From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ranch Subject: Re: 300bps Packet (and EHAS) - what is pam, psk, and newpsk, Date: Sat, 27 Nov 2010 09:30:38 -0800 Message-ID: <4CF1403E.5080303@trinnet.net> References: <4CEB5074.2070008@complete.org> <4CEB5C66.1050803@exemail.com.au> <6CE4D96A7B544D30919A49105B458915@LIVINGROOM> <4CEC16EF.8060106@radagast.org> <4CED5B60.5040108@radagast.org> <40C75B79D58C4ECDBC044010559CE8CA@LIVINGROOM> <4CEEB394.3020305@trinnet.net> <4CEF444F.6010308@trinnet.net> <4CEF5A70.4050600@radagast.org> <4CF0040D.3000303@trinnet.net> <4CF03057.7080402@sral.fi> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4CF03057.7080402@sral.fi> Sender: linux-hams-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="windows-1252"; format="flowed" To: Tomi Manninen , linux-hams@vger.kernel.org Hello Tomi, > You have used the "AFSK" input to do something that the Yeasu > manual describes as "AFSK based data modes". The manual seems to > happily use terms that are at the very least confusing, even > downright wrong if you ask me... Oh yes, and a lot of documentation out there online and in the books ha= s=20 lots of conflicting information.=20 > "=93Packet=94 operation also applies to SSB-based AFSK data modes, su= ch as=20 > PSK31, etc." -- yeah, right.. :) Well, on the FT-950, the dedicated button for RTTY is enables the FSK=20 inputs and also activates some specific narrow filters and processing. = =20 The PACKET button activates the AFSK inputs but also enables different=20 specific filters and processing. I do realize that Packet can be FSK=20 but it's not on this radio. > It is also important to realize that for example in the > G3UH case, the pulses are not rectangular, they are shaped. > This greatly affects the used bandwidth. You've mentioned a few times of how the G3UH does unique things such as= =20 scrambling and now waveform shaping. I'm going to have to look around=20 to see if I can find some documentation on all this that doesn't quickl= y=20 go into hardcore math. I've always loved the concept of signal=20 processing but I don't know if my brain can handle it. > >> I think most HAMs are in agreement that HF packet doesn't work well= =20 >> for various reasons. Since you mentioned "FM", I assume this mode i= s=20 >> not suitable for use with SSB on the HF bands? Any thoughts on its= =20 >> width of spectrum it uses, etc? > > Like I said, feeding PAM to an FM modulator results in (shaped) > FSK signals over the air and that is the ultimate goal in a > system like "G3RUH packet". > > Feeding this kind of PAM to an SSB modulator would result in > a completely different kind of modulation over the air. Of the > top of my head, I can't say what it would actually be but > most probably nothing useful. I'm quite sure it wouldn't > work at all as like Dave Platt said, this needs a very > low frequency response and the typical ham SSB modulator > cuts at around 300Hz in the low end. Ahhh... understood and from this thread, I never realized that a=20 souncard mode needs to be specifically designed for say SSB vs. FM. I=20 naively thought that the modulation would only impact the noise=20 immunity, spectrum used (and the resulting power) use, etc. The concep= t=20 that an digital waveform from a soundcard sent into a SSB vs FM=20 modulator and the results being very different is a foreign concept to=20 me. I'm going to have to read up on this... interesting! > >> 1) You mentioned a "DSP56002EVM"... is that a specific DSP chip and=20 >> this mode was then ported into Soundmodem running on X86?=20 > > Yes, the Motorola 56002 was a member of an old DSP chip family > and the DSP56002EVM was an evaluation kit with the dsp chip, > memories, codecs etc. > > Pawel wrote the original modem in assembler for the 56002 > and I ported it to C to be run on Linux. You know, I was optimizing my Linux packet system startup scripts=20 yesterday (=20 http://www.trinityos.com/HAM/CentosDigitalModes/usr/local/sbin/packetri= g.sh=20 ) and when playing around with the Linux AX.25 "kissparms" program, I=20 noticed that the man page states: -- -e FEC error correction level Sets the FEC error correction level in a DSP card=20 based modem (KISS parameter 8). Larger correction level means better noise resistance, but= =20 slower throughput on a good connection. This is an experimental feature found in a QPSK mode= m=20 for the Motorola DSP56001 based DSP4 and EVM cards only. -- Maybe this support is derived from some of the work you and Pawel did? > >> 3) This mode is interesting to me and I think I once saw it on the=20 >> air. If there are 15 carriers, how wide is each carrier, and what i= s=20 >> the spacing between them? What's the total consumed spectrum at say= =20 >> 2500? It seems that 300BAUD AFSK packet is a bit less than 400Hz. > > Carrier spacing is 125Hz at 2500 and thus occupied bandwidth > is about 15 * 125 Hz, ie. little less than 2 kHz. Right.. and what I expected you to say. That's a chunk of bandwidth an= d=20 I was hoping that if I was to lower the speed, maybe I could lower the=20 BW but it doesn't sound like the mode supports that approach. Again, m= y=20 goal would be to use a FEC-enabled mode for AX.25 that would give an=20 effective 300BAUD throughput. Even if I was to dig through your code,=20 hacked out a few carriers, I highly doubt the mode would find any real= =20 traction. It seems most hams have a general disdain for packet though = I=20 think it's fantastic (though slow). > The carrier frequencies, their spacing, the occupied bandwidth, the=20 > symbol rate all scale 1:1 with the "bps" setting. > > But like I said, don't do that. I really regret that I made > the soundmodem implementation so flexible. QSL and when I try this out (if I can find any other HAMs to maybe test= =20 this with), I'll keep this in mind. > Besides, you are now confusing Baud (ie. symbols per second) with > bits per second. They are not the same. At 2500 bps the newqpsk > modem runs at 83.333 Baud (symbols per second). Right, and I know better. Sorry. > However as to IP over AX.25 over newqpsk on HF. Been there, done that= , > it was fun. :) So, if that was been there, done that. What's fun for you now? Maybe= =20 data and CODEC2 over GMSK? Maybe WinMor? --David -- To unsubscribe from this list: send the line "unsubscribe linux-hams" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html