[ARC5] Smart People: IF Curve- What Am I Doing Wrong?

[Leslie Smith]

  To all readers

  CIRCUIT DIAGRAM - SCHEMATIC   
  I have a one page document - "Fig 7-10 Transmitter-Receiver
  RT-91/ARC-2 Schematic Diagram"  
  The page I have is marked 155/156.
  I say this to check/establish I have the circuit to the set that
  interests our Mr.  Stinson.  
  Perhaps you can confirm that, David.
  Once I have the correct diagram, I will send a copy to any-one on this
  list who wants one.
  If you want a circuit - please e-m me direct.  Note the comment below
  about file size.

  Next - this circuit is HUGE and I need IRFANview to see the detail
  (otherwise it's like a microdot - just a blob).
  With IRFANview I can zoom in and see the detail, but it's still not
  easily read.
  I have the circuit (schematic if you must) as a *.png file and I
  converted this to *.jpg.
  File sizes:  As PNG it's 711kB.  As JPG it's 3.6Mb.  Yes, 3.6
  megabytes.  

  More on the file source.  Words at the top of the diagram: 
  AN16-30ARC2-12.
  I think that will identify the document.
  
  THE 5 pF CAPACITOR
  David, next, I'd like to establish the capacitor(s) you exchanged.
  I understand the swap was 5pF to 3 pF to 5pF.
  If you have this circuit, can you identify the part by designation for
  me?  
  (I'll send the circuit I have, if this helps.  If it doesn't help, I
  won't send it.)
  It will help if you can identify a 'toob' near the capacitor.

  Dave, next, I'm going to assume your observation about bandwidth is
  correct
  i.e. a 50% reduction in coupling "C" makes a huge difference between
  'broad' and 'narrow'.
 
  Dave, can you tell me the type of cap?  Is it dog-bone or is it
  silver-mica "postage stamp" style?

  DISRUPTION OF LINEARITY.
  Of course, I don't know the cap in question (yet), and I think you use
  the words "disruption of linearity" to mean non-linear tracking
  between the front end and I.F.
  I think this is more likely to result in poor sensitivity.  If you cut
  one side-band (on AM) won't you still get good quality by hearing the
  other side-band?
  (Maybe you have lost one side-band completely, and half-cut the other
  - by shifting the alignment between the stages)

  I'll watch this with interest.
  
  That's all for this message. 
  AR-K

  73 de Les Smith
  vk2bcu at operamail.com


On Tue, Apr 8, 2014, at 23:27, David Stinson wrote:
> Thanks for writing, Bill and Neil.
> 
> There are no fixed-tuned local oscillators on any band.
> The IF tuning is mechanically ganged with the 
> PTO and RF AMP tuning- all together.
> The IF tracks the PTO tuning 1.0-1.5 MC.
> 
> The PTO is multiplied 3 times on bands A and C,
> four times on band B and 5 times on band C.
> 
> Examples:  
> Fo = 3 MC
> PTO = 1.5 MC x 3 = 4.5 MC.  
> Fo 3 MC mixed with 4.5 MC = 1.5 MC IF Freq.
> 
> Fo = 6 MC
> PTO = 1 MC x 5 = 5MC
> Fo 6 MC mixed with 5 MC = 1 MC IF Freq.
> 
> I think the disruption of linearity is the likely answer.
> 
> Thanks again,
> Dave AB5S
> 
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