[ARC5] Converter/front end for Q5-er Sets

Leslie Smith vk2bcu at operamail.com
Thu Apr 16 16:53:32 EDT 2015


  Hello Phil,
  Received your message.  Will reply this Sunday.
  For a long time I drew my circuits using DOS-based software - and this
  didn't create to a *.jpg file.
  I'll must print the circuit and then photograph that to convert of
  *.jpg.  At the moment rain threatens, and I'm working out-doors.
  I need to beat the rain.


  73 de Les Smith
  vk2bcu at operamail.com


On Wed, Apr 15, 2015, at 01:41, Phillip Carpenter wrote:
> Hi Les,
> 
> I'm not a member of the Yahoo site.
> 
> Can you please send me the latest iteration of your BC-453 front end
> 160-80-BCB converter circuit and parts list?
> 
> I want to try one on my BC-453.
> 
> Thank you in advance for your reply!
> 
> Respectfully,
> 
> Phillip W4RTX 
> 
> Sent from my iPhone
> 
> > On Jan 9, 2015, at 5:20 PM, Leslie Smith <vk2bcu at operamail.com> wrote:
> > 
> > 
> > 
> >               CNV-412, MF/HF converter for Q5-ers
> > 
> > For some time I wanted to build a general purpose converter to use in
> > front of a 'command' 'navigation' receiver (e.g. BC-453/946 or R-23/4). 
> > The circuit of a prototype, still under development, is shown in the
> > ARC-5Radio files, in a folder called Exptl_(LNS).
> > 
> > Find the circuit here:
> > 
> > File Name:  "CNV-412, R12 (on 5-0110).png" 
> > Folder: Exptl_(LNS)
> > Yahoo Group: ARC-5Radio
> > Web Reference: www.groups.yahoo.com
> > 
> > The circuit is quite conventional, although the local oscillator uses
> > the not-so-common source coupled oscillator.  Some mistakenly call this
> > a Franklin oscillator, and there are similarities, but the two are
> > somewhat different.  
> > 
> > Operational objective.  
> > To build a generic 'front end' to use with the Q5-er sets that will
> > operate on the 160/80/40m band and also the AM broadcast band.  The
> > circuit will be a solid state implementation of the popular converter
> > presented by Don Stone, but have the capability to use both a xtal
> > controlled and variable local oscillator.  
> > 
> > Construction.  I built the prototype circuit on strip-board, using the
> > more-modern 20 way edge connectors used in digital circuits.  Using a
> > plug-in type of construction shortens the develop time.  The mixer and
> > oscillator tank circuits are connected (at the moment) using alligator
> > clips to the LC tank components.  The AM broadcast band has a good
> > mixture of strong local and weak distant stations, and the oscillator
> > will be more stable at the lower frequency, so initial design focused on
> > 520 - 1650kHz.  
> > 
> > It takes little imagination to see how quickly this could be moved to
> > 160m and after that to 80m.
> > 
> > Present functionality.
> > The Q5-er used for this experiment is a not-so-badly hacked BC-453.  The
> > outer box and shield over the tuning gang were both gone; the 'common'
> > mods to the utility box on the front of the set were apparent.  The BFO
> > circuit had been re-wired, but speaking generally the set was quite
> > function, I thought.  After routine troubleshooting I could hear the
> > local 'nav' broadcast on 362kHz using a few meters of wire on the
> > aerial.
> > 
> > I run my 'command' sets on a 60V B+ supply; in this particular set I
> > replaced the 'flower-pot' caps with 100V mylar types, so the B+ absolute
> > limit is 90V DC.  I haven't used a 90V supply enough to say it would
> > give better performance than a 60V supply, but it may.  
> > 
> > To drive a loudspeaker I bought a surplus 110-11V power transformers,
> > and put this 'in series' with the existing 600 ohm transformer.  In
> > other words, I feed the 600 ohm output to the 110V primary, and connect
> > my speaker to the secondary.  Using this with the 60V B+ supply my set
> > give useful volume in a quiet room.  (More volume might be got by
> > reducing the value of the cathode resistor on the 12A6 output 'tube',
> > but I haven't done that yet.  I avoid modifying the set as much as
> > possible.)
> > 
> > Using the converter, I hear broadcast stations.  My idea of using the
> > Q5-er at a fixed 
> > frequency went out the window, because the tuning was 'touchy'.  That
> > surprised me, as a 'lash-up' oscillator I built previously (but using a
> > negative resitance oscillator) would stay zero-beat on the local ABC
> > radio station for long periods of time (I mean hours at a time).  The
> > next stage of development will be around the tank circuits - fitting
> > them to a metal chassis, with shielding.
> > 
> > I suspect the I.F. coupling transformer (at the 'top end' of the mixer)
> > lacks impedance.  In other words, I think I need more turns.  I'm going
> > to plot the response of this transformer, and rewind it if it is found
> > to lack performance.  
> > 
> > The signal from the local oscillator changes (in amplitude) a good deal
> > over the frequency range.  It's too low, even in mid-band.  It should
> > provide 5V p-p to the 'top' gate in the mixer, allowing class "C"
> > operation.  An earlier lash-up gave an output signal that varied no more
> > than 10% mid-band to the low and high frequency limits.  Clearly I must
> > do more work to the local oscillator circuit.  
> > 
> > I built the circuit so the L.O. signal came "off" the card, thru a link
> > and "onto" the card to the mixer gate circuit.  This allowed some
> > flexibility - if I wanted to substitute a different local oscillator,
> > all I had to do was open the link and insert the new L.O. signal.   This
> > idea works so well I'm going to use RCA connectors to switch the signal
> > path in the link circuit.  
> > 
> > Problems, deficiencies, bugs, work needed and so on.
> > First, the stability and tuning rate of the L.O is unsatisfactory.  To
> > tune SSB I need a tuning rate of about 50kHz per revolution of the
> > tuning knob.  I have no idea about a good tuning rate for AM, but
> > probably only 1/4 that needed for SSB.  Perhaps someone here can tell
> > me?  
> > 
> > The mixer tank tuning is hopelessly 'wrong'.  It doesn't peak
> > adequately; it's broad, and I suspect I should reduce the tank inductor
> > from the present 370uH to about 260 .. 300uH.  However, the problem is
> > more than simply wrong values.  When I peak the tank circuit I hear a
> > noise that (I suspect) comes from instability.  Yes .. I think my superb
> > design is oscillating.  I suspect I could replace the cascode mixer with
> > a straight single source coupled JFET mixer.  I don't need the gain the
> > cascode gives, at least not at the low end of the H.F. spectrum.  It may
> > be useful on 6m, but that wild-eyed idea (using a BC-455) is still a
> > distant flicker of hope.  
> > 
> > So - I need to debug or modify the mixer.  Ideas about how this might be
> > done are welcome.  
> > 
> > I think I might get the circuit working to my satisfaction after two or
> > three more months of work.  At the moment my prototype suggests the idea
> > is sound, but Don Stoner proved that decades ago, so that doesn't
> > surprise me.  Still, it's nice to start with a handful of components and
> > a circuit and slowly, slowly see the 'thing' come to life.
> > 
> > In the end I want a front-end 'box' that can sit proudly alongside a
> > 'command' radio, knowing it is designed and built as well as the
> > original set.  The prototype might be strip-board and chewing gum, but
> > the finished rig-owner (me, in this case) should be proud of the final
> > article.
> > 
> > I want to say a few things about the drawing.  First, it's clearly
> > incomplete.  I hope it's sufficiently accurate to not confuse anyone
> > reading it.  Next, I drew this using the 'freeware' program TinyCAD,
> > running under Windows XP.  The program isn't perfect, but I like to use
> > 'freeware' developed by an amateur coder.  This is 'neat' software.  If
> > enough people use this software it will survive, and wouldn't that be
> > nice?  The TinyCAD package allows users (I'm a 'user' not a 'loser') to
> > create libraries & symbols.  I created a library (I called it 'common')
> > and drew most of the symbols in the circuit you see.  Useful, eh?  As
> > for the European symbol for the resistor you see - if you don't like it
> > - it's easily changed, and the the more common 'zig-zag' resistor symbol
> > IS in the library too.  
> > 
> > TinyCAD from SourceForge.  Get yours today.  Don't leave home without
> > it!  Notice the size of the *.png file produced when I 'export' the
> > drawing.  27kB.  Neat eh?
> > 
> > Observations, suggestions and even hateful criticisms (or flames) about
> > my converter (the fabulous and exotic - at times quixotic - CNV-412) are
> > welcome!
> > 
> > Les
> > formerly VK2BCU.
> > 
> > -- 
> > http://www.fastmail.com - Send your email first class
> > 
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