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maemo.org - Talk (https://talk.maemo.org/index.php)

- Nokia N900 (https://talk.maemo.org/forumdisplay.php?f=44)

- - N900 Radio Transmitter: ways to amplify the radio signal (https://talk.maemo.org/showthread.php?t=38582)

smage

2009-12-29 00:34

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by anidel (Post 444526)

Btw, it sucks on both.

Today I used my K850i from SE as Radio (it also has RDS).
I had to place the N900 right on the headset cable (the 'antenna') to have clear audio in the 'radio' (the K850).

If I kept the N900 in my hands, sitting at the table, thus few cm away from the 'radio', the quality would drop a lot.
Rotating the N900 did affect the quality (from nothing to good quality) of the audio in the 'radio'.

And I was in my room... not in a shielded car.

this pretty much sums up my experience on the device...

how come we have such a huge difference in use experience of the radio transmitter?

myk	2009-12-29 01:02

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by smage (Post 444640)

how come we have such a huge difference in use experience of the radio transmitter?

Different receivers?
Have you tried your phone with other cars, or car with other transmitters?

danielz000

2009-12-30 14:09

Re: N900 Radio Transmitter: ways to amplify the radio signal

Hi All!

My first post...

I just tried the "cat /sys/class/i2c-adapter/i2c-2/2-0063/power_level" command and it returned 112...

I'm in the UK and when I tested the FM transmitter inside the car and my house I was disappointed to say the least.

Is 112 the maximum signal strength?

Cheers,

Daniel

Kurare

2009-12-30 15:36

Re: N900 Radio Transmitter: ways to amplify the radio signal

The preset power level was 114 for me (scandinavian sales SW).

Setting it to 118 removed almost all of the audible static and made the signal strong enough to be captured decently in all cars I tried it in (and older Golf, a Scudo and and shiny new Insight; only the Scudo initially struggled with it).

One thing to remember with the numbers is that the chip may have some kind of built-in Tx power management by monitoring the actual power pushed to the air vs. power reflected back from the antenna. As the antenna itself seems to be a just a metal sliver with carefully formed shape suited for antenna use and the contact is a standard metal-gold-spring-loaded touch-gold-nickel-copper contact, it is subject to variance in quality from device to device and also WILL vary as the device ages and gets dropped, dusted, humid, squeezed, dipped in beer and so on. The Tx power can quite likely be controlled to some degree by the chip itself, though the problem here is not frying the gain stage - even the maximum output is but a candle compared to the supernova-like relative luminosity of the "real" transmitter stations - but power usage that should always be minimized.

One nasty thing I noticed about the transmitter is that there's quite little fitering from the main power net of the phone to the transmitter. I noticed this when I was trying it with the not-that-good-but-adequate minihifi set I use as computer speakers and not that low sound level as I wanted to hear if the static changed as I played with the settings - the bundled charger distorted the transmitted signal to a horrible shriek that made my cat go from sleepy rest to VERY puffy in about 3,8 µs and resulted in eight bleeding deep puncture wounds on my shoulder, lots of swearing and bodily pain due to the shock from the shriek and the cat wanting to suddenly delocalize itself, which in turn resulted my computer chair toppling over and me lying on the floor, bleeding and wondering what the hell had just happened - and the shrieking just wouldn't stop until got up from the floor and pulled the charger cable - it was closer than the power button for the speaker set.

Perhaps this is why the SW is not sure whether to allow the FM transmitter to work while a power-carrying cable is plugged in? :D

danielz000

2009-12-30 15:58

Re: N900 Radio Transmitter: ways to amplify the radio signal

Hahah! Well i'm glad to hear you survived that attack!

Would you mind sharing how you changed the default power level? I'm a total n900 / linux noob! :(

Do you think changing it could invalidate the warranty?

*EDIT* I should probably just learn to UTFSE! Sorry!

tirtawn

2009-12-30 16:34

Re: N900 Radio Transmitter: ways to amplify the radio signal

Noob Question:
How to change it manually ?
is it something like this ?

sudo gain root
cat 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

Thanks

danielz000

2009-12-30 17:03

Re: N900 Radio Transmitter: ways to amplify the radio signal

I think you're going to get a file not found error with that command.

I tried using vi to edit the file but got scared when I got a file could not be opened fully error... (or something to that affect)

jsharper

2009-12-30 17:29

Re: N900 Radio Transmitter: ways to amplify the radio signal

close.

Code:

echo 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

tpinhao

2009-12-30 18:06

Re: N900 Radio Transmitter: ways to amplify the radio signal

Hello Guys

Are you sure the changing the contents of that file is going to change the Power Level ?

I think that that file is not a "config" file but it is a Log file, if you notice that file is updated whenever you start the FM Transmitter, so the only thing that that file is telling you is the current power-level.

The contents of my file where:

0

And after i started the FM Transmitter it changed to 111.

So i really think is a Log file

Maybe it cannot be changed this easily

fnordianslip

2009-12-30 18:08

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by tpinhao (Post 446927)

I've tried echoing 118 to that file whilst the device is connected to the charger. Before echoing 118, cat returns 88, and the signal is weak. Echoing 118 increases the signal strength so that the receiver is fully quieted.

So, it works for me :)

jsharper

2009-12-30 18:12

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by tpinhao (Post 446927)

Files in /sys and /proc are not real files -- they are special interfaces to the kernel and drivers that are exposed to act like files. writing to the power_level "file" actually sends the new value directly to the running driver which appears to then immediately send the new value to the Si4713 fm transmitter chip via the i2c bus. I can confirm through observation that there is indeed an audible pop followed by an adjustment in the ability to receive the fm signal the moment after echoing a new value to that file.

mason

2009-12-31 00:26

Re: N900 Radio Transmitter: ways to amplify the radio signal

pretty nice find, thanks guys .. now we just need to find out to mod the kernel driver to set the value ;)

SM6VIT

2009-12-31 01:01

Re: N900 Radio Transmitter: ways to amplify the radio signal

I get 113 on mine.

Rick

tirtawn

2009-12-31 07:15

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by jsharper (Post 446890)

close.

Code:

echo 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

Blah...my bad :P..I should use echo not cat..not sure what i was thinking when i type that mesg :)..

Thanks.

tangs

2009-12-31 19:17

Re: N900 Radio Transmitter: ways to amplify the radio signal

does it really work ? could you explain very precisely how to do ?

thanx :)

JuhS	2009-12-31 19:23

Re: N900 Radio Transmitter: ways to amplify the radio signal

I have tested the radio transmitter in a Volvo V70, and it serves it's purpose. Compared to the old fashioned way of burning CDs I couldn't ask for more. Remember, it's a phone, not a radio station..

Bratag

2009-12-31 19:37

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by tangs (Post 448259)

does it really work ? could you explain very precisely how to do ?

thanx :)

yes it really works - to do it - simply open a terminal, run root, type in the echo command a few posts back.

tangs

2009-12-31 20:21

Re: N900 Radio Transmitter: ways to amplify the radio signal

and...... how to run root ?

egoshin

2009-12-31 22:03

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by tangs (Post 448323)

and...... how to run root ?

http://wiki.maemo.org/Root_access

YoDude

2009-12-31 23:56

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by Bratag (Post 448279)

yes it really works - to do it - simply open a terminal, run root, type in the echo command a few posts back.

Is it persistent?
Must the transmitter be powered up?

j.s	2010-01-01 00:04

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by YoDude (Post 448462)

Is it persistent?

No.

Quote:

Originally Posted by YoDude (Post 448462)

I
Must the transmitter be powered up?

Yes.

titi974

2010-01-01 14:19

Re: N900 Radio Transmitter: ways to amplify the radio signal

it's maybe an idiot question but... can we put a higher value than 118 ? actually it is strength enough for me but i was just wandering ^^

smage

2010-01-01 14:41

Re: N900 Radio Transmitter: ways to amplify the radio signal

or to better put it?

legal issues asides? what's the highest transmit value that is safe for the radio transmitter (as in not burning it) :)

titi974

2010-01-01 14:42

Re: N900 Radio Transmitter: ways to amplify the radio signal

yeah, I'd like to know

fnordianslip

2010-01-01 14:48

Re: N900 Radio Transmitter: ways to amplify the radio signal

The datasheet linked in an earlier post shows the figure of 118 dbuV typical for the programmable TXO output voltage. No minimum and maximum figures are specified.

Until someone finds application notes or other detailed documentation, I wouldn't consider going above 118, and would advise sticking with the initial figure obtained by cating the file without a charger plugged in (so as not to advise dangerously).

I've ran mine for a couple of hours at 118 and noticed no issues, but am generally using 112dBuV. IIRC an increase of 6dB will double the voltage.

smage

2010-01-01 14:56

Re: N900 Radio Transmitter: ways to amplify the radio signal

Ok ı'm running at 122 now, the device is still alive and running and seems stable, but I wouldn't use it like that for extended periods of time... I just felt naughty, and tbh it wouldn't be of use to me anyway with high noise so I had to do it.

Flandry

2010-01-01 15:04

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by Kurare (Post 446738)

One thing to remember with the numbers is that the chip may have some kind of built-in Tx power management by monitoring the actual power pushed to the air vs. power reflected back from the antenna. As the antenna itself seems to be a just a metal sliver with carefully formed shape suited for antenna use and the contact is a standard metal-gold-spring-loaded touch-gold-nickel-copper contact, it is subject to variance in quality from device to device and also WILL vary as the device ages and gets dropped, dusted, humid, squeezed, dipped in beer and so on. The Tx power can quite likely be controlled to some degree by the chip itself, though the problem here is not frying the gain stage - even the maximum output is but a candle compared to the supernova-like relative luminosity of the "real" transmitter stations - but power usage that should always be minimized.

One nasty thing I noticed about the transmitter is that there's quite little fitering from the main power net of the phone to the transmitter. I noticed this when I was trying it with the not-that-good-but-adequate minihifi set I use as computer speakers and not that low sound level as I wanted to hear if the static changed as I played with the settings - the bundled charger distorted the transmitted signal to a horrible shriek that made my cat go from sleepy rest to VERY puffy in about 3,8 µs and resulted in eight bleeding deep puncture wounds on my shoulder, lots of swearing and bodily pain due to the shock from the shriek and the cat wanting to suddenly delocalize itself, which in turn resulted my computer chair toppling over and me lying on the floor, bleeding and wondering what the hell had just happened - and the shrieking just wouldn't stop until got up from the floor and pulled the charger cable - it was closer than the power button for the speaker set.

Perhaps this is why the SW is not sure whether to allow the FM transmitter to work while a power-carrying cable is plugged in? :D

When they said to cat that /proc/ interface, they meant the shell command "cat". ;)

Haha just kidding and thanks for the tragic but comedic tale. I hope you have recovered!

Quote:

Originally Posted by fnordianslip (Post 448866)

I've ran mine for a couple of hours at 118 and noticed no issues, but am generally using 112dBuV. IIRC an increase of 6dB will double the voltage.

Thanks for testing this. My electronics knowledge is fairly rudimentary, so i'm curious how that works. Since 3dB is basically a doubling in output power, does that mean that the voltage and current both increase linearly in a transmitter? I suppose either one could cause a failure.

BTW when i turn off my radio, i still get "112" as the power_level. Isn't it supposed to go away or to 0 when turned off?

fnordianslip

2010-01-01 15:15

Re: N900 Radio Transmitter: ways to amplify the radio signal

Well, power in Watts = voltage squared divided by the impedance (or resistance), so it isn't linear.

Voltage expressions in dB use the "20 log rule" whereas power expressions in dB use the "10 log rule", hence the figure of +6dB for a doubled voltage level, and +3dB for a doubled power level.

Edit. Actually, you said voltage and current both increase linearly, and they actually do, as according to Ohms law R=V/I, so V and I rise linearly, but the power goes up exponentially, as P=VI.

Flandry

2010-01-01 15:57

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by j.s (Post 444581)

Bug https://bugs.maemo.org/show_bug.cgi?id=7425 entered. I am in region 2. /sys/class/i2c-adapter/i2c-2/2-0063/region_bottom_frequency is 87500

If you have a region_bottom_frequency less than 88100 and 88.1MHz is the lowest frequency available to you in the FM transmitter GUI and you want to set a freq below 88.1, please vote for bug 7425.

I voted on this bug report, but then noticed it has been closed:

Quote:

Originally Posted by Andre Klapper (maemo.org) 2009-12-29 13:00:00 GMT+3

The reason for 88.1MHz lower limit of the FM Transmitter is to use the common band with FCC countries. Frequencies under 88.1MHz are removed since the allowed output power under 88MHz is lower than on 88.1-107.9MHz band in FCC countries.

This will not be changed.

While that seems likely due to the overlap with channel 6, the amount of power output by our phone transmitters is surely orders of magnitude less than the licensed stations i would expect such a regulation would apply to.

What i was able to find with a short search is that the real reason is that
the unlicensed broadcast band only goes down to 88.0 MHz, which means a center frequency of 88.1 MHz. I would assume that's the legal realm in which the FM transmitter on the N900 is working. The power of said broadcast is expressly limited to

Quote:

250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.

Any transmission over that power level is "punishable by law and confiscation of all broadcast equipment".

Quote:

Originally Posted by fnordianslip (Post 448886)

Voltage expressions in dB use the "20 log rule" whereas power expressions in dB use the "10 log rule", hence the figure of +6dB for a doubled voltage level, and +3dB for a doubled power level.

Thanks; i didn't know that about voltage dB units.

Quote:

Edit. Actually, you said voltage and current both increase linearly, and they actually do, as according to Ohms law R=V/I, so V and I rise linearly, but the power goes up exponentially, as P=VI.

Yeah i was thinking of Ohm's law and assuming that dB was referring to power, not voltage. Is the value in the /proc/ a voltage amplification? Funny to call it "power_level" if so. :D

fnordianslip

2010-01-01 16:04

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by Flandry (Post 448917)

Is the value in the /proc/ a voltage amplification? Funny to call it "power_level" if so. :D

It is a voltage value, described as " Programmable Transmit Output Voltage, TXO", in units of dBμV, according to the linked datasheet.

DaveQB

2010-01-01 16:28

Re: N900 Radio Transmitter: ways to amplify the radio signal

Code:

cat /sys/class/i2c-adapter/i2c-2/2-0063/power_level

88 here.

I tried setting it to 118 while transmitting and what a difference! Suddenly so much clearer.

I did find that file /sys/class/i2c-adapter/i2c-2/2-0063/power_level did exist when FM transmitter was off.

I also found that plugging in a wall charger dropped the power level to 88.

Now to make it persistent...

go1dfish

2010-01-01 19:31

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by smage (Post 448872)

Did you notice any significant difference between 118 and 122?

i.e. I'm wondering since the chip specs specify 118, if the driver/chip knows enough to treat any values above 118 as 118.

iKneaDough

2010-01-01 19:53

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by go1dfish (Post 449114)

Did you notice any significant difference between 118 and 122?

i.e. I'm wondering since the chip specs specify 118, if the driver/chip knows enough to treat any values above 118 as 118.

I tried a bunch of different numbers past 118.

With each increase in number between 111 to 118, there is a noticeable improvement, but once you reach 118, any higher number doesn't seem to make any difference and sounds the same as 118 itself.

yorg	2010-01-01 20:39

Re: N900 Radio Transmitter: ways to amplify the radio signal

mine is at 114 and works ok in a ford focus

i just wish I could set the freq below 88.1 as everything above 88 seems to be taken

funny enough my region_bottom_freq value is set to 87500 so the 88.1 thing may be a gui limmitation

smage

2010-01-02 01:59

Re: N900 Radio Transmitter: ways to amplify the radio signal

yes above 118 doesn't seem to make any noticeable difference.

I just wish we could get some more juice out of the radio transmitter as I could really use it :)

Ads	2010-01-02 03:10

Re: N900 Radio Transmitter: ways to amplify the radio signal

Hi - any of you guys that are looking at these files related to the FM transmitter know if there is anything that enables or disables the transmitter? I might be treading on thin ice here, but I have an N900 from Nokia.co.uk and it currently has the FM transmitter disabled! I'm awaiting a call from Nokia about this - but I was just hoping someone might know of an easy answer - unless of course this is a fault and it says it is disabled because it cannot contact it!?!?

Hmm, anyway, just thought I'd throw that in there. Sorry it isn't directly related - other than asking how I can increase my power from, well.. disabled...

optimaxxx

2010-01-02 04:42

Re: N900 Radio Transmitter: ways to amplify the radio signal

have people covered the fact that the transmitter's digital?

i based this on the fact that when i use my phone in my brand new vehicle, it actually displays "NOKIA" on the car's display, it also has perfect sound quality. but in our 1999 Mazda 626, it doesn't display NOkia, and the sound quality is terrible!

YoDude

2010-01-02 23:55

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by DaveQB (Post 448941)

Code:

cat /sys/class/i2c-adapter/i2c-2/2-0063/power_level

Can an xTerm script @root be tied to a desktop shortcut like this command was >> http://talk.maemo.org/showpost.php?p=409122&postcount=3

Having a button to press from the desktop while the transmitter is running is a lot easier to do in a moving vehicle where this hack is most useful.
Opening xTerm, entering root, opening notepad, copying the script, then pasting it in xTerm is a bit cumbersome and I do not have the skills to easily confirm that something like:

Code:

[Desktop Entry]

Encoding=UTF-8

Version=0.1

Type=Application

Terminal=true

Name=POW

Exec=sudo gainroot

Exec=echo 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

Icon=     

#X-Window-Icon=timerwidget

X-Window-Icon=     

X-HildonDesk-ShowInToolbar=true

X-Osso-Type=application/x-executable

would even work and I would have to run back and forth to my car where my only FM radio lives...

...in the dark, on a cold rainy night. Brrrrr! :)

DaveQB

2010-01-03 01:33

Re: N900 Radio Transmitter: ways to amplify the radio signal

Quote:

Originally Posted by YoDude (Post 450532)

Can an xTerm script @root be tied to a desktop shortcut like this command was >> http://talk.maemo.org/showpost.php?p=409122&postcount=3

Code:

[Desktop Entry]

Encoding=UTF-8

Version=0.1

Type=Application

Terminal=true

Name=POW

Exec=sudo gainroot

Exec=echo 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

Icon=     

#X-Window-Icon=timerwidget

X-Window-Icon=     

X-HildonDesk-ShowInToolbar=true

X-Osso-Type=application/x-executable

would even work and I would have to run back and forth to my car where my only FM radio lives...

...in the dark, on a cold rainy night. Brrrrr! :)

I am not familiar with the Desktop files that much, so not sure how having to Exec lines works. Is that right?

And as sudo gainroot launches a login shell, any subsequent commands shouldn't run in there, atleast in a shell script it doesn't, again, not familiar with desktop files.
So one could setuid bit on a script that just runs this command, so it runs with root privileges.

Ok I just read your linked thread. That is a command running as normal user. So it gets tricky to escalate privileges in a command.

The setuid is the best I can think of for now, but people will complain it is not a secure option :)

I need to take a look at that this "gainroot" argument actually does; we might be able to add this command to the suders file so we can simply sudo the command without the need for a password....

DaveQB

2010-01-03 01:40

Re: N900 Radio Transmitter: ways to amplify the radio signal

I openned up /etc/suders and an excerpt.

Code:

### Automatically added by update-sudoers start ###

Defaults env_check+="HOME DISPLAY"

Defaults env_keep+="HOME DISPLAY"

Defaults env_reset

user ALL = NOPASSWD: /usr/sbin/gainroot

user ALL = NOPASSWD: /usr/sbin/mmc-mount /dev/mmcblk0 /media/mmc1

user ALL = NOPASSWD: /usr/sbin/mmc-mount /dev/mmcblk0p1 /media/mmc1

user ALL = NOPASSWD: /bin/umount /media/mmc1,/bin/umount -l /media/mmc1

user ALL = NOPASSWD: /usr/sbin/osso-usb-mass-storage-enable.sh, /usr/sbin/osso-usb-mass-storage-disable.sh

user ALL = NOPASSWD: /sbin/mkdosfs /dev/mmcblk0*, /usr/sbin/mmc-rename /dev/mmcblk0*

user ALL = NOPASSWD: /etc/init.d/af-base-apps stop , /etc/osso-af-init/gconf-daemon.sh stop

user ALL = NOPASSWD: /etc/init.d/af-base-apps start , /etc/osso-af-init/gconf-daemon.sh start

user ALL = NOPASSWD: /etc/init.d/osso-systemui restart

user ALL = NOPASSWD: /usr/sbin/gconf-clean.sh

user ALL = NOPASSWD: /usr/sbin/chroot /mnt/initfs /usr/bin/retutime *

user ALL = NOPASSWD: /sbin/insmod /mnt/initfs/lib/modules/current/g_file_storage.ko stall=0 file=/dev/mmcblk0

user ALL = NOPASSWD: /sbin/insmod /mnt/initfs/lib/modules/current/g_ether.ko

user ALL = NOPASSWD: /sbin/rmmod g_file_storage

user ALL = NOPASSWD: /sbin/rmmod g_ether

user ALL = NOPASSWD: /usr/sbin/osso-backup-restore-locale

user ALL = (install) NOPASSWD: /usr/bin/app-installer-tool

### Automatically added by update-sudoers end ###

### Automatically added by update-sudoers start ###

%users ALL = NOPASSWD: /usr/libexec/apt-worker

%users ALL = NOPASSWD: /usr/bin/hildon-application-manager-util restore-catalogues

%users ALL = NOPASSWD: /usr/bin/hildon-application-manager-util restore-catalogues2

%users ALL = NOPASSWD: /usr/bin/hildon-application-manager-util clear-user-catalogues

### Automatically added by update-sudoers end ###

### Automatically added by update-sudoers start ###

user ALL = NOPASSWD: /usr/bin/personalisation

### Automatically added by update-sudoers end ###

### Automatically added by update-sudoers start ###

user ALL = NOPASSWD: /usr/bin/hildon-input-method-configurator.bin

So, as root, we can add the command we need and then the script can simply be

Code:

sudo echo 118 > /sys/class/i2c-adapter/i2c-2/2-0063/power_level

This is a quick look, I'll spend some more time on it later..

All times are GMT. The time now is 02:14.

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