[aprssig] Dirty signals vs. hardware TNCs

spam8mybrain spam8mybrain at yahoo.com
Thu May 12 10:07:54 CDT 2016


I know. The question in this case is "do we want to use a super decoder to make the offending stations _think_ they are clean by retransmitting their dirty signal cleanly?"

-------- Original message --------
From: david vanhorn via aprssig <aprssig at tapr.org> 
Date: 05/11/2016  10:09 PM  (GMT-05:00) 
To: wb2osz at comcast.net, TAPR APRS Mailing List <aprssig at tapr.org> 
Subject: Re: [aprssig] Dirty signals vs. hardware TNCs 

"do we use hardware TNCs that will reject their signals as QRM and keep them from propagating?"

You do know that the digi does not copy the distortion, right?  It creates a new packet and the quality is the same as any other packet it puts out.  

On Wed, May 11, 2016 at 8:07 PM, John Langner via aprssig <aprssig at tapr.org> wrote:




Suggested reading on the subject.





Sometimes it's a little mystifying why an APRS / AX.25 Packet TNC will decode some signals and not others. A weak signal, buried in static, might be fine while a nice strong clean sounding signal is not decoded. Here we will take a brief look at what could cause this perplexing situation and a couple things that can be done about it.



https://github.com/wb2osz/direwolf/raw/master/doc/A-Better-APRS-Packet-Demodulator-Part-1-1200-baud.pdf







Here, we take a closer look at some of the frames on the TNC Test CD in hopes of gaining some insights into why some are easily decoded and others are more difficult. There are a lot of ugly signals out there. Many can be improved by decreasing the transmit volume. Others are just plain weird and you have to wonder how they are being generated.



https://github.com/wb2osz/direwolf/raw/master/doc/A-Closer-Look-at-the-WA8LMF-TNC-Test-CD.pdf

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