Re: GB> Chaffee Spark Gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of \"Terrell W. Fritz\" <terrellf-at-qwest-dot-net> by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Parpp807-at-aol-dot-com>

This is from Ralph that my interust us.

Cheers,

        Terry

========
In a message dated 11/28/01 10:45:54 PM Central Standard Time, 
Sparkwireless-at-aol-dot-com writes:

Terry,
This may be of interest to the Tesla group.
Ralph

In a message dated 11/28/01 10:45:54 PM Central Standard Time, 
Sparkwireless-at-aol-dot-com writes:

Terry,
This may be of interest to the Tesla group.
Ralph

Subj:  GB Chaffee Spark Gap

Here is the piece on Chaffee and his gap, which I typed in for you're reading
enjoyment, since so many of you requested it.  Roy KJ4TG

Chapter III
b. Radio Frequent Sparks
 
"It has occurred to a number of investigators that practically 
Sustained radiation could be secured in an antenna by using spark transmitters,
but having these transmitters so arranged that the extremely high frequency of
the sparks (above the limits of audibility) would render the usual "spark tone"
inaudible.  If, then, the antenna energy were modulated by a microphone or
otherwise, radiotelephony would become possible.  To 
Specify in further detail, imagine a special form of spark gap and associated 
Circuit so arranged that discharges occurred more or less regularly across the 
Gap at an average frequency of, say, 50,000 sparks per second.  If the circuit 
 In which these sparks occurred were connected inductively to an antenna, 
There would be produced in the antenna practically sustained radiation, 
Susceptible to suitable telephone modulation by a microphone transmitter, or
otherwise.
 
    "In figure 32 is given a graphic delineation of the effects.  It will 
Be noticed that highly damped oscillations occur rather irregularly in the
primary circuit and that each of these short oscillation groups starts a
decadent wave train, which has still large current amplitude when the
succeeding spark takes place.  In as much as the sparks follow each other so 
  Frequently and since the antenna circuit damping is low, the effect at the
distant receiver would be appreciably that of sustained radiation at the
transmitter, and particularly is this quiescence the changes in antenna
radiation occur above audio frequency.  Most of the radio frequent spark 
  Transmitters for radiotelephone operate in the faction indicated, but there
is a second special case, which has certain interesting features.  It is
illustrated in figure 33, and occurs with the Chaffee "arc" (which is really a
spark phenomenon).  To begin with, in this case the spark gap has such
excessively high intrinsic damping that the spark discharges in the primary
circuit tend to be periodic.  (The structure of the Chaffee is is described on
page 56.)
   
      "The tendency toward periodicity just mentioned is enhanced by Chaffee in
that he couples the secondary circuit very closely to the primary, thereby
obtaining a "quenching" action through the secondary reaction on the primary. 
In addition, the direct current feed circuit of the arc and the coupling to the
energy-absorbing secondary are so arranged that the spark frequency is an 
  Integral fraction, (e.g. one-half, one-third, one-fourth, etc.) of the
frequency of the oscillation in the secondary circuit.  Thereby it occurs that
the successive discharges come at just the right time to be in phase with the
secondary, (or antenna) oscillation, and not at random (with 
  Possible interference) as is the case for the conditions illustrated in
Figure 32.  In figure 34 are shown oscillograms of the actual phenomena.   
Chaffee uses the term "inverse charge frequency" for the ration between the
radio frequency in the secondary circuit and the spark frequency in the primary
circuit.  The inverse spark frequency is a whole number for the 
  Chaffee spark.      "In general, spark methods of radio telephony are open to
very serious 
  Objections.  Unless the sparks not only follow eight great regularity, but 
  Also have nearly equal current amplitudes, (neither of which conditions 
Are easily fulfilled, particularly in steady operation), there will be produced

  In the receivers of the distant station an annoying hissing sound, which will

  Interfere seriously with clear articulation in the speech.  This accounts, 
  Naturally for the frequently poor quality of spark radiophone transmitters.
   
      "Nevertheless, many investigations have been carried on in the se 
  Directions and in some cases with marked success, and these will now be 
  Considered.
   
      "In the fall of 1900, working with a special interrupter, enabling him 
 To 
  Obtain as many as 10.000 regular sparks per second, Feddenden succeeded in 
  Transmitting set over 1 mile, but the quality was poor, and there was 
Much 
 
  Noise.  1903 obtained better speech, though the extra noise was 
Still present.  It does not appear that Fessenden developed this method
further, 
  Although he describes a special rotary gap, (with 40 percent 
  Platinum-irridium studs) operated on 5,000 volts direct current and 
Arranged to give 20,000 sparks per second by successive charging and
discharging of 
A condenser. * * * RadioTelephony by Alfred N. Goldsmith, pH. D. PP 44-47 
  Inclusive, The Wireless Press, Inc., 326 Broadway, New York. 1918.
   
      "* * * Continuing our discussion of radio telephone by means of 
  Radio-frequently spark transmitters, we consider next a system developed by 
  Dr. E. Leon Chaffee in conjunction whit Professor George W. Pierce.  This 
  System will be found unique in certain respects.
   
      "The wiring diagram of the transmitter is shown in its essentials in 
  Figure 47, and presents no unusual features.  The direct current generator 
  Supplies 500 volts an from .3 to .8 amperes; (i.e., from 150 to 400 
Watts) per gap.  The resistance provided in the supply circuit is made in two 
Parts, in series, one roughly variable in considerable steps and the other 
Smoothly and continuously variable.  This is desirable, since the operation of
the 
Gap, though steady, depends on a proper choice of the current, this current 
 Partly determining the inverse charge frequency.  The phenomenon of an inverse

  Charge frequency (that is, a whole-number ratio between the secondary 
  Oscillation frequency and the primary impulse frequency) has been treated 
  Above, and is illustrated in figure 33.  It constitutes a distinctive 
 Feature of the Chaffee gap, and depends on the intrinsically great damping of
the 
  Gap."  (I feel that the author meant, "quenching" rather than damping, in
that 
  Last statement, Ed.)
   
      "The primary condenser C need not be a high tension condenser with the 
  Usual low power sets, and generally ahs a value in the neighborhood of 
0.009 
 
  Microfarad."  (9000 pF. Ed.)  "The coupling between L1 and L2 is close.  
  Ordinarily, the microphone M is an ordinary Bell Transmitter, though 
Chaffee   has stated that this type of microphone deteriorates somewhat under
radio 
  Frequency currents of one ampere or more.
   
      "The cross section of the Chaffee gap, constructed by Messieurs. Cutting 
  And Washington, (under patent license from Dr. Chaffee) is shown in figure 
  48.  The gap consists of plugs of aluminum and copper, respectively, one 
Or two square centimeters (or roughly tow or four-tenth of a square inch) in 
  Area, larger dimensions being undesirable in the station ray forms of the 
  Gap.  Originally the gap was run in an atmosphere of moist hydrogen, but
hydrogen being difficult to obtain in ordinary practice, it was found by
Cutting and Washington that alcohol vapor could be substituted, provided it was
distilled into the gap, by the gap hear, from a wick entering the 
Bottom of the gap chamber.  The form of gap shown is made airtight by the use 
Of the flexible phosphor bronze diaphragm, A, which is held in place against a 
  Soft rubber gasket by a brass ring.  Such a diaphragm permits the necessary 
  Movement required in adjustment of the gap electrode separation.  The 
  External appearance of the gap with its adjusting handle and cooling fins 
Is given in figure 49.  For larger powers, a still later modification of the 
 Gap is used wherein the discharges pass between a rapidly rotating aluminum 
Disc and a stationary copper plate, in hydrocarbon vapor.  High efficiency (up 
To 60 or 70 per cent. ) Can be obtained with these last gaps.  
   
      "The discharge begins when the switch is closed, provided the distance 
  Between the electrode is not over 0.1mm, (0.004 inch.)  It is a noiseless 
  And fixed arc of a vivid violet or purple color.  Occasionally it moves to 
A fresh point on the electrodes.  The explanation of the extreme quenching 
  Action lies, according to Chaffee, in the "practically instantaneous 
  Re-establishment of the high initial gap resistance when the current 
Becomes zero, due probably to the formation of an insulating oxide (sic) film
on 
The aluminum; the high cathode drop of the anode metal; and the absorption of 
  Energy by the secondary, although rectification usually takes place without 
  This aid.)  The best operating gap lengths are from 0.04 to 0.09 mm. (0.0016 
 
  To 0.0036 inch.)"* * * Id pp. 56-57.   
      "It has been jointed out elsewhere by the Author that a marked tendency 
  Exists in radio development toward having all stations operate with sustained
radiation.  This tendency is much to be encouraged because of the remarkable
possibilities in the direction of selectivity with beat reception at the short
wave0lengths.  While beat reception is not particularly suited to radiophone
work, it is hoped that ship and small shore stations, and all amateur station
will at least employ sustained wave generators.  If this is done, the Chaffee
arc would seem to be a suitable device, and has marked possibilities." Id p. 59