#1 2015-08-27 21:40:30

IW3IJQ
Member
Registered: 2015-07-27
Posts: 13

De-emphasized signal poor decoding

Hello,

I'm testing Micromodem circuit (MicroAPRS FW)using TNC test CD (http://wa8lmf.net/TNCtest/).

On track 1, 3 and 4 (non-de-emphasized audio) modem has a good packet deconding rate.
On track 2 (de-emphasized audio) modem does't decode any packet.

Are possibles some improvements? Better if software improvements....

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#2 2015-09-20 07:03:27

Stanley
Member
From: Kuala Lumpur, Malaysia
Registered: 2014-12-01
Posts: 65
Website

Re: De-emphasized signal poor decoding

A quick questions, what are non-de-emphasized and de-emphasized for ??


Stanley
9W2SVT/ N5SVT
http://9W2SVT.blogspot.com

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#3 2015-09-20 10:03:33

IW3IJQ
Member
Registered: 2015-07-27
Posts: 13

Re: De-emphasized signal poor decoding

Have a look here http://www.febo.com/packet/layer-one/transmit.html here http://wa8lmf.net/TNCtest/ and here https://en.m.wikipedia.org/wiki/Emphasi … nications)

Quick response : a signal without de-emphasis has high tone and Low Tone at the same level. A signal with de-emphasis has high tone at Lowe level than high tone (if trasmitted signal has not pre-emphasis applied )

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#4 2015-09-24 18:48:01

N2KIQ
Member
Registered: 2015-09-24
Posts: 6

Re: De-emphasized signal poor decoding

Stanley wrote:

A quick questions, what are non-de-emphasized and de-emphasized for ??

A related answer, though strictly not to your question.  What I understand is that de-emphazised audio is what a "normal" ham radio sends out the speaker for human consumption.  Non-de-emphasized audio is better for data processing because there is less filtering involved.  If you have a dedicated data radio, I suspect that the "emphasis" circuit is missing on the transmit side as well, so no de-emphasis is required.

If you have a din "data" connector on your radio, the "9600 baud" output pin is non-de-emphasized and the "1200 baud" output pin is de-emphasized. This was done because "9600 baud" packet has a much wider audio spread than 1200 baud. 1200 baud was designed to stay well within the normal voice audio band.

Though I'm coming off several days of little sleep, so this all could be rubbish.  smile

'73
-Paul

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#5 2016-01-19 01:06:08

IW3IJQ
Member
Registered: 2015-07-27
Posts: 13

Re: De-emphasized signal poor decoding

Hi to all!!!

I'm still thinking to a way to improve decoding... I found "Dire Wolf" (https://github.com/wb2osz/direwolf).
Here the demodulator: https://github.com/wb2osz/direwolf/blob … mod_afsk.c
Here HDLC decoder with error recovering: https://github.com/wb2osz/direwolf/blob … dlc_rec2.c

Maybe some parts of code could be ported....

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