DYNAS (from Dynamic Selectivity[1][2][3]) is a dynamic analog filtering and tuning technology to improve the reception of FM radio broadcasts under adverse conditions.
The trademarked[4] DYNAS system is based on the same principles as the In Channel Select (ICS) system by H.u.C. Elektronik. The novel tracking filter arrangement was originally conceived by the German engineer Jens Hansen[2][3] in 1982.[5] The concept was prototyped as High Select in summer 1983.[5] With funding from innovation funds of the city of Berlin, Hansen left Bosch/Blaupunkt to start, with companion Klaus Müller-Catito, his own company H.u.C. Elektronik in 1984.[5][6][7][8][nb 1][nb 2] When licensing negotiations with his former employer failed,[8] the system was marketed in the early 1990s as DYNAS by the German Telefunken electronic[2] (a spin-off of AEG-Telefunken and DASA, firming as TEMIC TELEFUNKEN microelectronic [de] since 1992),[9][10][11][12][13][14] who, with the related Telefunken Semiconductors [de][3][2] (the former AEG-Telefunken Halbleiterwerk in Heilbronn), also designed integrated circuits implementing the system, the TEMIC/TFK[3] U4290B (stand-alone FM IF DYNAS system in 68-pin PLCC package),[3][2][15][16][17][4][12][18] U4291B (DYNAS coprocessor)[18] and U4292B (software-controlled DYNAS system in 44-pin SSO package).[1][18]
Compared to conventional receivers, DYNAS has a more than 26 dB better selectivity and a typically twice as good sensitivity (improved by 6 dB) thereby almost doubling the reception area and allowing to receive even extremely noisy stations.[1] This is achieved by an adaptive bandwidth of the IF filter and by dynamically tracking of the center frequency of the IF filter in real-time.
With a transmitter spacing of 200 kHz an undisturbed reception in stereo is possible, with 100 kHz a largely undisturbed mono reception is still possible.
The principle has been adopted in some high-end FM tuners like the analog Burmester Tuner 915 (1991)[19] or the digital synthesizer tuners Onkyo[nb 3] Integra T-4970 (1992)[16][2][3] and T-488F (1993)[15][20] as well as in various car radios, such as the Alpine 7619R (1989) and 1310R/3681 (1990),[17] the JVC KS-CG10 (1992),[4] the Clarion CRX121R (1993),[21] CRX123R (1993),[21] CRX121RM[22] and CRX123RM,[22] the Gelhard GXR 990S (1993) or the Conrad Soundcraft AR6800 DYNAS,[nb 4] which are particularly affected by difficult and rapidly changing reception conditions.
The In Channel Select (ICS) system by H.u.C. Elektronik in 1984[5][23][24] is a DYNAS predecessor mainly for narrowband FM receivers.[25][26][27][28] It is based on the High Select tracking filter (German: Mitlauffilter aka MLF) developed by Jens Hansen since 1982.[5] ICS improved the selectivity by about 20 dB and the sensitivity by about 6 dB.[25]
A very similar technology is the Active Real-time Tracing System (ARTS), as was implemented in the Pioneer Elite F-91 and some versions of the F-717[nb 5] high-end tuners in 1987.[29][30][31][32][33]
Super Sound Tracing (SST) is a similar technology by Sony affecting the RF rather than the IF stage.[33][34][35] A four-stage SST system was implemented in high-end tuners such as the ST-S555ESX (1986), ST-S333ESX (1986), ST-S444ESX[36]/ST-S700ES (1987),[36] ST-S800ES (1987)[37] and ST-S333ESX II (1987)[38][36][39][34]/ST-S730ES (1988).[39][36] Advanced SST,[40][35] dividing the tuning range into 32 sections, was implemented in some model variants[nb 6] of the ST-S739ES, ST-S333ESG (1989)/ST-S770ES (1990)[36][41][35][40][42][nb 6] ST-S333ESA (1991), ST-S333ESJ (1993), ST-S707ES (1993)[36][43][44][nb 6] and ST-SA5ES (1994/1996).[45][36][nb 6]
Blaupunkt's Sharx technology, as introduced in 1997 in the Modena & Lausanne RD 148 car radios with "DigiCeiver", is a similar digital solution implemented in software. The original Sharx implementation still relied on a bank of switchable analog ceramic resonators for the IF filter stage before the A/D conversion for further processing of the signal in the DSP section. Around 2000, the switchable IF filter moved into the digital domain as well, that is, it was integrated into the DigiCeiver/TwinCeiver chip leaving only the first stage of the IF filter a discrete part.[46][47]
The U4292B is a bipolar integrated FM-IF circuit, which is controlled by software. It performs all the functions of the DYNAS system. The device is designed for car radio and home receiver applications. DYNAS is a completely new system of FM-IF processing. It uses bandpass filters with a bandwidth down to about 20 kHz compared to 160 kHz for a conventional bandpass filter, and tracks the resonant frequency to the actual frequency. Implementation of the DYNAS system drastically enhances both of the basic, classic characteristics of radio reception: selectivity and reception sensitivity. DYNAS ensures enhancement up to levels which until now were not considered physically feasible.Alt URL.
Petsuya Toyama, Tunerentwickler von Onkyo [...] Dafür bietet der Newcomer sieben weitere hyperschmale Trennschärfepositionen an. Nach der von dem Berliner Jens Hansen ausgetüftelten Methode [...] stehen die entsprechenden, sich je nach Ernst der Empfangslage stufenweise mehr oder minder verengenden Türchen nicht mehr fest an einer Stelle. Damit die Musik-vermittelnden Frequenzauslenkungen noch durchpassen, versucht ihnen der Wackelschlitz so gut wie möglich zu folgen. Sobald der T 4970 Dynas-(Dynamic-Selectivity-)-Kunststückchen aufführen soll, wird die Zwischenfrequenz von 10,7 Megahertz noch einmal auf eine Lage um 700 Kilohertz umgesetzt. In härtesten UKW-Situationen versuchen dann gleich vier auf "scharf" gestellte, von elektronisch steuerbaren Kapazitätsdioden nachgezogene Schwingkreise den Modulationsschlenkern hinterherzuhechten. Die Abstimmspannung erzeugt sich der von der deutschen Firma Telefunken Electronics hergestellte Dynas-Chip dabei hintenrum, aus dem niederfrequenten Musik-Ausgangssignal. [...] Das klappt aber nur mit dem Mono-Summensignal perfekt, bei Stereo wüßte der arme [68-]beinige Siliziumkäfer ja nicht hü oder hott. Die wirksameren schmaleren Trennschärfetürchen kommen deshalb erst dann zum Einsatz, wenn es aufgrund der Feldstärke und bösartiger Frequenznachbarn ohnehin ratsam wird, auf die unkritische Mono-Wiedergabe umzuschalten. [...]
[...] Dann hilft nur noch jene Schaltung, die von einem Berliner Ingenieur entwickelt, von Telefunken als Chip realisiert und von Onkyo jetzt erstmals serienmäßig in einem Heimtuner eingesetzt wurde: Dynas. [...] Der Name steht für "Dynamic Selectivity", also dynamische Trennschärfe. Der Grundgedanke von Dynas ist, das konventionelle, statische Zwischenfrequenzfilter durch einen Mitlauffilter zu ersetzen, das den Frequenzänderungen des UKW-Signals folgt. Ein solches Filter kann entsprechend schmalbandiger sein und verbessert die Trennschärfe. Zusätzlich wird die Filterbandbreite je nach Stärke der störenden Nachbarsender in mehreren Stufen automatisch umgeschaltet. Dazu sind aufwendige Kontrollschaltungen notwendig, die aus dem Dynas-Chip einen veritablen Vielbeiner gemacht haben. [...]
[...] DYNAS is a trademark of H.u.C. Ele[k]tronik GmbH [...] The DYNAS system has been modified from the intermediate system. Although the FM P.C. board and parts list are present, any FM adjustment procedure is not described. Until the FM adjustment method is published, therefore, the FM P.C. board should be replaced by the P.C. board ass'y. [...](NB. IC801 on the tuner PCB is a 68-pin U4290B.)
Wer hat sich nicht schon geärgert, wenn er beim Empfang seiner Lieblingssendung auf UKW in den entscheidenden Augenblicken durch überlagerte Nachbarsender gestört wurde. Ähnlich beklagenswert ist es für den Funkamateur, wenn der Empfang von der Großwetterlage abhängt und die atmosphärischen Störungen "Gewitterstimmung" verbreiten. [...] Nach dem Prinzip der Rauschunterdrückung versucht die Industrie daher seit Jahren, die Empfangsqualitäten von Radios und Funkgeräten entscheidend zu verbessern. Dolby und High Com sind Begriffe, mit denen dieses Prinzip bekannt wurde. [...] Für den Neuberliner Hansen und seinen Partner Müller-Catito ist die Leistungsfähigkeit dieser Verfahren auf die Dauer ungenügend. Um erheblich höhere Empfangsempfindlichkeiten und damit stark verbesserte Reichweiten zu erreichen, haben sie das Mitlauffilterverfahren (MLF) "High Select" entwickelt und sich damit selbständig gemacht. Mit diesem neuen Verfahren können Signale empfangen werden, die mit einem üblichen Empfänger nur noch als "Leerlaufrauschen" wahrnehmbar wären. [...] Die völlige Neuentwicklung benutzt anstelle eines in seiner Resonanzfrequenz feststehenden Zwischenfrequenzfilters ein schmalbandiges, in der Resonanzfrequenz steuerbares Filter, wobei die Steuerung dafür sorgt, daß der Filter-Resonanzbereich stets bei der Momentanzwischenfrequenz liegt. Das Ergebnis läßt sich hören. [...] Abschattungen, Reflexionsstörungen, Nachbarkanalstörungen in kritischen Versorgungsgebieten und Grenzempfindlichkeiten sind ausgeschaltet. Selbst völlig verrauschte Signale erklingen klar und deutlich. Die Realisierung des MLF-Verfahrens und die Gründung des eigenen Unternehmens sind das Ergebnis eines mehrjährigen Entwicklungsprozesses. 1982 kam der Erfinder Jens Hansen zur TVA und stellte seine Konzeption mit den durchgeführten grundlegenden Untersuchungen vor. Um den Nachweis der Realisierbarkeit anzutreten, mußte ein Funktionsmodell gebaut werden. Durch die Vermittlung der TVA wurde der Forschungsförderungsfonds des Senators für Wissenschaft und Forschung genutzt. [...] Für die Experten war das Konzept so überzeugend, daß es gefördert wurde. Ein Hochschullehrer der Technischen Fachhochschule Berlin ermöglichte Untersuchungen im Meßlabor. [...] Im Sommer 1983 konnten Hansen/Catito bereits das Funktionsmodell vorstellen, das die gewünschten Eigenschaften aufwies. [...] Dieser Erfolg ermutigte sie, selbst das neue Verfahren in marktfähige Produkte umzusetzen. Mit der TVA stimmten sie die nächsten Schritte ab. Die Unternehmensberatung für die Wirtschaft (ubw) wurde eingeschaltet, um im Rahmen des Förderprogramms "Existenzgründungsberatung" eine Unternehmenskonzeption auszuarbeiten. Mit der Unterstützung der TVA konnte die neue Firma Hansen/Catito Elektronik in das Berliner Innovations- und Gründerzentrum (BIG) einziehen. [...] Im Rahmen des Modellversuchs "Förderung technologieorientierter Unternehmensgründungen" wurde ein Antrag auf Förderung beim VDI TZ gestellt, um die Existenzgründer beim Aufbau eines eigenen Produktions- und Vertriebssystems zu unterstützen. [...] Hansen/Catito Elektronik - ein Beispiel für eine eindrucksvolle Initiative aus Berlin.
Two years ago, Jens Hansen, 42, a telecommunications engineer, won the Berlin Innovation Prize [de] for inventing an enhanced reception system for frequency modulated signals. [...] Spurred by the award, he and Klaus Müller-Catito, a close colleague, launched H & C Electronics last June in the Ackerstrasse complex. His staff of seven produce accessory devices for radio systems, VHF units and satellite receiving systems. "We are small at present but growing rapidly," said Mr. Hansen, who formerly worked for Bosch in Berlin as a research engineer.
[...] 1984 [...] System für die Erhöhung und Erweiterung der Frequenzmodulation im UKW-Bereich [...] Sico-Elektronic GmbH [...] Gustav-Meyer-Allee 25, 13355 Berlin [...] Herr Jens Hansen [...] Tel. 030/ 46 320 38, Fax 030/ 46 307 300 [...]
[...] es ein dynamischer ZF-Filter. Dynas ändert aber nicht nur seine Bandbreite[,] sondern auch seine Durchlaßfrequenz. Zuerst wird die ZF von 10,7 MHz auf 700 kHz heruntergemischt. Danach wird das Signal durch 4 LC-Kreise gefiltert [...] Durch zugeschaltete Widerstände können die LC-Kreise bedämpft werden[,] d.h. ihre Bandbreite wird größer. Mit diesen Filtern läßt sich eine Bandbreite bis [...] runter zu 10–15 kHz realisieren. Da diese Bandbreite nicht für UKW-Rundfunk reicht, müssen die Filter [...] nachgeregelt werden. Dies geschieht mittels Kapazitätsdioden. Die Steuerspannung dafür wird aus dem Mono-NF-Signal gewonnen. Dessen augenblicklicher Wert steht im direkten Zusammenhang mit der aktuellen Frequenz der ZF. Die Filter werden mit einer geringen Verzögerung nachgeführt. Ein normaler 85 kHz ZF-Filter dämpft einfach die Störungen[,] aber auch das Nutzsignal. Dynas hingegen läßt das Nutzsignal (Monosignal) komplett durch. Bei geringen NF-Pegeln grenzt es so die Störungen perfekt aus, bei hohen NF-Pegeln müssen die Filter so stark auslenken[, daß] auch Teile der Störfrequenzen mit durch kommen. Letztendlich hängt die Trennschärfe von Dynas also vom Programminhalt des Senders ab. Die heutige Dynamikkompression bei den Sendern ist da ungünstig für Dynas. [...] In einer Zeitschrift (AutoHifi), die [19]91/[19]92 herum Dynas noch als Prototyp vorstellte, stand drin, dass Dynas von einem ehemaligen Mitarbeiter von Blaupunkt, der eine eigene kleine Firma gegründet hatte, entwickelt bzw. heraus gebracht wurde. Die haben damals oder kurze Zeit später auch verschiedene Hersteller befragt[,] ob sie Dynas einsetzen wollen. [...]
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The DYNAS system features an approach which many would consider to be physically impossible: the reception of a broadband transmission spectrum via narrowband filters. This principle seems self-contradictory at first consideration; at any rate, specialists could all easily agree that it does, however, satisfy many of the most critical needs and requirements actually encountered in receiving operations. The following are, of course, the advantages of broadband transmission: high signal-to-noise ratios, high dynamics, and a broad audio-frequency spectrum. The DYNAS principle would couple the above advantages with the following benefits of narrowband transmission: great reception sensitivity, and great immunity to interference. The DYNAS principle would, in addition, eliminate the following disadvantages: relative great susceptibility to interference, and poor signal quality. The above advantages, needs, and requirements are in fact implemented by DYNAS by the technique of dynamic selectivity.[20]
[...] U4290B-CP FM IF for Dynas System [...] U4291B-FP Coprocessor for Dynas [...] U4292B-FS Soft Dynas [...]
Erwin David [...] draws attention to a short piece he wrote for the East Kent Radio Society's Carrier newsletter, based on an item by [Dick W. Rollema] in Electron November 1986. This describes a new "in-channel-select" (ics) technique that can significantly improve the sensitivity and selectivity of vhf/uhf fm receivers. A commercial "blackbox" adapter is being made and marketed by the German firm H&C Ele[k]tronik Hansen & Co of Berlin, which is claimed to improve the s:n ratio of weak fm signals by 6 dB and rejection of in-channel splatter from stronger adjacent-channel signals by some 20 dB. [...] the ics technique appears to be a form of threshold-extension demodulation, as originally developed for professional reception of weak satellite signals, but implemented in a form suitable for use with typical amateur radio fm transceivers. The German unit [...] features a very narrow voltage-controlled filter that automatically tracks the fm signal. For 145 MHz (25 kHz channelling) the filter bandwidth is only 1,800 Hz, ie about one-tenth of the usual i.f filter bandwidth. The receiver's fm detector output voltage, proportional to the instantaneous deviation, steers the ics filter so that it tracks the incoming signal. In demonstrations at a Dutch/German hamfest last year, [Rollema] reports that audibility of weak signals was improved by the unit from Q1 to Q4, though never completely to Q5. For strong signals it is usually advisable to switch threshold-extension demodulators out of circuit. The German hardware is being offered primarily as an external unit for base-station receivers, although the principle can be applied to mobile receivers. A threshold extension demodulator does not, of course, improve the front-end noise factor of a receiver, but there is no doubt that the technique does make it possible to copy signals that would otherwise be unintelligible. It certainly seems a development worth keeping in mind.[27]
[...] In the case of [the] conventional system, [the] signal pass[es] through the filter without generat[ing] distortion [...] filter is wide. At this time, the system is affected by undesired signal. In the case of [the] new system, [the] signal pass[es] through [...] [a] narrow filter follow[ing] the signal. [...] the system is not affected by undesired signal. This system's filter is controlled by feed[-]forward control, therefore, [the] stability is very high and [there is] no [...] oscillation. This system [implements a] follow[-]type filter so that [the] input FM signal frequency controlled for center of the filter at any time. ([In a] conventional system, [the] filter is followed the input signal.) [...] [The] system [...] consists of the control block and filter block. [The] control block [...] consists of [a] band pass filter [...], FM detector [...] and low-pass filter [...] The band-pass filter [...] has the same characteristic as conventional tuner's narrow filter, and this filter has selective characteristic sufficiently. When FM signal is inputed, FM signal is detected by FM detector [...] after pass through the band-pass filter [...] then, output signal of FM detector [...] is cut the useless high-frequency elements by low-pass filter [...] Filter block [...] consists of two mixer [...] band-pass filter [...] and VCO. Mixer [...] perform frequency change so that multiply input FM signal by VCO output. F-91 introduce the secondary IF frequency as 13.45 MHz. Band-pass filter [...] has the same narrow bandwidth characteristic as the band-pass filter [...] This filter (BPF2) cut the obstruction wave including input signal. Input signal of passed through the band-pass filter (BPF2) is multiplied by VCO output at mixer [...] again, then change to the original frequency. Original signal is detected by FM detector [...] then audio output is obtained. In this way, in spite of use the filter of fixed the center frequency, F-91 operate to the variable filter so that center frequency follow the input signal as equivalent. [...][29][30][31] (4 of 40 pages)
[...] ARTS Cleans Up Your Act [...] Pioneer's new Active Real-Time Tracing System - ARTS for short - helps the F-91 deliver clean and optimum signal reception. It replaces the "WIDE/NARROW" filtering technique in which the WIDE position provided better sound quality at the expense of selectivity and, conversely, the NARROW position provided better selectivity at the expense of sound quality (see oscillophotos). Using a kind of "servo-filtering", its IF filter circuit "tracks" the tuned frequency in real time, eliminating interference ONLY where it actually exists, thus providing optimum sound quality AND selectivity. [...] F-91 - Reference Digital Synthesizer Tuner [...] Pioneer's ARTS (Active Real-Time Tracing System): Tuned frequency is followed in real time by IF filter circuit to eliminate interference and pass on purest possible signal to audio output. [...]
[...] an FM i.f. circuit that has been given the acronym ARTS (for Active Real-time Tracing System). This system eliminates the need for choosing between narrow and wide i.f. bandwidths. Pioneer states that it actively follows the selected signal to provide both the lower distortion normally resulting from wide bandpass and the high selectivity of narrow bandpass. I gathered that the system dynamically tailors bandwidth to the instantaneous modulation of the incoming signal. [...] I also saw evidence that the r.f. section has some capability of tracking the signal; even when my FM signal generator was deliberately detuned from the frequency indicated on the F-91's display, minimum distortion and perfect center tuning were maintained. [...]
[...] Pioneer came up with a very innovative solution to the "narrow filters distort the signal" problem. They used this solution in the F-91 tuner. It is such a good idea that it could have gotten someone a Ph.D. (Indeed, a related concept did get someone a Ph.D.—see [Rich 1991].) What the engineers at Pioneer observed was that, although the spectrum of an FM signal is wide when averaged over time, at any instant in time the signal has just one spectral line at the instantaneous frequency. So, if you build a time-varying filter with a very narrow band-width that moves with the instantaneous frequency of the desired signal, then you can eat your cake and have it too. The very narrow bandwidth removes the interferers, but the time-varying nature of the filter insures that the FM signal is not distorted. To move the filter around, a complete auxiliary IF strip designed in the conventional manner and a PLL FM detector are required. We now have a chicken and egg problem, since the conventional receiver has to place the passband of the time-varying filter in the correct place. This is what limits the performance of the system. One very interesting (at least to this author) variation on this is to replace the bandpass filter with a notch filter. Then the stronger signal is removed, but a weaker cochannel interfering signal may now be revealed. Further information on this is in—you guessed it—[Rich 1991]. [...] Sony uses a variation on the tracking-filter theme that involves dynamically varying the position of the RF and mixer filters in response to the signal level at the output of the FM demodulator (which represents how far the instantaneous frequency has moved from the carrier frequency). This is easier to implement in the RF and mixer stages than in the IF because these filters are already tunable. One would think the large signal delay in the IF strip and detector would prevent this from working well, but Sony is shipping tuners with this thing, so it must do something positive. [...]
[...] SST (Super Sound Tracing) Significantly Improves Filter Characteristics [...] The task of the front end of an FM tuner is to capture the desired frequency with accuracy and without interference. Interference can be more efficiently eliminated by narrowing the bandwidth of a filter and by sharpening its curve. In the front end, tracking error occurs when there is a discrepancy between the frequency of the broadcast station and the center of the band-pass filter. A narrower band-width, such as the ST-S333ESXII's, allows less margin for this sort of error and improves selectivity. Previously, it was difficult to [achieve] accurate reception throughout the FM band, because FM broadcast frequencies fluctuate with the strength of their signal. If the FM frequency reception is perfectly adjusted on both ends of a bandwidth - that is, at 87.5 MHz and 108 MHz - an error of up to 100 kHz will occur when attempting to receive frequencies broadcast between these points. Likewise, if the FM frequency reception is perfectly adjusted at the center of the bandwidth, error will occur at either end. S.S.T. Circuitry effectively solves this problem. With the ST-S333ESXII's frequency range divided into four separate sections between 87.5 MHz and 108 MHz, perfect frequency reception can be [achieved] at each of these points, and the error occurring between them is effectively minimized. You'll enjoy better FM selectivity, less tracking error and less distortion, thanks to the S.S.T. Circuitry. [...] WOIS - Wave Optimized IF System [...] The WOIS automatically selects the ideal IF characteristics for both the monaural and stereo positions at the IF Filter stage. The results are system selectivity of 65 dB and THD (Total Harmonic Distortion) minimized at 1 kHz to 0.005% in mono and 0.0095% in stereo. This sophisticated technology has been integrated to create overall sound quality that is noticeably better. [...]
[...] WOIS (ZF mit optimierter Filtercharakteristik) [...] Um eine optimale Signalverarbeitung zu gewährleisten, sind für Mono- und Stereo-Rundfunksignale unterschiedliche Filtercharakteristiken im Zwischenfrequenzverstärker erforderlich. Die WOIS-Technik selektiert automatisch die entsprechende Charakteristik und sorgt so bei Stereo- und Mono-Empfang für die jeweils optimale Selektivität, d.h., daß auch eng benachbarte Sender sauber voneinander getrennt werden. Das verbesserte Gruppenlaufzeitverhalten und das linearisierte Amplitudenverhalten reduzieren die Verzerrungen und tragen zur Klangoptimierung bei. [...] SST (Super Sound Tracing) [...] Die wichtigste Anforderung an einen Tuner ist der präzise Empfang der jeweils eingestellten Frequenz. Sonys SST-Technik stellt die Bandbreite der Eingangsstufe exakt auf die Empfangsfrequenz ein und verbessert so die Trennung des Nutzsignals von störenden benachbarten Senderfrequenzen. Diese verbesserte Vorselektion sorgt für störungsfreien Empfang. [...](218 pages + technical data and pricelist inlays) (NB. This 1992 product catalog describes the SST technology, and explicitly lists SST as a feature of the ST-S770ES, but also shows a photo of an opened ST-S770ES where the "Advanced SST" section is unpopulated on the PCB. While the 1993 catalog no longer describes SST, it is still listed as a feature of the ST-S770ES, until the tuner was replaced by its successor model, the ST-S707ES, in the subsequent 1993/1994 catalog.)
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: Cite uses generic title (help)This paper discusses the possibility of using a high degree of negative feed-back of frequency modulation in the I.F. section of a frequency modulation receiver, for the purpose of (a) minimising the necessary I.F. band width and (b) making the detected output independent of amplitude without the use of an amplitude-limiter in the I.F. amplifier.(6 pages)
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