[aprssig] TNC vs AGWPE
scott at opentrac.org
scott at opentrac.org
Tue Apr 18 12:13:31 EDT 2006
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
>
>
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