725 bps is much compared to 1400 or the IVOX system and with 1725 bps I have no good results. When you speak of a codec, do you mean a method or a DLL? Any Internet link or information is welcome. For about the transmission, I expected to use a sort of Throbx transmission but with 20 carriers separated by 25 Hz, without any coding. 73 Patrick - Original Message - From: cesco12342000 To: digitalradio@yahoogroups.com Sent: Saturday, November 17, 2007 1:11 AM Subject: [digitalradio] Re: digital voice within 100 Hz bandwidth Hi Patrick, At each 1/T it was necessary to send NxL elements of information, which gives the final rate. Im not shure i understand your method 100%. My own tests found that you can transfer comprehensible, but unvoiced speech with 10 carriers. But i did not restrict number of levels. For voiced (natural sounding) speech the addition of a pitch-carrier is necessary. I did those tests with ideas and help from G3PLX. But this might not be the easiest way. The EZ way would be to use an existing 1400bps codec, and squeeze the 1400bps into a 500hz wide multi- carrier qam-16 or psk-16 (4 bits per symbol) modulation. The codec produces 54 bits per 40ms. 54 / 4 = 14 carriers. 40ms = 25 baud, proposed carrier spacing 37.5 hz, BW = 37.5 * 14 = 525 hz. 500hz BW should be possible with a little tweaking. With 23 carriers, 8 levels and T=40 ms (which can be send through a 500 Hz channel), it is very difficult to understand a (French) speech. 23 * 8 bit = 69 bit per 40ms. 69*25=1725 bps. More than enough for the 1400bps codec. I can help you with this codec if needed. 73, Cesco
Re: [digitalradio] Re: digital voice within 100 Hz bandwidth
One thing to try might be an encoding that takes more time to send than the audio it encodes. If blank space compression is used, the effect can be reduced. But there is nothing that says the encoding must be able to transmit voice in 100% of real time to be interesting or useful. 73, Leigh/WA5ZNU
[digitalradio] Re: digital voice within 100 Hz bandwidth
I did send you a PM.
Re: [digitalradio] Re: A challenge to RTTY operators!
Rick wrote: I have to concur with Jose on this. I was a very active HF and VHF digital ham starting around 1981 with a homebrew XR2206/XR2211 TU that was from QST magazine and called The State of the Art TU. It most assuredly was not, but being naive and new to RTTY found it to be a very poor performer. It was actually only detecting one of the tones with the tone decoder! My good friend CO2KG, by his own words, was fooled to build it, and he told me that it actually was WORSE than Hamcom itself. This was before computers became popular and I was interfacing with a Model 15 TTY and a homebrew loop circuit. I was able to borrow an huge tube ST-6 design TU and that was much better. Then computers started to be available at more affordable prices and I moved to the Commodore 64 and a ROM based software package. Later I had the Kantronics UTU, and eventually an AEA CP-1 using the BMKMulty DOS software. This was before it could do Pactor, but the program already cost $100 for basic RTTY/AMTOR and then you had to buy the CP-1 or some kind of interface to key the rig. BMKMulty eventually had a Pactor upgrade for I think another $100, but I have heard it was not that good. In fact, none of the third party hardware for Pactor was as good as the SCS modems, probably because they did not duplicate the memory ARQ. My modem, which never got a case, was quite elaborate (had quite a few parts) and I looked for performance more than any other criteria. It was a mixture of an AN93 and a KAM, depending on the available parts and my own choices. Its post-demodulator low pass filter meant a lot for its performance. I finally settled for 150 Hz as a compromise for RTTY and packet. It actually worked better than my KPC-2 with its AM7910 on receive. I used two bandpass active filters tuned at 2000 / 2200 Hz, with full wave AM detectors, which left very little residual carrier and gave very clean data waveforms. It worked well with Hamcom / Mix / TERMAN93 and BPQ/BPQAX25. Terman93 allowed me to work Pactor at 100 baud quite well after I tweaked my old 386 dot clock to exactly 14.318 MHz (it had a cheapo oscillator that actually was working on 14312 before) to be within the permissible speed error range. Of course, it did not have memory ARQ nor automatic upwards speed switch to 200 baud. I discovered the difference later, when I got my PTC-II. After that, I lost momentumno wonder The post demodulator LPF made copiable signals that the AM7910 could not copy, being open as a barn door as a compromise between 300 and 1200 baud operation. The FSK modulator used a marine band crystal I had at hand, a chain of 4029's as programmable counters and a 4018 with a resistor network to generate a syntethic sinewave after a low pass filter. Mark/space tones were toggled from a serial port line using a 4049 as RS-232 interface. It was a quite instructive hands on experience. Way before that, I wrote my own CW/RTTY program for the C64 using compiled BASIC and the KPC-2 as dumb modem. Compiled BASIC made possible to transmit very clean morse at 50 WPM without having to program in 6510 assembler. 73, Jose, CO2JA __ Participe en Universidad 2008. 11 al 15 de febrero del 2008. Palacio de las Convenciones, Ciudad de la Habana, Cuba http://www.universidad2008.cu
