rtl_fm help

[Len Taing]

Hi!

I'm using a RTL2838 ezcap USB 2.0 DVB-T/DAB/FM dongle to try some of this rtl_sdr stuff.  I have run rtl_test -t and it seemed like things are ok: 

Found 1 device(s):

  0:  ezcap USB 2.0 DVB-T/DAB/FM dongle

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle

Found Elonics E4000 tuner

Supported gain values (14): -1.0 1.5 4.0 6.5 9.0 11.5 14.0 16.5 19.0 21.5 24.0 29.0 34.0 42.0 

Benchmarking E4000 PLL...

[E4K] PLL not locked for 51000000 Hz!

[E4K] PLL not locked for 2237000000 Hz!

[E4K] PLL not locked for 1119000000 Hz!

[E4K] PLL not locked for 1245000000 Hz!

E4K range: 52 to 2236 MHz

E4K L-band gap: 1119 to 1245 MHz

As a initial test, I'm trying to get rtl_fm to just pick up any fm radio.  Here's the call that I'm using:

rtl_fm -f 88100000 -s 44100 -g 9 -l 0 - | play -t raw -r 24k -e signed-integer -b 16 -c 1 -V1 -

88.1 is a local fm radio station.

I can only get static on my headphones with this.  So to debug the problem, here's what I'm thinking: 

1. maybe my antenna is not picking up the fm signal

2. maybe i'm missing a parameter that will help fine-tune the signal to FM broadcast

3. maybe my device is broken

How should I TEST each of these hypothesis?--is there a way to confirm, for example, that the device is functioning correctly?

Thanks!

[Colorado Rob]

My RTL dongle used to work just fine for broadcast FM. It is now deaf on the VHF band.  I no longer get FM or 2m. I can receive strong UHF signals - anything with an antenna in a 5 mile radius. But 2m repeaters at the same site and strength as the 70cm repeaters are not detected.  I don't know if this is a blown LNA on the E4000 or something in the code that changed.

Rob

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[jdow]

Blown LNA. Did your device have protection diodes on the front end?

{^_^}

On 2012/09/25 12:57, Colorado Rob wrote:
> My RTL dongle used to work just fine for broadcast FM. It is now deaf on the VHF
> band. I no longer get FM or 2m. I can receive strong UHF signals - anything
> with an antenna in a 5 mile radius. But 2m repeaters at the same site and
> strength as the 70cm repeaters are not detected. I don't know if this is a
> blown LNA on the E4000 or something in the code that changed.
>
> Rob
>
> On Sep 25, 2012 7:46 PM, "Len Taing" <len....@gmail.com

> <mailto:ultra-c...@googlegroups.com>.

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[Varda]

Dont throw out SDR yet,

Must try removing rtlsdr drivers, reinstalling of drivers to system- installing newest one only, to be rebooting.

Different parts/versions of several drivers sometimes are to be conflict

[Colorado Rob]

Took it apart last night.  Took lots of magnification to tell but they are certainly missing.  I've ordered a new one.

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[limaunion]

in a couple of days I'll receive my first SDR dongle from China, how should I check if it has LNA protection diodes? how do they look?
(my field is not electronics...)
thanks!

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[Masanobu Tsuji]

Hi Limaunion,

Look at the following jpg.

http://www.steve-m.de/pictures/rtl-sdr/ezcap_elonics.jpg

This is EzTV-668 photo. Just right side of PAL connector, you can find protection diodes.

White letters show "U7".

Masanobu

2012年9月27日木曜日 22時28分21秒 UTC+9 limaunion:

[limaunion]

Hi Masanobu, thanks for the info, excellent photo.

How hard would it be for a non electronic guy like me to solder one of this protection diodes? I think that this is what is called SMD right? so no chance probably for me. Maybe someone can post a video in youtube to show how to perform this mod.

73

[Sean]

Limaunion,

if you are not an electronics man and no experience in SMD soldering and highly sensitive chip such as E4000, then I would leave it alone. I would guess you may do more harm than fix. Either by excessive heat to the diode/pads or static to the chip/short etc.

Look around on Youtube there are loads of videos out there. Good luck.

73

[jdow]

Hm, there is an opportunity for somebody to develop both a small MCX
extension and a PAL extension that have protection diodes soldered
in the resulting barrel.

{^_^} Joanne, W6MKU

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[Sander Jonkers]

Len,

Have you made any progress on this?

With

sudo rtl_fm -f 98.9e6 -s 12000 -g 9 -l 10 - | play -t raw -r 12k -e signed-integer -b 16 -c 1 -V1 -

... and I only get noise.

Sander

[Paulino Kenji Sato]

Hi,
rtl_fm is intent to demodulate Narrow FM, not wide FM (broadcast FM).
Try to tune some NFM transmissions.
Like, 2m HAM repeater (144MHz to 148MHz, 430MHz-470MHz).
And, lots others services what use NFM.

--
Paulino

[Adam Nielsen]

> With
>
> sudo rtl_fm -f 98.9e6 -s 12000 -g 9 -l 10 - | play -t raw -r 12k -e
> signed-integer -b 16 -c 1 -V1 -
>
> ... and I only get noise.

You're setting the channel bandwidth to 12kHz with -s, but WBFM needs 170+kHz.
You probably mean -r instead, to set the output audio sampling rate.

You probably also want to use -W to set wideband FM parameters, which also
sets -l 0.

Cheers,
Adam.

[Paulino Kenji Sato]

Hi,
Sorry, I make mistake.
I have tested with old rtl_fm version, what not support WFM.
With new version, WFM works fine.

./rtl_fm -f 97100000 -W -s 200000 -r 48000 - | aplay -r 48k -f S16_LE
-t raw -c 1
or
./rtl_fm -f 97100000 -W -s 230400 -r 48000 - | play -t raw -r 48k -e

signed-integer -b 16 -c 1 -V1 -

-s must be great what 150kHz.

And, don't need root permission (sudo) to run rtl_fm or other
application to use rtl usb dongle.
Just copy rtl-sdr.rules to /etc/udev/rules.d and restart udev service.

get latest version of rtl-sdr, compile and install
git clone git://git.osmocom.org/rtl-sdr.git
cd rtl-sdr
mkdir build
cd build
cmake ../
make
[sudo] make install
[sudo] ldconfig
cd ../
[sudo] cp rtl-sdr.rules /etc/udev/rules.d
[sudo[ service udev reload

plug the dongle, and use.

--
Paulino

[mrzfrn]

Il giorno lunedì 19 novembre 2012 00:11:56 UTC+1, pksato ha scritto:

With new version, WFM works fine.

./rtl_fm -f 97100000 -W -s 200000 -r 48000 - | aplay -r 48k -f S16_LE -t raw -c 1

-t raw -c 1

rtl_fm  send to soundcard the FM decoder output ,i.e.  the MPX signal ( 75 kHz)  filtered a 48 kHz.
That's OK only on mono WFM quite unusual today, stereo WideFM on air instead.
It's needed  a second stage decoder that picks up mono, stereo, RDS signal
Look at
http://en.wikipedia.org/wiki/FM_stereo#Stereo_FM

fM

[mrzfrn]

[Sander Jonkers]

Wow, I have sound! Thank you!

Sound is still very noisy, antenna has to be close to a windows, but it is a start.

Oh: If I want to tune into 98.9 MHz, I have to put 98.485 MHz onto the command line. Is that normal?

sander@R540:~$ sudo rtl_fm -f 98485000 -W -s 200000 -r 48000 - | aplay -r 48k -f S16_LE -t raw -c 1 

Found 1 device(s):

  0:  Realtek, RTL2838UHIDIR, SN: 00000013

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle

Found Rafael Micro R820T tuner

Oversampling input by: 2x.

Oversampling output by: 4x.

Buffer size: 5.12ms

Tuned to 98900000 Hz.

Sampling at 1600000 Hz.

Output at 48000 Hz.

Tuner gain set to automatic.

Playing raw data 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono

^CAborted by signal Interrupt...

Signal caught, exiting!

User cancel, exiting...

Signal caught, exiting!

sander@R540:~$

[Adam Nielsen]

> Oh: If I want to tune into 98.9 MHz, I have to put 98.485 MHz onto the command
> line. Is that normal?

No, if you put 98.485MHz on the command line that's the frequency you will
get, which is probably why it sounds so noisy. rtl_fm tunes off-centre to
avoid the DC spike at the tuning frequency.

The value you put on the command line is the actual RF frequency you will decode.

Cheers,
Adam.

[Sander Jonkers]

OK, thank you for your input. Indeed I hear radio (and a lot of noise) when I use 98.8 MHz. I guess I'll have to try a better antenna.

The "off-centre" ... when I google "FM spectrum", it shows a spike a the centre frequency (the carrier, without any signal?), and a 'hill' on the left side, and a 'hil' on the right side. Is the hill what rtl_frm tunes to?

Another question: my ultimate goal is to listen to DAB (which is broadast on 227.36 MHz here in the Netherlands). Can I use rtl_* to listen to DAB?

Sander

 sander@R540:~$ sudo rtl_fm -f 98900000 -W -s 200000 -r 48000 - | aplay -r 48k -f S16_LE -t raw -c 1

Found 1 device(s):

  0:  Realtek, RTL2838UHIDIR, SN: 00000013

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle

Found Rafael Micro R820T tuner

Oversampling input by: 2x.

Oversampling output by: 4x.

Buffer size: 5.12ms

Tuned to 99315000 Hz.

Sampling at 1600000 Hz.

Output at 48000 Hz.

Tuner gain set to automatic.

Playing raw data 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono

 

Cheers,
Adam.

[Paulino Kenji Sato]

Hi,

On Mon, Nov 19, 2012 at 8:02 PM, Sander Jonkers
<sander....@gmail.com> wrote:
> Wow, I have sound! Thank you!
>
> Sound is still very noisy, antenna has to be close to a windows, but it is a
> start.
>
> Oh: If I want to tune into 98.9 MHz, I have to put 98.485 MHz onto the
> command line. Is that normal?
>
>

What happens if put a correct frequency on command line?

rtl_fm avoid center on I/Q tuner (Zero IF, like E4000), re tuning
above or below desired frequency (~1/4 of rtl sample rate).
R820T tuner is low IF tuner, and don't have DC spike on center. No
matter where FM signal is present.

> Another question: my ultimate goal is to listen to DAB (which is broadast on 227.36 MHz here in the Netherlands).
> Can I use rtl_* to listen to DAB?

I don't know any FOSS implementation of DAB demodulator and audio decoder.
But, check this http://mmbtools.crc.ca/
Windows software that comes with the dongle is capable of relieve DAB,
DAB+, FM and DVB-T.

Before someone ask, HD-Radio don't allow software receivers (except embedded).

For DRM30, has DReaM, and DRM+ Wavesink, not public release.

For analog modes, linrad is the best.


--
Paulino

[mrzfrn]

SDR-J is quite good SDR software as well , IMHO the best on WFM .
You get even RDS decoding ( strong stations of course)
http://www.sdr-j.tk/index.html
Linux (source) and  Windows ( binary)
fM

[Sander Jonkers]

FWIW:

1) I was able to connect my cable company's radio signal to my Realtek-USB-stick using a self-made male-male-cable. Explanation: the Realtek-USB-stick is a TV-device, so the connector is opposite of the radio cable / connector.

2) There was still a lot of noise. I varied the sample rate between 100.000 and 400.000, and 150.000 gave me the best result: no noise anymore. So the command is now:

sudo rtl_fm -f 96900000 -W -s 150000 -r 48000 - | aplay -r 48k -f S16_LE -t raw -c 1

Can someone explain thy the 'medium' sample rate gives the best result? I would think a higher sample rate would be better?

Sander

[Adam Nielsen]

> 1) I was able to connect my cable company's radio signal to my
> Realtek-USB-stick using a self-made male-male-cable. Explanation: the
> Realtek-USB-stick is a TV-device, so the connector is opposite of the radio
> cable / connector.

You can buy these adapters quite readily in case the one you made yourself is
introducing noise.

> 2) There was still a lot of noise. I varied the sample rate between 100.000
> and 400.000, and 150.000 gave me the best result: no noise anymore. So the
> command is now:
>
> sudo rtl_fm -f 96900000 -W -s 150000 -r 48000 - | aplay -r 48k -f S16_LE -t
> raw -c 1

If you read "rtl_fm --help" it tells you the -W option includes "-s 170000",
so you are overriding that with a slightly smaller sample rate, which will
introduce a bit of noise in loud parts of the broadcast.

> Can someone explain thy the 'medium' sample rate gives the best result? I
> would think a higher sample rate would be better?

-s doesn't set the sample rate, it sets the bandwidth of the signal. If you
capture too much signal you will get noise from adjacent signals, and if you
capture too little you will get noise because parts of the signal are lost.

The bandwidth you set with -s should match the bandwidth of the signal you are
listening to, so you capture the entire signal but nothing more.

Cheers,
Adam.

[Sander Jonkers]

Hi Adam,

Thank you for you reply.

On Sunday, December 2, 2012 10:48:01 PM UTC+1, Adam Nielsen wrote:

> 1) I was able to connect my cable company's radio signal to my
> Realtek-USB-stick using a self-made male-male-cable. Explanation: the
> Realtek-USB-stick is a TV-device, so the connector is opposite of the radio
> cable / connector.

You can buy these adapters quite readily in case the one you made yourself is
introducing noise.

I had been looking for a 'gender-bender coax', but did not find one.

Anyway: I think the self-made cable is quite good.

 

> 2) There was still a lot of noise. I varied the sample rate between 100.000
> and 400.000, and 150.000 gave me the best result: no noise anymore. So the
> command is now:
>
> sudo rtl_fm -f 96900000 -W -s 150000 -r 48000 - | aplay -r 48k -f S16_LE -t
> raw -c 1

If you read "rtl_fm --help" it tells you the -W option includes "-s 170000",
so you are overriding that with a slightly smaller sample rate, which will
introduce a bit of noise in loud parts of the broadcast.

Let's check:

[-W enables WBFM mode (default: off)]

(-N -s 170e3 -o 4 -A -r 32e3 -l 0 -D)

Ah ... there it is! Thanks. 

BTW: With -s 170e3 I get a bit of noise. Does that mean 170e3 is 'too wide'?

 

> Can someone explain thy the 'medium' sample rate gives the best result? I
> would think a higher sample rate would be better?

-s doesn't set the sample rate, it sets the bandwidth of the signal.  If you

rtl_fm --help says:

[-s samplerate (default: 24000 Hz)]

so I really thought -s set the sample rate?

 

capture too much signal you will get noise from adjacent signals, and if you
capture too little you will get noise because parts of the signal are lost.

The bandwidth you set with -s should match the bandwidth of the signal you are
listening to, so you capture the entire signal but nothing more.

Is there a rule for commercial FM radio? Is it normally 170e3? Does it depend on the geographical region you're in, or is it the same all over the world?

 

Thanks.

Sander

[Adam Nielsen]

> I had been looking for a 'gender-bender coax', but did not find one.
> Anyway: I think the self-made cable is quite good.

If it's the European aerial connector you're talking about "pal male to male"
would give you more results. But as long as your home made connector is
shielded properly, it will probably give you better results than a lot of the
cheap mass-produced versions.

> Ah ... there it is! Thanks.
> BTW: With -s 170e3 I get a bit of noise. Does that mean 170e3 is 'too wide'?

No, it probably just means there is noise in the signal. Moving the antenna
further away from your PC might help.

> [-s samplerate (default: 24000 Hz)]
>
> so I really thought -s set the sample rate?

Yes it's very badly described, lots of people are making this mistake because
the --help is badly worded.

> Is there a rule for commercial FM radio? Is it normally 170e3? Does it depend
> on the geographical region you're in, or is it the same all over the world?

I think it's the same all over the world. But I did think it was officially
200kHz rather than 170. But maybe the audio signal doesn't occupy the full
200kHz?

Cheers,
Adam.