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Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder


Peter 1956
 

Often RDS Spy grabs a PI when the native RDS decoder draws a blank. In one case RDS Spy had full RDS when the SDR Console V3.0.26 had nothing!
https://youtu.be/9y2X-_eHwHA
 
Peter

Botswana


Simon Brown
 

It would be very interesting to see the BFM Spectrum as well, especially the RDS portion with a decent resolution.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Peter 1956
Sent: 29 December 2020 09:53
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

Often RDS Spy grabs a PI when the native RDS decoder draws a blank. In one case RDS Spy had full RDS when the SDR Console V3.0.26 had nothing!

 

Peter

Botswana


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Peter 1956
 

Hello Simon

Photos of the BFM Spectrum attached. Three levels of RDS decode.
106.6 YARONAFM full RDS in RDS Spy, PI only in V3
96.2 PI in RDS Spy, nothing in V3
95.8 Full RDS in RDS Spy and V3 Jacaranda FM A407

Peter


Simon Brown
 

Peter,

 

This time please start the BFM Spectrum window?

 

For RDS to decode you must remember Carlson’s rule! Watch the BFM Spectrum, make sure the selected bandwidth is enough for the RDS to be visible.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Peter 1956
Sent: 29 December 2020 13:15
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

Hello Simon

Photos of the BFM Spectrum attached. Three levels of RDS decode.
106.6 YARONAFM full RDS in RDS Spy, PI only in V3
96.2 PI in RDS Spy, nothing in V3
95.8 Full RDS in RDS Spy and V3 Jacaranda FM A407

Peter


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Peter 1956
 

Eh?

I'm lost. RDS was decoding.

Peter


Simon Brown
 

Hi,

 

  1. Please enable the BFM Spectrum window! There’s NO signal, your screenshots just show an empty window .
  2. You MUST respect Carlson’s rule – in at least one of your screenshots the bandwidth was so low that the RDS at 57kHz didn’t have a fair chance.

 

I would like to see the BFM Spectrum with a signal present – pretty please?

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Peter 1956
Sent: 29 December 2020 13:15
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

Hello Simon

Photos of the BFM Spectrum attached. Three levels of RDS decode.
106.6 YARONAFM full RDS in RDS Spy, PI only in V3
96.2 PI in RDS Spy, nothing in V3
95.8 Full RDS in RDS Spy and V3 Jacaranda FM A407

Peter


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Peter 1956
 

How was I supposed to know if you didn't tell me exactly what you wanted?
Using the term "BFM" is confusing enough

RDS was being received by RDS Spy in each of the three photos I sent before.

I think I'll go back to using SDR# - much more intuitive  ;)


Mag loop Simon
 

Ohhh

Lesson in how to lose friends here..

Mag loop Simon


Simon Brown
 

Bye.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Peter 1956
Sent: 29 December 2020 16:07
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

How was I supposed to know if you didn't tell me exactly what you wanted?
Using the term "BFM" is confusing enough

RDS was being received by RDS Spy in each of the three photos I sent before.

I think I'll go back to using SDR# - much more intuitive  ;)


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Simon Brown
 

Meh.

Win some, lose some.

Simon Brown, G4ELI
https://www.sdr-radio.com

-----Original Message-----
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Mag
loop Simon
Sent: 29 December 2020 16:31
To: main@sdr-radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR
Console native RDS decoder

Ohhh

Lesson in how to lose friends here..

Mag loop Simon









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Siegfried Jackstien
 

normal friends come and go ... enemies are forever :-)

only REAL friends also are forever (if you have some ... keep them ... be good to them ... they are worth it)

73 de dg9bfc sigi

Am 29.12.2020 um 16:38 schrieb Simon Brown:

Meh.

Win some, lose some.

Simon Brown, G4ELI
https://www.sdr-radio.com

-----Original Message-----
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Mag
loop Simon
Sent: 29 December 2020 16:31
To: main@sdr-radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR
Console native RDS decoder

Ohhh

Lesson in how to lose friends here..

Mag loop Simon









Paul White
 

On Tue, Dec 29, 2020 at 03:06 PM, Simon Brown wrote:
  • Please enable the BFM Spectrum window! There’s NO signal, your screenshots just show an empty window .
  • You MUST respect Carlson’s rule – in at least one of your screenshots the bandwidth was so low that the RDS at 57kHz didn’t have a fair chance.
Hi, Simon. Hope you don't mind a couple of questions on this?
  1. The BFM window is very neat, and a godsend, but sadly doesn't also show the current IF bandwidth. Given that sufficient bandwidth is vital for (native) RDS decoding, I'm wondering if IF filter profile could somehow be superimposed?
    Of course, asymmetric lower/upper would complicate the result - could even both be shown?
  2. How much bandwidth is required for RDS decoding is not easy for dummies like me to judge, and seems dependent on filter profile as well as SNR. Naively, one might have expected 125 kHz (±62.5 kHz) to be adequate but that seems not to be true (because filters are not brick wall?). If you have any guidance, that would be most appreciated.
All the best


Jim Smith G0OFE
 

Paul,

I have always used 120khz as a benchmark.. having experimented with the FM Broiadcast spectrum and seeing the twin peaks of the RDS and seeing how they rise and fall with tweaking the bandwidth. I have had very few occasions when I've needed to have the filter any wider to make any difference in getting a PI Code.

Your mileage, as always, may vary.

================================
Need help with SDR Console? If you have a problem:
Go to https://www.sdr-radio.com/support
Please follow instructions in that link.
===================================
Jim, Bournemouth, Dorset. IO90BR.
Elad FDM-S2, Airspy HF+, SDRPlay and Funcube Dongle SDR Recievers
8-element OP-DES for Band 2, 8-element LFA for 2m, 3-element LFA for 6m, 20m Windom for HF,. Wellbrook 1530 Loop for LF


On 29/12/2020 18:01, Paul White wrote:
  1. How much bandwidth is required for RDS decoding is not easy for dummies like me to judge, and seems dependent on filter profile as well as SNR. Naively, one might have expected 125 kHz (±62.5 kHz) to be adequate but that seems not to be true (because filters are not brick wall?). If you have any guidance, that would be most appreciated.
All the best


Simon Brown
 

Hi,

 

I could show the filter info in the spectrum window, may add that tomorrow or Thursday.

 

What’s important for RDS is that the RDS ‘humps’ at 57 kHz are visible and ~10dB above the rest of the nearby noise/signal. Try adjusting the filter and you’ll see how this changes. I tend to use 150kHz as being the minimum, but due to the nature of FM you really want as much of the signal as possible. FM’s not the same as AM or SSB – in fact a very different beast.

 

If you want to go Googling look for Carlson’s rule for FM.

 

https://en.wikipedia.org/wiki/Carson_bandwidth_rule

 

And Broadcast FM modulation index. I can’t remember off the top of my head what a typical modulation index is here.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Paul White
Sent: 29 December 2020 18:01
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

On Tue, Dec 29, 2020 at 03:06 PM, Simon Brown wrote:

  • Please enable the BFM Spectrum window! There’s NO signal, your screenshots just show an empty window .
  • You MUST respect Carlson’s rule – in at least one of your screenshots the bandwidth was so low that the RDS at 57kHz didn’t have a fair chance.

Hi, Simon. Hope you don't mind a couple of questions on this?

  1. The BFM window is very neat, and a godsend, but sadly doesn't also show the current IF bandwidth. Given that sufficient bandwidth is vital for (native) RDS decoding, I'm wondering if IF filter profile could somehow be superimposed?
    Of course, asymmetric lower/upper would complicate the result - could even both be shown?
  2. How much bandwidth is required for RDS decoding is not easy for dummies like me to judge, and seems dependent on filter profile as well as SNR. Naively, one might have expected 125 kHz (±62.5 kHz) to be adequate but that seems not to be true (because filters are not brick wall?). If you have any guidance, that would be most appreciated.

All the best


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


Brian Morrison
 

On Tue, 2020-12-29 at 18:24 +0000, Simon Brown wrote:
And Broadcast FM modulation index. I can’t remember off the top of my head what a typical modulation index is here.

For broadcast FM it's normally 5, with 75kHz deviation and max audio frequency of 15kHz.

-- 

Brian  G8SEZ



Paul White
 

On Tue, Dec 29, 2020 at 06:16 PM, Jim Smith G0OFE wrote:
I have always used 120khz as a benchmark.
Thanks, Jim, pretty much the conclusion I came to.


Simon Brown
 

Yes,

 

120kHz is probably the lowest limit. When I took a break after shipping 3.0.26 I spent a week redesigning some of the RDS filtering – it’s a somewhat complicated DSP path. I found some bugs, some filters were far from optimal, I added a few extras such as AGC and improved data smoothing. The result was an improvement is sensitivity. I have one last part to do next year – show the 1187.5 Hz bit stream in a similar fashion to RDSSPY so I can be sure I’m correctly in sync.

 

I’ve attached one example of how the processing is performed. You can take shortcuts, but at the risk of seriously reduced sensitivity.

 

Good decoding of RDS is no trivial matter, and we have RDS 2 coming sometime…

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Jim Smith G0OFE
Sent: 29 December 2020 18:17
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

Paul,

I have always used 120khz as a benchmark.. having experimented with the FM Broiadcast spectrum and seeing the twin peaks of the RDS and seeing how they rise and fall with tweaking the bandwidth. I have had very few occasions when I've needed to have the filter any wider to make any difference in getting a PI Code.

Your mileage, as always, may vary.

================================
Need help with SDR Console? If you have a problem:
Go to https://www.sdr-radio.com/support
Please follow instructions in that link.
===================================
Jim, Bournemouth, Dorset. IO90BR.
Elad FDM-S2, Airspy HF+, SDRPlay and Funcube Dongle SDR Recievers
8-element OP-DES for Band 2, 8-element LFA for 2m, 3-element LFA for 6m, 20m Windom for HF,. Wellbrook 1530 Loop for LF

On 29/12/2020 18:01, Paul White wrote:

  1. How much bandwidth is required for RDS decoding is not easy for dummies like me to judge, and seems dependent on filter profile as well as SNR. Naively, one might have expected 125 kHz (±62.5 kHz) to be adequate but that seems not to be true (because filters are not brick wall?). If you have any guidance, that would be most appreciated.

All the best


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


Paul White
 

On Tue, Dec 29, 2020 at 06:24 PM, Simon Brown wrote:
FM’s not the same as AM or SSB – in fact a very different beast.
Really grateful you pointed that out (wish I'd spent more time learning than dreaming).
So a filter overlay would be of limited use (except perhaps as a graphical cue), and may not be worth you diverting effort :D


Paul White
 

On Tue, Dec 29, 2020 at 07:02 PM, Simon Brown wrote:
I’ve attached one example of how the processing is performed.
Phew! Sooner you than me.


Simon Brown
 

So if I get grumpy at times you know why 😊 .

 

Seriously bad for the brain.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Paul White
Sent: 29 December 2020 19:17
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Troposcatter with RDS. Comparing RDS Spy with SDR Console native RDS decoder

 

On Tue, Dec 29, 2020 at 07:02 PM, Simon Brown wrote:

I’ve attached one example of how the processing is performed.

Phew! Sooner you than me.


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