Модулятор ам передатчика катодник: Супермодулятор

Простые самодельные AM передатчики на 27 МГц (КТ3107, КТ3102)

Принципиальные схемы простых самодельных передатчиков КВ диапазона с амплитудной модуляцией (АМ), частота – 27 МГц. Схемы содержат минимум деталей и построены на транзисторах и микросхемах. Подойдут для изготовления как начинающими радиолюбителями, так и профессионалами.

ЧМ-передатчики в основном используются для УКВ-диапазона. При всех достоинствах данного типа передатчиков для более низких частот чаще применяются АМ-передатчики, требующие для своей работы меньшей полосы частот. Это значит, что в пределах одного частотного диапазона большее число передатчиков могут вести передачу, не мешая друг-другу (примерно в 5-10 раз больше АМ-передатчиков по сравнению с числом ЧМ-передатчиков).

Маломощный АМ-передатчик на 27 МГц

На рис.5.10 представлена схема маломощного АМ-передатчика на 27 МГц. При чувствительности АМ-приемника 3-5 мкВ, этот передатчик обеспечивает дальность 200-300 м на открытой местности.

Рис. 1. Схема АМ-передатчика на 27 МГц ; б – УНЧ на 1 транзисторе, в – УНЧ на ИС 122УС1Д, г – УНЧ на ОУ К548УН1А.

Схема этого АМ-передатчика (рис. 1, а) состоит из следующих основных частей: УНЧ, АМ-модулятора (Т1) и задающего ВЧ-генератора (Т2).

Для данного радиопередатчика (рис. 1) предложено 3 варианта УНЧ, схемы которых приведены на рисунке 1 (б-г): на 1 транзисторе (схема с ОЭ), на УНЧ на ИС 122УС1Д, на ОУ К548УН1А.

Элементы для схемы АМ-передатчика на рисунка 1 (а-г):

• R1=1к-10к, R2=1.8к, R3=4.Зк, R4=2.4к, R5=4.7к, R6=100,
• R7= 100к, R8=1.5к, R9=50-100, R10=100, R11=10к, R12=200к;
• С1=4.7мкФ-20мкФ, С2=1мкФ-10мкФ (неполярный конденсатор),
• С3=200, С4=500, С5=500, С6=1н, С7=50, С8=50, С9=50,
• С10=10мкФ-50мкФ, С11=10мкФ-50мкФ, С12= 10мкФ-50мкФ, С13=50мкФ-200мкФ;
• Т1 – КТ3107,
• Т2 – КТ3102 или другие аналогичные транзисторы,
• L1, L2, L5 – ВЧ-дроссели, например, Д0.1 индуктивностью 60-200 мкН;
• катушки L3, L4 – бескаркасные, внутренний диаметр – 6 мм, диаметр провода – 0.6 мм, L4 – 10 витков, L3 – 3-4 витка.

Настройка. Изменением величины резистора R7 установить напряжение на коллекторе транзистора Т3 УНЧ (б) равным половине напряжения питания, при 9В – это ЗВ-6В. Другие варианты УНЧ в настройке не нуждаются. Чувствительность УНЧ на ОУ регулируется R11.

Частота генерации устанавливается конденсатором С7 и сжатием и/или растягиванием катушки L4. Возможно потребуется подбор С8. Настройка антенны осуществляется изменением величины емкости конденсатора С9.

Монтаж выполняется на 2-стороннем фольгированном стеклотекстолите. Одна сторона (со стороны деталей) используется как общий провод и экран, другая – для печатных проводников схемы. Проводники, соединяющие детали, должны иметь минимальную длину.

Для повышения стабильности частоты целесообразно поместить задающий генератор или все устройство в экран. При этом частота генератора, возможно, несколько изменится (увеличится). В качестве антенны может быть использована стандартная телескопическая антенна или толстый медный провод.

Простые АМ передатчики (вариант 2)

На рисунке 2 представлены еще два примера маломощных АМ-передатчиков на 27 МГц. Их характеристики практически совпадают с предыдущем вариантом.

Схема на рисунке 2 (а) во многом совпадает со схемой на рисунка 1, те же три варианта УНЧ, такой же АМ-модулятор (Т1), однако схема задающего генератора (Т2) в этом варианте АМ-передатчи-ка использована другая. Кстати, аналогичная схема генератора использована в передатчике комплекта радиоуправления “Сигнал”, поэтому часть элементов, методика настройки и особенности монтажа для данной конструкции совпадают с передатчиком из указанного комплекта.

Рис. 2. Схемы AM-передатчиков на 27 МГц .

Элементы для схемы АМ-передатчика на рисунка 2,а:

• R1=1к-10к, R2=1.8к, R3=4.Зк. R4=43к, R5=750, R6=15к, остальные резисторы в схемах УНЧ на рис.5.10;
• С1=4.7мкФ-20мкФ, С2=1мкФ-10мкФ (неполярный конденсатор), С3=200, С4=200, С5= 18, С6=82, С7=68, С8=120, С9=15, остальные конденсаторы в схемах УНЧ на рис.5.10;
• Т1 – КТЗ107, Т2 – КТЗ102 или другие аналогичные транзисторы:
• L1, L2, LЗ – ВЧ-дроссели, например, Д0.1 индуктивностью 60 мкН или самодельные -100 витков ПЭВ-2 на резисторе МЛТ-0.5 более 100к;
• L4 – на стандартном полистироловом каркасе диаметром 7 мм с подстроечником диаметром 2.8 мм и длиной 12 мм из феррита 600НН, 8.5 витка провода ПЭЛШО 0.18 (можно ПЭВ-2 0.15 или 0.2), намотанных виток к витку у основания каркаса.

Настройка (рисунок 2,а). Изменением величины резистора R7 установить напряжение на коллекторе транзистора Т3 УНЧ (б) равным половине напряжения питания, при 9В – это ЗВ-6В. Другие варианты УНЧ в настройке не нуждаются. Чувствительность УНЧ на ОУ регулируется R11.

Настройка задающего генератора осуществляется изменением положения подстроенника L4 и изменением величины значений конденсаторов С7, С8.

Монтаж выполняется на 2-стороннем фольгированном стеклотекстолите аналогично предыдущим конструкциям передатчиков. В качестве антенны может быть использована стандартная телескопическая антенна или толстая медная проволока.

В следующей схеме АМ-передатчика на 27 МГц – рисунок 2 (б) использован такой же задающий генератор, как и в предыдущем варианте, однако здесь использованы другие УНЧ и АМ-модулятор. Для этой схемы как и у предыдущей конструкции часть элементов, методика настройки и особенности монтажа совпадают с передатчиком щ комплекта радиоуправления “Сигнал”.

Элементы для схемы АМ-передатчика на рисунке 2 (б):

• R1=1к-10к, R2=160к, R3=6.8к, R4=180к, R5=43к, R6=750, R7=15к;
• С 1=4.7мкФ-20мкФ, С2=4.7мкФ-20мкФ, СЗ=4.7мкФ-20мкФ, С4=0.022,
• С5=0.022, С6=18, С7=82, С8=68, С9=120, С10=15, С11 = 10н-33н;
• Т1,Т2,ТЗ – КТЗ102, КТЗ15 или другие аналогичные транзисторы:
• L1 – ВЧ-дроссель, например, Д0.1 индуктивностью 60 мкН или самодельный – 100 витков ПЭВ-2 на резисторе МЛТ-0.5 более 100к;
• L2 – на полистироловом каркасе диаметром 7 мм с подстроечником диаметром 2.8 мм и длиной 12 мм из феррита 600НН, 8.5 витка провода ПЭЛШО 0,18 (можно ПЭВ-2 0.15 или 0.2), намотанных виток к витку у основания каркаса катушки задающего генератора.

Настройка (рисунок 2, б). УНЧ (Т1) и модулятор (Т2) в настройке не нуждаются. Настройка задающего генератора осуществляется изменением положения подстроечника L2 и изменением значений конденсаторов С8, С9.

Монтаж выполняется на 2-стороннем фольгированном стеклотекстолите аналогично предыдущим конструкциям передатчиков. В качестве антенны может быть использована стандартная телескопическая антенна.

Простые транзисторные АМ передатчики (вариант 3)

Еще две схемы АМ-передатчиков предоставлены на рисунке 3, они также на диапазон частот 27 МГц. Основные характеристики конструкции, схема которой приведена на рисунке 3 (а), примерно совпадают с предыдущим вариантом (вариант 2 выше). Мощность второго передатчика несколько выше, что обеспечивает большую дальность – примерно в 2-3 раза. При чувствительности приемника 1-5 мкВ дальность достигает 500 м.

Схема на рисунке 3 (а) подобна схеме на рисунке 2 (6): совпадают УНЧ и АМ-модулятор, однако схема задающего генератора в этом варианте АМ-передатчика (27 МГц) использована другая. Этот вариант генератора (положительная обратная связь – за счет емкости между эмиттером и коллектором) был описан и использован ранее в конструкциях ЧМ-передатчиков на биполярных транзисторах.

Рис.3. Схемы простых AM-передатчиков 27МГц на транзисторах.

Элементы для схемы АМ-передатчика на рисунке 3 (а):

• R1=1к-10к, R2=160к, R3=6.8к, R4=180к, R5=26к, R6= 10к, R7=50-100;
• С1=4.7мкФ-20мкФ, С2=4.7мкФ-20мкФ, СЗ=4.7мкФ-20мкФ,
• С4=0.022, С5=0.022, С6=30, С7=3н-10н, С8= 10-50, С9=4.7мкФ-20мкФ, С10=10н-33н, С11=10-30;
• Т1,Т2,ТЗ – КТЗ102, КТЗ15 или другие аналогичные транзисторы;
• L1, L2 – катушки генератора намотаны на ПЧ-контурах от стандартных радиоприемников, каркас – 6 мм, L1 – 11 витков ПЭВ-2 0.5 мм – 0.6 мм, L2 – 4 витка ПЭВ-2 0.5 мм, катушки – с экранами и сердечниками.

Настройка. УНЧ (Т1) и модулятор (Т2) в настройке не нуждаются. Настройка задающего генератора осуществляется изменением положения подстроечника общей катушки L1, L2 и изменением значений конденсаторов С6.

Возможно потребуется подбор значений R5 (ток транзистора задающего генератора) и С8 (величина обратной связи), подбор осуществляется по достижению максимального значения мощности излучения при минимальных искажениях ВЧ-колебаний (синусоидальный сигнал).

Монтаж выполняется на 2-стороннем фольгированном стеклотекстолите аналогично предыдущим конструкциям передатчиков. В качестве антенны может быть использована стандартная телескопическая антенна.

Схема на рисунке 3 (б) отличается от схемы на рисунке 2 (б) дополнительным ВЧ-каскадом, увеличивающим мощность АМ-передатчика. Для данного варианта передатчика на 27 МГц АМ-модуляция осуществляется изменением напряжения питания не задающего генератора, а следующего ВЧ-каскада. Схемы УНЧ и АМ-модулятора – совпадают со аналогичными схемами предыдущего варианта АМ-передатчика.

Элементы для,схемы АМ-передатчика на рисунке 3 (б):

• R1=1к-10к, R2=160к, R3=6.8к, R4=180к, R5=26к, R6=10к, R7=50-100;
• С1=4.7мкФ-20мкФ, С2=4.7мкФ-20мкФ, СЗ=4.7мкФ-20мкФ, С4=0.022, С5=0.022, С6=30, С7=3н-10н, С8=10-50, С9=24, С10=10н, С11= 10мкФ-50мкФ, С12=10н-33н, С13=10н-30н, С14=100;
• Т1,Т2 – КТ3102, КТ315 или другие аналогичные транзисторы, Т3 -КТ368, КТ3102 или аналогичные, Т4 – КТ603Б или аналогичные;
• L1, L2, LЗ – катушки генератора намотаны на ПЧ-контурах от стандартных радиоприемников, каркас – 6 мм, L1 – 11 витков ПЭВ-2 0.5 мм – 0.6 мм, L2 – 3 витка ПЭВ-2 0.3 мм, LЗ – 3+3+6 витков ПЭВ-2 0.5 мм (отводы, считая сверху), катушки – с экранами и сердечниками;
• L4 – ВЧ-дроссель 50-100 мкН.

Настройка и монтаж передатчика выполняется аналогично так же как и в предыдущей схеме.

АМ передатчики большой мощности

На рис. 4представлены два примера АМ-передатчиков повышенной мощности на 27 МГц. Данные схемы отличаются предыдущего варианта наличием еще одного ВЧ-каскада – дополнительного усилителя мощности.

Это увеличило мощность АМ-передатчиков. При чувствительности АМ-приемника 3-5 мкВ и тщательной настройке передатчика дальность связи достигает 3 км и более.

Рис.4. Схемы AM-передатчиков повышенной мощности на 27 МГц .

Элементы для схемы АМ-передатчика на рисунка 4 (а):

• R1=1к-10к, R2=160к, R3=6.8к, R4=180к, R5=26к, R6=10к, R7=50-100, R8=270, R9=10;
• С1=4.7мкФ-20мкФ, С2=4.7мкФ-20мкФ, СЗ=4.7мкФ-20мкФ, С4=0.022, С5=0.022, С6=30, С7=3н-10н, С8=10-50, С9=24, С10=300, С11=10н, С12= 100-300, С13=100-300, С14= 1000, С15= 10мкФ-50мкФ, С16=10н-33н, С17=10н-33н;
• Т1,Т2 – КТЗ102, КТЗ15 или другие аналогичные транзисторы, Т3 -КТ368, КТ3102 или аналогичные, Т4 – КТ603Б или аналогичные, Т5=КТ606;
• L1, L2, L3 – катушки генератора намотаны на каркасах от ПЧ-конту-ров, используемых в стандартных радиоприемниках, каркас – 6 мм, L1- 11 витков ПЭВ-2 0.5 мм – 0.6 мм, L2 – 3 витка ПЭВ-2 0.3 мм, LЗ -3+3+6 витков ПЭВ-2 0.5 мм (отводы, считая сверху), катушки – с экранами и сердечниками;
• L5 – катушка согласования с передающей антенной, 8 витков, ПЭВ-2 0.6 мм, каркас 6 мм, длина намотки 8 мм.
• L4, L6 – ВЧ-дроссель 50-100 мкН.

Настройка мощного АМ передатчика. УНЧ (Т1) и модулятор (Т2) в настройке не нуждаются. Настройка задающего генератора осуществляется изменением положения подстро-ечника общей катушки L1, L2 и изменением значений конденсаторов С6.

Возможно потребуется подбор значений R5 (ток транзистора задающего генератора) и С8 (величина обратной связи), подбор осуществляется по достижению максимального значения мощности излучения при минимальных искажениях ВЧ-колебаний (синусоидальный сигнал). Следующий каскад – настройка LЗ. При настройке антенны (С12, С13, L5) целесообразно использовать волномер, варианты схем которого были представлены ранее.

Используемая стандартная телескопическая антенна меньше оптимальной длины (четвертьволновой антенны), поэтому возникают определенные трудности по оптимизации работы выходного каскада. Для улучшения его работы и повышения мощности излучения иногда используют специальный прием – вводят дополнительную индуктивность, включаемую последовательно с антенной (на схеме не показана).

Этот прием позволяет увеличить эквивалентную длину антенны. Примерные значения: дополнительная катушка – 18 витков ПЭВ-2 0.6 на каркасе 6 мм, С12= 120, С 13=150. Точные значения подбираются эмпирически в процессе настройки по показаниям волномера.

Монтаж мощных АМ передатчиков выполняется аналогично предыдущим конструкциям передатчиков. В качестве антенны может быть использована стандартная телескопическая антенна или толстый медный провод. Вместо данного традиционного типа антенны можно использовать компактную спиральную антенну.

Схема АМ-передатчика на 27 МГц, представленная на рисунке 4 (6), отличается от предыдущей схемой задающего генератора. В данном варианте генератора использована схема с кварцевым резонатором. Это позволило стабилизировать частоту ВЧ-колебаний и упростить настройку передатчика.

Элементы для схемы АМ-передатчика на рисунке 4 (б):

• R1=1к-10к, R2=160к, R3=6.8к, R4=180к, R5=24к, R6=20к, R7=1к, R8=270, R9=10;
• С1=4.7мкФ-20мкФ, С2=4.7мкФ-20мкФ, СЗ=4.7мкФ-20мкФ, С4=0.022, С5=0.022, С6=30, С7=10н, С8=10н, С9=24, 00=300,
• С11 = 10н, С12=100-300, С13=100-300, С14=300-500, С15=10мкФ-50мкФ, С16=10н-33н, С17=10н-33н;
• Т1,Т2 – КТ3102, КТ315 или другие аналогичные транзисторы, Т3 -КТ368, КТ3102 или аналогичные, Т4 – КТ603Б или аналогичные, Т5=КТ606;
• L1, L2, L3 – катушки генератора намотаны на каркасах от ПЧ-конту-ров, используемых в стандартных радиоприемниках, каркас – 6 мм, L1 – 11 витков ПЭВ-2 0.5 мм – 0.6 мм, L2 – 3 витка ПЭВ-2 0.3 мм, L3 -3+3+6 витков ПЭВ-2 0.5 мм (отводы, считая сверху), катушки – с экранами и сердечниками;
• L5 – катушка согласования с передающей антенной, 5 витков, ПЭВ-2 0.6 мм, каркас 8 мм, длина намотки 8 мм.
• L4, L6 – ВЧ-дроссель 50-100 мкН.

Настройка АМ передатчика с кварцом. УНЧ (Т1) и модулятор (Т2) в настройке не нуждаются. Настройка задающего генератора осуществляется изменением положения подстроечника общей катушки L1, L2 и изменением значений конденсаторов С6 по максимуму волномера.

Следующий каскад – L3. Возможно потребуется подбор значений R5 (ток транзистора задающего генератора). При настройке антенны с помощью изменений С12,С13 и подстройки L5 целесообразно использовать волномер. При настройке выходного каскада и его согласования с антенной целесообразно учитывать неоптимальность ее длины, что снижает излучаемую мощность передатчика.

Поэтому целесообразно (как и в предыдущем случае) использовать дополнительную индуктивность (хотя это не является обязательным), увеличивающую эффективную длину передающей антенны передатчика. Эта катушка включается последовательно с антенной (на схеме не показана). Параметры элементов П-образного фильтра (C12, C13, L5) и дополнительной катушки совпадают с параметрами предыдущей конструкции.

Представленные и описанные устройства АМ-передатчиков на 27 МГц могут быть использованы в составе радиостанций (приемопередатчиков) для диапазона 27 МГц.

Литература: Рудомедов Е.А., Рудометов В.Е – Электроника и шпионские страсти-3.

Схема AM модулятора –

Описание:
Эта схема использует два генератора сигналов для моделирования амплитудно-модулированный несущей РФ. Выход может быть использована для моделирования реакции LC и танковых цепей.

Заметки:
Два генератора сигнала используются в этой цепи, одна из которых представляет высокую частоту (200kHz) РФ перевозчика, VG2, другой генератор сигналов используется для введения сигнала 1KHz аудио. Два сигнала смешиваются и усиливается транзистора и амплитудно-модулированного сигнала появляется на коллекторе BC548. Постоянная составляющая удаляется C2 и R3 и ВЧ выход теперь появляется на R3 нагрузочного резистора. Сигналы ниже производится с использованием Тина.

SPICE Netlist:
Специи список соединений показан ниже. Скопируйте все линии между AM и *. END и вставить в новый текстовый файл с именем vmod.cir или аналогичный.

* AM модулятор
. AC декабря 16 1 1.0MEG
. TRAN 4U 2M
. DC LIN VG2 0 1 10M
. УЧАСТОК V (3)
Vcc 1 0 30
VG2 2 0 DC AC 0 1 0 SIN (0 10M 200K 0 0-90)
VG1 4 0 DC AC 0 1 0 SIN (0 5 1K 0 0-90)
C3 5 0 100N
C2 6 3 470P
C1 2 7 100N
R5 0 7 15K
R4 7 1 56K
R3 0 3 1K
R2 4 5 4.7K
R1 1 6 10K
QT1 6 7 5 Q_BC548_N
. МОДЕЛЬ Q_BC548_N NPN (IS = 16.9F NF = 1 NR = 1 567M RE = RC = 1
+ RB = 10 VAF = 56.7 VAR = 28.3 ISE = 154F ISC = 154F
+ NE = 1.5 NC = BF = 1.5 1.16K BR = 5 ИКФ = 29.5M
+ IKR = 29.5M ЗАО = 3.35P CJE = 6.85P VJC = 3.57 VJE = 1.09
+ MJC = 489M MJE 432M = TF = TR = 796P 103N EG = 1.11
+ KF = AF = 0 1)
. END

Для производства продукции в Специи Opus запустить программу и загрузить новые vmod.cir модулированный сигнал появляется на R3 который сейчас узла 3 и земля. После загрузки цепи командой “список” будет отображать список соединений. Команда “Выполнить” будет моделирования схемы, “Дисплей” выведет список всех переменных в цепи. Команда участке V (3) будет отображать AM волны между узлом и 3 0 т.е. R3 нагрузочного резистора.

Обратите внимание, чтобы ускорить моделирования ВЧ несущей была ограничена только 200KHz, а выходной сигнал просто показывает два полных циклов звуковой волны, т.е. 2ms в качестве модулирующих частот 1k. Там будут какие-то специи учебники вскоре на моих страницах.

90000 AM Modulators – Base, Collector, Grid and Plate Modulators 90001 90002 AM Modulator is one which is used for superimposing a low frequency signal on a high frequency carrier signal. In this modulator the amplitude of a carrier is varied in accordance with instantaneous value of message signal. 90003 90002 Types of AM Modulators are listed below. 90003 90006 90007 Plate Modulator 90008 90007 Grid Modulator 90008 90007 Cathode Modulator 90008 90007 Base Modulator 90008 90007 Emitter Modulator 90008 90017 90018 Plate Modulator 90019 90002 It is so named because the message signal (AF) is superimposed on + Vsb and tVsb and then applied to the plate of a triode tube.Now we will study how modulation occurs in this modulator. 90003 90006 90007 The audio voltage (AF) is placed in series with the plate supply voltage + Vbb of a class C amplifier. In actual circuits as shown in figure, how this condition is obtained? AF signal is applied to the AF driver transformer which varies the grid bias of both triodes in accordance to the message signal. Due to which plate currents of both triodes vary with respect to the frequency of AF signal hence the voltage + Vbb applied to the plate of class C amplifier vary in accordance to the amplitude of the AF signal.90024 90008 90007 90002 Now we will see that RF (radio frequency) is superimposed on the plate voltages (which in accordance to AF)? 90003 90002 -Ve bias of the grid of class C amplifier is controlled by the RF driver transformer. Due to which plate current, varies in accordance to the RF. In this way, the RF is superimposed on AF and the amplitude modulated signal is coupled to the load through the tuned transformer. 90003 90002 Note: 90003 90002 RFC chode is placed in series with the modulating transformer to protect it from RF damage.90003 90008 90017 90018 Grid Modulator 90019 90039 90002 It is so named because the input signals RF, AF and negative Vc voltages are applied to the grid of class C amplifier. 90003 90006 90007 The modulating voltage (AF) is in series with the negative bias. The modulating voltage is superimposed on the fixed battery bias. Therefore, the amount of bias is proportional to the amplitude of the modulating signal and varies at a rate equal to the modulating frequency. 90008 90007 The RF input voltages are superimposed on the total bias.90008 90007 The resulting plate flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. 90008 90007 The application of these pulses to the tuned tank circuit will give amplitude modulation. 90008 90017 90018 Collector Modulator 90019 90002 The output stage of the transmitter is a high power frequency class C amplifier. Class C amplifiers conduct for only a portion of the positive half cycle of their input signal.The collector current pulses cause the tuned circuit to oscillate or ring at the desired output frequency. The tuned circuit, therefore, reproduces the negative portion of the carrier signal. 90003 90002 The modulator is a linear power amplifier that takes the low level modulating signal and amplifies it to a high power level. The modulating output signal is coupled through modulation transformer T1 to the class C amplifier. The secondary winding of the modulation transformer is connected in series with the collector supply voltage Vcc of the class C amplifier.90003 90058 90002 With zero modulation input signal. There will be zero modulation voltage across the secondary of T1. Therefore, the collector supply voltage will be applied directly to the class C amplifier, and the output carrier will be a steady sine wave. 90060 When the modulation signal occurs, the AC voltage across the secondary of the modulation transformer will be added to and subtracted from the collector supply voltage. 90003 90002 This varying supply voltage is applied to the class C amplifier.Naturally, the amplitude of the current pulses through transistor Q1 will vary. As a result, the amplitude of the carrier sine wave varies in accordance with the modulated signal. For example, when the modulating signal goes positive, it adds to the collector supply voltage, thereby increasing its value and causing higher current pulses and a higher amplitude carrier. When the modulating signal goes negative, it subtracts from the collector supply voltage making it less. For that reason, the class C amplifier current pulses are smaller, thereby causing a lower amplitude carrier output.Hence amplitude modulated wave is obtained which is then transmitted through antenna. 90003 90018 Base Modulator 90019 90066 90002 It is so named because RF carrier and the message signal both are provided to the base of the transistor. 90003 90006 90007 Message signal is amplified and then superimposed on the fixed bias Vbb which varies in accordance to the message signal. Then this superimposed bias is provided to the base of the transistor through RFC (radio frequency choke). 90008 90007 The RF carrier is also provided to the base of the transistor through coupling capacitor which is then superimposed with the message signal bias.This superimposed bias voltages control the collector current which is proportional to the amplitude of the message signal, hence this modulated waveform is coupled to the secondary of the transformer. 90008 90017.90000 Amplitude Modulation »Electronics Notes 90001 90002 Specific AM modulators are often needed for the transmission of amplitude modulation. A variety of circuits can be used to generate the amplitude variations needed. 90003 90004 90005 90006 Amplitude Modulation, AM Tutorial Includes: 90007 90008 Amplitude modulation, AM AM basic theory & formulas AM bandwidth & sidebands Modulation index & depth AM efficiency AM demodulation / detection Diode detector Synchronous detector AM modulators Single sideband, SSB SSB demodulation 90009 90005 90011 Modulation formats: 90012 Modulation types & techniques Frequency modulation Phase modulation Quadrature amplitude modulation 90009 90004 90005 Transmitters that transmit amplitude modulated signals require an AM modulator circuit to produce the required signal.90009 90005 There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. 90009 90005 In early AM transmitters the amplitude modulator circuit was a key element of the transmitter. Today with software processes and multi-mode transmitters, the amplitude modulator is likely be contained within an overall modulator circuit that is able to provide a number of different types of modulation. 90009 90005 Nevertheless many transmitters still require AM modulators and the concepts and theory behind them is still relevant.90009 90005 Many AM modulators were used with valve transmitters – AM was widely used for many communications applications when thermionic valve or vacuum tube technology was used. Accordingly many of the circuits that were developed were for use with these devices. However the principles are the same for both valve and semiconductor technologies. 90009 90025 High and low level AM modulators 90026 90005 AM modulators may be classed as either high or low level dependent upon their level in the overall signal chain.90009 90029 90030 90006 90011 High level modulator: 90012 90007 A high level modulator is defined as one that modulates a high power section of the circuit, typically the final RF amplifier. It has the advantage that linear amplifiers are not required for the RF amplification stages after AM modulation has been applied. The drawback is that high power audio amplifiers are needed. For broadcast transmitters where very high power levels are used, class D or class E amplifiers may be employed for the audio output.90035 90030 90006 90011 Low level modulator: 90012 90007 A low level AM modulator would be one where the modulation is applied to low power stage of the transmitter, typically in the RF generation stages, or via the digital signal processing areas. The drawback of this approach is that linear amplification is required for the RF stages. 90035 90042 90025 Anode or plate modulator 90026 90005 This form of AM modulator arrangement required a high power audio amplifier to provide audio to the anode or plate of the vacuum tube / thermionic valve.90009 90005 In this way the audio modulates the voltage supplied to the final amplifier, and the level of the output signal is modulated in line with the audio. This form of modulation is referred to as high-level modulation, and the audio power level must be 50% of that of the RF amplifier to provide 100% modulation. 90009 90005 Typically a transformer is used to enable the output of the audio amplifier to drive the anode voltage of the final power amplifier within the transmitter. The audio transformer is placed in into the line connecting the anode circuit to the supply.In this way it modulates the anode voltage. 90009 90005 By applying the modulation to the final RF amplifier it meant that all the RF amplifiers could be driven in Class C, making the RF chain more efficient. If the audio was applied to earlier amplifiers, the later ones would all need to be linear. 90009 90005 Semiconductor devices, both bipolar transistors and FETs can be used in the same configuration as well. 90009 90025 Heising or constant-current AM modulator 90026 90005 This form of AM modulator is very similar in many respects to the ordinary plate modulation using a traditional transformer.This type of AM modulator is also known as a choke modulator because of the fact that it uses a choke rather than a transformer. 90009 90005 In the modulator circuit, the RF amplifier anode or plate voltage is fed through a choke. The anode for the audio amplifier is also fed via the same choke and as a result the audio amplifier valve / tube diverts current from the RF amplifier. The choke acts as a constant current source in the audio range. 90009 90005 Although cheaper because audio chokes are cheaper than audio transformers, this type of AM modulator circuit has a comparatively low power efficiency.90009 90025 Grid modulator 90026 90005 Another method of creating an AM modulator is to apply the audio to the grid of the final (or other) amplifier. This has the advantage that a much lower level of modulation is required. 90009 90005 In this type of AM modulator, the input signals including the RF as well as the AF and the DC bias are applied to the grid of the amplifier, which will be running in Class C. 90009 90005 The modulating AF acts on top of the existing DC bias and varies the level of voltage applied to the grid.This changes the operating point for the RF which runs in class C. 90009 90005 The overall effect of the system is to superimpose or modulate the audio onto the RF signal. 90009 90005 Grid based AM modulators were not as successful as anode based ones because unless carefully designed, the distortion levels of grid modulators could be much higher. 90009 90005 90006 More Essential Radio Topics: 90007 90008 Radio Signals Modulation types & techniques Amplitude modulation Frequency modulation OFDM RF mixing Phase locked loops Frequency synthesizers Passive intermodulation RF attenuators RF filters Radio receiver types Superhet radio Receiver selectivity Receiver sensitivity Receiver strong signal handling 90008 90006 90011 Return to Radio topics menu.. . 90012 90007 90009.90000 A simple AM ​​modulator 90001 A simple AM ​​modulator 90002 90002 90004 Introduction 90005 90006 In the last years medium-wave (MW) amplitude-modulated (AM) broadcast stations are gently disappearing, at least in Europe. For people who like vintage radios (wooden radios!) this is a bad news: because of the specific propagation characteristics of this band only the local station can be received during the day, since ionosphere propagation is completely blocked by the D layer.If the local station has been switched off as it was the case end of 2010 with the Sottens transmitter that was the last Swiss MW transmitter, one has to wait the evening when the D-layer disappears and medium waves can be reflected by the E-layer to hear some stations on this band. 90007 90006 90007 90006 It’s easy to buy an MP3 player FM modulator for a cheap price, but bad luck: vintage radios do not have (or very rarely) the FM VHF band.So the idea described in this page is an AM modulator for the MW band that will allow hearing the music of a CD or MP3 player during daytime on such radios. 90011 This is not a transmitter: 90012 the output power is very low (only 10 mW) and is intended to be connected to the antenna input of the radio, or to be closely coupled with it. Amplifying the signal would be a bad idea, since transmitting in this band is strictly forbidden in many countries.90007 90002 90004 Circuit description 90005 90006 The complete circuit is visible in the figure below. Click for a larger version with all details. 90007 90006 90007 90021 Audio amplifier section 90022 90006 The audio signal is connected to CN1 and CN2. The input stage is designed for stereo signals of 0.7 Vrms (2 Vpp) and has an impedance of 47 kΩ because this is usually what is needed to connect the line output of a CD player.If one wants to use the earphone output of an MP3 player, shorting JP1 and JP2 will drop the input impedance to 33 Ω to match this kind of output. AM only supports mono signals, so both channels are just added together in U1: A. In case of connection of a mono signal source, one can use either CN1 or CN2, but should always short the jumper of the other channel to make sure it does not pick up noise. 90007 90006 The RC networks C3-R2 and C6-R6 limit the lower side of the bandwidth to about 50 Hz preventing DC from shifting the bias of the modulator.U1 is an ordinary NE5532 low noise audio operational amplifier. U1: A is just an inverting additioner with a gain of -2 (6 dB). The network R7-C7 limits the upper part of the bandwidth to about 4.8 kHz. U1: B is an inverting amplifier whose gain can be adjusted via R8 between -0.45 (-7 dB) and -4.5 (+13 dB). This is used to adjust the modulation factor as close as possible to 100% according to the exact amplitude of the input signal. To avoid distortion, 80% will be good enough, since power efficiency is not an issue for this application.If this range is not enough, one could change R9 and R8 to increase or decrease the gain. The network R5-C5 limits again the upper edge of the bandwidth of this amplifier to 4.8 kHz. 90007 90006 Capacitors C8 and C9 make sure the inverting inputs of the two operational amplifiers are grounded at RF preventing the operating point to shift because of RF leakages from the modulator stage. R1 and R4 bias both operational amplifiers at about 5 Vdc, while bypass capacitors C2 and C4 removes RF leakages from the bias line.Capacitor C1 is used as energy tank to supply the amplifiers during audio peaks. The output of U1: B directly feeds the modulator stage. The bias of this amplifiers directly controls the bias point of the modulator. It was fixed to 5 V to allow voltage swings almost from 0 to 10 V. Changing the bias voltage will reduce the maximum undistorted RF amplitude. 90007 90006 90007 90021 Carrier generation section 90022 90006 In this circuit, the carrier frequency is generated by a crystal oscillator.Using a VFO was considered for its simplicity, but neutralizing thermal drift will make the circuit more complex to adjust and since old radios do also have significant drift, having a stable frequency would simplify its use and allows using this modulator as test equipment for fixing defective receivers. 90007 90006 In Europe, AM broadcast stations use a 9 kHz channel raster and all carrier frequencies are an integer multiple of 9 kHz.It would be nice if this modulator could match this rule. Ok, one could argue that old radios have a continuous tuning range and can tune in any frequency, but if this modulator is used as a laboratory tool to repair or align more recent receivers, having a correct frequency would be an important feature. 90007 90006 Since it’s almost impossible to find a crystal that has directly a suitable frequency in the AM MW band (531 to 1611 kHz in Europe) a crystal with a higher frequency was chosen, requiring the frequency to be divided down.Several standard crystals divided by 16 give correct AM MW carrier frequencies as shows in the following table: 90007 90039 90040 10.368 MHz / 16 = 648 kHz 90041 90040 13.824 MHz / 16 = 864 kHz 90041 90040 14.400 MHz / 16 = 900 kHz 90041 90040 18.432 MHz / 16 = тисячу сто п’ятьдесят два kHz 90041 90048 90006 For this project a crystal of 10.368 MHz was used but other crystals will work as well. If the correct channel alignment is not needed, any crystal between 8.496 MHz and 25.776 MHz will work. 90007 90006 The oscillator is a classical 4060 C-MOS oscillator and divider. For this application the 74HC4060 version was used because of its ability to deal with frequency higher than a few MHz and because it produces fast rise and fall time pulses. There is not much to say about this stage: the output frequency, already divided by 16, is available at pin 7 of U2 in the form of 50% duty-cycle square wave.The other outputs are not used. The crystal oscillator has no frequency adjustment (capacitors C19 and C20 are fixed), since this functionality was considered unnecessary for AM applications. 90007 90006 90007 90021 Modulator section 90022 90006 T1 is used as some sort of D-class amplifier / modulator and works as an ON / OFF switch. The carrier signal at MW frequency coming from U2 drives transistor T1 via R12 and C14.While R12 limits the current in T1’s base to reasonable amount, C14 helps T1 in switching fast ON and OFF. Without it, the charge accumulated in T1 base would have to slowly pass through R12 making the switching edges too soft. T1 is just a very common general purpose transistor type 2N2222. Probably, any similar transistor will work fine as well. 90007 90006 The AM modulation is achieved by varying the collector voltage if T1 with the audio signal provided by U1: B and the bias point of the audio amplifier sets the carrier power and peak envelope power available.Since T1 is directly powered by U1: B output, the maximum available current is 30 mA. In order to limit the current used by T1 (and reduce it’s power), resistor R11 has been connected in series with T1. In a normal class-D amplifier such a resistor would be a shame, but the goal of this circuit is not to produce high power or high efficiency: we just want a clear modulation at very low power. Reducing or removing R11 to increase the output power would be a bad idea: U1: B can not supply the extra power and distortion would be dramatically increased.90007 90006 L1 acts as an RF load for the modulator and also prevents the RF to go back to the audio section. C10 is in charge of shorting to ground any RF signal that leaked though L1. When no audio is present, the modulator is biased at 5 Vdc (Imposed by R1 and R4). The audio modulation changes this voltage down to 0 V and up to 10 V during modulation peaks, therefore modulating the output up to 100%. 90007 90006 90007 90021 Output filter section 90022 90006 The modulator output goes to the output filters though C13, that preventing the DC present on T1’s collector from reaching the output.The output filter is composed by C11, C12, C15, C16, C17, L2 and L3. This is a fifth order Cauer filter with a cutoff frequency of 900 kHz. It’s designed to pass all frequencies below 900 kHz with a maximum attenuation of 0.13 dB and block all frequencies above 1.8 MHz more than 60 dB. Nominal impedance is, of course, 50 Ω. Theoretical values ​​are reported in brackets, but of course, only standard values ​​components have been used. 90007 90006 If an output frequency above 900 kHz is used, all filter capacitance and inductance values ​​should be reduced proportionally to shift the cutoff frequency upwards.Halving all values ​​will double the cutoff and stop-band frequencies. 90007 90006 At the output, the carrier level is 2 Vpp on 50 Ω, meaning 10 mW (+10 dBm) of carrier power. The peak envelope power is, of course 4 times higher: 40 mW (+16 dBm). 90007 90006 90007 90021 Power supply section 90022 90006 The whole circuit is powered by an external 12 Vdc power supply such as a wall wart.This has the advantage that no dangerous voltage is present on the board. DC power is applied to CN4 and D1 protects the circuit from polarity inversions. L4, C23 and C21-C25 form a low-pass filter preventing the RF from escaping through the power supply cord. C24 is used as local energy storage and avoid strong current pulses on the supply line. 90007 90006 U3, a 78L05, generates the 5 V supply voltage for the carrier generator that requires a standard TTL power supply like all 74HC C-MOS ICs.U4, a 78L08, generates the 10 V supply voltage for the audio amplifier. Since a 78L08 usually generates 8 V, its output voltage is increases by about 2 V by the three diodes D2, D3 and D4. 90007 90006 90007 90006 Care should be used in selecting the right power supply for this circuit. All noise introduced by the power supply will be at the modulator output, so cheap switching mode power supplies should be avoided or extra filtering before CN4 will be required.It’s also a good idea to install a common mode ferrite choke on the power supply DC cord. 90007 90002 90004 Assembling the circuit 90005 90006 For this project a single layer PCB was designed. Only through holes component are used since this components are massively present in many junk-boxes. Of course, given the relatively low RF frequency, any other assembly techniques would work as well, but assembling a PCB is a much easier job.All connectors are directly soldered to the PCB and no cabling is needed. The assembly plan is visible in the figure below. Click for a larger version with all details readable. 90007 90006 90007 90006 Bill of meterial. 90007 90006 For those who want to make the PCB, the layout is visible in the figure below. The exact dimensions are 114.3 x 68.6 mm 90095 2 90096 and it’s viewed from below (solder side).90007 90006 90007 90006 The picture below shows the board completely assembled. 90007 90006 90007 90006 In spite of what one may think by looking at the picture at the beginning of this page, the modulator should be installed in a metallic box to shield it and preventing the radio from picking up noise generated from U2. 90007 90002 90004 Testing the circuit 90005 90006 When the board is finally assembled, let’s connect the power supply and switch the power on.As described earlier, it should use about 40 mA at 12 V. Let’s first check if the oscillator works by connecting an oscilloscope to the oscillator buffered output (U2, pin 9). A square signal with TTL levels (0 to 5 V) at the crystal frequency should be clearly visible (10.368 MHz in this case). This signal is visible in the figure below (Ch3, pink). One could also view the signal on the oscillator amplifier output (U2, pin 10), but in this case a low capacitance high impedance (10x) probe should be used to avoid loading the oscillator circuit.90007 90006 On the same figure, one can also see the board output signal (With no modulation), where the frequency has been divided by 16 by U2 (648 kHz in this case) and the square wave has been filtered out to sinusoidal wave by the output filter (Ch2, yellow). The output must be connected on a 50 Ω load; many oscilloscopes can switch their input impedance to 50 Ω, otherwise an external resistor must be used. The amplitude is 2 Vpp (0.7 Vrms, +10 dBm), as expected. 90007 90006 90007 90006 Now, let’s have a look at the output spectrum. Since the power is low, the output can be directly connected to the spectrum analyzer input without taking the risk of damaging it (most spectrum analyzers can survive powers of +20 to +30 dBm). On the other hand, you may want to activate the attenuator function (30 dB in this case) to avoid the analyzer to saturate and give inaccurate results.The spectrum analyzer already has in input impedance of 50 Ohms, so there is no need to bother with an external load. The output spectrum is visible in the figure below. The spectrum analyzer agrees with the previous measurement taken with the oscilloscope and finds a carrier power of +10.8 dBm. The second and third harmonics are clearly visible and their power are -26 dBm (2.5 μW, 36 dB below the carrier) and -50 dBm (10 nW, 60 dB below the carrier).These harmonic levels are fine for a simple modulator that is not supposed to be used as a transmitter. 90007 90006 90007 90006 Now, let’s add the modulation. For this, a CD or MP3 player has to be connected to CN1 and CN2. JP1 and JP2 are set according to the required impedance of the audio source. The oscilloscope is connected at the board output which is loaded with 50 Ω. This signal is visible in the figure below (Ch2, yellow).To have a comparison, the audio signal is measured as well (Ch3, pink) and to take advantage of the additionner circuit, it was measured on U1: A’s, pin 1. The AM modulation is clearly visible. 90007 90006 90007 90006 Then, R8 has to be adjusted to the highest possible modulation factor without clipping (distorting) the signal. It’s not easy to find the best possible adjustment because CD players have a very high dynamic range and some songs may produce very high audio peaks.It’s safer to adjust R8 to a lower modulation factor: even if the factor is 70 or 80%, the modulated audio level will be enough and for this application we do not care about power efficiency. If the modulation is adjusted too low, one will have to increase the volume on the connected radio. 90007 90006 The figure below shows the linearity of this modulator. On the horizontal (X) axis is the modulated RF signal at the output of the board, on the vertical (Y) is the audio signal at the modulation amplifier output (U1: B, pin 7).The nice symmetric trapezoid shape shows a good linearity. If this was not the case the two tilted sides were curved. It the modulation factor is increased, the trapezoid becomes a triangle (100% modulation) and a triangle plus a line (over-modulation). In this case the modulation factor is safely below 100%. 90007 90006 90007 90006 Finally, let’s have a look at the sidebands with the spectrum analyzer.The board output is connected directly to the spectrum analyzer, the center frequency is set to match the carrier frequency and the span is set to 50 kHz. Receiver and video bandwidth are set as small as possible (300 and 100 Hz respectively in this case) and the display is set in peak-hold mode, since reducing the bandwidth dramatically slows down the analyzer and one has to accumulate a lot of sweeps to see the final shape. So, the measure is taken for several minutes while modulating with some music.The result is in the figure below: the carrier is visible in the center and the sidebands are symmetrical to it. The modulation is wider than the expected 9 kHz, because the low-pass filters in U1 only have a total attenuation of 20 dB / decade, but again, this spectrum is fine if it’s not intended to be transmitted. 90007 90006 90007 90002 90004 Connecting the modulator to the radio 90005 90021 Direct antenna connection 90022 90006 The first solution one would think about is connecting the output of the modulator to the antenna connector of the radio with a suitable attenuator.90011 But this solution could be very dangerous because old radios often do not have a ground connection and the insulation almost half a century old may be not as effective as it should. An electrical shock may result. 90012 There is the risk of having mains potential on the radio chassis. The situation can be even worse, because cheap vintage radios often use an autotransformer instead of an isolated transformer and the chassis is physically connected to one of the AC mains line wires.This can be very dangerous because the mains potential would also reach our modulator and the MP3 player via the antenna and audio cables. 90011 For these reasons this solution is not recommended. Use it only if you know what you are doing and that you are sure about the quality of the ground connection of your radio, and of course at your own risk. 90012 90007 90006 On the other hand, for more recent radios, connecting the RF output of the modulator to the antenna input of the receiver via a suitable attenuator is definitively the best solution, and for this reasons this solution is discussed anyway.If we consider that a S9 signal strength (50 μV) represents -73 dBm (on 50 Ω) and that the power available at the output of the modulator is +10 dBm, we have to attenuate 83 dB. Old radios usually have an input impedance of 300 Ω, therefore an S9 signal would be -81 dBm and the attenuator should remove 91 dB. The exact value of the attenuator is not really e problem, since the signal strength will be compensated bay the automatic gain control of the radio.We just want to avoid a too strong signal that may introduce distortion and a too weak signal that would introduce noise. Any attenuator in the 80 to 90 dB range will do the job. The one shown in the figure below attenuate 90 dB and also converts the impedance from 50 Ω to 300 Ω. 90007 90006 90007 90006 If one would like to add some extra security, the attenuator could be connected to the radio via two 10 nF 1 kV capacitors, in order to limit a possible AC mains current due to bad isolation.90011 But in any case, this solution is not recommended for connecting to a vintage radio. 90012 90007 90021 Inductive coupling 90022 90006 A much safer way to connect the modulator to the radio is via an inductive coupling: in this way there is no direct connection to the radio circuit and there is no risk of electrical shock in case of bad radio insulation. 90007 90006 The basic idea is to connect the output of the modulator to a coil and put this coil in close vicinity of the receiver antenna tuned circuit, in order to make a transformer between the two coils.Wooden radios are usually not (or very badly) shielded, so the coupling coil can be outside the radio and no connection nor modification is required. 90007 90006 The simplest coil one could build is something like 8 turns of thin insulated wire over a diameter of about 110 mm and connect it directly to the modulator output via a coaxial cable. Coil dimensions and geometry are far form being critical. Than, one has to try to get the best coupling by moving the coil position and orientation near the radio.Depending on the model, the coil could be on the back, below, or close to one side of the radio. Usually the antenna tuner circuit is located in close proximity of the band switch, if the receiver has one. 90007 90006 A more elaborated coil can be made using e ferrite rod antenna that are usually found in old transistor radios. It’s easy to make a resonant circuit and increase the desired signal. The nice thing is that there are big chances that in the broken transistor radio from where the ferrite antenna comes from, there is the variable capacitor needed to resonate it into the MW band.If not, as it was the case with the rod in the figure below, one has to find another (variable) capacitor to do the job. Of course the values ​​of the capacitors depend on the kind of rod antenna used. 90007 90006 90007 90006 90007 90006 Moving the coupling coil only a meter or so away from the radio makes the signal completely disappear, showing that we have really a “transformer” type coupling and that 90011 the RF energy is not radiated by the coupling coil in the form of an electromagnetic wave.90012 So we are now sure that this is not a transmitter and that we are not radiating any signal in the MW band. 90007 90002 90004 Conclusion 90005 90006 In this page a simple AM ​​modulator for the MW band has been described. It allows listening to some musing on vintage radios even if the local broadcast transmitter has been switched off. The results were quite good and the same circuit can be used as test modulator for repairing AM receivers.90007 90002 90002 .90000 Review of the SSTRAN AMT3000 AM transmitter kit 90001 90002 90003 90002 Regular 90005 SWLing Post 90006 readers know that I’m a sucker for vintage radios – especially those of the WWII era. Indeed, I’m pretty much a fan of anything from the 1930s and 40s. I love the technology of that era and have an affinity for the culture and history, especially film and music. 90003 90002 Last year, I acquired a beautiful Scott Marine Radio Model SLR-M – a receiver that quickly became the centerpiece of my modest vintage radio collection.90003 90002 90003 90002 Scottie (yep, I call her Scottie) produces beautiful, rich audio from her internal speaker. It’s truly an amazing piece of over-engineered technology that still sounds this good after 70 years. 90003 90002 Edythe Wright 90003 90002 Only a week or so after plugging Scottie into an antenna, my wife and I picked up a $ 1 CD at a church yard sale. The CD featured big band music from the late 30s / early 40s. Though we already had much of the music on the CD, we bought it anyway to keep in our car.One beautiful fall day, I was driving down a rural road and had the CD playing when a Tommy Dorsey recording of “The Music Goes Round And Round” with Edythe Wright on vocals, began playing. It had been ages since I heard this song … I then wondered how many GIs might have heard this song during WWII via GI Jive or the Armed Forces Radio Network. Perhaps they heard it on the Navy version of my Scott Marine radio, the Navy REH? 90003 90002 It was then I decided to finally pull the trigger and order a proper low-power AM transmitter for our home – something with which I could broadcast period music via my vintage gear.90003 90002 There are a number of AM transmitters on the market, but the one that always stands out from the crowd is the SSTRAN AMT3000. My buddy, The Professor, has one and uses it to consume much of his digital audio content including podcasts and Internet radio stations. He sang the AMT3000’s praises, and I trust the Prof; he’s something of a medium wave guru. 90003 90002 Thing is, the AMT3000 only ships 90005 as a kit 90006. In the past, this had stopped me from ordering the transmitter as I figured it was more than my beginner kit-building skills could manage.But after building David Cripe’s Ozark Patrol regenerative receiver, and loving the experience, I felt confident enough to make the order. 90003 90002 And, boy, am I glad I did! 90003 90028 The SSTRAN AMT3000 kit 90029 90002 The kit arrived within a few days of ordering it. Upon unboxing it, I felt like I had gotten my money’s worth, as it was packaged carefully in a quality box: components were clearly labelled in their own poly bags, the board was clearly marked with component numbers and the assembly / instruction manual was in a plastic binder, all clear and straightforward.90003 90002 SSTRAN suggests taking your time building the kit, as there are a lot of components to solder, and you risk making mistakes that are not necessarily easy to remedy if you rush through the process. I tried to follow this advice – well, I 90005 intended 90006 to follow this advice. Thing is, I find it very difficult to put down a kit once I’m in the zone, so I zipped along a bit more quickly than I intended. 90003 90002 But it helped that SSTRAN took out a lot of the head-scratching and guesswork; the process could not have been more smooth.I carefully checked and double-checked each component and marked it off the assembly list. First, you install all of the resistors, then capacitors, and on to other components. Other than having to hunt for some of the component locations on the board, it really was 90005 quite 90006 simple. 90003 90002 90003 90002 I started building the kit on a Friday afternoon and actually finished it the following Saturday morning. Much to my delight, after performing the tuning procedure, the transmitter worked on the first go.Whew! 90003 90028 Powerful (low power) broadcasting 90029 90002 90003 90002 The AMT3000 can be configured to work with the supplied simple wire antenna, which will essentially broadcast AM to radios throughout your home, or it can be configured for a Part 15 compliant outdoor base-loaded vertical antenna which will extend your range up to 3 / 4 of a mile, should your shack be down the road or in an outbuilding. 90003 90002 For the moment, I have my transmitter set up for in-house broadcasting only.If I ever want to build the base-loaded vertical, I only need to make a simple modification to the board to do so. 90003 90002 90003 90002 The supplied manual does a great job of explaining the best ways to maximize your signal, reduce any electrical hum and tweak your audio fidelity. 90003 90002 I’ve been using the AMT3000 nearly every day since I finished building it in mid-November. It seems to have a 100% duty cycle, does not overheat, and has no drift. 90003 90002 It produces high fidelity audio with a flat frequency response – and of course, with modulation and compression controls, you can tailor the audio to your particular taste.90003 90002 Result? It sounds 90005 amazing 90006 piping WWII-era tunes through my Scott Marine SLR-M, Hallicrafters SX-24, and SX-99 and my Hammarlund SP-600. 90003 90002 As a bonus, I can hook my shortwave receivers up to the AMT3000 and listen to received audio via other radios throughout my house. Many times, I’ve listened to live broadcasts of ERT Open on 9,420 kHz via my kitchen AM radio … Very cool! 90003 90002 I also hook the AMT3000 up to my shack PC and stream my favorite internet radio station: the UK 1940s Radio Station via TuneIn radio.Absolutely brilliant! 90003 90002 I set my transmitter to 1410 kHz, and have left it there. You’ll need to do a medium wave (AM) survey to find the clearest spot on your AM dial. I’m sure results will vary, depending on the level of medium wave broadcast activity in your area. 90003 90002 Here’s what my Scott Marine SLR-M sounds like playing “March of the Toys” by Tommy Dorsey and his Orchestra via the SSTRAN AMT3000 (note that this was recorded with just an iPhone, so audio fidelity is somewhat lacking): 90003 90002 90073 90074 90003 90028 Conclusion 90029 90002 90003 90002 If you’re looking for a high-quality, low-power legal AM transmitter, I 90005 highly 90006 recommend the SSTRAN AMT3000.Even if you’re a novice kit builder, with time and patience, you can successfully construct the AMT3000, too. If I did it, you certainly can! 90003 90002 If you’d prefer buying a 90005 pre-assembled 90006 AMT3000, they do occasionally turn up on eBay. Click here to search. 90003 90002 As for me, I’m happy to have achieved my modest goal of being able to broadcast 1930s and 1940s music to vintage radios of the same era. 90003 90002 SSTRAN sells the AMT3000 directly on their website. Click here to view.90003 90092 90002 90094 SSTRAN AMT3000 Models and Prices (via SSTRAN) 90095 90003 90002 90094 AMT3000 90095 90100 10 kHz channel spacing for use inside North and South America. Includes enclosure and 120 Volt AC Adapter. The single surface-mount IC is pre-soldered on the board. 90100 Price: $ 92.95 90003 90002 90094 AMT3000-9K 90095 90100 9 kHz channel spacing for use outside North and South America. Includes enclosure and 120 Volt AC Adapter. The single surface-mount IC is pre-soldered on the board.* 90100 Price: $ 92.95 90003 90002 90094 AMT3000-9KNT 90095 90100 Same as AMT3000-9KSM, except the US-standard 120 Volt AC Adapter is not included. ** 90100 Price: $ 88.95 90003 90002 90116 90005 Related 90006 90119 90003.