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[aprssig] TNC vs AGWPE

Phillip B. Pacier ad6nh at arrl.net
Tue Apr 18 16:21:30 UTC 2006


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
>>>       
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>>
>>     
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