TESLA'S COLORADO SPRINGS RECEIVERS(A Short Introduction)
byKenneth L. Corum and James F. Corum, Ph.D.
© 2003 by K.L. Corum and J.F. Corum"While experimenting in Colorado...I had perfected a wireless receiver of extraordinary sensitiveness, far beyond anything known."
Nikola Tesla (Albany Telegram, February 25, 1923)§1 Introduction*
A significant segment of Nikola Tesla's 1899 Colorado
Springs research effort encompassed the detection andmonitoring of VLF radio waves emitted f rom atmosphericelectrical storms. (Twenty-nine years later, Karl Jansky
was conducting much the same research, at short-wave,
when he observed thunderstorms and discovered radio
noise emanating from the galactic plane.) Indeed, thisbranch of radio science may be traced directly to Tesla.
Tesla also reported detecting a peculiar extra-terrestrial
signal, which he subsequently concluded was from theplanet Mars. How did the1899 receivers of Tesla's
work?
Using Tesla's patent applications, correspondence, andColorado Springs laboratory notes1 (abbreviated as CSN),
about 15 years ago we conducted a study of his novel
coherer techniques and reconstructed models of his
receiving apparatus. The results were surprising to us, forthey revealed an unanticipated level of sophistication notinitially apparent in the simple circuit diagrams. His 1899
coherer operation was nothing like the coherer circuits ofBranly, Lodge, or Bose. Not only did Tesla's detector
circuits include high Q tuned resonators, but also oscillator
injected negative resistance [similar to the peak (or"boost") operation of the shunt type Q-multipliers of the
1950s, which raised the effective Q and increased theresonant rise of voltage]. This has the same effect as
making the detector stage regenerative. A detailed
technical discussion of Tesla's 1899 receivers was
published in 1994,2 and an analysis of the "radio
telescope" system parameters associated with his Colorado
Springs observatory was presented in 1996. 3 As withArmstrong's super-regenerative receiver, which waspatented in 1922, Tesla's sensitive detectors require only
a few components and are deceptively simple.
§2 Tesla's Receiver Drawings
Let us turn to the receivers shown in the Colorado*This note was condensed from material published in References 2 and3, which may be obtained through Jim Hardesty's PV Scientific website
at http://www.arcsandsparks.com .

Springs Notes. There are many, many circuit
configurations systematically studied, and recorded in his
notebook between June and September of 1899. Fi gure 1,
from August 3, 1899, shows Tesla's use of feedback.
Consider the receiver of September 1, 1899 shown
schematically in Figure 2, and re-drawn in Figure 3.
Notice the all important ground connection, and theposition of the coherer at the high voltage, high impedance
point on the resonator-secondary. The final receiverrecorded in the Diary was discussed by Tesla on
September 17, 1899.

Fig.1 Tesla's "self-excited receiver" employing
feedback and "... the condenser method ofmagnification".
§3 Receiver Operation
During the course of his professional career, Tesla
employed and developed a broad variety of RF detectors
and receivers. Prior to going to Colorado Springs, he had
employed magnetic receivers, which he used in the mid1890's in New York.4 (This remarkable research predates,by forty years, the spectral translation property of timevarying reactances later rediscovered by Hartley, 5 and its
explanation by Bennett,6 and Manley and Rowe7 by half acentury!) He also patented several synchronous detectors
and invented various other demodulators ('tikkers', gaseous
detectors, etc.). However, at Colorado Springs he createda sensitive, regenerative, negative resistance coherer
detection scheme that incorporates triggered AF.

2Fig. 2 Tesla's receiver of September 1, 1899.

the pulse repetition frequency (in pulses per second) andalso the pulse duration.
(c) The construction and characterization of thecoherer(element "a") is discussed in great detail in Tesla's
notes and in several of his patents. (See the footnote at
the close of section 3.4 below.) Historically, the early
application of the coherer was for an RF "detector", notin the sense of how we use "demodulators" today, butrather for determining whether RF was present or notpresent. As a result of experimental measurement, wenoted that as the RF voltage across the device wasincreased, the DC resistance decreased, from 1 megohm
down to 50 ohms.* (The coherer's DC resistance vs. RF
signal voltage is discussed in Ref. 2.) The resistance thenremained almost constant until the voltage was raised to an
avalanche point, where the device became a short. With
the RF removed, if the device was tapped then its
resistance resumed the 1 megohm value. The RF
sensitivity of the detector is highest for device ingredientswith the steepest slopes for DC resistance vs. RF bias, e.g.
tiny particles of silver. The measured family of coherer
characteristic curves is shown in Figure 4.

Fig. 3 Redrawn version of Tesla's Sept. 1, 1899
receiver.

Fig.4§3.1 Circuit Components
Most of the circuit elements in the schematic diagrams
are self-evident. However, let us call attention to some ofthe (now) unconventional symbols and components that
Tesla employed in his drawings.
(a) The element marked "R" was called the receiver,which was merely a relay, Morse telegraph sounder, or
telephone receiver - a high impedance earphone (which
Tesla sometimes referred to as a "telephone"). The
component, R, was simply the radio receiver's
electromechanical output transducer (and not what wewould call a "receiver" today).
(b) The two nodes marked by small circles ("d") wasan electromechanical switch that was commonly called abreak or circuit interrupter. Tesla referred to breaks as"circuit controllers", and h e took out many patents on thistechnology during the 1890s. The break permitted thecontrol of repetitive switching transients: capacitor
charging and discharges. With breaks, one could control

The facts that the coherer's characteristic curves are
nonlinear and nonuniformly spaced, and that the device
decreases its resistance with increasing amounts of RFbias, makes it a unique component. However, in Tesla's
mode of operation the coherer holds one more surprise.
§3.2 Regenerative Process
Bearing the conventional electrical characteristics in
mind, one might want to apply a small amount of locallygenerated RF and a DC bias to push the coherer device
toward the knee in the resistance transition, making it
more sensitive to low voltage RF signals. (At the knee ofthe characteristic curve, the forward and reverse
resistances are substantially different.) Remarkably, thisidea of employing locally generated RF in conjunction*

Measured DC characteristics for a nickel chipcoherer with varying levels of injected RF bias.

This is consistent with Tesla's measurement described on July 23, 1899,"... unexcited they measured more than 1,000,000 ohms while theresistance would sink down to 300 or even 50 ohms or still less when
excited." Similar measured values are presented on July 28,1899.

3with a coherer shows up again 18 years later in thediscussion following Edwin Armstrong's pioneering
publication on regenerative detectors. (Regeneration, isthe process of supplying energy to a circuit to reinforce theoscillations existing in it.) A workable technique forregeneration (positive feedback) by self-heterodyning iscommonly traced to Armstrong, and in 1917 Armstrong
published a masterful engineering study of thephenomenon.8 He discovered that appropriately phased
RF feedback9 of a received signal, coupled from a singlestage plate circuit back to the grid circuit, would make anextremely weak received carrier signal grow in amplitude,
virtually to the point of overload distortion. [In aconventional regenerative detector, the plate circuitcurrent has two spectral components, one is thedemodulated baseband signal and the other is an amplified
RF signal. The high frequency component of the plate
current is coupled back through a tickler coil to the gridand serves for RF amplification (regeneration), and thebaseband component of the amplified plate current
provides the output detected signal in this remarkable
receiver circuit.10] At that time, voltage gains of 35 dB
could be attained from a vacuum tube operating as a gridbiased Class A amplifier (which was invented andpatented by Tesla's assistant, Fritz Lowenstein,11 the IRE's
first Vice-President when it was formed in 1912). But,
Armstrong's approach gave RF gains in excess of 74 dB
with the available tubes of that day!
Is a triode, or three element device, required for thisprocess? No. The overall process of regeneration isequivalent to passing a signal through a tuned tank circuit
into which a negative resistance has been injected. (RFfeedback amplification is the mechanism by which
negative resistance arises in the tank circuit in Armstrong's
embodiment.) The result is to neutralize the positive (loss)
resistance of the tank. Not only does the amplitude of the
RF signal grow (the amplification is limited by the tube
breaking into self oscillation), but the tank circuit's Q
multiplies as the net loss decreases.12,13 Similar results canbe obtained with any negative resistance component, suchas a tunnel diode, which is a two terminal device.
In the discussion correspondence following
Armstrong's 1917 regeneration paper, Carl Ort14 points outthat in Austria he and his colleagues obtained gains of 20fold (26 dB) when using coherers made "very sensitive"by local oscillator RF injection. (This regenerative
process is not the superheterodyne principle.15 Neither is
it super-regeneration,16,17 which provides sensitivity rightdown to the thermal noise floor.) IRE Vice-President
J.V.L. Hogan found that the increase in receiver sensitivity
was even obtained when RF injection was employed witha crystal detector.18 According to Ort's 1917 remarks thereason for the great gain was never understood until
Armstrong's landmark regeneration investigation.
"Mr. Armstrong's experiments have shed new light on these
phenomena and have indicated that the amplification

obtained with a rectifying detector depends on the energyof the local oscillations which are applied to the detector,
and that, while the energy received is not magnified at all,the sensitiveness of the detector is increased. This increaseis independent of the frequency of oscillation of the local
source."19This is remarkably similar to Tesla's description 18 years
earlier. Tesla's patents teach us that when his coherer is
exposed to an injected RF signal, it behaves as a voltage
controlled resistor. He recognized that it was not merely
a go/no-go indicator of RF (as originally used by Branly
and Marconi20), and not a rectifying diode (as in the Lodge
and Bose21 envelope detector mode of coherer operation).
§3.3 Negative Resistance
It is true that the coherer's family of characteristic
curves (a plot of device current vs. applied voltage forvarious biases) clearly displays nonlinearity (see Fig. 4),
especially for small signals biased out near the knee. But,
where is the negative resistance that Ort (and Tesla)
observed?
A short discussion of two-terminal negative resistancedevices is attached as an appendix below. In the case of
a tunnel diode, the current rises with junction voltage(positive resistance), then decreases with further rise injunction voltage (negative resistance), and finally rises
parabolically with any further increase in junction voltage.
On the characteristic curves shown in Figure 4, suppose
the initial coherer operating point is at VDC = 4 volts, VRF= 30 volts PP, and IDC = 0.3 mA. Then, with VDC = 5
volts, suppose VRF swings through 25 volts, where IDC hasdecreased to 0.1 mA. Clearly, the device would exhibit
incremental negative resistance, of value Rn = - 5 kS. It
would appear that the Local Oscillator RF injection isfreely shifting the operating point to make negative
resistance occur. If this is true, then the resonator Q
would increase substantially.
In our opinion, what Tesla had created was a sensitive,
voltage controlled variable resistor with an accessible
operating region of negative slope. Tesla's discovery (anddocumentation by means of patent protection) of thisfourth mode of coherer operation not only makes possiblea realm of sensitive coherer operation, but also creates anentirely new dimension to receiver architecture.
§3.4 Architecture
Permit us to emphasize again that the Tesla receivercircuits are deceptively simple!
First, notice thearchitecture of the schematic drawing shown in Figure 3.
This is important: there are actually four superimposed
circuits:A.

The CP charging circuit. B1 charges CP throughresistance r with time constant J1 = rC1. This places
a DC voltage on CP. For reasons which will soon beevident, this will be called the "Sensitivity Control".

B.

The LPCP damped-wave oscillator including the

4

C.

tightly coupled coils, LP-LS, and break d. This is alocal RF oscillator, but its output and application are
different than the LO for mixer injection taking
place in a superheterodyne receiver. Tesla's LO
generates double-peaked high voltage RF (on theorder of several hundred volts) in a shaped passband
to impress upon the coherer device "a". Note theposition of "a" at the top of the secondary coil, or
resonator stage. The bottom of the secondary coil isgrounded.* When the coherer's resistance is high (1MS) its presence will not impact the operation of
the LO circuit.

follows:
1.

The B1r circuit charges CP (which controls theamount of RF energy which the oscillator impresseson the coherer). As a result, r sets how much RF is
generated locally in the receiver and the sensitivity
point of the coherer, i.e. - its DC resistance. Further,it controls the time constant on CP, which is desired
to be huge with respect to the make/break of theswitching device d. The resistor r is the receiver's"Sensitivity" control. Typically, r . 100 kS and CP. 0.1-0.5 µF. This would give J . 10-50 ms.

A baseband detector stage, which operates while thebreak device (d) is closed. This consists of thecoherer "a", the primary inductor LP, the secondary
coil LS (which at baseband behaves as a low
impedance resistance - 50S for a DC return pathfor battery B through the coherer "a"), and theindicator R (a 900 S DC relay, telegraph indicator,
or earphone) which is battery driven. The coil L is
an RF choke to provide a high impedance to any RF
in the baseband AF stage.

2.

An RF signal induced in the ground end of theresonator (secondary) is stepped up by the VSWR (Qfor lumped coils). Enough RF is desired to take thedevice to the knee of its characteristic curve.
(Initially, the signal appears almost entirely across theresonator.)

3.

The two RF voltages together are sufficient to place
the operating point on the i-v characteristic where
the DC resistance of the coherer is lower by a verysmall amount (1 MS drops to, say, 900 k S). [Theoperating point starts migrating up the i-v curve towhere the DC resistance is smaller.]

4.

The DC resistance now being somewhat less meansthat CP can charge to a greater portion of the voltage
on battery B.

5.

When "d" closes CP and LP will produce a large RF
out of the resonator LS, further raising the operating
point to where the DC resistance of "a" has been
reduced again (say, going from 900 kS down to 500kS). The initial antenna signal now being over, VRF
is now totally due to the LO action.

6.

This allows CP to charge to a larger portion of B,
which will make the output of the resonator rise evenfurther, and the coherer's new operating-point DC
resistance will drop dramatically (say, down to 1000
S).

7.

This process repeats successively until the coherer's
operating-point resistance drops low enough (about
50S) for the telegraph sounder (or earphone) toindicate a response.

D.

The antenna-ground circuit, which provides the input
RF signal. This circuit consists of the antenna
capacitance C', the coherer device "a", theresonator coil LS, and the ground connection, which
is most important. The resonator is "tuned" to thedesired frequency of reception as shown in Tesla's
patents. When there is no RF signal between C' andground, the coherer resistance is high (- 1MS).
When RF signals of sufficient strength are present,
the coherer resistance drops considerably(ultimately to about 50S). The LO injection throughthe coupled coils establishes the initial operating
point on the coherer's characteristic curves.
As mentioned above, the sensitivity of the classical Branly
coherer was known to be quite poor, requiring signal
levels on the order of tens of volts. Both Tesla and Lodge
placed the coherer in a tuned circuit which not only raised
the RF voltage across the coherer (by resonant rise), butalso provided selectivity. Tesla's use of this circuit can be
documented since it was part of the 1898 Patent
Application for his radio controlled "telautomaton", orrobot.**However, Tesla had discovered something new that
greatly increased the detector circuit's sensitivity - and thatwas the injection of locally generated RF into the coherer.
§3.5 Operation
We think that Tesla's receiver may be operating as*The importance of this cannot be stressed strongly enough.
**There is a surprising amount of discussion on the construction, physics,
and operation of coherers in Tesla's US Patents #613,809 (Filed: July 1,
1898; Issued: Nov. 8, 1898), #685,954 (Filed: Aug. 1, 1899; Issued: Nov.
5, 1901); #685,956 (Filed: Nov. 2, 1899; Issued: Nov. 5, 1901).

The RF signal initiated the process,but after its expiration
the device continued to avalanche until a click registered.
8.

Nothing more will(or can) happen unt il the device isdecohered (shaken) back to 1 M S by rotation.

The problem with coherer detection of CW carriers is that5
the continuously present RF keeps the coherer DC
resistance at 50 S. Consequently, this active mode ofcoherer operation (unlike those of Lodge and Bose) is
virtually useless for envelope replication, and works bestfor pulsed signals. Our experiments indicated a 66 dB
improvement in sensitivity when we used the same coherer
and went from Branly's mode of operation to Tesla's.
§3.6 Receiver Construction
Following Tesla's circuits, we constructed several
receiver models, more-or-less to the layout andspecifications given his Notebook. Photos of a receiverconstructed to embody the schematic of Figure 3 is shownin Figures 5 and 6. (Click on the photos to hear audio
clips.) The measured parameters for the reconstructed
receiver shown in the photos were as follows:
CP =
CS =
LP
=
LS
=
RP =
RS =
QP =
QS =
M
=
k
=
kc
=
fP
=
fS
=
Rcoh =
L
=
r
=
B1 =
B
=

§3.7 Analysis of the Local RF Oscillator
A circuit analysis of the coupled coils gives a "double
humped" spectrum, with spectral peaks at 22.3 kHz and22.7kHz (as would be expected with such tight coupling).
The voltage across the secondary capacitor, V CS(t), is
especially interesting. It is a double side-band signal with
an effective "carrier" at about 22.5 kHz (Tesla's Colorado
Springs receivers operated closer to 10 kHz) and a "beat"period of 2500 µs, which corresponds to a frequency of
400 "beats per second". Interestingly, the envelope ofVC2(t) was maximum at about t = 900 µs, and the 400 hertz
beats could be heard as audio pulses through theearphones.

0.1 µF (Tesla used 1/2 µF)
500 pF500 µH
100 mH
1S
60 S
72.3
235
450 µH
0.02010.007722.5 kHz22.5 kHz
1 MS (open) and 50 S (closed)
RFC
100 kS
9 Volts
1.5 volts.

Many coherers were constructed (following Tesla's
laboratory notes) and experimented with. (See CSN pg.
97 and the patents referenced in section 3.4 above.)
Instead of mechanical clockworks, a small electrical motor
was used to slowly rotate the coherer. Our "break" device("d") was a TTL driven micro-relay running at 72 BPS(the same rate as Tesla's clockwork-driven break, see CSN
pg. 110) with contact durations on the order of amillisecond, or so.* Tesla reports placing the portable
receivers in two boxes 9"×10"×14". His "synchronizedcoils" were wound on a form 10" diameter by 48" high and24" diameter by 18" high supported on a photographic
tripod (CSN, pp. 187-188). In the model shown in Figure
5, we used interchangeable high Q pancake coils as
resonators, which seemed to work satisfactorily andpermitted operation on several bands.

*In the Diary, July 29, 1899 (pg. 110), Tesla gives the speed of rotationof the coherers as "about 24 per minute" and the break speed as "72 persecond". He also tells us that the coherer resistance was "over 1,000,000
ohms, but when excited the resistance fell almost exactly to 50 ohms."

Fig. 5 Embodiment of the circuit shown in Fig. 2.
§3.8 VLF Receiver Performance
Tesla took Branly's existing coherer element (withsensitivities on the order of 10 volts) and placed them at
the high impedance end (the top) of his tuned resonators,
which had voltage magnifications proportional to Q, andin so doing he increased the voltage sensitivity of thedetector by a factor on the order of 200 (i.e., 46 dB).(Italso gave the detector selectivity, which was somethingnew.) He injected a local oscillator RF voltage across thecoherer (by tightly link coupling the local oscillator to theresonator) for the purpose of bringing the coherer's
operating point near avalanche, to further increase thesensitivity another 26 dB. Tesla discovered a technique by
which the nonlinear resistance of a coherer (as a functionof injected locally generated RF) could be triggered andexploited by an exterior pulse signal. The Tesla
regenerative detector circuit appears to simultaneously

6
oscillate, heterodyne, amplify, provide selectivity, anddetect. Having a weak signal initiate the process andusing the resulting (voltage controlled) resistance decrease
to regeneratively "ratchet up" the Local Oscillator RF,
which further decreased the coherer resistance, gave Tesla
an improvement on the order of 70 dB in sensitivity overcontemporary receiver technology. The resulting receiver
tangential sensitivity was on the order of 50-500µV. And,

Fig. 6 Parts layout for the circuit of Fig. 2.
an audio "beep" is heard each time the receiver is pulsedby an RF transient signal in the passband of its groundedspiral or helical resonator stage: the baseband earphone
response is a triggered tone at the coupled oscillator beatfrequency. This response is not heard with a conventional
envelope detector. Where Tesla's receivers give "beeps",
all you would hear with a communications receiver would
be clicks and static.
§4 Summary
There are four modes of operation for coherer
receivers:

behaves as an analog envelope detector.
3.) Bose's mode - which built on Lodge's mode,22
utilized torsional compression,23 and was aforerunner of the point-contact diode.
4.) Tesla's mode - in which locally generated RF
injection exploits the voltage-controlled operatingpoint resistance of the coherer.
The first three modes are "passive" in that only themessage signal is applied to the coherer. In modes 1 and4 coherer agitation is required to decohere the device
between pulses, and the detector does not respond wellfor CW. (It stays on!) Mode 2, instead of mechanicaldecohering, requires extreme mechanical stability. Sharp
chips work best for the envelope detector mode of Lodge(which simulates crystal sets). Fine particles work best to
get the go/no-go, steep-knee'd RF detector curves ofBranly. But, either a strong signal is required to get
operation at the knee of the characteristic curve (as Branly
did), or a large bias is needed to get operation out at theknee. (The resistance is asymmetric at the knee of thecharacteristic curve, huge for a sinusoidal signal's negative
half wave and small for its positive half wave.)
In addition to the message signal, Tesla injected a
locally generated RF bias to swing the operating point, andhis discovery of a controlled, frequency-selective,
incremental negative resistance gave his detectors
remarkable gain. Even by today's standards, his receivers
were more than adequate to detect the presence of RF
pulses in the 50-500 µV range. It would appear that theactual limitation on his observations was set by theambient atmospheric noise field. It was not until
Armstrong's monumental discovery of regeneration (USPatent #1,113,149) that receivers could again be made thissensitive.
APPENDIX - Negative Resistance Q-Multiplication
Consider the classical parallel tank circuit composed ofpassive elements, as shown in Figure 7(a). The Q of this networkis given by(1)
where R = Rsh is the terminal point shunt resistance of the
network measured at resonance. (For a lossless network, Rsh6
4.) The transient response voltage of the tank is of the form

1.) Branly's mode - in which the coherer DC
resistance collapses from a megohm to a few ohms
when an RF signal exceeds the knee in the i-v
characteristic.
2.) Lodge's mode - for which the coherer crudely(2)

which is an exponentially damped oscillation.

7

Fig. 7 Negative resistance oscillator. (From Electronic
Fundamentals and Applications, by J.D. Ryder, Prentice-Hall,
4th edition, 1970, p. 410.)
In conventional regenerative oscillators with passive tankcircuits, link-coupled positive feedback is used to supply energy
to overcome circuit losses. With 2-terminal negative resistancedevices, such as tunnel diodes operating in the negative
resistance region, negative resistance R2 = - Rn , is injected into
the passive network. The equivalent parallel load resistance is24
(3)
which is greater than Rsh. From Equation (1), the effective Q
then becomes Qo increased by a multiplicative factor - the Q
multiplier:(4)
The resulting Q can be made arbitrarily large, even permitting
sustained oscillations, by letting |R n| 6 Rsh. This narrows theselectivity curve and magnifies the circulating current, producing
substantial gain from a simple circuit with surprisingly few
components.

_____________________________________
References
1.

2.

3.

4.

5.

Tesla, N., Nikola Tesla, Colorado Springs Notes: 18991900, compiled and edited by A.Marincic, Nolit, Beograd,
Yugoslavia, 1978.
Corum, K.L., J.F. Corum, and A.H. Aidinejad,"Atmospheric Fields, Tesla's Receivers and Regenerative
Detectors," Proceedings of the 1994 International Tesla
Symposium, International Tesla Society, Colorado Springs,
Colorado, 1994. This paper, and others, are available
through PV Scientific, http://www.arcsandsparks.com .
Corum, K.L. and J.F. Corum, "Nikola Tesla and theElectrical Signals of Planetary Origin," presented at the
1996 International Tesla Symposium, Colorado Springs,
Colorado, and at the Fifth International Tesla Conference:"Tesla III Millennium", Serbian Academy of Sciences andArts, October 15-19, 1996, Belgrade, Yugoslavia. (Thecomplete eighty-one page report is available through PV
Scientific, http://www.arcsandsparks.com . An abbreviatedsynopsis, including audio clips of the receiver output, canbe examined at http://teslasociety.com .)Tesla, N., Nikola Tesla On His Work With Alternating
Currents and Their Application to Wireless Telegraphy,
Telephony, and Transmission of Power, edited by L.I.
Anderson, Sun Publishing, Denver, 1992, pp. 25, 159-163.
Hartley, R.V.L., "Oscillations with Non-Linear
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3, July, 1936, pp. 424-440.

6.

Bennett, W.R., "A General Review of Linear Varying
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Rowe, H.E., "Some General Properties of Nonlinear
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8.

Armstrong, E.H., "A Study of Heterodyne Amplification by
the Electron Relay," Proc. of IRE, Vol. 5, 1917, pp. 146168.

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Armstrong, E.H., (Regenerative Feedback Invention), US
Patent #1,113,149. Filed: October 29, 1913; Issued: 1914.

10. Lauer, H., and H. Brown, Radio Engineering Principles,
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138-140.
13. McCoy, L.G., "The Heathkit Q Multiplier," QST, April,
1956, p. 39.
14. Ort, C., "Discussion," Proc. IRE, Vol. 5, 1917, pp. 163166.
15. Armstrong, E.H., (Superheterodyne Receiver), US Patent#1,342,885. Filed: February 8, 1919; Issued: June 8,1920.
16. Armstrong, E.H., (Superregenerative Receiver), US Patent# 1,424,065; Issued 1922.
17. Armstrong, E.H., "Some Recent Developments ofRegenerative Circuits," Proc. IRE, Vol. 10, 1922, pp. 244260.
18. Hogan, J.L., and L. Lee, Proceedings of the IRE, Vol. 1,
July, 1913; and US Patent 1,141,717.
19. Ort, C., "Discussion," Proc. IRE, Vol. 5, 1917, pp. 163166.
20. Phillips, V.J., "The 'Italian Navy Coherer' Affair: A Turnof-the-Century Scandal," Proc. IEE, Series A, Vol. 140,
May, 1993, pp. 175-185; Reprinted in Proc. IEEE, Vol. 86,
1998, pp. 248-258.
21. Bondyopadhyay, P.K., "Sir J.C. Bose's Diode Detector
Received Marconi's First Transatlantic Wireless Signal of
December 1901 (The 'Italian Navy Coherer' Scandal
Revisited)," Proc. IEEE, Vol. 86, 1998, pp. 259-285.
22. Sengupta, D., T.K. Sarkar, and D. Sen, "Centennial of the
Semiconductor Diode Detector," Proc. IEEE, Vol. 86,
1998, pp. 235-243.
23. Bose, J.C., "Detector for Electrical Disturbances," USPatent #755,840. Filed: Sept. 30, 1901; Issued March 24,
1904. See Proc. IEEE, Vol. 86, 1998, pp. 230-234.
24. Harris, H.E., "Simplified Q Multiplier," Electronics,
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