[aprssig] TNC vs AGWPE
Phillip B. Pacier ad6nh at arrl.netTue Apr 18 16:21:30 UTC 2006
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http://www.aprsca.net/phg.html 73 Phil - AD6NH scott at opentrac.org wrote: > Speaking of the wiki, is there anything there yet on PHGR? Someone on the > OpenTracker list brought up the fact that it's hard to find proper > documentation. A link to an online calculator would be good, too. > > Scott > N1VG > > >> -----Original Message----- >> From: aprssig-bounces at lists.tapr.org >> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Chris Howard >> Sent: Tuesday, April 18, 2006 9:07 AM >> To: TAPR APRS Mailing List >> Subject: Re: [aprssig] TNC vs AGWPE >> >> I think this post would be a very good addition to the aprs wiki! >> Steve, if you don't mind, can I put it up there? >> Or if you would do it, even better. >> >> We've got a page about agwpe that needs filled out >> and another about soundcard as tnc. >> >> Chris >> w0ep >> >> >> >> On Tue, 2006-04-18 at 09:42, Stephen H. Smith wrote: >> >>> kc5zrq at gmail.com wrote: >>> >>>> Don't use the "9600" out. As far as I know, the ISS uses >>>> >> 1200 baud. >> >>> 1) The so-called "9600 out" is not a data output. It's >>> >> actually >> >>> non-squelched non-de-emhasized AUDIO out, directly from >>> >> the receiver's >> >>> FM discriminator. (This is the kind of audio connection >>> >> you MUST HAVE >> >>> for connecting external TNCs running at 9600 baud, although >>> >> it is also >> >>> usable for TNCs running at 1200.) >>> >>> The "9600" output is usually about 50millivolts which will >>> >> overload the >> >>> typical PC "mic input" and cause severe distortion unless >>> >> you use about >> >>> a 5:1 or 10:1 attenuator pad. >>> >>> Further, many PC mic input jacks have 3-5 volts DC on them to power >>> active electret external mics. The proper way to couple >>> >> the radio's >> >>> audio into the PC is to first use a 1:1 turns ratio audio >>> >> transformer in >> >>> order to avoid a common ground between the radio and the >>> >> computer. (The >> >>> typical 600:600 ohm transformer used in telephone devices >>> >> like modems, >> >>> answering machines, etc. is ideal). The secondary side of the >>> transformer should be connected across a voltage divider >>> >> network of two >> >>> resistors in series. The one closer to ground should be >>> >> around 1K while >> >>> the upper one typically will be somewhere between 4.7K and 10K. >>> Finally connect the center point of the two resistors, to >>> >> the PC audio >> >>> input using something like a .1 to .5 uF series capacitor >>> >> to block any >> >>> DC that may be present on the mic input. >>> >>> Note that the PC mic input is SINGLE CHANNEL even though it uses a >>> stereo TIP-RING-SLEEVE (3-conductor) mini-plug. Normally the TIP >>> carries +5 VDC power WHILE the ring carries AUDIO. The >>> >> ring may or may >> >>> not also have 3-5 VDC on it for use with mics that carry DC >>> >> and audio on >> >>> the same conductor. >>> >>> >>> >>> >>> 2) Once you have your audio network in place, click the >>> >> AGW icon in >> >>> the system tray and choose "Soundcard Tuning Aid". One the >>> >> resulting >> >>> screen, click the radio button for " Oscilloscope Sine >>> >> Wave". Watch >> >>> the display as packet bursts come in. You should see a >>> >> clean sinewave >> >>> display here. Use the Windows RECORD mixer (not the >>> >> default PLAYBACK >> >>> mixer that you get initially when you click the speaker icon in the >>> tray) to adjust the audio level for a clean sine wave. >>> >> Note that you >> >>> will see white-noise random grass between bursts since this is >>> non-squelched audio. It's perfectly normal for this noise >>> >> to clip on >> >>> peaks. The goal is that the sine wave DURING packet >>> >> bursts be smooth >> >>> and rounded with no flat topping. >>> >>> Note that the options in the Windows mixer for the mic >>> >> input channel on >> >>> many sound cards includes a checkbox for a "+20 dB Mic >>> >> Booster". This is >> >>> for the benefit of low-output non-amplified mics (i.e. >>> >> passive dynamic >> >>> mics) instead of electret ones. You definitely want this >>> >> box UNCHECKED. >> >>> >>> >>> 3) Most modern PCs, both laptop and desktop no longer >>> >> have dedicated >> >>> sound card hardware in them. The built-in "AC97 Compatible" sound >>> systems are basically an A-D converter and nothing else. >>> >> The "heavy >> >>> lifting" precisely-timed sampling and processing of sound >>> >> that was >> >>> traditionally done by a dedicated processor, RAM and >>> >> accurate clock on >> >>> the sound card is now done by the main CPU of the computer. >>> >>> >>> The CPU clock usually isn't as accurate as the one on a >>> >> sound card. >> >>> Further, the CPU is sharing it's available pool of clock >>> >> cycles between >> >>> a varying number of other processes with varying interrupt response >>> times (latencies). The result is that the sampling rate is >>> >> frequently >> >>> far off of the desired 11,025 or 8,000 samples/sec that >>> >> ham soundcard >> >>> apps expect. Further IT VARIES depending on how many >>> >> other programs >> >>> are running at the same time! There are several >>> >> utilities that will >> >>> measure the actual sampling rate of the sound card. >>> >>> >>> Unfortunately, unlike some ham sound card programs such as >>> >> mmSSTV and >> >>> MixW, AGW has no provision for entering corrections for the >>> >> sampling >> >>> rate errors. If the sample rate is severely off, your >>> >> only recourse >> >>> is to try a different sound card -- in the case of a >>> >> laptop this will >> >>> mean either a PCMCIA -card based sound system, or an external >>> USB-connected one. >>> >>> >>> Ironically, the older Pentium I and Pentium II laptops >>> >> often had far >> >>> superior sound systems based on dedicated Soundblaster, >>> >> ESS, or Crystal >> >>> Audio chip sets just like add-on PCI-card sound systems in >>> >> desk top >> >>> PCs. Today's hotrod P4 or Centrino laptops usually have the >>> far-inferior "brain-dead" host-based AC97 sound systems. But AC97 >>> systems reduce parts count, power consumption and are CHEAP >>> >> CHEAP. I >> >>> have a couple of 10-year-old Dell 3000 Pentium I 200MHz >>> >> MMX - based >> >>> laptops that I keep around exclusively for ham soundcard >>> >> operating with >> >>> mmSSTV, AGW, MixW and Echolink precisely because their >>> >> sound systems are >> >>> superior to my newer machines. Further these "classic" >>> >> machines have >> >>> the audio LINE input in addition to the MIC input which is >>> >> far superior >> >>> for ham sound card applications. With AGW, the true stereo line >>> input actually allows you to create a DUAL-PORT tnc similar to a >>> Kantronics KAM or 9624, with one radio connected to the >>> >> left channel and >> >>> a second radio on the right channel. >>> >>> >>> >>> >>> >>> >>> >>> Stephen H. Smith wa8lmf (at) aol.com >>> EchoLink Node: 14400 [Think bottom of the 2M band] >>> Home Page: http://wa8lmf.com >>> >>> >>> NEW! JavAPRS Filter Port 14580 Guide >>> http://webs.lanset.com/wa8lmf/aprs/JAVaprsFilters.htm >>> >>> UI-View Misc Notes and FAQ >>> http://webs.lanset.com/wa8lmf/aprs/UIview_Notes.htm >>> >>> "APRS 101" Explanation of APRS Path Selection & Digipeating >>> http://webs.lanset.com/wa8lmf/DigiPaths >>> >>> Updated "Rev G" APRS http://webs.lanset.com/wa8lmf/aprs >>> Symbols Set for UI-View, >>> UIpoint and APRSplus: >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> _______________________________________________ >>> aprssig mailing list >>> aprssig at lists.tapr.org >>> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig >>> >> _______________________________________________ >> aprssig mailing list >> aprssig at lists.tapr.org >> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig >> >> >> > > > > > _______________________________________________ > aprssig mailing list > aprssig at lists.tapr.org > https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig > > >
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