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RE: [sdr-radio-com] NFM de-emph pictures. [2 Attachments]

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  • Simon Brown
    Excellent. Are these made with my software? Simon Brown (G4ELI/HB9DRV) http://v2.sdr-radio.com From: sdr-radio-com@yahoogroups.com
    Message 1 of 13 , Feb 25, 2014
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      Excellent.

       

      Are these made with my software?

       

      Simon Brown (G4ELI/HB9DRV)
      http://v2.sdr-radio.com

       

      From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Paul PD0PSB
      Sent: 25 February 2014 09:44
      To: sdr-radio-com@yahoogroups.com
      Subject: [sdr-radio-com] NFM de-emph pictures. [2 Attachments]

       

       

      [Attachment(s) from Paul PD0PSB included below]

      Hi,

      This is a pretty nice quick&handy audio analyzer:
      http://www.hitsquad.com/smm/programs/VA/

      Attached two pictures to compare.
      Correct NFM de-emph is quite steep and gives a nice mellow "dark brown" noise.
      This in combination with 250-3500Hz BPF should be excellent to keep CTCSS out.

      73
      Paul
      PD0PSB

    • Simon Brown
      I mean were the recordings made with my stuff? Simon Brown (G4ELI/HB9DRV) http://v2.sdr-radio.com From: sdr-radio-com@yahoogroups.com
      Message 2 of 13 , Feb 25, 2014
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        I mean were the recordings made with my stuff?

         

        Simon Brown (G4ELI/HB9DRV)
        http://v2.sdr-radio.com

         

        From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Simon Brown
        Sent: 25 February 2014 12:12
        To: sdr-radio-com@yahoogroups.com
        Subject: RE: [sdr-radio-com] NFM de-emph pictures.

         

         

        Excellent.

         

        Are these made with my software?

         

        Simon Brown (G4ELI/HB9DRV)
        http://v2.sdr-radio.com

         

        From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Paul PD0PSB
        Sent: 25 February 2014 09:44
        To: sdr-radio-co m@yahoogroups.com
        Subject: [sdr-radio-com] NFM de-emph pictures. [2 Attachments]

         

         

        [Attachment(s) from Paul PD0PSB included below]

        Hi,

        This is a pretty nice quick&handy audio analyzer:
        http://www.hitsquad.com/smm/programs/VA/

        Attached two pictures to compare.
        Correct NFM de-emph is quite steep and gives a nice mellow "dark brown" noise.
        This in combination with 250-3500Hz BPF should be excellent to keep CTCSS out.

        73
        Paul
        PD0PSB

      • Simon Brown
        Paul, Many, many thanks. I had my de-emphasis time constant far too low, cut-off / corner frequency was ~ 2.65kHz! For Ham repeaters what is the suggested
        Message 3 of 13 , Feb 25, 2014
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          Paul,

           

          Many, many thanks. I had my de-emphasis time constant far too low, cut-off / corner frequency was ~ 2.65kHz!

           

          For Ham repeaters what is the suggested cut-off / corner-frequency? On the internet there’s plenty of waffle but I can’t find a definitive standard.

           

          Simon Brown (G4ELI/HB9DRV)
          http://v2.sdr-radio.com

           

          From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Paul PD0PSB
          Sent: 25 February 2014 09:44
          To: sdr-radio-com@yahoogroups.com
          Subject: [sdr-radio-com] NFM de-emph pictures. [2 Attachments]

           

           

          [Attachment(s) from Paul PD0PSB included below]

          Hi,

          This is a pretty nice quick&handy audio analyzer:
          http://www.hitsquad.com/smm/programs/VA/

          Attached two pictures to compare.
          Correct NFM de-emph is quite steep and gives a nice mellow "dark brown" noise.
          This in combination with 250-3500Hz BPF should be excellent to keep CTCSS out.

          73
          Paul
          PD0PSB

        • Simon Brown
          Hi, Here’s how it looks now: · First shot – white noise, shows slope as expected · Second shot – transmission, not speaking, flat as
          Message 4 of 13 , Feb 25, 2014

          Hi,

           

          Here’s how it looks now:

           

          ·        First shot – white noise, shows slope as expected

          ·        Second shot – transmission, not speaking, flat as expected

           

          Simon Brown (G4ELI/HB9DRV)
          http://v2.sdr-radio.com

           

          From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of pd0psb@...
          Sent: 25 February 2014 13:13
          To: sdr-radio-com@yahoogroups.com
          Subject: RE: [sdr-radio-com] NFM de-emph pictures.

           

           

          Audio recordings are labeled.
          The "SDR-Radio V2 de-emph" recording is directly via VAC out of V2.
          The "NFM correct de-emph" recording is from another source.

          Here is a good link with info on the matter:
          http://www.cliftonlaboratories.com/fm_receivers_and_de-emphasis.htm
          On the bottom of the page are some examples.

          I think BPF 250-3500Hz and a 6dB/oct downhill slope should be close to ideal.

          73
          Paul
          PD0PSB

        • Simon Brown
          And FWIW I have set the corner (cut-off) frequency to 300Hz. Does sound better despite the bar hearing here… Simon Brown (G4ELI/HB9DRV)
          Message 5 of 13 , Feb 25, 2014
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            And FWIW I have set the corner (cut-off) frequency to 300Hz.

             

            Does sound better despite the bar hearing here…

             

            Simon Brown (G4ELI/HB9DRV)
            http://v2.sdr-radio.com

             

            From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Simon Brown

            Here’s how it looks now:

            ·        First shot – white noise, shows slope as expected

            ·        Second shot – transmission, not speaking, flat as expected

             

          • Simon Brown
            Thanks, As far as I can tell the de-emphasis corner frequency is the low-end of the BPF. The K3 seems very narrow… Simon Brown (G4ELI/HB9DRV)
            Message 6 of 13 , Feb 25, 2014
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              Thanks,

               

              As far as I can tell the de-emphasis corner frequency is the low-end of the BPF. The K3 seems very narrow…

               

              Simon Brown (G4ELI/HB9DRV)
              http://v2.sdr-radio.com

               

              From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of pd0psb@...
              Sent: 25 February 2014 13:37
              To: sdr-radio-com@yahoogroups.com
              Subject: RE: [sdr-radio-com] NFM de-emph pictures.

               

               

              Looks to sound nice.
              There does not really seem to be a strict standard, especially not in Ham equipment.

              I once measured the Elecraft K3 NFM response.
              It has a BPF from 400-2500Hz and a 6dB/oct downslope, but it sounds a bit pushed narrow.
              Other brands have milder BPF allowing a bit more low end (250Hz) and a bit more high (3 to 3,5kHz)
              I hardly ever see the highest CTCSS tones used (200-254Hz) since they overlap with vocal cord.

              I guess your curve should please most :-)

              73
              Paul
              PD0PSB

            • Jack Smith
              I have some measured de-emphasis data on my web site at: http://www.cliftonlaboratories.com/fm_receivers_and_de-emphasis.htm It includes the K3 (an older
              Message 7 of 13 , Feb 25, 2014
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                I have some measured de-emphasis data on my web site at:

                http://www.cliftonlaboratories.com/fm_receivers_and_de-emphasis.htm

                It includes the K3 (an older firmware release than is current) and three commercial two-way receivers, as well as an FM broadcast tuner.

                There's quite a variation in how RCA, GE and Motorola implemented frequency shaping in their two-way gear.

                Jack K8ZOA

                On 2/25/2014 7:56 AM, Simon Brown wrote:
                 

                Thanks,

                 

                As far as I can tell the de-emphasis corner frequency is the low-end of the BPF. The K3 seems very narrow…

                 

                Simon Brown (G4ELI/HB9DRV)
                http://v2.sdr-radio.com

                 

                From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of pd0psb@...
                Sent: 25 February 2014 13:37
                To: sdr-radio-com@yahoogroups.com
                Subject: RE: [sdr-radio-com] NFM de-emph pictures.

                 

                 

                Looks to sound nice.
                There does not really seem to be a strict standard, especially not in Ham equipment.

                I once measured the Elecraft K3 NFM response.
                It has a BPF from 400-2500Hz and a 6dB/oct downslope, but it sounds a bit pushed narrow.
                Other brands have milder BPF allowing a bit more low end (250Hz) and a bit more high (3 to 3,5kHz)
                I hardly ever see the highest CTCSS tones used (200-254Hz) since they overlap with vocal cord.

                I guess your curve should please most :-)

                73
                Paul
                PD0PSB


              • Simon Brown
                Ah, In my code that’s broadcast FM. I don’t think there’s a deviation for Wide-FM (48kHz)? Simon Brown (G4ELI/HB9DRV) http://v2.sdr-radio.com From:
                Message 8 of 13 , Feb 25, 2014
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                  Ah,

                   

                  In my code that’s broadcast FM. I don’t think there’s a deviation for Wide-FM (48kHz)?

                   

                  Simon Brown (G4ELI/HB9DRV)
                  http://v2.sdr-radio.com

                   

                  From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of pd0psb@...
                  Sent: 25 February 2014 14:11
                  To: sdr-radio-com@yahoogroups.com
                  Subject: RE: [sdr-radio-com] NFM de-emph pictures.

                   

                   

                  >As far as I can tell the de-emphasis corner frequency is the low-end of the BPF.
                  Correct.
                  Except for WFM, where the de-emph downslope starts at around 2,1kHz.
                  (That might have been the initial mix up)

                  BTW if you feed the squelch with post-deemphasis output: recheck levels with new curve ;-)

                  73
                  Paul
                  PD0PSB

                • Jack Smith
                  While it s not 100% clear on whether the 137 MHz WX satellite transmissions use pre/de emphasis, the NOAA s 2009 Handbook on weather satellite receivers makes
                  Message 9 of 13 , Feb 25, 2014
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                    While it's not 100% clear on whether the 137 MHz WX satellite transmissions use pre/de emphasis, the NOAA's 2009 Handbook on weather satellite receivers makes no mention of modifications to FM receivers to bring out audio ahead of the de-emphasis network. Rather the audio output is conventional speaker or line-output, after the de-emphasis circuit.
                    http://www.noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Stations_March_2009.pdf.

                    In the days of AFSK RTTY over 2-meter band FM gear, we used 2125/2975 Hz tones and the usual practice was to set the transmit level such that the received level of the two tones was matched. Hence de/pre-emphasis was used and the levels adjusted to net it out.

                    Jack K8ZOA

                    On 2/25/2014 11:56 AM, pd0psb@... wrote:
                     

                    For datamodes in Wide-FM (WX Sats, POCSAG, etc), I would expect no de-emphasis is wanted.
                    Not 200% sure

                    I would call 15-45kHz intermediate/medium bandwidth.
                    Broadcast is already in the books as WBFM.
                    Flavours,flavours...

                    73
                    Paul
                    PD0PSB


                  • Simon Brown
                    Jack, I doubt very much that the WX sats use pre-emphasis. Simon Brown (G4ELI/HB9DRV) http://v2.sdr-radio.com From: sdr-radio-com@yahoogroups.com
                    Message 10 of 13 , Feb 25, 2014
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                      Jack,

                       

                      I doubt very much that the WX sats use pre-emphasis.

                       

                      Simon Brown (G4ELI/HB9DRV)
                      http://v2.sdr-radio.com

                       

                      From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Jack Smith
                      Sent: 25 February 2014 18:17
                      To: sdr-radio-com@yahoogroups.com
                      Subject: Re: [sdr-radio-com] NFM de-emph pictures.

                       

                       

                      While it's not 100% clear on whether the 137 MHz WX satellite transmissions use pre/de emphasis, the NOAA's 2009 Handbook on weather satellite receivers makes no mention of modifications to FM receivers to bring out audio ahead of the de-emphasis network. Rather the audio output is conventional speaker or line-output, after the de-emphasis circuit.
                      http://www.noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Stations_March_2009.pdf.

                      In the days of AFSK RTTY over 2-meter band FM gear, we used 2125/2975 Hz tones and the usual practice was to set the transmit level such that the received level of the two tones was matched. Hence de/pre-emphasis was used and the levels adjusted to net it out.

                      Jack K8ZOA

                      On 2/25/2014 11:56 AM, pd0psb@... wrote:

                       

                      For datamodes in Wide-FM (WX Sats, POCSAG, etc), I would expect no de-emphasis is wanted.
                      Not 200% sure

                      I would call 15-45kHz intermediate/medium bandwidth.
                      Broadcast is already in the books as WBFM.
                      Flavours,flavours...

                      73
                      Paul
                      PD0PSB

                       

                    • Jack Smith
                      Simon: I can think of several factors suggesting it is used: 1) Pre-emphasis / de-emphasis increases the S/N by removing high frequency noise. The link margins
                      Message 11 of 13 , Feb 25, 2014
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                        Simon:

                        I can think of several factors suggesting it is used:

                        1) Pre-emphasis / de-emphasis increases the S/N by removing high frequency noise. The link margins were carefully engineered for a 5 watt orbiting transmitter and it's difficult to believe the benefits of improved S/N were ignored.
                        2) I've looked at several technical papers describing various APT decoding hardware and receiver connections. None have suggested a direct discriminator connection (ahead of de-emphasis).  This means the picture decoding hardware was fed with audio that rolls off at 6 dB/octave (or in some receivers 12 dB/octave) above a threshold point. None of the decoding hardware schematics I looked at (including the NASA developed one from the early 1970's) had other than a flat frequency response characteristic. The only way to achieve a flat frequency response from audio into TX through audio out of RX when the RX is a stock receiver with de-emphasis is via pre-emphasis at the transmitter.
                        3) pre-emphasis / de-emphasis has widely been used in broadband analog microwave systems "back in the day" when you might find 3600 SSB voice channels multiplexed onto a wideband FM modulated microwave network. The reasoning was to improve the S/N for the upper frequency sub-carriers as without P/D the S/N would degrade due to the bath-tub shape of an FM receiver without de-emphasis.  Whilst the lower frequency sub-carriers might have good S/N, the higher frequency sub-carriers would not without P/D.

                        These reasons lead me to believe it more probable than not that the AM data subcarrier / FM modulated main carrier approach used in the 137 MHz band used P/D, but so far I've been unable to find a definitive statement one way or the other.

                        Jack K8ZOA



                        On 2/25/2014 12:22 PM, Simon Brown wrote:
                         

                        Jack,

                         

                        I doubt very much that the WX sats use pre-emphasis.

                         

                        Simon Brown (G4ELI/HB9DRV)
                        http://v2.sdr-radio.com

                         

                        From: sdr-radio-com@yahoogroups.com [mailto:sdr-radio-com@yahoogroups.com] On Behalf Of Jack Smith
                        Sent: 25 February 2014 18:17
                        To: sdr-radio-com@yahoogroups.com
                        Subject: Re: [sdr-radio-com] NFM de-emph pictures.

                         

                         

                        While it's not 100% clear on whether the 137 MHz WX satellite transmissions use pre/de emphasis, the NOAA's 2009 Handbook on weather satellite receivers makes no mention of modifications to FM receivers to bring out audio ahead of the de-emphasis network. Rather the audio output is conventional speaker or line-output, after the de-emphasis circuit.
                        http://www.noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Stations_March_2009.pdf.

                        In the days of AFSK RTTY over 2-meter band FM gear, we used 2125/2975 Hz tones and the usual practice was to set the transmit level such that the received level of the two tones was matched. Hence de/pre-emphasis was used and the levels adjusted to net it out.

                        Jack K8ZOA

                        On 2/25/2014 11:56 AM, pd0psb@... wrote:

                         

                        For datamodes in Wide-FM (WX Sats, POCSAG, etc), I would expect no de-emphasis is wanted.
                        Not 200% sure

                        I would call 15-45kHz intermediate/medium bandwidth.
                        Broadcast is already in the books as WBFM.
                        Flavours,flavours...

                        73
                        Paul
                        PD0PSB

                         


                      • Jack Smith
                        Paul: I understand Dolby A to be, at its core, a compandering system applied to high frequencies. Compression at the transmit end (or going into the tape) and
                        Message 12 of 13 , Feb 25, 2014
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                          Paul:

                          I understand Dolby A to be, at its core, a compandering system applied to high frequencies.  Compression at the transmit end (or going into the tape) and expansion at the receive end (out of the tape), so it combined pre-emphasis / de-emphasis, and compandering.

                          Compandering was used in the early analog cellular systems in the USA -- the AMPS system.  I don't know if it was used in NMT or the German NetZ-A or B systems or the others. But the AMPS compandering was separate from the pre-emphasis / de-emphasis, unlike Dolby A.

                          To the best of my knowledge, compandering was not used on common analog two-way radio systems. I suspect this was due to several reasons:

                          1) Interoperability with existing inventory of equipment and with other systems
                          2) Dolby A wasn't really necessary; normal pre-/de-emphasis worked fine in the narrow band two-way spectrum.  The movie sound systems with optical density recording were trying to get much more bandwidth de-noised than the usual 300 Hz - 3 KHz audio range in two-way systems, so more heroic measures were necessary.

                          The FCC in the US tried to push "amplitude compandered SSB" as a more spectrum efficient replacement for conventional 5 KHz deviation two-way FM in the late 1970's/early 80's. In theory, you could put 4 or 5 ACSSB channels in the place of one 5 KHz standard FM channel of 16 KHz bandwidth.  However, ACSSB was never adopted beyond a few experimental systems for several reasons. One being that the technology was on the edge of being commercially reasonable at the time. And second, huge interoperability problems--a police department or taxi company would have to replace 100% of its mobile radios and 100% of base stations, remote receivers, repeaters, etc. if it switched from NBFM to ACSSB. Huge expense compared with purchasing new equipment to replace obsolete gear. Money seems to be no problem these days; governments just have to say they need to protect their communications systems from unwanted interception and millions of dollars are magically made available for digital radio networks involving 100% replacement of analog equipment.

                          Jack
                           


                          On 2/25/2014 3:40 PM, pd0psb@... wrote:
                           

                          Hi Jack,


                          Just for nerdiness sake J:
                          Do you know why Dolby technology was never adopted in NFM/WFM?

                          I know that wireless lavalier mics (for film/tv production) have always used this to improve SNR, but why was it never adopted in ordinary two-way voice comms?

                          It did help to fight tape hiss, and fill Mr.Dolby's wallet :-)

                          73
                          Paul
                          PD0PSB


                        • Steve Dove
                          Hi Paul, Well, they tried, at least on broadcast FM in the US. Dolby A was the professional multiband noise reduction system mostly used on pro-audio tape
                          Message 13 of 13 , Feb 25, 2014
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                            Hi Paul,

                            Well, they tried, at least on broadcast FM in the US.

                            Dolby A was the professional multiband noise reduction system
                            mostly used on pro-audio tape recorders in studios and such.
                            Dolby B was the consumer hf-only variant everyone knows from
                            cassettes.

                            In the early seventies when FM stereo really took off it
                            became plain that background hiss was a problem (stereo, by
                            nature of the added baseband bandwidth and the 'triangular'
                            nature of demodulated FM noise was much, much worse than
                            mono). Now the obvious answer, which was to use a decent
                            receive antenna, was of course never going to catch on. So -
                            why not add Dolby B into the chain to help suppress the hiss?

                            If a B encoder was used on a transmitter, it would sound
                            unnaturally bright on a receiver with no decoder, so, as a
                            compromise, the normal broadcast 75uS pre-emphasis was reduced
                            to 25uS when B was transmitted. This of course stole away
                            from any noise advantage the compansion was giving, so ho-hum,
                            all a bit of a wash in performance.

                            The underwhelming improvement (lost on most consumers) plus
                            the fact that receiver manufacturers balked at paying a Dolby
                            license fee on each unit manufactured brought it all to a
                            fizzle fairly quickly.

                            You can STILL sometimes find receivers of that era with a
                            25/75 switch, and STILL, occasionally, find one with - gasp -
                            a Dolby B chip in it...

                            Cheers,

                            Steve W3EEE


                            On 2/25/2014 8:40 PM, pd0psb@... wrote:
                            >
                            >
                            > Hi Jack,
                            >
                            > Just for nerdiness sake J:
                            > Do you know why Dolby technology was never adopted in NFM/WFM?
                            >
                            > I know that wireless lavalier mics (for film/tv production)
                            > have always used this to improve SNR, but why was it never
                            > adopted in ordinary two-way voice comms?
                            >
                            > It did help to fight tape hiss, and fill Mr.Dolby's wallet :-)
                            >
                            > 73
                            > Paul
                            > PD0PSB
                            >
                            >
                            >
                            >
                            >
                            > No virus found in this message.
                            > Checked by AVG - www.avg.com <http://www.avg.com>
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                            > Date: 02/25/14
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