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Homebrewing using the radio's RF section

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  • cybertheque_museum
    Greetings, I would appreciate learning of anyone s experience using the RF section from this radio (with modifications of course) in other receiver projects.
    Message 1 of 9 , May 1 8:17 AM
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      Greetings,

      I would appreciate learning of anyone's experience using the
      RF section from this radio (with modifications of course) in
      other receiver projects. I have had good results using a
      much modified Grundig YB400 RF section in a receiver project,
      but successful reuse requires a good set of documentation.
      For the YB400, there is a bit more published information on
      the performance of various stages, but I needed to measure
      everything to do any serious work.

      Has anyone done measurements on each of the stages for NF, IMD,
      gain, freq. response, filter performance, etc? How about
      a circuit analysis with theory of operation? Or perhaps a
      redrawn schematic that does one function block per A-size
      drawing? A casual inspection of the RF pcb suggests a lack
      of attention to isolation between stages; has anyone kludged
      some interstage shield strips on the solder side or perhaps
      tin-can shields on the component side? For the YB400, isolation
      was designed into the RF board, but the entire subassembly
      needed to be encased in a faraday can with feedthroughs for the
      leads to reduce received RFI in my receiver project.

      Old reviews of this radio suggest that it has a homebrew following,
      but I don't see much evidence of that on this mailing list. Old
      Usenet posts (early 1990s) suggest some projects that interfaced
      to the existing mcu to remotely control the keyboard, but these
      appreared to use the unmodified radio.

      All replies appreciated.

      Michael
    • JOHN NORTH
      Yes, Yes! Michael, you are right regarding the lack of technical discussion and sharing the little tricks...unless you consider wall wort sizes as very
      Message 2 of 9 , May 1 11:12 AM
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        Yes, Yes! Michael, you are right regarding the lack of technical discussion and sharing the little tricks...unless you consider "wall wort" sizes as very technical. That seems to get the most play here lately. However that does and could be a wonderful and simple place to start...I mean the noise the buggers generate is outrageous and who knows, this might set off a new spark of enthusiasm to the more inner workings a one of the best radios ever design and mass produced! Lead on Brother
        Regards,
        John

        cybertheque_museum <michael.grigoni@...> wrote:
        Greetings,

        I would appreciate learning of anyone's experience using the
        RF section from this radio (with modifications of course) in
        other receiver projects. I have had good results using a
        much modified Grundig YB400 RF section in a receiver project,
        but successful reuse requires a good set of documentation.
        For the YB400, there is a bit more published information on
        the performance of various stages, but I needed to measure
        everything to do any serious work.

        Has anyone done measurements on each of the stages for NF, IMD,
        gain, freq. response, filter performance, etc? How about
        a circuit analysis with theory of operation? Or perhaps a
        redrawn schematic that does one function block per A-size
        drawing? A casual inspection of the RF pcb suggests a lack
        of attention to isolation between stages; has anyone kludged
        some interstage shield strips on the solder side or perhaps
        tin-can shields on the component side? For the YB400, isolation
        was designed into the RF board, but the entire subassembly
        needed to be encased in a faraday can with feedthroughs for the
        leads to reduce received RFI in my receiver project.

        Old reviews of this radio suggest that it has a homebrew following,
        but I don't see much evidence of that on this mailing list. Old
        Usenet posts (early 1990s) suggest some projects that interfaced
        to the existing mcu to remotely control the keyboard, but these
        appreared to use the unmodified radio.

        All replies appreciated.

        Michael






        [Non-text portions of this message have been removed]
      • Bob Betts
        Okay, I ll start. First; the radio is probably better designed than most owners realize. Years ago - probably 15 years - I experimented with RF preamps and
        Message 3 of 9 , May 1 12:16 PM
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          Okay, I'll start. First; the radio is probably better designed than most owners realize. Years ago - probably 15 years - I experimented with RF preamps and preselectors. Due to lack of room inside the cabinet, I built a small external preselector with about 15-18 dB of gain. Out in the back yard, on picnics, or camping, I found that there was a lot of DX available that I didn't receive at home (lack of neighborhood noise). Generally I used 40 to 60 feet of endfed antenna and sometimes a temporary ground. The 803 has more head room than I previously thought and with judicious use of the preamp or attenuator, added to the selective filtering of the preselector, the radio surprised (even) me! And I'm a tough customer.
          Second; This then led to me adding an actual (switched) speaker jack to the side of the radio case. The reason why is that its performance is so good, that the stock, internal speaker really does not do it justice. And I don't listen to FM very often - this was mostly for AM broadcast and Intl. SW.
          I don't know about the internal mods or additions ... there really isn't much room for a lot of playing, but if you want to have an improved receiver, try some additional RF gain, with a true RF attenuator and some serious, high-Q filtering - so you can selectively boost or cut or select - it really works.
          I've spent many chair-side hours DXing the AM band (one of my passtimes, and some International stuff as well), but the added control that these "pre" circuits contribute can be quite amazing.
          You can see the preselector I first made to be compatible with the 803 here. It's the one with the white face, marked "Type-2".
          http://www.bobsamerica.com/preselectors.html
          Bob, N1KPR


          JOHN NORTH <johnpnorth@...> wrote:
          Yes, Yes! Michael, you are right regarding the lack of technical discussion and sharing the little tricks...unless you consider "wall wort" sizes as very technical. That seems to get the most play here lately. However that does and could be a wonderful and simple place to start...I mean the noise the buggers generate is outrageous and who knows, this might set off a new spark of enthusiasm to the more inner workings a one of the best radios ever design and mass produced! Lead on Brother
          Regards,
          John

          cybertheque_museum <michael.grigoni@...> wrote:
          Greetings,

          I would appreciate learning of anyone's experience using the
          RF section from this radio (with modifications of course) in
          other receiver projects. I have had good results using a
          much modified Grundig YB400 RF section in a receiver project,
          but successful reuse requires a good set of documentation.
          For the YB400, there is a bit more published information on
          the performance of various stages, but I needed to measure
          everything to do any serious work.

          Has anyone done measurements on each of the stages for NF, IMD,
          gain, freq. response, filter performance, etc? How about
          a circuit analysis with theory of operation? Or perhaps a
          redrawn schematic that does one function block per A-size
          drawing? A casual inspection of the RF pcb suggests a lack
          of attention to isolation between stages; has anyone kludged
          some interstage shield strips on the solder side or perhaps
          tin-can shields on the component side? For the YB400, isolation
          was designed into the RF board, but the entire subassembly
          needed to be encased in a faraday can with feedthroughs for the
          leads to reduce received RFI in my receiver project.

          Old reviews of this radio suggest that it has a homebrew following,
          but I don't see much evidence of that on this mailing list. Old
          Usenet posts (early 1990s) suggest some projects that interfaced
          to the existing mcu to remotely control the keyboard, but these
          appreared to use the unmodified radio.

          All replies appreciated.

          Michael

          [Non-text portions of this message have been removed]






          http://www.bobsamerica.com

          [Non-text portions of this message have been removed]
        • cybertheque_museum
          ... Thanks for your reply Bob, and the photos of the preselectors are quite impressive; you re site is also a good resource. Have you any thoughts on doing a
          Message 4 of 9 , May 1 5:14 PM
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            --- In Sangean803@yahoogroups.com, Bob Betts <rwbetts@...> wrote:

            > You can see the preselector I first made to be compatible with
            > the 803 here. It's the one with the white face, marked "Type-2".
            > http://www.bobsamerica.com/preselectors.html

            Thanks for your reply Bob, and the photos of the preselectors are
            quite impressive; you're site is also a good resource. Have
            you any thoughts on doing a tracking preselector? (Of course
            it would need to grok the tuning commands sent to the PLL).

            The lack of shielding in the 803A, especially at the front end,
            is a big problem in hostile RF environments. I imagine enclosing
            the board in a can would mitigate pickup, but that may introduce
            other deleterious changes (proximity effects, etc.). Has anyone
            tried some shielding that works?

            I should mention that the reason that the 803A's tuning is so
            clunky (chuffs, skips and jumps at high encoder rotation), is
            that the mcu is only clocked at about 32kHz, and the datastream
            sent to the PLL is too slow to produce smooth tuning. In my
            project that used the RF section of the YB400, I clock the PLL
            at 1MHz which gives smooth tuning with essentially no artifacts
            like clicks, chuffs, etc. The down side is the complication of
            mitigating RFI from the data lines which is much worse at higher
            speeds and the mcu clock (24 MHz) is difficult to isolate (note
            that this is NOT the mcu from the original design).

            If a higher noise floor from the fast mcu is tolerable, one can
            use techniques like perturbing the mcu clock to move birdies
            dynamically, out of the way, across a tuning range.

            Michael
          • Bob Betts
            Thanks Michael: I m sure there s a lot to all that. For example, I have noticed that a lot of junk gets into the headend through the plastic case. Used in the
            Message 5 of 9 , May 2 6:13 AM
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              Thanks Michael:
              I'm sure there's a lot to all that. For example, I have noticed that a lot of junk gets into the headend through the plastic case. Used in the car or out in the field, the influence of radiated RFI is nonexistant. It would be very interesting to modify one and try some of these things that you mention.
              Bob


              cybertheque_museum <michael.grigoni@...> wrote:
              --- In Sangean803@yahoogroups.com, Bob Betts <rwbetts@...> wrote:

              > You can see the preselector I first made to be compatible with
              > the 803 here. It's the one with the white face, marked "Type-2".
              > http://www.bobsamerica.com/preselectors.html

              Thanks for your reply Bob, and the photos of the preselectors are
              quite impressive; you're site is also a good resource. Have
              you any thoughts on doing a tracking preselector? (Of course
              it would need to grok the tuning commands sent to the PLL).

              The lack of shielding in the 803A, especially at the front end,
              is a big problem in hostile RF environments. I imagine enclosing
              the board in a can would mitigate pickup, but that may introduce
              other deleterious changes (proximity effects, etc.). Has anyone
              tried some shielding that works?

              I should mention that the reason that the 803A's tuning is so
              clunky (chuffs, skips and jumps at high encoder rotation), is
              that the mcu is only clocked at about 32kHz, and the datastream
              sent to the PLL is too slow to produce smooth tuning. In my
              project that used the RF section of the YB400, I clock the PLL
              at 1MHz which gives smooth tuning with essentially no artifacts
              like clicks, chuffs, etc. The down side is the complication of
              mitigating RFI from the data lines which is much worse at higher
              speeds and the mcu clock (24 MHz) is difficult to isolate (note
              that this is NOT the mcu from the original design).

              If a higher noise floor from the fast mcu is tolerable, one can
              use techniques like perturbing the mcu clock to move birdies
              dynamically, out of the way, across a tuning range.

              Michael






              http://www.bobsamerica.com

              [Non-text portions of this message have been removed]
            • Shane Seckler
              ... I ve got mainly hawks and bluebirds around here, a few mockingbirds; but none of them have ever interfered with the reception of my radio. :-D
              Message 6 of 9 , May 2 12:27 PM
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                >If a higher noise floor from the fast mcu is tolerable, one can
                >use techniques like perturbing the mcu clock to move birdies
                >dynamically, out of the way, across a tuning range.


                I've got mainly hawks and bluebirds around here, a few mockingbirds;
                but none of them have ever interfered with the reception of my radio. :-D
              • arbee185
                Hi All, I have always found it more rewarding to build from scratch instead of trying to modify an existing design for high performance. There is ample
                Message 7 of 9 , May 4 8:16 AM
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                  Hi All,

                  I have always found it more rewarding to build from scratch instead of
                  trying to modify an existing design for high performance. There is
                  ample literature (ARRL handbook, etc.) on building high performance
                  radios. Modern preselector design, double balanced mixers, and modern
                  high frequency crystal filters allow extremely good performance with an
                  almost total lack of birdies (it is possible to build single conversion
                  receivers without a second local oscillator, which leaves the MCU clock
                  as about the only source of birdies- which can be well filtered and
                  shielded from the receiver circuits, unlike a second L.O.).

                  The 803 is a decent receiver in it's own right, and is ideal for
                  travel, camping trips, and other portable uses. I have found little
                  reason to modify it much. I have built other radios which I use for
                  home listening. I do use my 803 at home as well. I have shortwave
                  radios in several locations around my place so that I can listen while
                  working, etc. I also retransmit over FM so that I can listen portably
                  where it is not reasonable to place a radio.

                  One item that I have built for the 803 is an external regulator circuit
                  to allow operation from an unregulated 12 volt supply. I can now use it
                  in my vehicle (moving or parked) without having to hassle with
                  batteries. It is also useful at home with a 12 volt wall wart.) With
                  this regulator, I don't have to worry about the radio getting damaged
                  by voltage variations of the source, and it's performance is consistent.

                  For those who do want to modify their radio, all I can say is go for
                  it. I am interested in hearing about the mods and results. Good luck,
                  and happy experimentation!

                  I live in a rural area and experience little interference save an
                  arcing power line insulator or two in wet weather. (I need to locate
                  those so the power company can replace them. Never enough time to do
                  everything!)

                  Arbee



                  --- In Sangean803@yahoogroups.com, Shane Seckler <schieben@...> wrote:
                  >
                  >
                  > >If a higher noise floor from the fast mcu is tolerable, one can
                  > >use techniques like perturbing the mcu clock to move birdies
                  > >dynamically, out of the way, across a tuning range.
                  >
                  >
                  > I've got mainly hawks and bluebirds around here, a few mockingbirds;
                  > but none of them have ever interfered with the reception of my
                  radio. :-D
                  >
                • Michael Grigoni
                  ... Indeed, but often the issue is cost; starting with a subassembly that can be tweaked, at a very low acquisition cost, may drive the design. ... For sure.
                  Message 8 of 9 , May 4 8:58 AM
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                    arbee185 wrote:

                    > I have always found it more rewarding to build from scratch instead of
                    > trying to modify an existing design for high performance.

                    Indeed, but often the issue is cost; starting with a subassembly
                    that can be tweaked, at a very low acquisition cost, may drive
                    the design.

                    > There is ample literature (ARRL handbook, etc.) on building high performance
                    > radios. Modern preselector design, double balanced mixers, and modern
                    > high frequency crystal filters allow extremely good performance with an
                    > almost total lack of birdies (it is possible to build single conversion
                    > receivers without a second local oscillator, which leaves the MCU clock
                    > as about the only source of birdies- which can be well filtered and
                    > shielded from the receiver circuits, unlike a second L.O.).

                    For sure. I would much prefer to do a wide-open receiver, similar to a
                    countermeasures receiver that I once had which used a servo-driven
                    air line, or perhaps a single-conversion set with a 2Ghz I.F. to
                    cover DC to 1.999 GHz with perhaps a DDS L.O., or maybe an SDR,
                    but due to the dwindling availability of cheap surplus these days
                    (thanks to eBay and fewer DoD/DMRO sales) these options aren't
                    so affordable. I have a collection of heavy BWO and TWT frontends
                    plumbed to waveguide mixers that can do DC to millimeter, but building
                    a new receiver around them is a recipe for high maintenance and
                    power bills.

                    >
                    > The 803 is a decent receiver in it's own right...

                    And due to that opinion shared by many, I hoped to hear of some
                    successful projects that reused and tweaked the R.F. section,
                    perhaps by inclusion of missing shielding, changing switching
                    diodes to PIN types, adding preselectors, etc., etc. and
                    repackaging for R.F. isolation and ruggedizing. My YB400
                    reuse project required perhaps $30.00 in expenditure and resulted
                    in a high-performance computer-controlled general coverage rig
                    with 1Hz tuning resolution, decent long term frequency stability
                    (under controlled temperature -- I need to work on tempco issues)
                    and options for upgrading and improving R.F. characteristics as
                    well as signal processing features as time permits.

                    Since I must operate under bad QRN and QRM conditions, the stock
                    803 is nearly useless for me -- the front end is swamped by nearby
                    TV and FM stations, and the background of digital hash and proximal
                    oscillator clocks feeds through even with no antenna connected.
                    The properly shielded YB400 R.F. board is quiet with the antenna
                    disconnected, and using noise reduction techniques at the antenna
                    (9:1 torroid connected to a Marconi and good R.F. ground), I get
                    much reduced noise, but still need a backend DSP at times for
                    adaptive denoising and narrow CW filters.

                    There are very few portable shortwave radios sold at the big retailers
                    here (and I suppose the trend is elsewhere as well), but the excuse
                    usually given by sales people is that customers find that the radios
                    are useless due to poor front-end isolation and mixer dynamic range.
                    Considering that a vast majority of customers probably live in hostile
                    R.F. environments these days, wouldn't it behoove the designers of
                    portable consumer radios to do the front-end correctly and spend the
                    extra 25 cents for a tin shield, and the extra dollar or two for proper
                    mixer and trap components, rather than losing a sale?

                    Michael
                  • arbee185
                    Hi Michael, I have always built my designs around whatever neat stuff that I had accumulated since my last project, or had laying around. It is true that
                    Message 9 of 9 , May 4 5:36 PM
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                      Hi Michael,

                      I have always built my designs around whatever neat stuff that I had
                      accumulated since my last project, or had laying around. It is true
                      that military surplus is getting hard to find. I was fortunate to
                      live in a large city previously where there was an electronics flea
                      market where you could find a large selection of "junk". Much of it
                      was very useful to a discerning buyer. I still have quite a bit left
                      for future projects.

                      I feel that a good receiver design should probably use a fairly sharp
                      preselector at the antenna input to filter out all of the out of band
                      garbage. Very high overload level amplifiers and mixers are great,
                      but a good preselector can reduce the need for these items and reduce
                      power consumption at the same time. The downside of preselectors is
                      that you often need a switched bank of them to cover a wide frequency
                      range, and they never will track an oscillator which is operating at
                      a much higher frequency, requiring a secondary tuning means. They
                      really boost overall performance if properly used- worth the hassle
                      in most cases. I use them.

                      Where I now live, I have few issues with my 803. If I lived in the
                      middle of a large city, I might. I can appreciate it as a starting
                      point to end up with a higher performance receiver. If I had a second
                      unit, I might try to modify it if I could find the time. I only have
                      one, and like to keep it as it is for portable use.

                      Having worked as an engineer designing consumer stuff in the (distant-
                      when we actually designed it here) past, I can appreciate how well
                      the 803 actually does work. The cost and time pressures are enormous,
                      and nice items such as shields are often not included to save a
                      couple of pennies. Many items are designed by people fresh out of
                      school with little real world experience. All mass produced products
                      can certainly be improved- some greatly. Sad but true.

                      Here in the U.S., shortwave listening is not overly popular with the
                      masses. I think that it is losing out to the internet world wide. The
                      BBC does not even broadcast to the Americas anymore (they can still
                      be heard here however). This can not help but reduce the number and
                      quality of good products designed to receive shortwave, as listeners
                      fade away. This is extremely sad. I love my radios, and the world
                      that they bring me. I have no problem with the internet, but it can
                      be much more controlled than shortwave signals if those in power so
                      desire to exert that control, and the radios are more challenging to
                      use, and much more portable.

                      As I said before, I would love to see some good projects using the
                      803 internals- it would be very interesting.

                      Arbee

                      --- In Sangean803@yahoogroups.com, Michael Grigoni
                      <michael.grigoni@...> wrote:
                      >
                      >
                      > Indeed, but often the issue is cost; starting with a subassembly
                      > that can be tweaked, at a very low acquisition cost, may drive
                      > the design.
                      > > The 803 is a decent receiver in it's own right...
                      >
                      > And due to that opinion shared by many, I hoped to hear of some
                      > successful projects that reused and tweaked the R.F. section,
                      > perhaps by inclusion of missing shielding, changing switching
                      > diodes to PIN types, adding preselectors, etc., etc. and
                      > repackaging for R.F. isolation and ruggedizing. My YB400
                      > reuse project required perhaps $30.00 in expenditure and resulted
                      > in a high-performance computer-controlled general coverage rig
                      > with 1Hz tuning resolution, decent long term frequency stability
                      > (under controlled temperature -- I need to work on tempco issues)
                      > and options for upgrading and improving R.F. characteristics as
                      > well as signal processing features as time permits.
                      >
                      > Since I must operate under bad QRN and QRM conditions, the stock
                      > 803 is nearly useless for me -- the front end is swamped by nearby
                      > TV and FM stations, and the background of digital hash and proximal
                      > oscillator clocks feeds through even with no antenna connected.
                      > The properly shielded YB400 R.F. board is quiet with the antenna
                      > disconnected, and using noise reduction techniques at the antenna
                      > (9:1 torroid connected to a Marconi and good R.F. ground), I get
                      > much reduced noise, but still need a backend DSP at times for
                      > adaptive denoising and narrow CW filters.
                      >
                      > There are very few portable shortwave radios sold at the big
                      retailers
                      > here (and I suppose the trend is elsewhere as well), but the excuse
                      > usually given by sales people is that customers find that the radios
                      > are useless due to poor front-end isolation and mixer dynamic range.
                      > Considering that a vast majority of customers probably live in
                      hostile
                      > R.F. environments these days, wouldn't it behoove the designers of
                      > portable consumer radios to do the front-end correctly and spend the
                      > extra 25 cents for a tin shield, and the extra dollar or two for
                      proper
                      > mixer and trap components, rather than losing a sale?
                      >
                      > Michael
                      >
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