[aprssig] TNC vs AGWPE

[scott at opentrac.org]

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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