[aprssig] TNC vs AGWPE
Phillip B. Pacier
ad6nh at arrl.net
Tue Apr 18 12:21:30 EDT 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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