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Re: [softrock40] Re: Possible ways to modify the Ensemble II VHF

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  • Bill Maxwell
    That s true also Gordon, although some SSB receivers can be challenged by their available filter width when trying to get good audio from an AM signal. My
    Message 1 of 16 , May 31, 2012
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      That's true also Gordon, although some SSB receivers can be challenged by their available filter width when trying to get good audio from an AM signal.

      My comments were more addressed to the predominantly
      FM slant of the bands the questioner identified and were aimed to ensure that he appreciated that the airband still uses AM. It is surprising how many folk do not know that, as witnessed by the frequent questions raised on the various user groups dedicated to the various Chinese FM hand held radios these days.
      On 1/06/2012 4:27 PM, Gordon JC Pearce wrote:
      On 01/06/12 07:26, Bill Maxwell wrote:
      
      
      Yes Bob, I appreciate that and the fact that many of the current
      software offerings have the appropriate code aboard but not all do. That
      is exactly why I brought the need for AM capable software to his
      attention, if he is hoping to copy airband signals. I saw it as adding
      to his knowledge of what he required, although I possibly could have
      been more expansive.
      
      If a receiver can receive SSB, it can receive AM.
      
      
    • g8voip
      Hi Bill, Sorry for any confusion on my part! The way I read (missread) your posting was that you were suggesting AM be added to the list of modifications our
      Message 2 of 16 , Jun 1, 2012
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        Hi Bill,

        Sorry for any confusion on my part!

        The way I read (missread) your posting was that you were suggesting AM be added to the list of 'modifications' our friend was suggesting for the Ensemble VHF RX.

        If I recall correctly, not in the shack at the moment, all of the current popular SDR programs with the exception of Rocky support AM reception.

        73, Bob G8VOI

        --- In softrock40@yahoogroups.com, Bill Maxwell <wrmaxwell@...> wrote:
        >
        > Yes Bob, I appreciate that and the fact that many of the current
        > software offerings have the appropriate code aboard but not all do. That
        > is exactly why I brought the need for AM capable software to his
        > attention, if he is hoping to copy airband signals. I saw it as adding
        > to his knowledge of what he required, although I possibly could have
        > been more expansive.
        >
        > 73, Bob VK7MX
        >
        > On 1/06/2012 4:04 PM, g8voip wrote:
        > > Hi Bill,
        > >
        > > The design of the Ensemble VHF hardware has nothing to do with the modes of reception.
        > >
        > > This is 'Software Defined Radio' and the modes of demodulation are entirely defined by the SDR program you are running, that is the beauty (and whole point) of SDR.
        > >
        > > The majority of current SDR programs support AM reception.
        > >
        > > 73, Bob G8VOI
        > >
        > > --- In softrock40@yahoogroups.com, Bill Maxwell<wrmaxwell@> wrote:
        > >> add the need to give it AM capability, as that is what is used on the
        > >> Airband and is unlikely to ever change.
        > >>
        > >> Bill
        > >>
        > >
        > >
        > >
        > >
        > > ------------------------------------
        > >
        > > Yahoo! Groups Links
        > >
        > >
        > >
        > >
        >
      • Bill Maxwell
        No problem Bob. I probably contributed to the confusion by being less than specific. Maybe a throwback to the metaphorical nature of my celtic-scots cultural
        Message 3 of 16 , Jun 1, 2012
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          No problem Bob. I probably contributed to the confusion by being less than specific. Maybe a throwback to the metaphorical nature of my celtic-scots cultural ancestory.

          Bill

          On 1/06/2012 9:14 PM, g8voip wrote:
          Hi Bill,
          
          Sorry for any confusion on my part! 
          
          The way I read (missread) your posting was that you were suggesting AM be added to the list of 'modifications' our friend was suggesting for the Ensemble VHF RX.
          
          If I recall correctly, not in the shack at the moment, all of the current popular SDR programs with the exception of Rocky support AM reception.
          
          73, Bob G8VOI
          
          --- In softrock40@yahoogroups.com, Bill Maxwell <wrmaxwell@...> wrote:
          
          Yes Bob, I appreciate that and the fact that many of the current 
          software offerings have the appropriate code aboard but not all do. That 
          is exactly why I brought the need for AM capable software to his 
          attention, if he is hoping to copy airband signals. I saw it as adding 
          to his knowledge of what he required, although I possibly could have 
          been more expansive.
          
          73, Bob VK7MX
          
          On 1/06/2012 4:04 PM, g8voip wrote:
          
          Hi Bill,
          
          The design of the Ensemble VHF hardware has nothing to do with the modes of reception.
          
          This is 'Software Defined Radio' and the modes of demodulation are entirely defined by the SDR program you are running, that is the beauty (and whole point) of SDR.
          
          The majority of current SDR programs support AM reception.
          
          73, Bob G8VOI
          
          --- In softrock40@yahoogroups.com, Bill Maxwell<wrmaxwell@>  wrote:
          
          add the need to give it AM capability, as that is what is used on the
          Airband and is unlikely to ever change.
          
          Bill
          
          
          
          
          
          ------------------------------------
          
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        • tomshong
          Hi Bob, I have a lot of learn. I ve indeed learned a lot since I joined this group, and I very grateful for all the expert advise here. I wish I have found you
          Message 4 of 16 , Jun 1, 2012
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            Hi Bob,

            I have a lot of learn. I've indeed learned a lot since I joined this group, and I very grateful for all the expert advise here. I wish I have found you guys sooner. :P

            Yes I misread the info when I looked at the schematic in http://www.wb5rvz.com/sdr/ensemble_rx_ii_vhf/ and thought those `options' were 4 band selections like the case with HF. Thanks for pointing those out.

            That got me to wonder, why didn't Tony add a MUX to select the 4 band like the case with the HF board? Also, I notice that each of the options for the VHF board can only handle a bandwidth of about 4Mhz. Why is that?

            I thought up the idea of modify the firmware, because from reading another expert's post earlier (think from Jasmine Strong?), that the board's bandpass filter configuration is stored in the EEPROM of the ATtiny. That tells me, for each of the `options' there's a specific BPF info stored inside the ATtiny (and I assumed Tony flashed these chips before they were shipped).

            Which means if I want to to modify the VHF board to, say, listen a FM station at 102.7Mhz , that would require me to design/change the bandpass filter, and since it's to a frequency band that's `not' stored in the EEPROM, then I'd better add new band pass filter info to the ATtiny.

            Is that not what's going on?

            Tom


            --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@...> wrote:
            >
            > Hi (nameless person),
            >
            > Perhaps you would like to share with us the reasons you have come up with the following conclusions regarding the Ensemble VHF receiver:
            >
            > --- In softrock40@yahoogroups.com, "tomshong" <tomshong@> wrote:
            >
            > > Looks to me, to do so, it will require
            > > 1) Modify the LO's so it arrive at an IF that is exactly equal to the quadrature clock frequency
            > > 2) Modify the 4Mhz BPFs to accommodate those bands listed above
            > > 3) modification to the driver ExtIO.dll, and the firmware to the EEPROM of the ATtiny
            > >
            > > What's everyone's take? Am I missing anything else?
            > >
            >
            > I am sure many of us involved in the project would benefit from your insight.
            >
            > By the way, as pointed out before the Ensemble VHF RX can only be built for a single band. Take a look at the schematic as it appears you are assuming it is similar to the Ensemble HF which has 4 switched filters.
            >
            > Choosing the correct LO clock divider ratios, any ONE of the frequency segments you mention could potentially be covered if changes to the filtering were carried.
            >
            > Why would there be any need to modified the ExtIO_Si570.dll file? Possible not even used, depends on which SDR program you intend to use.
            >
            > Why would the ATtiny firmware need changing, already does the job.
            >
            > Questions and suggestions are always welcome and encouraged, but sometimes it is worth doing some research first yourself so at least you have some idea what you are talking about, otherwise it is very easy to give the wrong impression.
            >
            > 73, Bob G8VOI
            >
          • The Silver Fox
            Before you try to change the filters I suggest you look at the ones that are on the board and see what if anything they do to the frequencies you are
            Message 5 of 16 , Jun 1, 2012
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              Before you try to change the filters I suggest you look at the ones that are on the board and see what if anything they do to the frequencies you are interested in.  Most of the filters are to prevent transmissions that are not allowed.  The receiving filters are not as sensitive.

              73,

              Alan – W6ARH

               

              From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of tomshong
              Sent: Thursday, May 31, 2012 2:20 PM
              To: softrock40@yahoogroups.com
              Subject: [softrock40] Possible ways to modify the Ensemble II VHF

               

               

              Hi all,

              Per all the experts advise here, I think I will stick with playing the HF board, get it setup, and later on see if I can get it to work with LabView.

              Once I build it and get comfortable using it, maybe the VHF board will be next.

              So from what I can gathered, the Ensemble II VHF can only cover selective band due to hardware limitation. Nonetheless, I'd like to discuss ways one can tinker and tweak the VHF board (all in the name of science and education).

              I notice that as it each of the 4 branches of the broad covers 4 MHz of frequency in VHF band, so it got me to think....

              I wonder, if it's possible to modify the VHF board to pick up, say, some local FM (103.9~107.9MHz), air traffic (118~122MHz), 2meter amateur band (144~148MHz) and NOAA weather station (162.4~162.55MHz)

              Looks to me, to do so, it will require
              1) Modify the LO's so it arrive at an IF that is exactly equal to the quadrature clock frequency
              2) Modify the 4Mhz BPFs to accommodate those bands listed above
              3) modification to the driver ExtIO.dll, and the firmware to the EEPROM of the ATtiny

              What's everyone's take? Am I missing anything else?

            • Gordon JC Pearce
              ... Exactly. The filters on RX are there so that the cat can t get into the mousehole, the dog can t get through the cat flap, and the horse can t get into
              Message 6 of 16 , Jun 2, 2012
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                On 02/06/12 04:59, The Silver Fox wrote:
                >
                >
                > Before you try to change the filters I suggest you look at the ones that
                > are on the board and see what if anything they do to the frequencies you
                > are interested in. Most of the filters are to prevent transmissions that
                > are not allowed. The receiving filters are not as sensitive.
                >
                > 73,
                >
                > Alan – W6ARH

                Exactly. The filters on RX are there so that the cat can't get into the
                mousehole, the dog can't get through the cat flap, and the horse can't
                get into the dog kennel.

                They're not sharp in any way.

                --
                Gordonjcp MM0YEQ
              • g8voip
                Hi Tom, No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :) The Ensemble VHF RX is
                Message 7 of 16 , Jun 2, 2012
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                  Hi Tom,

                  No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :)

                  The Ensemble VHF RX is fundamentally different to the HF version.

                  The HF version has the 4 switched filters to cover the usable range from around 875kHz through to 30MHz. Everything operates directly at the received frequency range.

                  The techniques used for the HF RX have an upper frequency limit between 30 and 50MHz, components like the current standard CMOS Si570 generates 160MHz maximum, so limits the frequency to 160/4 = 40MHz. Also the FET switches and divider chips limit the maximum working frequency.

                  The Ensemble VHF RX is a completely different design. Its very much a throwback to VHF reception 30 or more years ago. Essentially it comprises two parts, a VHF down converter and a tunable IF.

                  The traditional method for say the 2m band (144MHz) was to have a down converter with a fixed 116MHz local oscillator for the mixer. This gave an IF output of 144 - 116 = 28MHz. By using a conventional HF receiver and tuning 28 - 30MHz gave coverage of 144 - 146MHz.

                  The Ensemble VHF RX works on the same principal, but with a clever twist by the designer Jan G0BBL. Instead of using a fixed local oscillator for the VHF converter section, by a clever choice of Si570 LO frequency it is possible for the one oscillator to provide both the LO for the converter plus when divided by 4 produce the quadrature clock needed for the following receiver operating at the IF frequency. The other major difference from the conventional VHF converter setup is that the LO is variable. This adds a slight complication to the understanding of its operation, but does work!

                  When building the Ensemble VHF RX the constructor has the choice of 3 major VHF ham bands, 50, 70 and 144MHz. Each of these works over a large range of frequencies simply by retuning the frontend of the VHF converter section. The 144MHz version can use optimised for use anywhere between around 130 and 165MHz without any component changes.

                  Originally there were just the two bands 50 and 144MHz.

                  The 50MHz version uses a tunable IF in the region of 16.66 to 18MHz to cover 50 - 54MHz. Potentially it could be used over a much wider range given the IF frequency, the only limitations are the frontend filtering and a simple diplexer following the mixer output. The diplexer is designed to be transparent at the operating frequency, but provide the mixer with a stable termination impedance outside of that range. Both of these will limt the actual frequency range that can be used before changes are needed.

                  Likewise the 144MHz version uses an IF out in the range 28.8 to 29.6MHz to cover 144 - 148MHz. Again the filtering and diplexer determine thefrequency range that can be covered without any modification. I have tested this version between 130 and 165MHz (IF between 26 and 33MHz)without any modification being needed.

                  The 70MHz version is really a combination of the two other designs, the frontend components chosen for 70MHz, and the IF side for around 29MHz (i.e. the same as the 144MHz version).

                  Playing around with the mix of designs, should be possible to build a version covering 88 - 108MHz quite easily. The front end filtering would need changing, but perhaps the 70MHz version might still be ok.

                  By changing the LO divider ratio (normally 4/3 or 1.333) for the 50/70MHz version to the same as the 144MHz version (4/5 or 0.8) that would give you:

                  88MHz = LO (88 x 0.8 = 70.4MHz) and IF 70.4 / 4 = 17.6MHz
                  108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz

                  Using the AVR firmware configuration program CFGSR, these LO settings can be entered.

                  As there are no switched filters to be controlled, the firmware settings on the ABPF page can be ignored.

                  As an aside, I do have a set up consisting three SoftRock v9.0 receivers, fitted with 6m, 4m and 2m versions of the VHF converter. I make use of the ABPF filter outputs, and have set the crossover points to suit so that the three receivers are switched automatically when I change from 6m to 4m to 2m.

                  There is plenty of scope for experimentation using the existing hardware, tweaking filters etc. The good thing is due to Fred PE0FKO's continuing great work in developing the AVR firmware from the original version, all possibilities are virtually already covered by the standard chip and have been extensively tested.

                  My advice would be build and get your Ensemble HF up and running, get familiar with configuring and running the various SDR programs avaialable and find which suits your needs the best before thinking about tackling the Ensemble VHF RX.

                  Sorry for the long posting, but hopefully might be of some interest to you and others, if not just bin it :)

                  73, Bob G8VOI
                • Bruce Tanner
                  Definitely a keeper. Thanks, Bob! Sent from my iPhone
                  Message 8 of 16 , Jun 2, 2012
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                    Definitely a keeper. Thanks, Bob!

                    Sent from my iPhone

                    On 2012-06-02, at 5:46 AM, "g8voip" <g8voi.reeves59@...> wrote:

                     

                    Hi Tom,

                    No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :)

                    The Ensemble VHF RX is fundamentally different to the HF version.

                    The HF version has the 4 switched filters to cover the usable range from around 875kHz through to 30MHz. Everything operates directly at the received frequency range.

                    The techniques used for the HF RX have an upper frequency limit between 30 and 50MHz, components like the current standard CMOS Si570 generates 160MHz maximum, so limits the frequency to 160/4 = 40MHz. Also the FET switches and divider chips limit the maximum working frequency.

                    The Ensemble VHF RX is a completely different design. Its very much a throwback to VHF reception 30 or more years ago. Essentially it comprises two parts, a VHF down converter and a tunable IF.

                    The traditional method for say the 2m band (144MHz) was to have a down converter with a fixed 116MHz local oscillator for the mixer. This gave an IF output of 144 - 116 = 28MHz. By using a conventional HF receiver and tuning 28 - 30MHz gave coverage of 144 - 146MHz.

                    The Ensemble VHF RX works on the same principal, but with a clever twist by the designer Jan G0BBL. Instead of using a fixed local oscillator for the VHF converter section, by a clever choice of Si570 LO frequency it is possible for the one oscillator to provide both the LO for the converter plus when divided by 4 produce the quadrature clock needed for the following receiver operating at the IF frequency. The other major difference from the conventional VHF converter setup is that the LO is variable. This adds a slight complication to the understanding of its operation, but does work!

                    When building the Ensemble VHF RX the constructor has the choice of 3 major VHF ham bands, 50, 70 and 144MHz. Each of these works over a large range of frequencies simply by retuning the frontend of the VHF converter section. The 144MHz version can use optimised for use anywhere between around 130 and 165MHz without any component changes.

                    Originally there were just the two bands 50 and 144MHz.

                    The 50MHz version uses a tunable IF in the region of 16.66 to 18MHz to cover 50 - 54MHz. Potentially it could be used over a much wider range given the IF frequency, the only limitations are the frontend filtering and a simple diplexer following the mixer output. The diplexer is designed to be transparent at the operating frequency, but provide the mixer with a stable termination impedance outside of that range. Both of these will limt the actual frequency range that can be used before changes are needed.

                    Likewise the 144MHz version uses an IF out in the range 28.8 to 29.6MHz to cover 144 - 148MHz. Again the filtering and diplexer determine thefrequency range that can be covered without any modification. I have tested this version between 130 and 165MHz (IF between 26 and 33MHz)without any modification being needed.

                    The 70MHz version is really a combination of the two other designs, the frontend components chosen for 70MHz, and the IF side for around 29MHz (i.e. the same as the 144MHz version).

                    Playing around with the mix of designs, should be possible to build a version covering 88 - 108MHz quite easily. The front end filtering would need changing, but perhaps the 70MHz version might still be ok.

                    By changing the LO divider ratio (normally 4/3 or 1.333) for the 50/70MHz version to the same as the 144MHz version (4/5 or 0.8) that would give you:

                    88MHz = LO (88 x 0.8 = 70.4MHz) and IF 70.4 / 4 = 17.6MHz
                    108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz

                    Using the AVR firmware configuration program CFGSR, these LO settings can be entered.

                    As there are no switched filters to be controlled, the firmware settings on the ABPF page can be ignored.

                    As an aside, I do have a set up consisting three SoftRock v9.0 receivers, fitted with 6m, 4m and 2m versions of the VHF converter. I make use of the ABPF filter outputs, and have set the crossover points to suit so that the three receivers are switched automatically when I change from 6m to 4m to 2m.

                    There is plenty of scope for experimentation using the existing hardware, tweaking filters etc. The good thing is due to Fred PE0FKO's continuing great work in developing the AVR firmware from the original version, all possibilities are virtually already covered by the standard chip and have been extensively tested.

                    My advice would be build and get your Ensemble HF up and running, get familiar with configuring and running the various SDR programs avaialable and find which suits your needs the best before thinking about tackling the Ensemble VHF RX.

                    Sorry for the long posting, but hopefully might be of some interest to you and others, if not just bin it :)

                    73, Bob G8VOI

                  • Philip
                    Excellent informative post... Thanks Bob Philip G4JVF
                    Message 9 of 16 , Jun 2, 2012
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                      Excellent informative post...

                      Thanks Bob

                      Philip G4JVF

                      --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@...> wrote:
                      >
                      > Hi Tom,
                      >
                      > No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :)
                      >
                      > The Ensemble VHF RX is fundamentally different to the HF version.
                      >
                      > The HF version has the 4 switched filters to cover the usable range from around 875kHz through to 30MHz. Everything operates directly at the received frequency range.
                      >
                      > The techniques used for the HF RX have an upper frequency limit between 30 and 50MHz, components like the current standard CMOS Si570 generates 160MHz maximum, so limits the frequency to 160/4 = 40MHz. Also the FET switches and divider chips limit the maximum working frequency.
                      >
                      > The Ensemble VHF RX is a completely different design. Its very much a throwback to VHF reception 30 or more years ago. Essentially it comprises two parts, a VHF down converter and a tunable IF.
                      >
                      > The traditional method for say the 2m band (144MHz) was to have a down converter with a fixed 116MHz local oscillator for the mixer. This gave an IF output of 144 - 116 = 28MHz. By using a conventional HF receiver and tuning 28 - 30MHz gave coverage of 144 - 146MHz.
                      >
                      > The Ensemble VHF RX works on the same principal, but with a clever twist by the designer Jan G0BBL. Instead of using a fixed local oscillator for the VHF converter section, by a clever choice of Si570 LO frequency it is possible for the one oscillator to provide both the LO for the converter plus when divided by 4 produce the quadrature clock needed for the following receiver operating at the IF frequency. The other major difference from the conventional VHF converter setup is that the LO is variable. This adds a slight complication to the understanding of its operation, but does work!
                      >
                      > When building the Ensemble VHF RX the constructor has the choice of 3 major VHF ham bands, 50, 70 and 144MHz. Each of these works over a large range of frequencies simply by retuning the frontend of the VHF converter section. The 144MHz version can use optimised for use anywhere between around 130 and 165MHz without any component changes.
                      >
                      > Originally there were just the two bands 50 and 144MHz.
                      >
                      > The 50MHz version uses a tunable IF in the region of 16.66 to 18MHz to cover 50 - 54MHz. Potentially it could be used over a much wider range given the IF frequency, the only limitations are the frontend filtering and a simple diplexer following the mixer output. The diplexer is designed to be transparent at the operating frequency, but provide the mixer with a stable termination impedance outside of that range. Both of these will limt the actual frequency range that can be used before changes are needed.
                      >
                      > Likewise the 144MHz version uses an IF out in the range 28.8 to 29.6MHz to cover 144 - 148MHz. Again the filtering and diplexer determine thefrequency range that can be covered without any modification. I have tested this version between 130 and 165MHz (IF between 26 and 33MHz)without any modification being needed.
                      >
                      > The 70MHz version is really a combination of the two other designs, the frontend components chosen for 70MHz, and the IF side for around 29MHz (i.e. the same as the 144MHz version).
                      >
                      > Playing around with the mix of designs, should be possible to build a version covering 88 - 108MHz quite easily. The front end filtering would need changing, but perhaps the 70MHz version might still be ok.
                      >
                      > By changing the LO divider ratio (normally 4/3 or 1.333) for the 50/70MHz version to the same as the 144MHz version (4/5 or 0.8) that would give you:
                      >
                      > 88MHz = LO (88 x 0.8 = 70.4MHz) and IF 70.4 / 4 = 17.6MHz
                      > 108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz
                      >
                      > Using the AVR firmware configuration program CFGSR, these LO settings can be entered.
                      >
                      > As there are no switched filters to be controlled, the firmware settings on the ABPF page can be ignored.
                      >
                      > As an aside, I do have a set up consisting three SoftRock v9.0 receivers, fitted with 6m, 4m and 2m versions of the VHF converter. I make use of the ABPF filter outputs, and have set the crossover points to suit so that the three receivers are switched automatically when I change from 6m to 4m to 2m.
                      >
                      > There is plenty of scope for experimentation using the existing hardware, tweaking filters etc. The good thing is due to Fred PE0FKO's continuing great work in developing the AVR firmware from the original version, all possibilities are virtually already covered by the standard chip and have been extensively tested.
                      >
                      > My advice would be build and get your Ensemble HF up and running, get familiar with configuring and running the various SDR programs avaialable and find which suits your needs the best before thinking about tackling the Ensemble VHF RX.
                      >
                      > Sorry for the long posting, but hopefully might be of some interest to you and others, if not just bin it :)
                      >
                      > 73, Bob G8VOI
                      >
                    • g8voip
                      Oh dear, brain fade again, old age catching up. Just noticed: 108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz Should read: 108MHz LO (108 x 0.8 =
                      Message 10 of 16 , Jun 2, 2012
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                        Oh dear, brain fade again, old age catching up. Just noticed:

                        108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz

                        Should read:

                        108MHz LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 21.6MHz

                        Sorry for any confusion.

                        73, Bob G8VOI

                        --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@...> wrote:
                        >
                        > Hi Tom,
                        >
                        > No problem, SDR is a pretty steep learning curve for all of us, just that some of us are a few years further up the curve :)
                        >
                        > The Ensemble VHF RX is fundamentally different to the HF version.
                        >
                        > The HF version has the 4 switched filters to cover the usable range from around 875kHz through to 30MHz. Everything operates directly at the received frequency range.
                        >
                        > The techniques used for the HF RX have an upper frequency limit between 30 and 50MHz, components like the current standard CMOS Si570 generates 160MHz maximum, so limits the frequency to 160/4 = 40MHz. Also the FET switches and divider chips limit the maximum working frequency.
                        >
                        > The Ensemble VHF RX is a completely different design. Its very much a throwback to VHF reception 30 or more years ago. Essentially it comprises two parts, a VHF down converter and a tunable IF.
                        >
                        > The traditional method for say the 2m band (144MHz) was to have a down converter with a fixed 116MHz local oscillator for the mixer. This gave an IF output of 144 - 116 = 28MHz. By using a conventional HF receiver and tuning 28 - 30MHz gave coverage of 144 - 146MHz.
                        >
                        > The Ensemble VHF RX works on the same principal, but with a clever twist by the designer Jan G0BBL. Instead of using a fixed local oscillator for the VHF converter section, by a clever choice of Si570 LO frequency it is possible for the one oscillator to provide both the LO for the converter plus when divided by 4 produce the quadrature clock needed for the following receiver operating at the IF frequency. The other major difference from the conventional VHF converter setup is that the LO is variable. This adds a slight complication to the understanding of its operation, but does work!
                        >
                        > When building the Ensemble VHF RX the constructor has the choice of 3 major VHF ham bands, 50, 70 and 144MHz. Each of these works over a large range of frequencies simply by retuning the frontend of the VHF converter section. The 144MHz version can use optimised for use anywhere between around 130 and 165MHz without any component changes.
                        >
                        > Originally there were just the two bands 50 and 144MHz.
                        >
                        > The 50MHz version uses a tunable IF in the region of 16.66 to 18MHz to cover 50 - 54MHz. Potentially it could be used over a much wider range given the IF frequency, the only limitations are the frontend filtering and a simple diplexer following the mixer output. The diplexer is designed to be transparent at the operating frequency, but provide the mixer with a stable termination impedance outside of that range. Both of these will limt the actual frequency range that can be used before changes are needed.
                        >
                        > Likewise the 144MHz version uses an IF out in the range 28.8 to 29.6MHz to cover 144 - 148MHz. Again the filtering and diplexer determine thefrequency range that can be covered without any modification. I have tested this version between 130 and 165MHz (IF between 26 and 33MHz)without any modification being needed.
                        >
                        > The 70MHz version is really a combination of the two other designs, the frontend components chosen for 70MHz, and the IF side for around 29MHz (i.e. the same as the 144MHz version).
                        >
                        > Playing around with the mix of designs, should be possible to build a version covering 88 - 108MHz quite easily. The front end filtering would need changing, but perhaps the 70MHz version might still be ok.
                        >
                        > By changing the LO divider ratio (normally 4/3 or 1.333) for the 50/70MHz version to the same as the 144MHz version (4/5 or 0.8) that would give you:
                        >
                        > 88MHz = LO (88 x 0.8 = 70.4MHz) and IF 70.4 / 4 = 17.6MHz
                        > 108MHz = LO (108 x 0.8 = 86.4MHz) and IF 86.4 / 4 = 82.4MHz
                        >
                        > Using the AVR firmware configuration program CFGSR, these LO settings can be entered.
                        >
                        > As there are no switched filters to be controlled, the firmware settings on the ABPF page can be ignored.
                        >
                        > As an aside, I do have a set up consisting three SoftRock v9.0 receivers, fitted with 6m, 4m and 2m versions of the VHF converter. I make use of the ABPF filter outputs, and have set the crossover points to suit so that the three receivers are switched automatically when I change from 6m to 4m to 2m.
                        >
                        > There is plenty of scope for experimentation using the existing hardware, tweaking filters etc. The good thing is due to Fred PE0FKO's continuing great work in developing the AVR firmware from the original version, all possibilities are virtually already covered by the standard chip and have been extensively tested.
                        >
                        > My advice would be build and get your Ensemble HF up and running, get familiar with configuring and running the various SDR programs avaialable and find which suits your needs the best before thinking about tackling the Ensemble VHF RX.
                        >
                        > Sorry for the long posting, but hopefully might be of some interest to you and others, if not just bin it :)
                        >
                        > 73, Bob G8VOI
                        >
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