464,443

PATENT SPECIFICATION

Application Date: Oct. 19, 1935. No. 28907/35.

" " " July 10, 1936. No. 19178/36.

One Complete Specification Left: July 10, 1936.

(Under Section 16 of the Patents and Designs Act 1907 to 1932.)

Specification Accepted: April 19, 1937.

-------------------------

PROVISIONAL SPECIFICATION

Improvements in or relating to Aerial Systems

We, ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, EDWARD CECIL CORK, of 50A, Kenilworth Road, Ealing, London, W.5, and JOSEPH LADE PAWSEY, of 28, Tudor Way, Hillingdon, Middlesex, all British Subjects, do hereby declare the nature of this invention to be as follows:-

The present invention relates to aerial systems.

In the case of a short wave transmitter feeding an aerial through a transmission line, it is usual to match the resistive impedance of the aerial to the characteristic impedance of the feeder, and, further, if possible, to match this characteristic impedance to the impedance of the transmitter.

When transmitting signals with a wide side band such as television signals, it is impracticable to match the transmitter impedance to the feeder impedance and also to the aerial impedance, and at the same time obtain the necessary band width; in fact the load thrown on the transmitter by the aerial seen through the feeder is usually much lower than the impedance of the transmitter. Any small errors or variations in the impedance of the aerial as seen through the feeder then affect the output. If these errors are variable with frequency, the response of the transmitter will also not be uniform, and will vary with the impedance of the aerial as seen through the feeder.

Now if the feeder is long and the aerial impedance does not match the characteristic impedance of the feeder, serious variations of impedance seen by the transmitter may take pace within the working range, and these variations of impedance will cause variations in the response of the transmitter. Such failure of matching between the aerial and the feeder may be due to maladjustment or to the variation of the aerial impedance with frequency. Even if the aerial has a natural frequency response curve adequately wide for the band in question, at small departures from the tuning frequency of the aerial considerable reactance may be present. For example, if an aerial has a natural band width ± 5 megacycles per second, the band width being taken as the width of the band within which the response does not fall more than 3 decibels below the maximum, then, at 5 megacycles per second from its tuned frequency, the reactance of the aerial will equal its resistance. At 1 megacycle per second from the tuned frequency the reactance will be approximately one fifth of (or five times if considered in parallel) the resistance. This is a 20% error in matching impedance and will cause a 20% error in impedance as seen from the transmitter. The phase angle of this impedance error will depend upon the length of feeder, and will change with small changes of frequency if the feeder is very long, causing a possible bump or hollow in the response of about 20%.

It is the object of this invention to provide mans whereby an aerial may be built out to a substantially pure resistance over a considerable frequency range, so as to form a substantially correct termination for a feeder.

According to this invention an aerial fed from a long feeder is built out to present a substantially constant termination resistance to the feeder at all frequencies within a considerable frequency range. The frequency range may be the working range of a transmitter connected to the feeder.

According to a feature of this invention a reactance or reactances with or without resistance are added to the feeder at or near the aerial to give a improved matching to the feeder impedance.

A known aerial system as seen from a potential antinode (for example, one end of a dipole fed at this end) can be represented conventionally by a resistance which will be denoted by R, a condenser C and an inductance L connected in shunt with one another between earth and a common point. A concentric feeder of characteristic impedance Z is connected at one end to a transmitter and, at its other end has its central conductor connected to a tapping point on inductance L and its outer conductor earthed. R, C and L represent the resistance, capacity and inductance respectively of the aerial. The tapping point on the inductance L is so chose that the inductance operates as an auto-transformer to match the aerial resistance R to the feeder impedance Z at the carrier frequency of the transmitter to which frequency the resonant circuit L, C, R is tuned. It will be seen that, at frequencies off resonance, even where the capacity reactance of L and C is still considerably greater than R, the feeder of impedance Z (assumed to be substantially resistive) will not be correctly terminated by the aerial.

In applying the present invention to the above circuit, an inductance L1 and capacity C1 may be connected in series between the aerial end of the central conductor of the feeder and the tapping point on inductance L. Capacity C1 and inductance L1 are shunted by a resistance r equal in magnitude to the resistance of the feeder. Suppose that the transformer ratio is equal to the square root of n where

EQUAT. HERE

, then the apparent inductance value of L at the tapping point will be EQUAT. HERE and the apparent value of C at the same point will be nC. L1 is then made equal to nCZ2 and C1 is made equal to EQUAT. HERE. Under these conditions (assuming a perfect transformer), the impedance facing the feeder will be invariant with frequency and equal to Z. If only comparatively small departures from the resonant frequency of the aerial are considered, the resistance r may be omitted altogether, since the variation of resistance presented to the feeder will not be serious and the only effect which it is necessary to correct is the reactance introduce by L and C. This can be corrected for small departures from resonance by the reactances L1 and C1. In practice L1 may be composed of the leakage inductance of a transformer so that in some cases only C1 need be added.

In the case of an aerial fed at its centre, the conventional diagram comprises an inductance L, a condenser C and a resistance R connected in series with one another and between the aerial end of the feeder and earth. It is assumed that the feeder impedance has been made equal to R. in Applying the present invention to this arrangement a shunt load comprising an inductance L1 and capacity C1 and resistance r may be added. One terminal of resistance r is earthed and its other terminal is connected to one terminal of capacity C1 and to one terminal of inductance L1. The other terminals of inductance L1 and capacity C1 are connected to the aerial end of the central conductor of the feeder. In this case it is arranged that EQUAT. HERE.

This is a counterpart of the previously described arrangement and similarly, to a first approximation, resistance r may be omitted (in this case it must be replaced by a short circuit).

In another method of applying the present invention to the first described aerial system, the tapping point on the inductance L remains directly connected to the end of the central conductor of the feeder and a shunted load is connected between the central conductor of the feeder and earth at a point located a quarter wavelength or an odd number of quarter wavelengths from the aerial end of the feeder. The shunt load is then of the type described above with reference to any aerial fed at its centre. That is, an inductance L1 and capacity C1 are connected at one end to the central conductor and their other ends are earthed through a resistance r. In this case EQUAT. HERE and C1=nC. As before, as a first approximation close to resonance, r may be omitted (short circuited). If this type of correction is employed, it is advisable to put the correcting circuit only a small number of quarter wavelengths way from the aerial if correction over a wide frequency band is required. By putting the load a quarter wavelength away, the impedance errors are inverted so that the type of circuit required is altered.

Dated this 19th day of October, 1935.

REDDIE & GROSE,

Agents for the Applicants,

6, Bream’s Buildings, London, E.C.4.

PROVISIONAL SPECIFICATION

No. 19178 A.D. 1936.

Improvements in or relating to Aerial Systems

We, ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, EDWARD CECIL CORK, of 50A, Kenilworth Road, Ealing, London, W.5, and JOSEPH LADE PAWSEY, of 28, Tudor Way, Hillingdon, Middlesex, all British subjects, do hereby declare the nature of this invention to be as follows:-

This invention relates to aerial and feeder systems for short wave transmitting apparatus and is moreover cognate with or a modification of that set forth in the Specification of co-pending Application No. 28907/35.

When an aerial consists of a single wire any change of reactance with frequency is usually much greater than the corresponding change in resistance and the selectivity of such an aerial is determined mainly by the reactance change. The reactance change causes the strength of signals radiated from or picked up by such an aerial to vary with different frequencies. Further, due to the additional reactance, reflection will occur and in the case of a television transmitting aerial connected with a transmitter through a feeder the length of which is comparable with the wavelength corresponding to the highest modulation frequencies, echo pictures will be produced due to the time of transmission along the feeder being appreciable. This effect is knows as "ringing".

In the Specification referred to alternative methods are described for building out the impedance of an aerial by the use of inverse impedance to represent a constant resistance over the working side band range of frequencies. The provision of such inverse impedances serves to prevent variations of impedance as seen from the transmitter end of an electrically long feeder from causing substantial irregularities in the response curve of the transmitter which may otherwise occur.

The object of the present invention is to provide an aerial system in which the effects of variation in reactance are substantially eliminated.

According to the present invention, in a feeder system for a short wave aerial, reactance variations are corrected by the impedance of the system to a substantially pure resistance. In particular applications of the invention, circuits in the form of lines having inverse circuit constants are inserted in series or parallel with the aerial.

In order that the nature of the invention may be more clearly understood, the theory upon which it is based will now be explained, and some short wave aerial feeder systems embodying the invention will be described by way of example with reference to Figs. 1 to 5 of the accompanying drawings.

Referring to Fig. 1, a dipole aerial 1 is represented diagrammatically and includes a parallel line circuit 2. Let it be assumed that the dipole aerial is a line of characteristic impedance ZA and of a length q a with a radiation resistance R1 in series, and further, that the line 2 has an impedance ZO, an electrical length q and has in series a resistance R2, then the impedance between the points A and B may be obtained from the following equation:

EQUAT. HERE

 

If, in this equation is inserted

EQUAT. HERE

and tan q A = tan q

then Z = R

from which it is seen that the reactance variation has disappeared.

Referring to Fig. 2 of the drawings, a concentric feeder having inner and outer conductors 3 and 4 is connected to a dipole aerial 5, 6. The parallel line corresponding with the line 2 in Fig. 1 is constituted by a sheath 7 enclosing the outer sheath 4 of the feeder. The sheath 7 is connected directly to the sheath 4 at a point 8 approximately one electrical quarter of a wavelength from the aerial 5, 6.

In Fig. 3 a symmetrical arrangement is shown in which the parallel line is formed by adding an inner conductor 9 to a hollow line 10 used normally as a dummy line serving the same purpose as an interference suppressing line of the kind described in the Specification of Patent No. 438,506.

In Fig. 4 again, a symmetrical arrangement is shown but in this case two parallel lines 11 and 12 are used as the correcting lines, the dummy line 10 shown in Fig. 3 being retained.

In Fig. 5 a further symmetrical arrangement is shown but in this case two auxiliary concentric lines having inner and outer conductors 13 and 14, and 15 and 16 respectively, are used for correction purposes.

It will be understood that the invention may be carried out in further ways which will occur to those skilled in the art, and it is further to be understood that the invention may be applied to aerials of other types than dipoles, the correction being made at the junction of the aerial and its feeder.

Dated this 10th day of July, 1936.

F. W. CACKETT.

Chartered Patent Agent

COMPLETE SPECIFICATION

Improvements in or relating to Aerial Systems

We, ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, EDWARD CECIL CORK, of 50A, Kenilworth Road, Ealing, London, W.5, and JOSEPH LADE PAWSEY, of 28, Tudor Way, Hillingdon, Middlesex, all British subjects, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in any by the following statement:-

This invention relates to aerial and feeder systems for short wave transmitting apparatus and has particular reference to aerial systems for use with signal frequencies of the order employed in television transmission systems.

In the case of a short wave transmitter feeding an aerial through a transmission line, it is usual to match the resistive impedance of the aerial to the characteristic impedance of the feeder, and further, if possible, to match this characteristic impedance to the impedance of the transmitter.

When transmitting signals with a wide side band such as television signals, it may be impracticable to match the transmitter impedance to the feeder impedance and also to the aerial impedance, and at the same time obtain the necessary band width; in fact the load thrown on the transmitter by the aerial seen through the feeder may be much lower than the impedance of the transmitter. Any small errors or variations in the impedance of the aerial as seen through the feeder then affect the output. If these errors are variable with frequency, the response of the transmitter will also not be uniform, and will vary with the impedance of the aerial as seen through the feeder.

Now if the feeder is electrically long and the aerial impedance does not match the characteristic impedance of the feeder, serious variations of impedance seen by the transmitter may take place within the working range of frequencies and these variations of impedance will cause variations in the resonance of the transmitter. Such failure of matching between the aerial and the feeder may be due to mal-adjustment or to the variation of the aerial impedance with frequency. Even if the aerial ahs a natural frequency response curve adequately wide from the band in question at small departures from the tuning frequency of the aerial considerable reactance may be present. For example, if an aerial has a natural band width of ± 5 megacycles per second, the band width being taken as the width of the band within which the response does not fall more than 3 decibels below the maximum, then, at 5 megacycles per second from its tuned frequency, the reactance of the aerial will equal its resistance. At 1 megacycle per second from the tuned frequency the reactance will be approximately one fifth of (or five times if considered in parallel) the resistance. This is in practice a serious error in matching impedance.

It is well known that if a feeder is not correctly terminated standing waves occur in the feeder and the impedance at the transmitter input will vary for any given aerial impedance and frequency with the length of the feeder. If the feeder is approximately an integral number of half wave lengths long at the side band frequency the impedance at the transmitter end f the feeder will also be in error by the same amount. If at the carrier frequency the feeder is different integral number of half wave lengths long, then at some frequency or frequencies between the carrier frequency and the one megacycle side band frequency, the feeder will be an integral number of ¼ wave lengths long and will act as a transformer so that at these frequencies the impedance at the transmitter end will be less than the impedance at the carrier frequency.

The response characteristic of the aerial instead of showing merely a droop towards the extreme side band frequencies will also exhibit alternate rises and falls which are of considerable magnitude for the degree of mis-match referred to.

If L is the length of the feeder and f0 and f1 are the carrier and side band frequencies respectively, the numbers of standing waves in the feeder at these two frequencies are

EQUAT. HERE

where c is the velocity of propagation of waves in the feeder I metres per second and approximating to the velocity of light while L is the length of the feeder in metres. The feeder is defined as being electrically long with respect to the highest modulation frequency if

 

EQUAT. HERE

 

Thus if (f1f0) = ± 2 megacycles the undesired effect will occur when L is greater than about 75 metres.

It is the object of the invention to provide mans for preventing variations of the impedance presented to a transmitter connected with an aerial by an electrically long feeder and so obtaining a substantially even response over a desired range of frequencies.

According to the present invention, in a short wave transmitting system including an aerial coupled with a transmitter by a feeder which is electrically long with respect to the highest modulation frequency, the reactance of the aerial at frequencies other than the resonant frequency is compensated by the insertion, either in series or in parallel with the feeder at the aerial or at a point an integral number of half wavelengths from the aerial, of a network including a resistance substantially equal to the resistance of the aerial at resonance, and a reactance which is substantially equal to the square of this resistance divided by the reactance o the aerial at all frequencies in the operating range, whereby the total impedance over that range is substantially equal to the resistance of the aerial at resonance.

In an alternative system embodying the invention the compensation network is inserted either in series or in parallel with the feeder at a point an odd number of quarter wavelengths from the aerial, the compensation network including a resistance substantially equal to the resistance of the aerial at resonance and a reactance substantially equal to the reactance of the aerial. Again, the desired compensation may be effected by inserting, either in series or in parallel with the feeder at the aerial or at a point an integral number of half wavelengths from the aerial, a reactance which at all frequencies in the operating range is substantially equal to the square of the resistance of the aerial at resonance divided by the reactance of the aerial at resonance divided by the reactance of the aerial. In a further system embodying the invention, compensation may be effected by the insertion either in series r in parallel with the feeder at a point an odd number of quarter wavelengths from the aerial of a reactance which at all frequencies in the operating range is substantially equal to the reactance of the aerial.

In order that the invention may be more clearly understood and readily carried into effect, some aerial and feeder systems embodying the invention will now be described by way of example with reference to the drawing accompanying this Specification and to the drawings left with Provisional Specification No. 1978/36.

Referring to the drawings accompanying this Specification, Fig. 1 illustrated diagrammatically a know dipole aerial system fed at a potential antinode in this case one end of the aerial. The aerial as represented includes a resistance R, a condenser C and an inductance L connected in shunt with one another between earth and a common point. A concentric feeder F of characteristic impedance Z is connected at one end to a transmitter (not shown) and at its other end has its central conductor G connected to a point H which is one end of the aerial. The outer conductor of the feeder F is earthed. R, C and L represent the resistance, capacity and inductance – respectively of the aerial. It will be seen that at frequencies off resonance, even when the reactance of L and C is still considerably greater than R, the feeder of impedance Z assumed to be substantially resistive will not be correctly terminated by the aerial. Fig. 2 illustrates the application of the invention to the aerial system shown in Fig. 1. An inductance L2 and condenser C2 are connected in series between the aerial and the feeder. Condenser C2 and inductance L2 are shunted by the resistance r equal in magnitude to the resistance of the feeder and have the values C2= EQUAT. HERE and L2 = CR2. Under these conditions the impedance facing the feeder will be invariant with frequency and equal to R, i.e. equal to Z. If only comparatively small departures from the resonant frequency of the aerial are considered, the resistance r may be omitted altogether since the variation of resistance presented to the feeder will not be serious and the only effect which it is necessary to correct is the reactance introduced by L and C. This can be corrected for small departures from resonance by the reactances L2 and C2.

If the impedance of the feeder does not match the impedance of the aerial directly, i.e. if Z is not equal to R, which is usual in practice when the end fed aerial is one half of a wavelength long, it is necessary to insert a transformer between the feeder and aerial. This may take the form of a tuned circuit connected between the earth and the end of the aerial, the central conductor of the feeder being connected to a tapping point on the inductance of the tuned circuit while the sheath of the feeder is earthed. The inductance and capacity of the tuned circuit are in parallel with the corresponding inductance and capacity of the equivalent aerial circuit. The resultant inductance and capacity are shown by L1 and C1 in Fig. 3, which shows the application of the invention to the aerial and transformer system. The inductance L3 and condenser C3 are connected in series between the aerial end of the central core G of the feeder F, and the tapping point on the inductance L1. The resistance r equal in magnitude to the resistance of the feeder shunts the condenser C3 and inductance L3 as in Fig. 2. If it is assumed that the transformer ratio is the square root of n, where n is equal to EQUAT. HERE, then the apparent inductance value of L1 t the tapping point will be EQUAT. HERE, and the apparent value of C1 at the same point will be nC1. L3 is then made equal to nC1 x Z2 and C3 is made equal to EQUAT. HERE. Under these conditions, assuming a perfect transformer the impedance facing the feeder will be equal to Z. as in the case of the arrangement shown in Fig. 2, the resistance r may be omitted if only small departure from the resonant frequency of the aerial are considered. Correction for the reactance introduced by L1 and C1 for small departures from resonance an be corrected by the reactances L3 and C3. In this case L3 may be composed of the leakage inductance of the transformer so that in some cases only C3 need be added.

Fig. 4 illustrates the case of an aerial fed at its centre, the aerial system being represented by an inductance L, a condenser C and a resistance R, connected in series with one another and between the aerial end of the feeder F and earth. It is assumed that the feeder impedance has been made equal to R. the present invention is shown applied to this arrangement by the addition of a shunt load comprising an inductance L4 and capacity C4 and resistance r. The lower terminal of resistance r is earthed and its upper terminal is connected to one terminal of condenser C4 and to one terminal of inductance L4. The other terminals of the inductance L4 and condenser C4 are connected to the aerial end of the central conductor G. In this case it is arranged that EQUAT. HERE is equal to R2 and EQUAT. HERE is also equal to R2 and r is equal to R. this is counterpart of the arrangement described with reference to Fig. 3, and again, as a first approximation, resistance r may be omitted and for this purpose may be short circuited.

Fig. 5 shows another method of applying the invention to the aerial system described with reference to Fig.3. the tapping point on the inductance L remains directly connected to the end of the central conductor G of the feeder F, and a shunt load is connected between the central conductor G of the feeder and earth at a point I located a quarter wavelength or an odd number of quarter wavelengths from the aerial end of the feeder. The shunt load is of the type described with reference to Fig. 4. Thus, an inductance L5 and capacity C5 are connected at one end to the central conductor G and their other ends are earthed through resistance r. In this case L5 is equal to EQUAT. HERE and C5 is equal to nC. As before, as a first approximation close to resonance r may be effectively omitted by short circuiting it. If this type of correction is employed, it is advisable to put the correcting circuit only a small number of quarter wavelengths away from the serial if correction over a wire frequency band is required. By putting the load a quarter wavelength away, the impedance errors are inverted so that the type of circuit required is altered.

Further applications of the invention are illustrated in Figs. 2, 3, 4 and 5 of the drawings left with Provisional Specification No. 19178/36 and will be more clearly understood when considered in relation to the following explanation of Fig. 1 of those drawings. In this figure a dipole aerial 1 is represented diagrammatically and includes a parallel line circuit 2. If it is assumed that the dipole aerial is a line of characteristic impedance AA and of a length q a with a radiation resistance R1 in series, and that the line 2 has an impedance Zo, an electrical length q and has in series a resistance R2, then the impedance between the points and B may be obtained by the following equation:-

 

EQUAT. HERE

 

If, in this equation is inserted

EQUAT. HERE

 

and tan q A = tan q

then Z = R

from which it is seen that the reactance variation has disappeared.

Referring to Fig. 2 of the drawings left with Provisional Specification No. 19178/36 a concentric feeder having inner and outer conductors 3 and 4 is connected to a dipole aerial 5, 6. The parallel line corresponding with the line 2 in Fig. 1 is constituted by an outer sheath 7 enclosing the sheath 4 of the feeder. The sheath 7 is connected directly to the sheath 4 at a point 8 approximately one electrical quarter of a wavelength from the aerial 5, 6 and s connected at the other end to the limb 5 of the aerial through a resistance $2.

In Fig. 3 a symmetrical arrangement is shown in which the parallel line is formed by adding an inner conductor 9 to a hollow line 10 used normally as a dummy line serving the same purpose as an interference suppressing line of the kind described in the Specification of Patent No. 438,506. This interference suppressing line renders the end of the feeder connected to the aerial electrically symmetrical with respect to earth, and also acts so that interference picked up by and propagated along the outside of the feeder acts equally on each half of the dipole aerial so that no potential difference due to interference is established between the conductors of the feeder 3,4. The line 9, 10 is quarter of a wavelength long at the resonant frequency of the aerial and is short circuit and connected to the sheath 4 at the end remote from the aerial. The resistance R2 equal in value to the resistance of the aerial at resonance is connected between the sheath 4 and the inner conductor 9.

Since in these figures 2 and 3, the short circuit quarter wavelength lines 7, 4 and 9, 10 act as parallel tuned circuits and are connected in series with resistances R2 across the aerial terminals, these arrangements are the equivalents of the arrangement shown in Figure 4 of the drawings accompanying this complete specification.

Referring now to Figure 4 of the drawings left with provisional specification No. 19178/36, a symmetrical arrangement is shown comprising a quarter wavelength of conductor 11 surrounding the sheath 4 of the feeder, and a further quarter wavelength of concentric line 10, 12. The ends of the conductors 10, 11 and 12 remote from the aerial are connected together and to the sheath 4 of the feeder as directly as possible. The conductors 11 and 12 form with the two resistances EQUAT. HERE the compensating circuit according to Figure 1. It will be seen that there is also connected across the aerial terminals the resistance EQUAT. HERE in series with the closed quarter wavelength line formed by the internal surface of the conductor 11 co-operating with the external surface of the sheath 4.

In order to preserve as complete balance as possible, the conductor 10 is shown connected to the central conductor 3 of the feeder by a conductor 17. It may be preferable to use as compensating circuits the lines 11, 4 and 10, 12 in series with their respective resistances. Since these two circuits are in parallel with respect to the aerial terminals the resistances will in this case have the values 2R2 instead of EQUAT. HERE. The impedance of the line 11, 12 will then be an unwanted shunt and may be made high so as to be negligible in effect, or it may be taken account of in the design of the other circuits.

The alternative values for the resistances will be clear from a more detailed consideration of the equivalent circuit of Fig. 4. Thus, as previously mentioned, the resistances and the tune circuit 11, 12 may provide the compensating circuit as in Fig. 1 of the drawings accompanying Provisional Specification No. 19178/36, and, in this case, the resistances will both have the value EQUAT. HERE. The tuned circuit 11, 4 is unwanted and is unavoidable and a balance is restored by the provision of circuit 12, 10, that is to say, by the provision of the central conductor 10 connected to the central conductor 3. The impedances of the circuits 11, 4 and 12, 10 should be high in order to limit their shunting effect, otherwise they will modify the values of the resistances and the impedance of the circuit 11, 12.

It will be seen that impedance compensation of the aerial may be provided by the circuits including the resistance R in series with 11, 4 in parallel with the other resistance R which is in series with 12, 10. In this case the resistances should have the value 2R2. As the circuit 11, 12 is unwanted it should be made of high impedance at all relevant frequencies. Owing to the dimensions of a possible practical arrangement, this latter mode of operation of the circuit will be the usual one.

Figure 5 of the drawings accompanying provisional specification No. 19178/36 shows an arrangement in which symmetry is again obtained. Across the aerial terminals, that is to say, between the inner conductor 3 and the sheath 4 of the feeder are connected two parallel circuits, one consisting of a resistance 2R2 of value twice the aerial resistance at resonance in series with the closed quarter wavelength line 13, 14 and the other consisting of a similar closed quarter wavelength line 15, 16 in series with a resistance of the same value. In parallel also across the aerial terminals is the impedance of the closed quarter wavelength line formed by the sheaths 4 and 14 which are connected together along their length co-operating with sheaths 10 and 16, which are also connected together along their length. This impedance will be high if the characteristic impedance of the line in question is high, that is to say, if the spacing of the conductors forming it is considerable; and is negligible in effect on the total aerial impedance. Since in the arrangement of Figure 5 and in one aspect of Figure 4 there are two circuits in parallel across the aerial instead of the one shown in Figure 1, the resistances are doubled as stated above, and the impedances of the lines are also doubled by increasing their characteristic impedance above the value required in Figure 1.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

  1. A short wave transmitting system including an aerial coupled with a transmitter by a feeder which is electrically long with respect to the highest modulation frequency, wherein the reactance of the aerial at frequencies other than the resonant frequency, is compensated by the insertion either in series or in parallel with the feeder at the aerial or at a point an integral number of half wavelengths from the aerial of a network including a resistance substantially equal to the resistance of the aerial at resonance, and a reactance which is substantially equal to the square of this resistance divided by the reactance of the aerial at all frequencies in the operating range, whereby the total impedance over that range is substantially equal to the resistance of the aerial at resonance.
  2. A short wave transmitting system including an aerial coupled with a transmitter by a feeder which is electrically long with respect to the highest modulation frequency, wherein the reactance of the aerial at frequencies other than the resonant frequency, is compensated by the insertion either in series or in parallel with the feeder at a point an odd number of quarter wavelengths from the aerial of a network including a resistance substantially equal to the resistance of the aerial at resonance, and a reactance which is substantially equal to the reactance of the aerial, whereby the total impedance over the operating range of frequencies is substantially equal to the resistance of the aerial at resonance.
  3. A short wave transmitting system including an aerial coupled with a transmitter by a feeder which is electrically long with respect to the highs modulation frequency, wherein the reactance of the aerial at frequencies other than the resonance frequency is substantially compensated by the insertion, either in series or parallel with the feeder at the aerial or at a point an integral number of half wave lengths from the aerial of a reactance which at all frequencies in the operating range is substantially equal to the square of the resistance of the aerial at resonance divided by the reactance of the aerial, whereby the total impedance over that range is substantially equal to the resistance of the aerial resonance.
  4. A short wave transmitting system including an aerial coupled to a transmitter by a feeder which is electrically long with respect to the highest modulation frequency, wherein the reactance of the aerial at frequencies other than the resonance frequency is substantially compensated by the insertion either in series or in a parallel with the feeder at a point an odd number of quarter wave lengths from the aerial of a reactance which at all, frequencies in the operating range is substantially equal to the reactance of the aerial, whereby the total impedance over that range is substantially equal to the resistance of the aerial.
  5. A modification of the short wave transmitting system according to Claim 1 or 2, wherein the aerial is fed through an impedance transforming device, and in which the compensating reactance and resistance if any, are connected in the primary side of the transforming device, and their values are determined by the resistance and reactance of the aerial measured at the primary of the transforming device.
  6. A short wave transmitting system according to any one of the preceding claims wherein portions of the transmission lines provide the reactance required in the additional circuits.
  7. A short wave transmitting system according to any one of the preceding claims and in which means of the type specified or illustrated with reference to Figs. 3, 4 and 5 of the drawings accompanying provisional specification No. 19178/36 are provided for the purpose of suppressing interference.
  8. A short wave transmitting system according to claim 6 wherein the portions of the transmission lines are constituted by lengths of conductor co-operating with the sheath of the aerial feeder.
  9. A short wave transmitting system including an aerial and feeder system substantially as described with reference to any of Figs. 2 to 5 of the accompanying drawings.
  10. A short wave transmitting system including an aerial and feeder system substantially as described with reference to any of Figs. 2 to 5 of the drawings left with provisional specification No. 1917/36.

Dated this 10th day of July, 1936.

F. W. CACKETT

Chartered Patent Agent

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. 1937.