Bias T

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FrancoisOZ
Posts: 4
Joined: Sun May 31, 2020 10:01 pm

Bias T

Post by FrancoisOZ » Mon Jun 01, 2020 1:24 am

Hi,
i have a RTL-SDR dongle V3.0,
Is it possible to turn on the Bias T permanently ?
I understand that if i turn it on (using the .bat or the command line), it will turn off if i unplplug it from the computer i used to turn it on.
Is that correct ?

Regards,
Francois

Aussie Susan
Posts: 49
Joined: Sun Jul 31, 2016 1:55 am

Re: Bias T

Post by Aussie Susan » Mon Jun 01, 2020 3:01 am

(From Memory) Use the rtl_eeprom software and there is a setting in that to turn on bias-t permanently.
Susan

FrancoisOZ
Posts: 4
Joined: Sun May 31, 2020 10:01 pm

Re: Bias T

Post by FrancoisOZ » Mon Jun 01, 2020 4:06 am

Hi,
thanks for your answer
just checking that i get it right,

1/ get the latest release at
https://github.com/rtlsdrblog/rtl-sdr-blog/releases (it contains the rtl_eeprom)
extract it.

2/use command prompt to navigate to the directory,
plugin the rtl-sdr dongle and then execute:
"rtl_eeprom -b y" to force the BT to be always ON
"rtl_eeprom -b n" to remove forced BT

is that correct?
thanks for your time and patience
F

btw, that should work for a win10 machine.

alanzfq
Posts: 144
Joined: Thu Oct 04, 2018 11:18 am

Re: Bias T

Post by alanzfq » Mon Jun 01, 2020 7:26 am

If you look in that zip you will find 2 batch files.
If you look at those files you will see they work with rtl_biast.exe
Alan

alanzfq
Posts: 144
Joined: Thu Oct 04, 2018 11:18 am

Re: Bias T

Post by alanzfq » Mon Jun 01, 2020 7:36 am

Or, if I look more carefully:-)
RTL_eeprom does it permanently.
Looks like your commands are correct.
Alan

FrancoisOZ
Posts: 4
Joined: Sun May 31, 2020 10:01 pm

Re: Bias T

Post by FrancoisOZ » Tue Jun 02, 2020 6:50 am

ok, i tried to switch the Bias T on and stick to that,
using the com prompt as admin i get

New configuration:
Bias-T Always ON: yes
__________________________________________
Write new configuration to device [y/n]? y

Configuration successfully written.
Please replug the device for changes to take effect.

which i did but i only get 250mV between the centre pin and the threads,
i believe that won't be enough to drive the LNA

any thought?
cheers
F

Aussie Susan
Posts: 49
Joined: Sun Jul 31, 2016 1:55 am

Re: Bias T

Post by Aussie Susan » Wed Jun 03, 2020 3:54 am

Check to make sure that you have a REAL RTL-SDR.
I bought one that was a cheap knock-off and it was completely missing the Bias-t hardware - the chip responded correctly (as did yours) but there was no hardware to provide the voltage.
May not be the issue - you seem to be getting some voltage whereas I only got a few mV.
Susan

FrancoisOZ
Posts: 4
Joined: Sun May 31, 2020 10:01 pm

Re: Bias T

Post by FrancoisOZ » Thu Jun 04, 2020 9:40 am

thanks for your answer,
i bought the dongle from the website link so i expect it to be genuine
i can always open it and check what is inside,
any idea where i can find a schematic?
it will be much easier if i know what to look for
and if i need to do some testing a schematic will be helpful too

cheers
F

rtlsdrblog
Site Admin
Posts: 2743
Joined: Mon Nov 19, 2012 11:54 pm

Re: Bias T

Post by rtlsdrblog » Thu Jun 04, 2020 9:51 am

What software are you running with the dongle? Remember that the EEPROM settings will only be recognized if you are using the rtl-sdr-blog drivers together with your software. Instructions for using the rtl-sdr-blog drivers with SDR# are written in the github readme https://github.com/rtlsdrblog/rtl-sdr-blog

Aussie Susan
Posts: 49
Joined: Sun Jul 31, 2016 1:55 am

Re: Bias T

Post by Aussie Susan » Fri Jun 05, 2020 2:53 am

FrancoisOZ wrote:
Thu Jun 04, 2020 9:40 am
i can always open it and check what is inside,
....
it will be much easier if i know what to look for
Check out https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/ for how it looks inside.
I'm not sure if a schematic is published and the reply in viewtopic.php?t=2197 says that it is not. Therefore I'd be cautious of any schematic you can find on the internet.
Susan

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