Decoding Problem

mattybe
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Decoding Problem

Postby mattybe » Mon Feb 03, 2014 9:13 pm

I've built a trackuino, but am having some trouble receiving packets. I drove close to a digipeater, and only about 10% of the packets were received. I get a bit worse results using an HTX-202 and qtmm (I'm using a mac).

Could anyone look at this audio on Google Drive and see if they can tell what's going on? Here's a couple screenshots from Audacity, but I'm not sure what it's supposed to look like to tell what's wrong.
clip_part1.jpg
clip_part2.jpg

Many thanks,
Matt
N1UGL
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EA5HAV
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Re: Decoding Problem

Postby EA5HAV » Sun Feb 09, 2014 8:05 pm

I looked at your mp3 capture.

The amplitude of the 2200 tones is much lower than that of the 1200 tones.

I emphasized the band around 2200 Hz in audacity (Effects -> Equalize):

n1ugl-1.png


And now both packets decode fine:

n1ugl-2.png


If you look at the spectrogram after equalization, the power is distributed more evenly between the two tones.

There is definitely some imbalance in the 1200/2200 tones caused by the HX1 filters, but it's usually not so bad that it prevents decoding. I guess some HX1 units behave different than others because you're not the first person I've seen with this problem.

There are a few solutions to this problem...

If you're going to use the tracker in a high altitude balloon, the signal will reach many receivers and chances are that one or another will decode the signal. Maybe the digi you're next to is especially picky about amplitude mismatch, but I understand this is kind of risky.

On your receiver there might be a setting to de-emphasize high tones, see if you have it and turn it off so that the 2200 tone doesn't suffer further attenuation.

The best option is to add a high-pass or a band-pass filter that attenuates the 1200 tone while keeping the 2200 intact. This has to be done carefully as the HX1 expects an input between 0 and 5v and a high pass filter would remove DC bias. This is something I haven't fully explored so I can't give you a proper / tested circuit (suggestions are welcome).

Also, are you using the -3 or the -10 version of the HX1? Some people claim the attenuation of the 2200 tone in the -10 is lower (ie. better) than that of the -3 unit.
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mattybe
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Re: Decoding Problem

Postby mattybe » Wed Feb 12, 2014 4:35 pm

Thank you for looking! I am using the -10 version.

I saw this recommendation for an earlier poster, but couldn't find those lines in the newest version of the code. Is it worth testing a software fix?
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Re: Decoding Problem

Postby EA5HAV » Wed Feb 12, 2014 5:35 pm

In afsk.cpp, around line 200, where it says:

Code: Select all

    uint8_t s = afsk_read_sample((phase >> 7) & (TABLE_SIZE - 1));
    afsk_output_sample(s);


Try this:

Code: Select all

    uint8_t s = afsk_read_sample((phase >> 7) & (TABLE_SIZE - 1));
    if (phase_delta == PHASE_DELTA_1200)
      s = s / 2 + 64;
    afsk_output_sample(s);


Would you please try to decode the signal resulting from that and post another mp3 with it?

Thank you!
Javi of trackuino
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Re: Decoding Problem

Postby mattybe » Wed Feb 12, 2014 7:13 pm

That helped! I'm now able to decode all the packets locally. I'm still not getting picked up by aprs.fi or the tracker app, but I may just be out of range of an iGate. Here's a sample packet. Should I tweak the code any further based on this?

Also, sorry about all the problems, but I plugged my GPS board in backwards after flashing, and now the led turns on but it doesn't seem to get a position lock =/ Does this debug look reasonable, or did I fry my GPS? Also possible that it's just refusing to get a lock indoors.

Code: Select all

.0,0.0*30 (OK!) 60070
$GPRMC,120108.000,V,0000.0000,N,00000.0000,E,000.0,000.0,280606,,,N*76 (OK!) 60157
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 60212
$GPG000.0000,N00,E,000.0,000.0,280606,,,N*7B
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 60313
$GPGGA,120207.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*6B (OK!) 60990
$GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30 (OK!) 61043
$GPRMC,120207.000,V,0000.0000,N,00000.0000,E,000.0,000.0,280606,,,N*7A (OK!) 61131
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 61185
$GPGGA,120208.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*64 (OK!) 61990
$GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30 (OK!) 62043
$GPRM
[62060] N1UGL-11>APRS,WIDE2-1:/000000h0000.00N/00000.00EO000/000/A=000000/Ti=70/Te=196/V=4122 HAB testing
t(fast,avg,slow)=129,161,381; pos=64/1169; sam=11; overruns/isr=62/60789
C,120208.000,V,0000.0000,N,00000.0000,E,000.0,000.0,280606,,,N*75 (OK!) 120129
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 120183
$GPGGA,120209.000,000.0,000.0,280606,,,N*7A
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 120286
$GPGGA,120307.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*6A (OK!) 120960
$GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30 (OK!) 121014
$GPRMC,120307.000,V,0000.0000,N,00000.0000,E,000.0,000.0,280606,,,N*7B (OK!) 121102
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02 (OK!) 121157
$GPGGA,120308.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*65 (OK!) 121960
$GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30 (OK!) 122013
$GPRMC,120308.000,V,0000.0000,N,0
[122060] N1UGL-11>APRS,WIDE2-1:/000000h0000.00N/00000.00EO000/000/A=000000/Ti=70/Te=196/V=4122 HAB testing
t(fast,avg,slow)=129,161,383; pos=24/1169; sam=8; overruns/isr=92/60789
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Re: Decoding Problem

Postby EA5HAV » Wed Feb 12, 2014 8:16 pm

Great! The tones look about equal now... I can't see you on aprs.fi either, you might be far from an igate, like you said. If you drive near the same digipeater the pickup rate shoud get somewhat better... Let me know.

The GPS output looks like it doesn't have any reception. In the GPGGA sentence, the 7th field (not counting $GPGGA) is the number of satellites in view and yours says "00".
Javi of trackuino
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Re: Decoding Problem

Postby Atif » Sat Mar 14, 2015 7:49 am

We have done five balloon launches since February 2010...We even managed to get four back. :) Our highest flight hit 106,502 feet. Our greatest distance traveled was around 180 miles. The shortest was 25.




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