US2102165A - Radio circuits - Google Patents

Description

' Dec. 14, 1937. K. POSTI-IIUMUS 2,102,165

RADIO CIRCUITS Filed Dec. 8, 1933 INVENTOR A2445 POJT/fl/MUS ATTORNEY Patented Dec. 14, 1937 CIRCUITS zKlaas Posthnmus,-Eindhoven, Netherlands, as-

. signer-t6 Radio Corp p -rationi is: Delaware oration of America, a cor- Al!!!)licatiorrDecember 8, 1933, SerialNo. 701,434

Germany December lZ, 1932 periodic damping variation. The increaseiof thesele'ctivity which is thus produced maybe explainedas follows: If in a tuned circuit the inductancalthe capacity and the resistance are denoted by L, C andR1, respectively, and if a tension E is applied to this circuit, the' total current passing through said (iircuit i SkqliaI to V If now the resistance yisgvaried' from R1 to R2 the variation of thegcurrent intensity will be: 7 B0 V l jwL lR wL-- +R9 wC V 1 wC (JQL;E+R1)(JWLE+R2) In such .If q denotes the frequency-of the v'ariation of the damping andif the variation of the current intensity is i 1 l 5. h pfkR pq 1 psin qt-I- P2 sin Zqt wh n .?81 i ii .If now agfilterjis provided-which is tuned to the frequency of the Variation of the damping, the selectivity is determinedby the term i. e. that the selectivity correspondsto that of two tuned circuits;

If the amplifier is tuned tothe second or third harmonic, the selectivity correspondstothat oi; three or four circuits. Inorder to obtainthe above mentioned effect it is howevernecessary that the variation of the resistance-shouldbe -a purely sinusoidal one, at least that only very-weak harmonics should be produced.

This result may be obtained in practice by arranging in parallel with the tuned circuit the anode-cathode resistance of a tube whose input circuit" has applied to it a voltagewhich-varies sinusoidally. This results in a sinusoidal varia-i tion of the slope oi the tube, i. e. that the internal resistance of thisktube varies inversely proportionally. As the above formulae apply for a resistah'ce connected in series' -within the circuit and a parallel resistance may bereplacedby a series resistance of the value J; CR

cussion-pfthe advantags arising. from providing ircuit. in thejoutput lciricuitrof the maple or the; fundaihg.

:rnental frequency of Tda fit an EI'M. F.'E iswdrkm irrian'pscillating cirv cuit comprising a resistance R, a self inductance L and a capacity C, there will ensue a current If a variable resistance R1 (1+sin qt) is inserted in the oscillatory circuit the current I changes to:

The selectivity is therefore equal to:

For the selectivity without the use of the variable resistance we find:

Substituting this last equation into the equation for Snq we find:

Now So is always greater than one, so that the part between the square brackets is always greater than one. It will therefore always be possible by choosing a harmonic of sufiiciently high order to obtain a selectivity greater than So.

The increase of selectivity is greatest when R1 is small with respect to R. For this case the above formula changes to: Sn =So"+ It will be immediately clear that the selectivity in this case is greater, the higher the order of the harmonic, which is filtered out. The choice of a value of R1, which is small with respect to R, involves the disadvantage that the output voltage is very small, as will easily be seen from the equation representing the development of the current I in a series.

For large values of R1, 1. e. for values of R1 larger with respect to R, the above formula changes to:

The third harmonic offers an increased selectiv-- ity, whereas the filtering out of the fundamental frequency would cause a decrease of the selectivity.

For :1.5; R1=1/2R, we find:

The use of the fundamental frequency in this case would not cause an appreciable increase of the selectivity, whereas the use of the second or third harmonic would yield a considerable improvement.

As to the validity of the above formulae it has to be remarked, that the components of frequency nq contained in the terms of the series with exponents 3nq, 5nq, etc., have been neglected. This does not involve a qualitative error in the results however, as the coeflicients of the higher order terms decrease rapidly with increasing values of the exponent for the frequency or and at a considerably slower rate for the fre-- quency me. As the selectivity is formed by dividing the amplitude for the frequency am by the amplitude for the frequency (.01, the said components of frequency nq can only bring about a further increase of the selectivity.

The invention will be explained more fully with reference to the accompanying drawing which represents by way of example two embodiments of the circuit arrangement according to the invention, whereof Fig. 1 shows the tuned circuit damping by a utilization of the internal resistance of a tube, and Fig. 2 shows therefor the use of a periodic alteration of a retroactive coupling.

The circuit arrangement shown in Figure 1 consists of a detector D1 whose grid circuit comprises a circuit LC tuned to the frequency m which is to be received. The damping of this circuit varies periodically as in parallel with the inductance or with part thereof is connected the internal resistance of a tube M. The resistance of this tube is sinusoidally varied with the aid of a generator g connected in the input circuit of said tube and producing oscillations of the ultra-audible frequency q, for example of 20,000 cycles. The detector D1 is followed by a medium frequency amplifier which is tuned to a harmonic of the frequency of the generator 9 (1w). The low frequency demodulation is brought about with the aid of a second detector Dz.

A variation of the resistance in the tuned circuit may be obtained not only as is shown in the form of construction above described, by parallel connection of the internal resistance of the amplifying tube, but also by periodically altering the retroactive coupling.

Such a circuit arrangement is shown in Figure 2. In the grid circuit of a detector D1 is included a circuit which is tuned to the frequency w to be received and which at the same time is located in the input circuit of an auxiliary tube M. This input circuit comprises in addition a generator g which produces an auxiliary frequency q. In the anode circuit of the tube M is connected a coil L1 which is coupled with the circuit LC and which consequently causes the damping of this circuit to vary periodically, viz. at the frequency q.

The output circuit of the detector again comprises a filter tuned to the frequency q or to a harmonic of said frequency (nq).

The latter method in which the variation of the damping is obtained by periodically altering the retroactive coupling, affords relatively to the method in which the damping of the, circuit is periodically increased, the advantage that thus the circuit is improved, that is to say that it obtains less damping whereas in the case of parallel connection of a resistance the damping is increased.

I claim:

1. A relay circuit arrangement for the selective reception of electrical oscillationscomprising a tuned input circuit for said relay, means for periodically varying the damping of said tuned circuit and a filter circuit for a multiple of the damping frequency connected in the output of the relay.

2. A circuit arrangement as claimed in the preceding claim in which the damping in the tuned circuit varies sinusoidally;

3. A relay circuit arrangement for the selective reception of electrica1 oscillations comprising a an electronic tube provided with an input cir-' cuit and'an output circuit, means for electrically connecting the source to the input circuit said input circuit being tunable to any frequency within a predetermined range of frequencies, a. variable resistance means shunted across at least a part of saidinput circuit, means for varying the value of said resistance at a predetermined rate to thereby periodically damp said input circuit, said output circuit including a tuned circuit tuned to a harmonic of the frequency of variation of said resistance and a utilizing circuit coupled to said output circuit. 7

5. In a circuit arrangement as claimed in the next preceding claim wherein said variable resistance means comprises an electronic tube having its output circuit connected across the portion of the said tuned circuit and an input circuit including a periodically varying source of energy.

6. The method of receiving signal modulated carrier energy which comprises impressing the modulated carrier upon a tuned circuit which is tuned to the frequency of the carrier and periodically varying the damping of the tuned circuit at a supersonic frequency which is different than the frequency of the carrier whereby there is introduced into the tuned circuit energy to compensate for the energy lost in the tuned circuit due to the inherent resistance of the tuned circuit, combining the two energies and utilizing, from the products of the combination, energy of a frequency which isa multiple of the supersonic frequency.

'7. In apparatus for the selective reception of signal waves, a thermionic tube circuit including a tunable input circuit adapted to be tuned to the frequency of the desiredsignal waves and an output circuit, damping means for the tunable input circuit including means for periodically varying the damping of said input circuit at a frequency which is low as compared to that of the signal waves, said output circuit including a resonant circuit tuned to an integral multiple of said variation frequency and a utilizing circuit coupled to said output circuit.

8..An arrangement as described in the next preceding claim characterized by that the damping means comprises a thermionic tube having,

an input circuit and an output circuit and coupling betweensaid circuits.

9. An arrangement as described in claim 7 characterized by that the damping means comprises an auxiliary electronic tube having an input circuit and an output circuit which are coupled together, said input circuit including at least a portion of the tunable input circuit and by that the means for periodically varying the damping of the input circuit of the first tube comprises an alternating current generator in the input circuit of the auxiliary tube.

10. In apparatus for the selective reception of signal waves, a detector circuit having a tunable input circuit adapted to be tuned to the fre- KLAAS POSTHUMUS.

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