[Boatanchors] Cheap & Easy Selectivity

[Alex Whitaker]

"...it is possible to capacitively couple the antenna directly to the
next RF amplifier grid, or to the mixer input grid, by wrapping an
insulated wire around any exposed wiring in the grid circuit.  This
forms a gimmick, which has a few picofarads of capacitance to the wire
around which it is connected."  Electronic Communication - 3rd Edition -
Robert L. Schrader.  

I personally have only heard the term gimmick in reference to one wire
twisted around another in the manner described above.  I believe Bob
Bethman's examples of glass between two copper plates, or a long screw
used as he states describe capacitors, but not a gimmick.  


73,

Alex 
AA9XY



On Sat, 2009-08-22 at 11:20 -0700, J. Forster wrote:
> No, Mr. Bethman. Here YOU go once more.
> 
> -John
> 
> ============
> 
> 
> > Here we ago once more.
> >
> > Definition
> >
> > (noun)
> >
> >    1.
> >          1. A device employed to cheat, deceive, or trick, especially a
> >             mechanism for the secret and dishonest control of gambling
> >             apparatus.
> >          2. An innovative or unusual mechanical contrivance; a gadget.
> >    2.
> >          1. An innovative stratagem or scheme employed especially to
> >             promote a project: / an advertising gimmick./
> >          2. A significant feature that is obscured, misrepresented, or
> >             not readily evident; a catch.
> >    3. A small object whose name does not come readily to mind.
> >
> > (transitive verb: -micked, -mick·ing, -micks.)
> >
> >    1. To add gimmicks to; clutter with gadgets or attention-getting
> >       details. Often used with / up. /
> >    2. To change or affect by means of a gimmick.
> >
> > Therefore, this term is only defined in the context being discussed by
> > Amateur Radio Operators.
> >
> > The ARC-5 is not the beginning of all, all of that, nor the end all.
> >
> > The term gimmick is indeed a handmade small value capacitor.  It only
> > manifested itself as two insulated, (normally varnished or enameled),
> > twisted together.
> >
> > The single aluminum rod with threads on the end in Heath gear could just
> > as easily be considered a gimmick.
> >
> > The idea that copper plates or sheets layered with glass between the
> > being STUPID shows lack of historical knowledge of the hobby.  This is
> > indeed ignorance,  Ignorance is curable by education.  Stupidity is
> > fatal, since one has already learned.
> >
> > The copper plates and glass were a COMMON had-made capacitor by Amateur
> > Radio Operators in the Spark Stations.  Seems to go a GOOD bit before
> > the '40s or '60s.
> >
> > Seems some folks need to go back and revisit their hobby's roots.
> >
> > Bob - N0DGN
> >
> > mac wrote:
> >> I'm with Bob on this one.  Been in the game since the late 1940's and
> >> the definition established by long use and common understanding is as
> >> he describes.
> >>
> >> Dennis D.  W7QHO
> >> Glendale, CA
> >>
> >> On Aug 21, 2009, at 6:35 PM, WA5CAB at cs.com wrote:
> >>
> >>
> >>> I'm sorry, but I've been in this business since the 60's (that's
> >>> 1960, not
> >>> 2060), and I disagree with both of you.
> >>>
> >>> First, the standard gimmick is two random parallel wires usually
> >>> twisted
> >>> together.  Not two metal plates with a piece of stupid window
> >>> glass.  Nor an
> >>> unusually long aluminum screw is some piece of junk built by Heath.
> >>>
> >>> Second, many military sets including the majority of the Command
> >>> Sets were
> >>> built with solid wire, not stranded.  Mostly #22 R&SCC.  There is a
> >>> well
> >>> known gimmick mod published for Command recievers.  It actually
> >>> works.  I made
> >>> it in one around 1963 while at LSU.
> >>>
> >>> The other common gimmick, more common in low-end civilian or
> >>> commercial
> >>> equipment is a length of zip cord cut to length.  Zip cord usually
> >>> stranded.
> >>>
> 
> 
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