[aprssig] 6 meter APRS

Stephen H. Smith wa8lmf2 at aol.com
Wed Aug 26 16:42:38 EDT 2009


Chris Moulding wrote:
> Thanks for your comments, Steve.
>
> My other main amateur radio interest beside APRS is the use of 
> digi-modes on 30m and I agree with
> your comments on symbol rates especially after using modes like OLIVIA 
> where you can have 100%
> copy on a signal you cannot hear.
>
>
>
> My motivation to design a PSK/QPSK TNC add-on program comes after 
> trying for months to get a
> 300 bd packet TNC design to work. It will decode a clean signal 
> perfectly but feed it with an off-air
> HF APRS signal with noise and signal corruption very few packets were 
> decoded. An alternative
> using PSK or QPSK would be far better for HF operation especially at 
> this stage of the sunspot cycle.
>
> 73s,
>
> Chris, G4HYG
>

I agree.  It's even worse with connected packet or APRS' kludge of "an 
ack in an unconnected packet" for APRS messages. 

I monitor 30M HF APRS here in southern California (Pasadena) 24/7 with 
the 300 baud HF side of a KAM TNC. The results are on my UIview 
webserver at:

    <http://wa8lmf.dyndns.org:14439>

Note that due to 1) My horribly high local noise level from a leaking 
digital cable TV trunk and 2) the current non-existent sun spot 
count,    it may be hours or days at a time before you see anything on 
the map.

I have watched a couple of stations, one in northern Cal (San Francisco 
Bay area) and one in Texas try to carry on a live chat using APRS 
messages numerous times.   Almost every time, each transmission goes 
through 4-10 retries, and the ack will go though 3-5 retries because 
either the message never gets to the other end, or the ack never gets 
back.   The net effect on the available bandwidth on 30M APRS in the 
western half of the US is disastrous. To add insult to injury, one of 
these stations tries to use ECHO,ECHO in their path so the endless 
retries wind up, in many cases, cluttering up the eastern US as well.

I've monitored the same thing with connected packet BBS systems on 20 
meters:  Every connect attempt retries at least 3-5 times, then every 
packet, and every ACK for every packet, during the conversation retries 
3-4-5 times. 


Don't know if you are aware of it , but years ago, G4IDE (author of 
UIview) also created a PSK31 plugin for UIview.  This "PSK31 Server" 
used the TCP/IP interface to UIview (i.e. emulated an Internet server -- 
any TCP/IP using application or Telnet client can also use it). 

I actually used it from my mobile successfully on 20 meters several 
times for coast-to-coast tracking.   This "PSK31 Server" app is used 
today by Propnet and is archived on their website.

------------------------------------------------------------------------

--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      WA8LMF  or 14400    [Think bottom of the 2M band]
Skype:        WA8LMF
Home Page:          http://wa8lmf.net

JavAPRS Filter Port 14580 Guide
  http://wa8lmf.net/aprs/JAVaprsFilters.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths

Updated "Rev H" APRS            http://wa8lmf.net/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:



. 




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