Thursday, December 02, 2010

APRS TNC

WB8WGA APRS TNC was a project waiting for the the 16F88 pic programing. Now that it's done I decided to test it using the TH-F7 audio output.
Some frames got decoded but not even 10 %, so it looks like that it has a worst performance than my previous APRS decoder with the 16F628 PIC (http://speakyssb.blogspot.com/search/label/PIC%20based%20packet%20decoder). From what i've seen the audio level must be set very well or else it has some difficulty decoding the frames (same on the 16F628 project).
Other ham's report better success than mine on their's project page, anyhow an absolute test will only be made when the VHF transceiver module is programed with the local APRS frequency.

Here's the external link to the schematic I used.


From here: http://www.kh-gps.de/minitnc.htm

And here fully assembled:


Remember TXD and RXD are reversed if you'r not using the GPS input but an RS232 for computer access to the terminal.

My configuration for the quick receiving test was just:

mycal CT2GQV (that's my call...)
mon all (monitor all the frames)
perm (to save configuration)

* use "help" at the prompt for full command list.

Computer terminal was set for 9600 8N1 no hardware or software flow control.

4 comments:

Julian said...

I don't know if yours is worse than it should be but I think the PIC based decoders are not very sensitive. For better results you need to use an MX614 modem chip.

Ricardo - CT2GQV said...

Hello Julian,
I considered that possibility but can't find locally the MX614 and for the price of one I built the PIC circuit...well, you get what you paid! :)

Anonymous said...

Hi Ricardo,

After a few months testing the wb8wga pic tnc I was able to increase its sensitivity by adding a band pass filter (between 1200Hz and 2200Hz) at the audio input.
I found that most of the problems were caused by low frequency noise from my radio, well below the 1200Hz.

73 de Joao CT2GYH

Ricardo - CT2GQV said...

Viva João,

Obrigado pela informação, vou ver se arranjo espaço para um filtro!

73 de Ricardo, CT2GQV