by the way, in the OT2m support area is still a schematic showing the wrong C2 value! http://www.argentdata.com/support/opentracker-ot2m-schematic.png which adds to the confusion.. 73 Mike
----- Original Message ----- From: Scott Miller To: [email protected] Sent: Wednesday, September 16, 2009 3:33 AM Subject: Re: [tracker2] Tracker2/Display & poor decoding Hi Mike, All of the component selection was done per the NJM2211 datasheet. Scott Mike Zwingl oe3mzc wrote: > > > Scott, > is there a reason for the design of R23 and C19 for this large bandwith > (1100Hz) > instead of R23..68k and C19 4,7nF (abt. 500Hz) ? > also C17 is a bit small?? > I realise several differences compared to the often used "standard > design of XR2211 fsk modem for 1200baud", > but assume you had some good reason for. > also see: > > http://www.febo.com/packet/layer-one/receive.html > <http://www.febo.com/packet/layer-one/receive.html> > > ---snip-- > a.. PLL demodulators (like the XR2211 used in the TNC-2 and many clones) > work, in a grossly simplified fashion, using the product of the amplitude > and the sine of the input frequency. This means that if the low tone has a > greater amplitude than the high tone, demodulator performance will suffer. > The problem is that if (Amplow*cos(Flow)) is nearly the same value as > (Amphigh*cos(Fhigh)), then the demodulator won't work very well. > This is why twisted audio causes problems. > > > a.. You need 20dB or more of signal to noise ratio to get a signal out of a > narrow-band FM receiver that can be decoded. Most modem implementations are > better than this value, so tweaking on the modem performance itself isn't a > rewarding experience. > > a.. The XR2211 demodulator can work with tones of only a few millivolts, > but > the internal noise level on most TNC boards is frighteningly high -- as > much > as several hundred millivolts peak-to-peak. The XR2211 can handle an input > level of many volts, so overdriving it isn't a problem. Therefore, it's > important to provide adequate drive -- ideally, a volt or so > peak-to-peak on > the low tone -- and to err on the side of overdrive, rather than underdrive. > --snip--- > but this should be taken care of by the input af filter of OT2m. > vy 73 de Mike > oe3mzc > > > ----- Original Message ----- > *From:* Scott Miller <mailto:[email protected]> > *To:* [email protected] <mailto:[email protected]> > *Sent:* Tuesday, September 15, 2009 6:10 AM > *Subject:* Re: [tracker2] Tracker2/Display & poor decoding > > > > How long ago did you get them? There's been a lot of discussion here > about RX performance variability, and the amount of testing they get > has > increased a lot in the last few months. > > Cleaning off any flux residue from around the 2211 chip is an easy > first > thing to try. > > Scott > > Kent Hufford wrote: > > > > > > I bought two OT2m's. I hooked one to a Yaesu FT-1900 in my shack and > > watched it try and decode packets. It is having a hard time. > > > > > > > > I also have a PK-232 on a IC-229H running UI-View 32 and it is > decoding > > fine at the same time. > > > > > > > > I thought I just am having a "learning" experience with the OT2m. Is > > there something I can do, or check to improve the decoding. We were > > going to put this combo in the southern part of the county to > give it > > better Digi coverage. But not yet. > > > > > > > > thanks, > > > > Kent > > > > KQ4KK > > > > > > > > *From:* [email protected] > <mailto:tracker2%40yahoogroups.com> [mailto:[email protected] > <mailto:tracker2%40yahoogroups.com>] *On > > Behalf Of *Mike Zwingl oe3mzc > > *Sent:* Sunday, September 13, 2009 11:55 AM > > *To:* [email protected] <mailto:tracker2%40yahoogroups.com> > > *Subject:* Re: [tracker2] Tracker2/Display & poor decoding > > > > > > > > > > > > Scott, > > > > I guess you are talking abt C13 and C17 ? > > > > > > > > When you replace them, do you see improved decoding? > > > > > > > > sorry for the hassel. > > > > vy 73 de Mike > > > > oe3mzc > > > > > > > > > > > > ----- Original Message ----- > > > > *From:* Scott Miller <mailto:[email protected] > <mailto:scott%40opentrac.org>> > > > > *To:* [email protected] > <mailto:tracker2%40yahoogroups.com> <mailto:[email protected] > <mailto:tracker2%40yahoogroups.com>> > > > > *Sent:* Sunday, September 13, 2009 4:42 AM > > > > *Subject:* Re: [tracker2] Tracker2/Display & poor decoding > > > > > > > > > > > > Hi Mike, > > > > I'm kind of fed up with the 2211 myself. I've been doing a lot more > > testing on the OT2ms before they ship these days, and a significant > > portion of them need to have the 0.027 uF capacitors replaced before > > they ship. I'm not sure the batch sent to the contract > manufacturer is > > really meeting specs. > > > > I haven't run into any that didn't get up to par with the capacitor > > replacement and a thorough cleaning of flux residue. Still, it's > a lot > > of hassle. I've got a few boards on the way to test a new MX614-based > > layout. When those come in (sometime late in the week) I'll start > doing > > some side by side comparisons. Assuming I can get my crashed > workbench > > PC up and running again. I already bought a replacement, but I can't > > run the software I need under Vista, and I can't get the machine to > > load > > XP Pro. > > > > Scott > > > > Mike Zwingl oe3mzc wrote: > > > > > > > > > Hi, > > > we have exactly the same problem and we are no newbies to packet > > radio > > > modems. > > > The XR2211 decoder should perform much better, than it sometimes > > does in > > > OT2m. > > > This modem chip is also used in some other tncs... > > > but I did not change it for an TCM3105 or similar in the OT2m -so > > far no > > > time to test this... > > > However we observe many OT2m units, that show POOR DECODE on > > 1200baud on > > > different radios and locations. > > > Some only decode less than one third of all heard packets..we > do not > > > know why... > > > However, we have also seen some OT2m units that do significantly > > better > > > than that, running same firmware. > > > We are also aware of the wrong capacitor in the audio filter > > circuit of > > > some OT2m serial No. batches, but even if we soldered the correct C > > > it is still showing very odd effects with poor decode and > digipeater > > > performance. > > > We would be glad to have some solution offered, since OT2m is > > starting > > > to get widely used in our national APRS network as an intelligent > > > digipeater > > > or replacing old tncs, that could not do the NEWn-n paradigm. > > > > > > hw? > > > vy 73 de Mike > > > oe3mzc > > > > > > > > > > > > ----- Original Message ----- > > > *From:* Mark Cheavens <mailto:[email protected] > <mailto:mcheavens%40usa.net> > > <mailto:mcheavens%40usa.net>> > > > *To:* [email protected] <mailto:tracker2%40yahoogroups.com> > > <mailto:tracker2%40yahoogroups.com> > <mailto:[email protected] <mailto:tracker2%40yahoogroups.com> > > <mailto:tracker2%40yahoogroups.com>> > > > *Sent:* Thursday, September 10, 2009 3:31 PM > > > *Subject:* Re: [tracker2] Tracker2/Display & decoding > > > > > > > > > > > > With the modem chip used it is rare that a "weak" or "noisy" signal > > > will get decoded. Is the audio "packet" 9600, 1200, or speaker > audio? > > > > > > With 1200 baud packet you need to have de-emphasized (sp?) audio to > > > the modem (TNC). Speaker audio DOES have de-emphasis, as should a > > > "1200" baud port of the radio. > > > > > > (FYI- 9600 had NO pre- or de- emphasis) > > > > > > Just because you can HEAR a packet, does not mean the TNC can > decode > > > it. The signal to noise radio need to have a LOT of signal, and > VERY > > > little noise. > > > > > > Mark > > > KC5EVE > > > > > > > > > At 01:02 AM 9/10/2009, you wrote: > > > > > >> > > >> > > >> Hi there, > > >> > > >> I've Tracker2 connected to a Nuvi350 and was wondering why > > >> sometime it > > >> took a while before I could see some of the callsigns get into the > > >> Favorite (after I did a delete all). So, I added an LCD display > > to my > > >> Tracker2 yesterday and found out that most of the time, Tracker2 > > >> couldn't decode the packets (i.e. not displayed on the LCD) > > >> especially > > >> the weak ones. Now I'm wondering what else I need to do .. > > Anyway, my > > >> setup is .. Kenwood TMV71A/Data/BandB <-> Tracker2 with LCD <-> > > Nuvi. > > >> I brewed my own cable between the TMV71A and the Tracker2.. > sending > > >> packet out does not seem to be a problem. Is there anything in the > > >> configuration that I need to do? > > >> > > >> TIA, > > >> Mohd/9W2TPT > > > > > > > > > > > >
