Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-db04.r1000.mx.aol.com (Internet Inbound) with ESMTP id 5505638000084; Sun, 6 May 2012 14:27:10 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1SR69Z-0008BX-AY for rs_out_1@blacksheep.org; Sun, 06 May 2012 19:25:53 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1SR69Y-0008BO-KQ for rsgb_lf_group@blacksheep.org; Sun, 06 May 2012 19:25:52 +0100 Received: from smtpout2.wanadoo.co.uk ([80.12.242.42] helo=smtpout.wanadoo.co.uk) by relay1.thorcom.net with esmtp (Exim 4.77) (envelope-from ) id 1SR69W-00025L-2J for rsgb_lf_group@blacksheep.org; Sun, 06 May 2012 19:25:51 +0100 Received: from AGB ([2.26.47.14]) by mwinf5d17 with ME id 6iRl1j00L0JMiBE03iRmtn; Sun, 06 May 2012 20:25:48 +0200 Message-ID: From: "Graham" To: References: <4F97E9C2.9030000@iup.uni-heidelberg.de><7B23411450514A5CB804E6D2C65A1876@JimPC><006601cd2ba5$30f197b0$0401a8c0@xphd97xgq27nyf> In-Reply-To: Date: Sun, 6 May 2012 19:25:45 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 X-Antivirus: avast! 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[...] Content analysis details: (0.2 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [80.12.242.42 listed in list.dnswl.org] 0.2 STOX_REPLY_TYPE STOX_REPLY_TYPE X-Scan-Signature: ad9c0e3658f56f4dbb01cd425a6a8031 Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ? 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G :) -------------------------------------------------- From: "Andy Talbot" Sent: Sunday, May 06, 2012 6:04 PM To: Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ? > Watchiing QRSS on a screen doesn't give the 4 - 7dB of gain you get > with the error correction inherent with weak signal data modes - when > comparing signalling with the same symbol rate. If you have to > repeat a CW message several times that slows down the rate (and adds a > sort of erro rcorrection). Always compare like with like > > QRSS and normal CW (at least in the hands of an old timer who knows > how to decode it) needs greater that at least 10dB S/N in its symbol > bandwidth. WSPR/FSK/Opera or whatever using non-coherent power > detection with error correction can usually manage 3 - 4dB in the > symbol bandwidth. > > Of course,QRSS at the moment offers the narrowest bandwidths of any > mode, the new OP4H with 60s symbols is only 16.7mHz compared with the > 4.5mHz and 500uHz being talked about on VLF. > > Assuming the radio link can support an arbitrarily narrow bandwidth > then you can always get better and better results by going narrower > and narrower, and slowing down your transmission rate. But the > Bits/second/Hz figure of merit will always remain constant.for a given > mode at an arbitrarliy adequate error rate. For CW/QRSS it will be > around 10 - 15dB for 1 Bit/second/Hz depending on opeator experience. > > And eventually ther ewill come a point where the RF link cannot > support signalling any slower. Has anyone actually stopped and > thought what the slowest data rate at 9kHz might be? Diurnal shifts > in the ionospheric waveguide height limiting you to one bit per 12 > hours perhaps ?? Discuss ..... > > To put the figures into real values, consider fast normal CW. A good > op has ears which filter t something like 20 - 50Hz bandwidth. 30WPM > (I'lll bet Mal can do that, another ex marine radio op I knew could > :-) is about 24Hz dot rate, so its in the region of 1Bit/s/Hz. And > 10db S/N in 24Hz is a pretty weak CW signal. I detect hear a tone at > that S/N quite easily, but doubt I would be able to decode CW at any > speed at it. > > BUT.... The same data rate, 24 Bits/s in 24Hz bandwidth ON off or > FSK will be decoded perfectly at 5dB S/N with proper error correction > built in. > > Incidently, 5dB at 1B/s/Hz corresponds to -29dB S/N using the > reference 2.5kHz that seems to have been adopted universally now. > Scale this magic figure to your symbol bandidth to see what S/N > 'ought' to be possible at any version speed of OP. WSPR / JTxx > > Andy > G4JNT > > > On 6 May 2012 17:26, mal hamilton wrote: >> Andy >> All these complications to accommodate the Appliance Operator who cannot >> read MORSE or watch QRSS on a screen. >> g3kev >> >> ----- Original Message ----- >> From: "Andy Talbot" >> To: >> Sent: Sunday, May 06, 2012 4:14 PM >> Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ? >> >> >> The problem with USB slippage comes about because of the Isochronos >> mode (yes, that is spelt correctly, it is not IsoSYNchronous) - >> where it sends puts real time rapid data transfer as more important >> than lost samples and sends samples in real time without checking >> This is probably just what music and audio people want, but it screws >> up using USB based sound cards as precision timed A/D converters. >> USB does have other modes with full error checking, albeit with some >> latency, but the latency wouldn't matter here. >> >> While it would be a pretty simple task these days to build an external >> A/D converter and interface to USB properly, the resulting data stream >> would need a custom driver written, then all the decoding software we >> know and love would have to be modified to work with this custom >> interface. Then someone else would come along with another design >> and we'd have to start again. >> >> I suspect it is going to be absolutely impossible to use the soundcard >> as a guaranteed glitch free A/D converter. >> >> Joe Taylor K1JT in the WSJT suite has a dead simple pragmatic >> solution. Instead of trying to read the data in real time, all the >> WSJT modes read the entire transmisisons' worth of data to a .WAV >> file, and the software works on that. While WSJT uses the soundcard >> to do the job it will suffer from the same slippages (which don't >> matter' of course' for those modes) the idea of an intermediate buffer >> file would help. >> >> A custom A/D could send its data in its own format via USB, or serial >> COM port or whatever, to software that saves blocks in the format of a >> .WAV file. Then the decoding software works on the resulting .WAV >> files. It won't be real time any more, but none of these slow data >> modes actually are that real time. The speed of reading and switching >> (using a pair of ping-pong files if necessary) can make the whole >> system pseudo real time - in the same way as WSJT appears to run >> continuously. >> >> Now, any A/D design can be used provided the results are written to a >> .WAV file. Wav files can have any sample rate (so long as it is an >> integer number of Hz) and do not have to be restricted to 48000, 11025 >> or whatever, so custom LF receivers using quite slow A/D converters >> and low sample rates are now valid. >> >> Just throwing that idea into the ring.. >> >> Andy >> www.g4jnt.com >> >> >> On 6 May 2012 16:14, James Moritz wrote: >>> Dear Andy, LF Group, >>> >>> A bit late, but never mind... >>> >>>> Has anyone tried using an external USB soundcard with a separate >>>> locked clock? Most work from a 12MHz crystal which can be replaces >>>> with a GPS locked source without too much effort. But I can't help >>>> wondering if there will be subsequent USB synchronisation glitches >>>> upsetting the input sampling. >>> >>> >>> >>> I can confirm that glitches do occur with USB sound cards. I have found >> this >>> to be a perennial problem trying to use such a sound card with the >>> laptops >> I >>> have available. For 9kHz reception, the relatively rapid temperature >>> fluctuations inside the laptop, and resulting cyclic drift of the >>> internal >>> soundcard sampling frequency interfere with the operation of DL4YHF's >>> ingenious sample rate correction facility in SpecLab, making the >>> internal >>> sound card unusable for FFT resolution below a few millihertz. I found >>> my >>> USB soundcard solved this particular problem quite well, but introduced >>> glitches that made achieving FFT resolution in the uHz range >>> impractical. >>> >>> Watching Speclab's sample rate correction "history" window, the USB card >>> sample rate typically starts off a few hundred ppm low (much larger than >> the >>> actual clock frequency error), but remaining stable to within a few ppm, >> but >>> then at unpredictable intervals abrupt jumps in sample rate of a similar >>> order of magnitude occur, with corresponding "blips" on the spectrogram >>> traces. The reported sample rate is always lower than the nominal value, >>> suggesting that some samples are being periodically discarded somehow. >>> >>> The sound card uses a single-chip integrated audio codec and USB >>> transceiver, using a single 12MHz crystal. I can't really believe in >>> "USB >>> slippage" in the hardware - surely losing some of the data would either >>> be >>> handled quietly by the USB error checking, or result in endless error >>> messages. The same sound card seems to work in a glitch-free way when >>> plugged into my desktop machine, where the reported sample rate error is >> in >>> line with the error in the crystal frequency. >>> >>> Cheers, Jim Moritz >>> 73 de M0BMU >>> >> >> >> >