DOCSLIB.ORG

Signal Issue 36

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Signal Issue 36 Issue 36 Signal Tricks of the Trade Dave Porter G4OYX and Alan Beech G1GXB Fifty years ago, in mid-1965, the UK offshore radio operations were nearing their peak with some of the earlier lower-powered setups being consolidated into more professional operations and a number of projects just about to come on the air. Three of the stations in the planning and construction phase at this time were Radio Scotland, Radio 270 and Radio 390; these all employed 10 kW versions of the RCA Ampliphase transmitter. The principle of outphasing (Ampliphase) to generate amplitude modulated carriers was described in the previous ToTT [1]. This article will develop our understanding of the RCA Ampliphase system and will examine the progress of the RCA design over the years following. In addition, some recently released documents detail what the BBC had researched and discovered concerning the RCA Ampliphase units. Detailed development history To provide for linearity correction and drive regulation, the RF drive to the PAs was progressively reduced by means The first RCA Ampliphase transmitter, the BTA-50G, was of a simple resistor connected between the PA grids, as released onto the market in 1955 but the outphasing the phase moved towards 180°. With 180° difference, a principle was already 20 years old at that time. The reasonable amount of drive power was lost in the resistor technique was first described by Henry Chireix in due to the current flow but, as the difference reduced, November 1935 [2] and just nine months before WH there was less current flow and therefore less power lost. Doherty patented his amplifier design. Information on early At zero degrees difference there would be no current flow outphased transmitters is now very scarce; however, by in the resistor and no power lost although, of course, the 1948, station KFBK in Sacramento, California had minimum phase difference of the system is 90°. The successfully home-built a 50 kW version. This station was original 50 kW transmitter had a “rather complex vacuum operated by McClatchy Broadcasting, which also operated tube RF voltage regulator” as did RCA's version when it KOH in Reno, Nevada and a 5 kW unit was subsequently was released several years later. built for that site. The May 1951 issue of Electronics magazine carried a three-page article, describing in great McClatchy Broadcasting also operated KMJ Fresno and detail the design and operation of the five kilowatt KBEE Modesto. It is possible that outphased transmitters transmitter, including a complete circuit diagram (Figure may have been used in at least one of these stations, 1). This design used a single modulator stage, followed by although no firm information on that is currently available. a tripler to provide the required phase shift at the carrier It is believed that, having pioneered outphasing frequency. However, it appears that the original KFBK modulation, McClatchy persuaded RCA to build these on system used three cascaded stages, as per the BTA-50G a commercial basis and the Ampliphase was born. The and BTA-50H. The PA stages at KOH were a pair of exact details of this ‘handover’ are also unknown to the 3CX2500F3s, driven from a pair of QY4-250As. author (G1BXG) at the present time. Figure 1. Circuit diagram of KOH homebrew Ampliphase transmitter, 1951 24 August 2015 Signal Issue 36 From Class B to Ampliphase In 1955, solid-state rectifiers were in their infancy so all the main power supplies to the BTA-50G utilised mercury arc The BTA-50G, the first example of which was shipped to rectifiers. The high voltage was 16.2 kV provided by a total WINS in New York on 28th December 1955, inherited a of twelve 6894 rectifiers. These were arranged as pairs in number of features from its Class B modulated a conventional six-way, three-phase, configuration. Six predecessor, the BTA-50F. This included the 807 oscillator 8008 valves were used in another three-phase full-wave block and the air-cooled 5671 PA valves. Whereas the 50F configuration to provide the low/intermediate voltages of had four such valves, two in the modulator and two in the 2.5 kV and 5 kV. Each rectifier (or pair of rectifiers) PA, plus two installed spares, the Ampliphase had just one required its own filament transformer which had to be pair. This PA valve was over two feet in length, 16 inches insulated to withstand the 16 kV HT voltage. As mercury in diameter and weighed just over 200 lbs. To place one of vapour rectifiers will not strike at low temperatures (the these valves into service was considered a two-man job vapour condenses) a 400 W heating panel had to be fitted and a small trolley-mounted crane was provided to assist into the rectifier cabinet to prevent the valve temperature with this operation. The driver valves on the BTA-50G dropping below 20°C. were type 6076 and the pre-driver a pair of QY4-250s as used on both the KOH/KFBK transmitters and on the later Once the transmitter was up and running, a blower motor BTA-50H and BTA-50J systems. The BTA-50G driver unit had to circulate air through the cabinet in the normal is shown in Figure 2. manner to prevent the valves from overheating. A selenium metal rectifier was used to provide the –400 V bias supply. RCA made claims in 1955 about the compact size and lightweight concept of the BTA-50G which was approximately half the length of the BTA-50F and, with no modulation transformer or reactor, was a third of the weight. High power MF versions Although produced as a 50 kW transmitter for the domestic market, there is evidence that 100 kW and 250 kW versions were manufactured and shipped to Iran and Mexico. No further information has as yet come to light on these variants except for early pictures of the prototype variant units which show a modulator with most of the components laid in a single horizontal line and that the crystal oscillators were all fitted at the bottom of the cabinet in the space which was later used to house the drive regulator. There are reasons to suspect that this transmitter used a single phase modulator followed by a tripler, but it is not known if this modulator was purely a prototype or if it was shipped with early units. Later versions of the BTA-50G had the ‘conventional’ cascaded modulator, arranged in four vertical columns, with the drive regulator at the bottom of the cabinet and the oscillators to the side. Approximately 30 examples of the BTA-50G are thought to have been shipped. From mercury vapour to silicon rectifiers The BTA-50H, released in late 1960, inherited features from the BTA-50G, including the four column cascaded 19- valve modulator, drive regulator, general electrical and physical layout and that ubiquitous 807 oscillator block. However, the BTA-50H contained many ‘new’ features such as silicon rectifiers throughout, an updated valve line- up and facilities for remote control. The massive and heavy RCA-5671 PAs were replaced by a pair of lightweight Machlett Laboratories 6697s and the 6076 drivers were replaced by a pair of 4CX5000A's. The QY4-250 drivers were retained but now ran from a 1 kV supply and not the dropped 2.5 kV volt supply of the BTA-50G. The intermediate and high voltages remained the same at 5 kV and 16 kV, though the bias was increased to –950 V to suit the new PAs. RCA claimed that the use of silicon rectifiers Figure 2. Early BTA-50G driver unit with crystal allowed operation at temperatures as low as –20°C, oscillator at the bottom, the modulator with although no claims were made for how well the indicating meters centre, and the 6076 drivers at engineering staff would operate at that temperature! the top August 2015 25 Issue 36 Signal The cosmetic total ‘New Look’ and oscillator at half carrier frequency was built around a 6AK5 followed by a 5763 buffer. A 6BX7, a gutsy power double- solid-state modulator crate triode, acted as a phase splitter, utilising a lumped L/C A later variant of the BTA-50H, the BTA-50H1, was delay line to obtain the initial phase separation. Phase produced sometime in 1966, though the technical modulation and frequency doubling was performed by a differences between that model and the earlier unit are not 6EA8 triode/pentode with audio applied to the triode grid. clear at the moment. However, with regard to cosmetics, A 6CL6 followed as a buffer with an 829B as exciter output the unit benefitted from RCA's ‘New Look’ marketing and providing approximately 40 W of drive. was shipped in a two-tone grey and blue finish. When RCA later produced a solid-state modulator, transmitters could be field-upgraded by RCA engineers to become a BTA-50H1S, which included the later alterations to the ‘H1’ (presumably without the new colours) plus the solid-state modulator designated by the ‘S’. It is believed that the first unit upgraded this way was for WNBC in New York. Upgraded units were given a new serial number plate, showing the new designation, although it seems that they retained the original serial number. It appears that a considerable number of units had the solid-state option fitted as the ageing and drift of the nineteen valves in the modulator was a frequent cause of poor performance – ‘Amplifuzz’. The prototype of the solid-state modulator is rumoured to have been built by Radio Pakistan and the design sold back to RCA.
Load more

Recommended publications
  • Signal Issue 35
    Signal Issue 35 Tricks of the Trade Dave Porter G4OYX and Alan Beech G1BXG We continue to celebrate the 50th anniversary of the start of offshore commercial radio in the UK and are now in June 1965. By this time, the number of stations on the air was increasing steadily, taking advantage of the (lack of) laws at the time with regard to operations in International Waters. The first two stations, Caroline and Atlanta, had used 10 kW AM transmitters by Continental Electronics employing their patented version of screen grid modulation but, just prior to Christmas 1964, the US-inspired and -built station of Radio London on the former US minesweeper USS Density renamed M/V Galaxy was on the air with test transmissions on 266 m, 1124 kHz, running, at first, 17 kW. This 50 kW transmitter was an RCA BTA-50H and was the first of many in the offshore fleet to employ the ‘Ampliphase’ approach. From ‘outphasing’ to ‘Ampliphase’ Amplitude from phase The theory of what became known as ‘Ampliphase’ was The principle of ‘Ampliphase’ is to take a single frequency proposed and developed in France by Henry Chireix in drive source, split it into two feeds, phase modulate each 1935 who called the technique ‘outphasing’. feed, amplify as required and add the two signals in a combining network. Amplitude modulation is achieved by ‘Outphasing’ was not taken up initially by RCA but by the degree of addition or subtraction due to the phase McClatchy Broadcasting in the late 1940s, first at KFBK, difference between the two signals.
    [Show full text]
  • Digital Audio Broadcasting : Principles and Applications of Digital Radio
    Digital Audio Broadcasting Principles and Applications of Digital Radio Second Edition Edited by WOLFGANG HOEG Berlin, Germany and THOMAS LAUTERBACH University of Applied Sciences, Nuernberg, Germany Digital Audio Broadcasting Digital Audio Broadcasting Principles and Applications of Digital Radio Second Edition Edited by WOLFGANG HOEG Berlin, Germany and THOMAS LAUTERBACH University of Applied Sciences, Nuernberg, Germany Copyright ß 2003 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone (þ44) 1243 779777 Email (for orders and customer service enquiries): [email protected] Visit our Home Page on www.wileyeurope.com or www.wiley.com All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP, UK, without the permission in writing of the Publisher. Requests to the Publisher should be addressed to the Permissions Department, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England, or emailed to [email protected], or faxed to (þ44) 1243 770571. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the Publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.
    [Show full text]
  • En 300 720 V2.1.0 (2015-12)
    Draft ETSI EN 300 720 V2.1.0 (2015-12) HARMONISED EUROPEAN STANDARD Ultra-High Frequency (UHF) on-board vessels communications systems and equipment; Harmonised Standard covering the essential requirements of article 3.2 of the Directive 2014/53/EU 2 Draft ETSI EN 300 720 V2.1.0 (2015-12) Reference REN/ERM-TG26-136 Keywords Harmonised Standard, maritime, radio, UHF ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 Siret N° 348 623 562 00017 - NAF 742 C Association à but non lucratif enregistrée à la Sous-Préfecture de Grasse (06) N° 7803/88 Important notice The present document can be downloaded from: http://www.etsi.org/standards-search The present document may be made available in electronic versions and/or in print. The content of any electronic and/or print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any existing or perceived difference in contents between such versions and/or in print, the only prevailing document is the print of the Portable Document Format (PDF) version kept on a specific network drive within ETSI Secretariat. Users of the present document should be aware that the document may be subject to revision or change of status. Information on the current status of this and other ETSI documents is available at http://portal.etsi.org/tb/status/status.asp If you find errors in the present document, please send your comment to one of the following services: https://portal.etsi.org/People/CommiteeSupportStaff.aspx Copyright Notification No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm except as authorized by written permission of ETSI.
    [Show full text]
  • Hans Knot International Radio Report April 2016 Welcome to Another
    Hans Knot International Radio Report April 2016 Welcome to another edition of the International Radio Report. Thanks all for your e mails, memories, photos, questions and more. Part of the report is what was left after the March edition was totally filled and so let’s go with this edition in which first there’s space for a story I wrote last months after again doing some research: ‘Ronan O’Rahilly, Georgie Fame and the Blue Fames. Where it really went wrong!’ On this subject I’ve written before but let’s go back in time and also add some new facts to it: ‘Was Ronan O’Rahilly the manager of Georgie Fame?’ I can tell you there was a problem with an important instrument. When in April 1964 Granada Television came with an edition of the ‘World in action’ series, which was a production from Michael Hodges, they informed the television public about a new form of Piracy, the watery pirates. Two radio ships bringing music and entertainment under the names of Radio Caroline and Radio Atlanta. Radio Caroline was the first 20th century Pirate off the British coast with programs, at that stage, for 12 hours a day. Interviews with the Caroline people were made in the offices of Queen Magazine in the city of London and included – among others – Jocelyn Stevens and the then 23-year old Irish Ronan O’Rahilly. During this documentary it became known, which we would also read in several newspapers in the then following weeks, that Ronan O’Rahilly had started his radiostation Caroline as he couldn’t get his artists played on stations like Radio Luxembourg.
    [Show full text]
  • FM Stereo Format 1
    A brief history • 1931 – Alan Blumlein, working for EMI in London patents the stereo recording technique, using a figure-eight miking arrangement. • 1933 – Armstrong demonstrates FM transmission to RCA • 1935 – Armstrong begins 50kW experimental FM station at Alpine, NJ • 1939 – GE inaugurates FM broadcasting in Schenectady, NY – TV demonstrations held at World’s Fair in New York and Golden Gate Interna- tional Exhibition in San Francisco – Roosevelt becomes first U.S. president to give a speech on television – DuMont company begins producing television sets for consumers • 1942 – Digital computer conceived • 1945 – FM broadcast band moved to 88-108MHz • 1947 – First taped US radio network program airs, featuring Bing Crosby – 3M introduces Scotch 100 audio tape – Transistor effect demonstrated at Bell Labs • 1950 – Stereo tape recorder, Magnecord 1250, introduced • 1953 – Wireless microphone demonstrated – AM transmitter remote control authorized by FCC – 405-line color system developed by CBS with ”crispening circuits” to improve apparent picture resolution 1 – FCC reverses its decision to approve the CBS color system, deciding instead to authorize use of the color-compatible system developed by NTSC – Color TV broadcasting begins • 1955 – Computer hard disk introduced • 1957 – Laser developed • 1959 – National Stereophonic Radio Committee formed to decide on an FM stereo system • 1960 – Stereo FM tests conducted over KDKA-FM Pittsburgh • 1961 – Great Rose Bowl Hoax University of Washington vs. Minnesota (17-7) – Chevrolet Impala ‘Super Sport’ Convertible with 409 cubic inch V8 built – FM stereo transmission system approved by FCC – First live televised presidential news conference (John Kennedy) • 1962 – Philips introduces audio cassette tape player – The Beatles release their first UK single Love Me Do/P.S.
    [Show full text]
  • AN1597 Longwave Radio Data Decoding Using an HC11 and an MC3371
    Freescale Semiconductor, Inc... microprocessor used for decoding is the MC68HC(7)11 while microprocessor usedfordecodingisthe MC68HC(7)11 2023. and 1995 between distinguish Itisnotpossible to 2022. and thiscanbeusedtocalculate ayearintherange1995to beworked out cyclecan,however, leap–year/year–start–day data.Thepositioninthe28–year available andcannotbeuniquelydeterminedfromthe transmitted and yeartype)intoday–of–monthmonth.Theisnot dateinformation(day–of–week,weeknumber transmitted the form.Themicroprocessorconverts hexadecimal displayed whilst allincomingdatacanbedisplayedin In thisapplication,timeanddatecanbepermanently standards. Localtimevariation(e.g.BST)isalsotransmitted. provides averyaccurateclock,traceabletonational Freescale AMCU ApplicationsEngineering Topping Prepared by:P. This documentcontains informationonaproductunder development. This to thecompanyleasingitforuseinaspecificapplication. available blocks areusedcommerciallywhereeachblockis other 0isusedfortimeanddate(andfillerdata)whilethe Type purpose.There are16datablocktypes. used foradifferent countriesbuthasamuchlowerdatarateandis European with theRDSdataincludedinVHFradiosignalsmany aswelltheaudiosignal.Thishassomesimilarities data using an HC11 and Longwave an Radio MC3371 Data Decoding Figure 1showsablock diagramoftheapplication; Figure data is transmitted every minuteontheand Time The BBC’s Radio4198kHzLongwave transmittercarries The BBC’s Ltd.,EastKilbride RF AMPLIFIERDEMODULATOR FM BF199 FILTER/INT.: LM358 FILTER/INT.: AMP/DEMOD.: MC3371 LOCAL OSC.:MC74HC4060
    [Show full text]
  • Amplitude Modulation(AM)
    Introduction to Modulation: Amplitude Modulation(AM) Sharlene Katz James Flynn Overview Modulation Overview Basics of Amplitude Modulation (AM) AM Demonstration GRC Exercise 2 Flynn/Katz 7/8/10 Why do we need Modulation/Demodulation? Example: Radio transmission Voice Microphone Transmitter Electric signal, Antenna: 20 Hz – 20 Size requirement KHz > 1/10 wavelength c 3×108 Antenna too large! 5 Use modulation to At 3 KHz: λ = = 3 =10 =100km f 3×10 transfer ⇒ .1λ =10km information to a higher frequency 3 Flynn/Katz 7/8/10 Why do we need Modulation/Demodulation? (cont’d) Frequency Assignment Reduction of noise/interference Multiplexing Bandwidth limitations of equipment Frequency characteristics of antennas Atmospheric/cable properties 4 Flynn/Katz 7/8/10 Basic Concept of Modulation The information source Typically a low frequency signal Referred to as the “baseband signal” X(f) x(t) t f Carrier A higher frequency sinusoid baseband Modulated Modulator Example: cos(2π10000t) carrier signal Modulated Signal Some parameter of the carrier (amplitude, frequency, phase) is varied in accordance with the baseband signal 5 Flynn/Katz 7/8/10 Types of Modulation Analog Modulation Amplitude Modulation, AM Frequency Modulation, FM Double and Single Sideband, DSB and SSB Digital Modulation Phase Shift Keying: BPSK, QPSK, MSK Frequency Shift Keying, FSK Quadrature Amplitude Modulation, QAM 6 Flynn/Katz 7/8/10 Amplitude Modulation (AM) Block Diagram x(t) m x + xAM(t)=Ac [1+mx(t)]cos wct Ac cos wct Time Domain Signal information
    [Show full text]
  • Mobile Tv: a Technical and Economic Comparison Of
    MOBILE TV: A TECHNICAL AND ECONOMIC COMPARISON OF BROADCAST, MULTICAST AND UNICAST ALTERNATIVES AND THE IMPLICATIONS FOR CABLE Michael Eagles, UPC Broadband Tim Burke, Liberty Global Inc. Abstract We provide a toolkit for the MSO to assess the technical options and the economics of each. The growth of mobile user terminals suitable for multi-media consumption, combined Mobile TV is not a "one-size-fits-all" with emerging mobile multi-media applications opportunity; the implications for cable depend on and the increasing capacities of wireless several factors including regional and regulatory technology, provide a case for understanding variations and the competitive situation. facilities-based mobile broadcast, multicast and unicast technologies as a complement to fixed In this paper, we consider the drivers for mobile line broadcast video. TV, compare the mobile TV alternatives and assess the mobile TV business model. In developing a view of mobile TV as a compliment to cable broadcast video; this paper EVALUATING THE DRIVERS FOR MOBILE considers the drivers for future facilities-based TV mobile TV technology, alternative mobile TV distribution platforms, and, compares the Technology drivers for adoption of facilities- economics for the delivery of mobile TV based mobile TV that will be considered include: services. Innovation in mobile TV user terminals - the We develop a taxonomy to compare the feature evolution and growth in mobile TV alternatives, and explore broadcast technologies user terminals, availability of chipsets and such as DVB-H, DVH-SH and MediaFLO, handsets, and compression algorithms, multicast technologies such as out-of-band and Availability of spectrum - the state of mobile in-band MBMS, and unicast or streaming broadcast standardization, licensing and platforms.
    [Show full text]
  • Federal Communications Commission § 73.1590
    Federal Communications Commission § 73.1590 the licensee must notify the FCC of the (2) FM stations. The total modulation date that normal operation was re- must not exceed 100 percent on peaks stored. If causes beyond the control of of frequent reoccurrence referenced to the licensee prevent restoration of the 75 kHz deviation. However, stations authorized power within 30 days, a re- providing subsidiary communications quest for Special Temporary Authority services using subcarriers under provi- (see § 73.1635) must be made to the FCC sions of § 73.319 concurrently with the in Washington, DC for additional time broadcasting of stereophonic or as may be necessary. monophonic programs may increase the peak modulation deviation as fol- [44 FR 58734, Oct. 11, 1979, as amended at 49 lows: FR 22093, May 25, 1984; 49 FR 29069, July 18, 1984; 49 FR 47610, Dec. 6, 1984; 50 FR 26568, (i) The total peak modulation may be June 27, 1985; 50 FR 40015, Oct. 1, 1985; 63 FR increased 0.5 percent for each 1.0 per- 33877, June 22, 1998; 65 FR 30004, May 10, 2000; cent subcarrier injection modulation. 67 FR 13232, Mar. 21, 2002] (ii) In no event may the modulation of the carrier exceed 110 percent (82.5 § 73.1570 Modulation levels: AM, FM, kHz peak deviation). TV and Class A TV aural. (3) TV and Class A TV stations. In no (a) The percentage of modulation is case shall the total modulation of the to be maintained at as high a level as aural carrier exceed 100% on peaks of is consistent with good quality of frequent recurrence, unless some other transmission and good broadcast serv- peak modulation level is specified in an ice, with maximum levels not to exceed instrument of authorization.
    [Show full text]
  • Licensed Devices General Technical Requirements
    Licensed Devices General Technical Requirements (Detailed Update October 2005) Steven Dayhoff Federal Communications Commission Office of Engineering & Technology October, 2005 ¾TCB Workshop 1 Sessions for licensed devices intended to give an overview of FCC Processes & Rules, not to show limits for every type of device. The information covered is mainly related to equipment authorization of the transmitting equipment and not the licensing of the station. 1 Overview General Information How to find information at the FCC Creating a Grant Organizing a Report Licensed Device Checklist October, 2005 ¾TCB Workshop 2 This session will cover general information related to the FCC rules and technical requirements for licensed devices. Assumption is that everyone is familiar with testing equipment so test setup and equipment settings will not covered. The approval process for these types of equipment was previously called Type Acceptance or Notification. Now all methods of equipment approval are called Certification. This information generally applies to all Radio Service Rules for scopes B1 through B4. 2 General Information Understanding how FCC rules for licensed equipment are written and how FCC operates The FCC rules are Title 47 of the Code of Federal Regulations Part 2 of the FCC Rules covers general regulations & Filing procedures which apply to all other rule parts Technical standards for licensed equipment are found in the various radio service rule parts (e.g. Part 22, Part 24, Part 25, Part 80, and Part 90, etc.) All material covered in this training is either in these rules or based on these rules October, 2005 ¾TCB Workshop 3 There are about 15 different radio service rule Parts which require equipment to be authorized before an operators license can be obtained.
    [Show full text]
  • Amplitude Modulation Transmitter Design
    Amplitude LAB Modulation 5 Transmitter Design Introduction The motivation behind this project is to design, implement, and test an Amplitude Modulation (AM) Transmitter. The Transmitter consists of a Balanced Modulator circuit which takes an audio signal stream from a Walkman and mixes it with a sinusoidal signal from a 1MHz oscillator. The resulting output is amplified by an output stage before being transmitted through a wire-antenna. AM Transmitter Floorplan: Design Goals Given the limited timeframe, we are providing you with the individual circuits that you need to design and construct. Fig. 1 shows the floorplan for the AM Transmitter. It consists of a Balanced Modulator which multiplies an audio fre- quency (20Hz to ~15kHz) signal with a 1MHz carrier frequency sinusoidal signal. The Balanced Modulator’s output is amplified by an output stage which drives an antenna (in this experiment, the antenna is just a 3” copper wire). The Balanced Modulator (Fig. 2) is essentially an analog multiplier: its time domain output signal, Vout(t) is linearly related to the product of the time domain input signals V1(t) (called the modulation signal) and V2(t) (called the carrier sig- nal). Its transfer function has the form: V ()t = k ⋅⋅V ()t V ()t out 1 2 The Balanced Modulator uses the principle of the dependence of the BJT’s transconductance, gm, on the emitter current bias. In order to demonstrate the principle, consider the load currents IL1 and IL2. From your knowledge of differ- ential amplifier operation, IL1 V1 I – I = g ⋅ V ≈ -------- ⋅ ------ L1 L2 m in VT 2 Also, the bias current IB in the differential amplifiers can be expressed as: V – 0.7 ≈ 2 IB ------------------ RE 1 Lab : Amplitude Modulation Transmitter Design Antenna Balanced O/P stage Walkman Modulator Amplifier 1MHz Oscillator Figure 1 — Amplitude Modulation Transmitter floorplan.
    [Show full text]
  • Broadcasting Equipment Photographs, Ca
    http://oac.cdlib.org/findaid/ark:/13030/c8b85b80 No online items Broadcasting Equipment photographs, ca. 1940s-1970s Processed by Sue Hwang with assistance from Julie Graham, 2012; machine-readable finding aid created by Caroline Cubé. UCLA Library Special Collections Room A1713, Charles E. Young Research Library Box 951575 Los Angeles, CA, 90095-1575 (310) 825-4988 [email protected] ©2014 The Regents of the University of California. All rights reserved. Broadcasting Equipment 1903 1 photographs, ca. 1940s-1970s Descriptive Summary Title: Broadcasting Equipment photographs Collection number: 1903 Contributing Institution: UCLA Library Special Collections Language of Material: English Physical Description: 38.5 linear ft.(77 boxes) Date (inclusive): ca. 1940s-1970s Abstract: The collection consists of photographs of various types of indoor and outdoor equipment related to mid-twentieth century radio and television broadcasting. Physical location: Stored off-site at SRLF. Advance notice is required for access to the collection. Please contact UCLA Library Special Collections for paging information. Restrictions on Access Open for research. STORED OFF-SITE AT SRLF. Advance notice is required for access to the collection. Please contact UCLA Library Special Collections for paging information. Restrictions on Use and Reproduction Property rights to the physical object belong to the UC Regents. Literary rights, including copyright, are retained by the creators and their heirs. It is the responsibility of the researcher to determine who holds the copyright and pursue the copyright owner or his or her heir for permission to publish where The UC Regents do not hold the copyright. Preferred Citation [Identification of item], Broadcasting Equipment photographs (Collection 1903).
    [Show full text]