DE1254718B - Equalizer for FM broadband radio relay systems - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4MVW> PATENT OFFICE Int. Cl .:

H04b

EDITORIAL

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German class: 21 a4 - 55

St 23074IX d / 21 a4 December 12, 1964 November 23, 1967

The invention relates to an equalizer for the cleavage of the conversion in frequency-modulated, broadband Radio links with a small hub.

It is known in radio relay systems with frequency modulation to achieve low-distortion Transmission to linearize the phase. Therefore, phase compensators are used in high-quality systems - · often also called group delay compensator - built-in. It is also known the amplitude response to linearize such transmission systems by appropriate amplitude compensators.

In the case of very broadband, frequency-modulated transmission systems, however, these measures are effective alone not yet with the aim of a transmission that is sufficiently low in distortion. There have already been Investigations into further causes of distortion of the above transmission systems made. It is known that broadband FM systems not only use the lower orders of the Group run to take into account temporal, but also to compensate for its higher orders, what requires the creation of very complex circuits without thereby achieving the desired improvement can be.

Furthermore, studies are already known, according to which the cause of a significant proportion of the Intermodulation noise in the amplitude modulation / phase modulation (AM / PM) conversion is recognized. These investigations showed that the AM / PM conversion was sufficient from the outset Must be kept small because there is no subsequent suppression of PM Possibility. Keeping the conversion small, however, is very complex in terms of the circuit design, as far as it can be measured exactly at all.

Further investigations have now shown that an AM-PM conversion or the intermodulation resulting therefrom can nevertheless be compensated. One must start from the knowledge that in high-quality systems with a broadband leveled amplitude curve (that is the frequency response of the damping), an amplitude modulation can only occur through a frequency response of phase b (ω) . However, only in the case of amplitude-leveled, all-pass-free circuits (minimum phase network), as used for filtering purposes, after subtracting the basic transit time integral, this is always an odd frequency function around a central frequency ω ₀ , with the A ω element being negative and the Δ w ³ - Link is positive. Ab {ω) therefore always shows in the case of bandpass filters the one shown in FIG. 1 shown in principle.

Equalizer for FM broadband radio relay systems

Applicant:

Standard Elektrik Lorenz Aktiengesellschaft, Stuttgart-Zuffenhausen, Hellmuth-Hirth-Str. 42

Named as inventor:

Dr.-Ing. Martin Müller, Pforzheim

Regarding the cause of amplitude modulation, reference is made to the work printed in AEÜ-Heft 1, 1962, pp. 25 to 35 and Book 2, 1962, pp. 93 to 99. Equation 32 there shows that the term designated by b _u (x) results in an amplitude modulation of the second degree.

Converting switching elements are, in particular, tubes, transistors or valves that are widely modulated Diodes. They usually create a phase lag as the amplitude increases. Mathematically this means that the AM terms, including those of the second degree, are multiplied by -7. From this it follows Then the interfering PM intermodulation of the second degree, which is no longer due to a limiter can be eliminated.

If one now looks at equation 44 of the above-mentioned publication, one sees that there is a "pointer increase" of the same character, which has already been multiplied by -7, but instead of b _u (x) contains the amplitude function a _u (x). It must therefore be possible to compensate for the clatter of the conversion by generating an amplitude or damping function α (ω) opposite to the phase function A b (ω).

The invention is based on the object of an equalizer for compensating for the distortion of the conversion to create, which in broadband radio relay systems with frequency modulation in addition to the known phase and amplitude compensators should be used.

The invention is characterized in that the equalizer preferably has an amplitude function odd order generated, which is multiplied by the conversion efficiency and around the Basic delay reduced phase function is opposite.

There is an odd amplitude function due to amplitude saddling on one side of the carrier frequency ω ₀ and an amplitude hump

709 689/173

can be implemented on the other side of the carrier frequency, according to the invention, the amplitude curve is used for this purpose by a suction circle-like amplitude decrease and a parallel circle-like amplitude increase corrected symmetrically to the carrier according to FIG.

Often the conversion efficiency is not exactly known. In these cases, too, can not do a measurement of the phase curve to the required depth or height of amplitude saddle or -stool can be closed to compensate for the distortion of the transformation. It is therefore beneficial to to make this adjustable with an equalizer for the clink of conversion. The in the F i g. 2 shown Size 2 ε is then set to a minimal clink.

The conversion efficiency can also be dependent on the modulation frequency. This means that the phase curve takes on a different shape after the conversion, for example has an almost flat turning tangent at the carrier frequency ω ₀ . This fact can be taken into account by making at least the frequency position of the amplitude _{saddle (W 1} ) and stool (ω ₂ ) and possibly also their bandwidth adjustable.

In FIG. 3 is a schematic diagram of an equalizer for the conversion rattle according to the invention shown.

The z. B. Equalizer connected between transistors consists of a suction circuit (C ₁ , L ₁ , R ₁ ) _{connected to a potentiometer P 1} and a parallel circuit (L ₂ , C ₂ ) parallel to a resistor R _z and the potentiometer P _{0 connected in} parallel to it. The potentiometers P ₁ and P ₂ , which can also be coupled and, at higher frequencies, are usually implemented by semiconductors whose resistance value can be changed, can primarily be used to set the depth or height of the amplitude fluctuation. By changing the capacitance C ₁ and the inductance L ₂ alone, the frequency position to the carrier frequency and by changing C ₁ with L ₁ and C ₂ with L _{2 in} the opposite direction, the bandwidth of the depression and increase of the ίο amplitude curve can be set.

Claims (3)

Patent claims: 1. Equalizer to eliminate the distortion of conversion in broadband, frequency-modulated Radio relay systems with a small hub, characterized in that it is preferably one Odd order amplitude or damping function generated by the The phase function multiplied by the conversion efficiency and reduced by the basic running time is opposite. 2. Equalizer according to claim 1, characterized in that the amplitude or damping curve the carrier frequency on the one hand by a parallel-connected suction circuit or a series-connected parallel circuit and on the other hand by a parallel-connected parallel circuit or a series-connected series circuit is raised. 3. Equalizer according to claim 1, characterized in that the lowering and raising changeable in their depth or height and / or in their frequency position and / or in their width are. 1 sheet of drawings