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[aprssig] Re: *** APRS TNC Test CD Now Available *** Updated Info

Stephen H. Smith wa8lmf2 at aol.com
Tue Oct 31 09:24:21 UTC 2006

dave at emv.co.uk wrote:
> The track numbering is a bit odd.  Track 1 is very short and blank,
> track two announces itself as "Track One" , track 3 announcement is
> "Track Two" and so on....
> The "De-emphasised" audio is "very" muffled, compared to what comes out
> of the rig speaker jacks hear in the UK.  I'm not aware of any US/EU
> differences in Ham FM radio charactersisics, but I suspect some TNC's
> will struggle with the "De-emphasised" tracks, where as they will work
> just fine with a real FM radio speaker jack feed.  I have a collection
> of TNC-220's, none have a problem with radio speaker feeds, so long as
> you load the radio with say a 10r resistor, and that's more like keeping
> the radio's speaker output chip bias point in the right place.
> The "Non de-emphasised" audio examples are as expected very "bright" to
> say the least.
I have added this to the TNCtest index page at:

just above the file download links.



The image file you download produces a _*MIXED MODE*_ disk that combines 
CD-ROM data and audio CD tracks.

    * _This is not a normal CD_ROM._
    * _This is not a normal audio CD.
    * It is a combination of the two.  When you place this disk in a
      computer CD drive, you will only see the CD-ROM data part of the
      disk.  _*The audio tracks will NOT show, and will NOT
      automatically start playing.*_

Go to the Windows Start menu and do Start -- Programs -- Accessories -- 
Entertainment, and select the "CD Player" applet.  You will get an 
on-screen display that looks like a car stereo CD player with start, 
stop and track select buttons and a volume control.  Use this software 
"device" to play the audio tracks.

In a non-computer audio player such as a boombox or DiskMan (or a CD-ROM 
drive being used stand-alone outside of a computer), the drive may 
mistakenly see the first (data) track as a defective unplayable audio 
track and do nothing. If so, use the track selector button to jump to 
the next (first actual audio) track.

The de-emphasis on track 2 sounds muddier than most radios because the 
de-emphasis in most radios doesn't conform to the official de-emphasis 
curve.  Many radios don't even begin to roll off until 1K or higher 
rather than starting at 300 Hz, in an effort to have "punchier" audio.  
The recording reflects "worse case" de-emphasis roll-off . 

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