#1 2014-12-13 23:06:22

AJ4ZS
Member
From: Mobil, AL
Registered: 2014-12-13
Posts: 6

No decode...

Hi guys.
My name is Hermann AJ4ZS / DL8MCP and I have been following this project for a while.
Now I decided to jump in and build the whole thing myself.
So here is whet I did:

1. Loaded the hex file to a Microduino
2. Opened Tera Term and set the COM port to 9600, 8, N, 1
3. Connected the Microduino
4. Tera Term says:
---------------
MicroAPRS v0.2a
unsigned.io/microaprs
Default configuration loaded!
Modem ready
---------------

So that seems to work...
Then I build the input stage (R10, R11, C3) on a bread board. I do not have a 1uF cap so I used 470nF. Is that value critical?
I connected LINE_LEVEL_IN to the speaker of my Baofeng GT-3 and... Nothing! No decode... I can hear some very strong and clear signals. I tried to set the volume higher and lower... When I connect my headphones to A0 I can hear a clear signal. The (DC) voltage on A0 is 2.31V. Depending on the volume setting, this voltage goes down when a signal comes from the speaker. Is that correct? At low volume it goes down to about 2.06V, at high volume it goes down to about 1.87V.

Any ideas what went wrong?

vy 73 de Hermann AJ4ZS / DL8MCP

Last edited by AJ4ZS (2014-12-13 23:17:12)


vy 73 de Hermann AJ4ZS / DL8MCP

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#2 2014-12-14 10:38:35

markqvist
Administrator
Registered: 2014-12-01
Posts: 109

Re: No decode...

It sounds strange that the voltage goes down when a signal is coming in... Do you have an oscilloscope you can connect? That offer a better view into whats going on. Maybe a stupid question, but did you also connect the ground of the speaker output to the ground of the microduino? And did you connect the 5V from the microduino to the input of R10/R11 for the 2.5v DC bias?

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#3 2014-12-14 10:45:53

DJ7OO
Member
From: Mainz Germany
Registered: 2014-12-02
Posts: 24
Website

Re: No decode...

Hello Hermann,
a good indicator could be a LED connected to Arduino Pin 10.
If there is any input noise, it should flicker ( flackern ), while it should burn steadily for the moments of incoming data. Of course you have to play around a little bit with input level. I am adjusting my radio to what we call "Zimmerlautstaerke", which means about 50% of maximum volume.

Here also was some discussion on some types of radios, requiring additional audio filtering. See on this Stefans Blog:
http://www.radio.cc/?tag=/Bandpass
Maybe this also could help in your case.

73 de Klaus, DJ7OO

Last edited by DJ7OO (2014-12-14 16:40:26)

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#4 2014-12-14 15:48:27

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

Re: No decode...

Hi Hermann,

Another tips to test if yr modem circuit is working is using the APRS / TNC Test CD found here http://wa8lmf.net/TNCtest/
I usually play them with LINE OUT and use alligator clips to clip them to 2.5mm tip ( Audio In ) and 2.5mm sleeve ( Gnd ) ..


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

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#5 2014-12-15 03:34:19

AJ4ZS
Member
From: Mobil, AL
Registered: 2014-12-13
Posts: 6

Re: No decode...

@Stanley
Thank you! That would have been my next question on where to find something like this!
I'm downloading the CD and will test it.

@Mark
A wise man once said: There are no stupid questions. There are only stupid answers. big_smile
But yes. I connected both wires and I connected the resistors according to the schematic you provided.
So I dusted off my oscilloscope and tested the signal. At A0 I have an audio signal of about 200mV pp. The signal itself looks pretty good. It is not clipped or distorted. At least from what I can tell from the short bursts I see.

@Klaus
The LED behaves just like you described. It flickers when I open the squelch and is on while an APRS signal is received. So I presume the signal is strong enough to be read by the ADC but for whatever reason it is not decoded... I also set the squelch setting to minimum sensitivity.

And last but not least:
I managed to decode two packets today! This is the last one:
SRC: [WB4QEV-4] DST: [WX-0] PATH: [KI4ELU-7] [W4IAX-7] [WIDE2-0] DATA: !!000000FF01ED0000----0205--------001E02D700000000
The first one got lost when I resized the Tera Term window...
Now it would be interesting to know what makes these two packets different from the 200+ packets that where not decoded during the two hours I had the decoder running...


Update:
The test with the TNC CD was a success! The decoding part works. Now I have to work on the radio part. I read in a forum that the Baofeng radios are known for having a slow squelch. So I am going to dust off my trusty old C528 and do some test with that. I'll report back...

Last edited by AJ4ZS (2014-12-15 04:29:00)


vy 73 de Hermann AJ4ZS / DL8MCP

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#6 2014-12-18 13:15:30

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Re: No decode...

Turn squelch off, especially if it prevents you from decoding. in the testphase you also listen to the signal, but if all is working you probably won't any more.

Last edited by PA3BAS (2014-12-18 13:15:50)

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#7 2015-01-10 03:55:11

AJ4ZS
Member
From: Mobil, AL
Registered: 2014-12-13
Posts: 6

Re: No decode...

As promised I am back with an update.
I works!

Today I loaded the "Basic_usage" example from LibAPRS and setting OPEN_SQUELCH to true it decodes every packet.
This confirms my theory about the slow squelch on the (my) Baofeng HT.

I am planing to build an APRS transceiver using those small Dorji 2m modules.


vy 73 de Hermann AJ4ZS / DL8MCP

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#8 2015-01-13 08:29:39

markqvist
Administrator
Registered: 2014-12-01
Posts: 109

Re: No decode...

Great to hear! Keep us updated with your project! I'm looking forward to seeing how it works out with the Dorji transceivers!

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#9 2015-09-18 17:19:33

user11
Member
Registered: 2015-09-18
Posts: 8

Re: No decode...

Good evening, I have the same problem with my both UV5R and TYT hand held transceivers. When feeding reference signal or just loop back everything from output to input it decodes fine, but it does not with transceivers.

With squelch closed I had no luck at all, very rarely packets were decoded when coming in chunks. Analysed waveform with oscilloscope and it takes approx. 350-400ms for squelch to open and approx. 150ms for signal to get into the proper level.  With squelch open situation is not much better, I somehow managed to find out proper position of volume knob after 30 minutes of experiments, which allowed me to decode few packets, but then I could not find it again. Looking at spectrogram of the audio signal it looks quite noisy to me, I was expecting to see some nice 1200 and 2200 Hz peaks, but it did not happen. Also, micromodem RX led is blinking when signal is received.

Note, that aprsdroid is able to decode all packets when feeding audio from UV5R to phone mic. So, I guess, phone is more powerful and is capable of running more advanced algorithm or maybe there is a way to improve decoding on arduino too? I don't know, but nice to know.

Last edited by user11 (2015-09-19 08:20:52)

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#10 2015-09-18 19:22:10

PA3BAS
Member
Registered: 2014-12-01
Posts: 20

Re: No decode...

Try to put a capacitor inline with the speaker to keep dc out. I have a suspicion that a baofeng av5r has dc on its output...

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#11 2015-09-18 21:19:32

user11
Member
Registered: 2015-09-18
Posts: 8

Re: No decode...

Managed to improve situation a lot (receiving every second or third packet) by changing C3 capacitor from polypropylene 1uF to tantalum 1uF capacitor and adjusting volume levels to this state (~500mV p-t-p), but, still, not every packet is decoded when sent periodically with 3 second delay between transmissions.

2wegndj.jpg

Last edited by user11 (2015-09-19 08:29:14)

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#12 2015-09-19 12:18:03

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

Re: No decode...

Hi, try to adjoust audio level to 2.5 vpp. Also  try to measure level difference between high and Low Tone coming out from baofeng  audio. Maybe that baofeng has a de-emphasis filter. MicroAprs doesn't decode this Kind of signal yet.

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#13 2015-09-19 14:06:14

user11
Member
Registered: 2015-09-18
Posts: 8

Re: No decode...

Yes, seems to be the case. Also, looking at RDA1846 programming manual (http://www.kc2ra.org/files/RDA1846_Prog … manual.pdf), which is used in UV5R, there is a way to bypass de-emph and even lpf/hpf, but radio does not have an option to disable them from the menu (((

Would be nice if LibAPRS will have support for de-emph signals or at least it would be nice to know if it is doable and what kind of modifications are needed.

Last edited by user11 (2015-09-19 14:26:15)

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#14 2015-09-19 16:11:21

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

Re: No decode...

I already opened a post about this. We need Mark's opinion. You could try to use a rc filter  to decresce the Low Tone level and increase general volume .

The the decode has a Chebyshev low pass filter tuned to 600HZ (afsk.h). So the phase detector already decode  an understated high tone. With a de-emphasis filter on radio side, the high tone is too small to pass the filter.

We have to  redesign the software filter....

Last edited by IW3IJQ (2015-09-19 16:33:50)

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#15 2015-09-19 18:15:10

user11
Member
Registered: 2015-09-18
Posts: 8

Re: No decode...

IW3IJQ, thank you a lot for the hint, placed RC filter with 100 Ohm resistor + 1uF non-polar capacitor (changed later to 1k + 100nF, seems to be better almost 100% of packets are decoded), increased the volume and 90% of packets are decoded now.

Added filter straight to the connector, which is used to connect radio with the tnc, so no need to modify tnc itself.

2ch3zwm.png

Last edited by user11 (2015-09-19 20:18:01)

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#16 2015-12-25 14:25:39

YT7FMS
Member
Registered: 2015-12-16
Posts: 6

Re: No decode...

Hallo everyone!
My name is Filip, QTH: JN95VA

I am trying to build microAPRS on an arduino nano v3.0 and so far I got the TX working allright.

But, I am also having small problems with demodulation.

I have build the modem with 3.3V reference and compiled with 3.3REF option and OPEN_SQUELCH true.
I am using a Baofeng UV-B6 for the TNC.

Setting volume knob from half to almost max volume microAPRS can decode 80-90% of packets (freely estimated, did not measured it).
I have tried using RC filter, but, as I am fairly new (noob) to electronics I am not quite sure I got that part right since only ONE packet got decoded smile
Also, I do not have ossciloscope to take correct measurments of signal coming into microAPRS.
@user11 can You please provide a schematic of that RC filter and how it connects between radio and TNC, and, what "increased the volume" exactly means in Your case?
Also, if anyone have any suggestions I would greatly appreciate it.
I hope I was clear in explaining my situation.

Thank You all in advance and for all the work and sugesstions and directions I have read so far!

--
EDIT:
I found a solution e.g. a problem with my setup. Conecting a roof antenna fixes the problem and as I can notice for now, most of packets (if not all, should monitor a bit longer) is being decoded.
Before that I had connected mobile antenna sitting in my room. So I guess the reception was bad allthough I could hear every packet clearly hmm

EDIT2:
Performance has improved but still every 5th packet is not being decoded (rough estimate).

Last edited by YT7FMS (2015-12-26 12:55:52)

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#17 2015-12-28 21:23:43

user11
Member
Registered: 2015-09-18
Posts: 8

Re: No decode...

Hi, YT7FTS.

I used  RC high pass filter to decrease the low tone (1200Hz) level and make low 1200Hz tone and high 2200Hz tone levels/amplitudes closer to each other. It improved decoding a lot.

circuit-design-rc.gif

Filter was connected between audio output of the transceiver and micromodem input. R1 = 1k and C1 = 100nF.

The problem comes from the fact that RDA1846, which is used in Baofeng has de-emph enabled, making voice more "pleasant" for ears by reducing amplitude of higher frequencies, but making afsk decoding problematic as 1200 tone and 2200 tones become quite different in amplitude.

615px-RIAA-EQ-Curve_rec_play.svg.png

Hope it helps.

Last edited by user11 (2015-12-28 22:01:59)

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#18 2015-12-29 17:38:22

YT7FMS
Member
Registered: 2015-12-16
Posts: 6

Re: No decode...

Thank You very much!
So, let's see if I got this right smile
1. De-emphasis on Baofeng sets 2200Hz level lower than of 1200Hz tone level ?
2. I should be using RC highpass filter ONLY, so that 1200Hz tone level is closer to 2200Hz tone level?
3. When using RC highpass filter, I should connect audio output from radio to both capacitor and resistor, and than draw signal from both sides of resistor to connect to modems input (to capacitor and volt divider) ?
4. Also, there is no need to ground resistor in RC highpass filter scheme?
EDIT: Ok, nevermind, I figured it out smile Indeed after placing RC HP filter packet demodulation rate has noticably improved! Thank You much for information!

Just this:
5. "Increased the volume" - using some kind of OpAmp circut or just radio volume?

Last edited by YT7FMS (2015-12-31 15:05:52)

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