RTL-SDR - Why 2.048MHz bandwidth?


Max
 

Could someone please explain to me why the RTL-SDR dongle offers both 2.000 and 2.048 MHz sampling bandwidths? What is the significance of 2.048 ?

Thanks

Max


Simon Brown
 

DAB/DAB+.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of Max via groups.io <radiomax@...>
Sent: 13 September 2022 09:57
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: [SDR-Radio] RTL-SDR - Why 2.048MHz bandwidth?
 
Could someone please explain to me why the RTL-SDR dongle offers both 2.000 and 2.048 MHz sampling bandwidths? What is the significance of 2.048 ?

Thanks

Max

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Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.


jdow
 

Utterly arbitrary coupled with "tradition".

{^_^}

On 20220913 01:57:07, Max wrote:

Could someone please explain to me why the RTL-SDR dongle offers both 2.000 and 2.048 MHz sampling bandwidths? What is the significance of 2.048 ?

Thanks

Max


Ray Lyford
 

It just allows you to change the amount of bandwidth you see on the screen. Larger bandwidth requires more processing power.

Ray

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of jdow <jdow@...>
Sent: 13 September 2022 16:39
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RTL-SDR - Why 2.048MHz bandwidth?
 

Utterly arbitrary coupled with "tradition".

{^_^}

On 20220913 01:57:07, Max wrote:

Could someone please explain to me why the RTL-SDR dongle offers both 2.000 and 2.048 MHz sampling bandwidths? What is the significance of 2.048 ?

Thanks

Max


Max
 

On Tue, Sep 13, 2022 at 05:51 PM, Ray Lyford wrote:
It just allows you to change the amount of bandwidth you see on the screen. Larger bandwidth requires more processing power.
Hi Ray. Thanks for that but that was not what I was asking. I was asking the relevance of the exact figure, 2.048, when 2.000 is available and almost identical. I wondered the reason for having 2048 at all because I onlt see it as a bandwidth option with RTL dongles, so I assume the figure is something to do with the chipset used in the RTL. But what is the "something". Just curiosity, nothing more!

Max


Ken Sejkora
 

Hi Max,

 

Just speculation on my part, but 2048 is a direct ‘binary’ scaling of the number 2, or 2 raised to the 11th power:

2

4

8

16

32

64

128

256

512

1024

2048

4096

8192

16384

  etc.

 

Again, just speculation.

 

Ken -- WBØOCV

 

From: Max
Sent: Tuesday, September 13, 2022 03:57 PM
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] RTL-SDR - Why 2.048MHz bandwidth?

 

On Tue, Sep 13, 2022 at 05:51 PM, Ray Lyford wrote:

It just allows you to change the amount of bandwidth you see on the screen. Larger bandwidth requires more processing power.

Hi Ray. Thanks for that but that was not what I was asking. I was asking the relevance of the exact figure, 2.048, when 2.000 is available and almost identical. I wondered the reason for having 2048 at all because I onlt see it as a bandwidth option with RTL dongles, so I assume the figure is something to do with the chipset used in the RTL. But what is the "something". Just curiosity, nothing more!

Max

 


jdow
 

On 20220913 12:57:25, Max wrote:
On Tue, Sep 13, 2022 at 05:51 PM, Ray Lyford wrote:
It just allows you to change the amount of bandwidth you see on the screen. Larger bandwidth requires more processing power.
Hi Ray. Thanks for that but that was not what I was asking. I was asking the relevance of the exact figure, 2.048, when 2.000 is available and almost identical. I wondered the reason for having 2048 at all because I onlt see it as a bandwidth option with RTL dongles, so I assume the figure is something to do with the chipset used in the RTL. But what is the "something". Just curiosity, nothing more!

Max

I realized this. I believe the very first users selected the set of sample rates you see. In reality there are ranges of numbers that will work. One starts at 900001 samples per second up to 3200000 sps that work programmatically. Speeds over 2.4 Msps seem to drop samples with some precise numbers better than others for unknown reasons. (I remember happening on one such and not noting it. My bad.) Let's see, the other range runs from 225001 sps to 300000 sps/I realize some aspects of those numbers seem silly and arbitrary; but, if you try to program a sample rate of 900000 sps the dongle itself returns an error.

As for going at all past "tradition" some people think decimal and some people think pseudo binary. (Nice power of 2 number of ksps? I never took if out of my tools because then somebody might have complained.)

{^_^}


Max
 

On Tue, Sep 13, 2022 at 10:17 PM, jdow wrote:
I realized this. I believe the very first users selected the set of sample rates you see. In reality there are ranges of numbers that will work. One starts at 900001 samples per second up to 3200000 sps that work programmatically. Speeds over 2.4 Msps seem to drop samples with some precise numbers better than others for unknown reasons.
Thank you Joanne and Ken. Both answers throw some light on it for sure. Attached is the list of the available bandwidths for the RTL. I think you would agree that 2048 is an odd bedfellow as seen in the progression of the list, especially at 2.0 is already in there. Would have expected to see 2.0, 2.1, 2.2 etc. But I've seen the 2048 crop up in other SDR software for the RTL-SDR so I assumed there was some good reason for it.

Anyway, not very important. Simply one of those "just wondered" moments!

Max


jdow
 

2097152 would be the real bit-head choice not that it would be accurate 1 Hz steps in any case.

{^_-}

On 20220913 14:40:38, Max wrote:

On Tue, Sep 13, 2022 at 10:17 PM, jdow wrote:
I realized this. I believe the very first users selected the set of sample rates you see. In reality there are ranges of numbers that will work. One starts at 900001 samples per second up to 3200000 sps that work programmatically. Speeds over 2.4 Msps seem to drop samples with some precise numbers better than others for unknown reasons.
Thank you Joanne and Ken. Both answers throw some light on it for sure. Attached is the list of the available bandwidths for the RTL. I think you would agree that 2048 is an odd bedfellow as seen in the progression of the list, especially at 2.0 is already in there. Would have expected to see 2.0, 2.1, 2.2 etc. But I've seen the 2048 crop up in other SDR software for the RTL-SDR so I assumed there was some good reason for it.

Anyway, not very important. Simply one of those "just wondered" moments!

Max

RTL1.jpg


Piotr Swiatkiewicz
 

I see it was precisely and accurately answered by Simon above. Realtek developed DLLs for DAB decoding and it was convenient to use the proper sampling rate for that purpose, i.e. one that exactly matches the symbol duration used in DAB transmission frames.

Hope it helps.
--
Piotr Świątkiewicz
SDR enthusiast
------
Wrocław, Poland


David J Taylor
 

While looking at this, I found an interesting set of lecture notes:

http://www.ee.ic.ac.uk/hp/staff/dmb/courses/dab/dab_1.pdf

A quite remarkable system!

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv


Max
 

On Wed, Sep 14, 2022 at 07:11 PM, Piotr Swiatkiewicz wrote:
I see it was precisely and accurately answered by Simon above. Realtek developed DLLs for DAB decoding and it was convenient to use the proper sampling rate for that purpose, i.e. one that exactly matches the symbol duration used in DAB transmission frames.
Many thanks Piotr and Simon, and also David for the link to DAB lecture. Exactly the answer I was looking for. Mystery solved!

Max


John Aldridge
 

A beautiful design sadly crippled by a combination of an obsolete inefficient codec (MP2) and commercial pressure to reduce bit rates in order to squeeze more channels :(

I recall going into a HiFi shop with money burning a hole in my pocket to buy a DAB receiver, and walking out an hour later without having bought anything, having decided that FM sounded better.

John

On 15/09/2022 08:30, David J Taylor via groups.io wrote:
While looking at this, I found an interesting set of lecture notes:
  http://www.ee.ic.ac.uk/hp/staff/dmb/courses/dab/dab_1.pdf
A quite remarkable system!


Simon Brown
 

Yes,

Good FM sounds better but​ on DAB we have stations that would otherwise not be available, for example Jazz FM (32 ksps). And a DAB transmitter uses far less power.

Even on BBC R3 (192 kbps) I can hear the digitisation which I can't on FM.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of John Aldridge via groups.io <jpsa@...>
Sent: 15 September 2022 11:24
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RTL-SDR - Why 2.048MHz bandwidth?
 
A beautiful design sadly crippled by a combination of an obsolete
inefficient codec (MP2) and commercial pressure to reduce bit rates in
order to squeeze more channels :(

I recall going into a HiFi shop with money burning a hole in my pocket
to buy a DAB receiver, and walking out an hour later without having
bought anything, having decided that FM sounded better.

John

On 15/09/2022 08:30, David J Taylor via groups.io wrote:
> While looking at this, I found an interesting set of lecture notes:
>
>    http://www.ee.ic.ac.uk/hp/staff/dmb/courses/dab/dab_1.pdf
>
> A quite remarkable system!







--
- + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.


Siegfried Jackstien
 

most fm stations have a compressed dynamic range so dab may sound better but if you hear THE SAME station on dab (to compare fm with dab) then you may have that same compression on the dab audio stream

 ... you hear digitalisation with 192k?? you must have "bat " ears :-)

greetz sigi dg9bfc


ps ... i know a trick how to listen to dab stations in sdr radio console ... receive it with a pluto and retransmit in fm stereo (with software qt-dab) ... works superb and even supports RDS!!!


greetz sigi dg9bfc

Am 15.09.2022 um 13:08 schrieb Simon Brown:

Yes,

Good FM sounds better but​ on DAB we have stations that would otherwise not be available, for example Jazz FM (32 ksps). And a DAB transmitter uses far less power.

Even on BBC R3 (192 kbps) I can hear the digitisation which I can't on FM.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of John Aldridge via groups.io <jpsa@...>
Sent: 15 September 2022 11:24
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RTL-SDR - Why 2.048MHz bandwidth?
 
A beautiful design sadly crippled by a combination of an obsolete
inefficient codec (MP2) and commercial pressure to reduce bit rates in
order to squeeze more channels :(

I recall going into a HiFi shop with money burning a hole in my pocket
to buy a DAB receiver, and walking out an hour later without having
bought anything, having decided that FM sounded better.

John

On 15/09/2022 08:30, David J Taylor via groups.io wrote:
> While looking at this, I found an interesting set of lecture notes:
>
>    http://www.ee.ic.ac.uk/hp/staff/dmb/courses/dab/dab_1.pdf
>
> A quite remarkable system!







--
- + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.


Piotr Swiatkiewicz
 

On Thu, Sep 15, 2022 at 01:19 PM, Siegfried Jackstien wrote:

ions in sdr radio console ... receive it with a pluto and retransmit in fm stereo (with software qt-dab) ... works superb and even supports RDS!!!

 

Hmmmm..... so you are saying it picks relevant data from DAB's FIC and re-packages those into RDS packets / groups? Interesting.
 
--
Piotr Świątkiewicz
SDR enthusiast
------
Kraków, Poland


Piotr Swiatkiewicz
 
Edited

Even on BBC R3 (192 kbps) I can hear the digitisation which I can't on FM.


Interestng. Can it be FM has far better content delivery to broadcasting centres (i.e. transmitters) than DAB? In my country people in the know say FM content delivery is 192 kbps, so FM actually is better quality compared to the same content delivered as a 112k or 96k stream (AAC) in DAB.
--
Peter


Piotr Swiatkiewicz
 

On Thu, Sep 15, 2022 at 12:24 PM, John Aldridge wrote:
A beautiful design sadly crippled by a combination of an obsolete inefficient codec (MP2) and commercial pressure to reduce bit rates in order to squeeze more channels :(
That's why an update emerged at some point, DAB+. It uses AAC codec. Somehow, the UK did not really switch over to this new concept and largely remained with old services on air.

----
Peter


Siegfried Jackstien
 

Yes... Takes station name, artist and title from dab stream and modulates the rds data stream with that info. 
I did a few local tests here... No i did not add a 100w w amp behind the pluto.. But it could be done... Grin
Works fine to receive your preferred dab radio stn on grandmas old kitchen radio 
Dg9bfc sigi

Ps there is a reason why i say one pluto is never enough... Just too many things can be done with it

Am 16.09.2022 06:54 schrieb Piotr Swiatkiewicz <pswiatki@...>:

On Thu, Sep 15, 2022 at 12:24 PM, John Aldridge wrote:
A beautiful design sadly crippled by a combination of an obsolete inefficient codec (MP2) and commercial pressure to reduce bit rates in order to squeeze more channels :(
That's why an update emerged at some point, DAB+. It uses AAC codec. Somehow, the UK did not really switch over to this new concept and largely remained with old services on air.

----
Peter


jdow
 

Anybody who thinks they can hear better audio at 192 ksps than 96 ksps is kidding themselves. Anybody who says they can hear a difference between 48 ksps and 96 ksps is most likely kidding themselves if they are not young and complain a lot about the squeal of ultrasonic burglar alarms. The same can be said about 32 bits vs 16 bits for most program material. Ravel's "Bolero" recorded in a setting with the HVAC system disabled might be an exception. The source material is generally noisy enough that only 80 dB above that noise your ears are taking damage and you may be in pain.

{o.o}   Work out the numbers yourself. Also learn how ears work. It's actually worse than I "assumed" above.

On 20220915 21:49:58, Piotr Swiatkiewicz wrote:

Interestng. Can it be FM has far better content delivery to broadcasting centres (i.e. transmitters) than DAB? In my country people in the know say FM content delivery is 192 kbps, so FM actually is better quality compared to the same content delivered as a 112k or 96k stream (AAC) in DAB.
--
Peter