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Amplitude Modulation

AM: Operating, Maintaining, Repairing, Building, Learning, New Technology!

From vintage tube-based gear, to military surplus, to modern, ultra-efficient FET-based Class E transmitters, Amplitude Modulation (AM) offers the experimenter, homebrewer, and radio restoration buff great opportunities to learn, build, and enjoy radio. AM was once the main voice mode in amateur radio. Now it is a well regarded specialty within the hobby. AM offers a warm, rich audio quality that provides for more personal interaction. The simplicity of AM circuit design encourages hands-on restoration, modification and homebrew construction to an extent no longer found among contemporary radios.

Take a Listen to Amplitude Modulation

LISTENING TO AM

by Paul Courson, WA3VJB 

One of the attractions of using Amplitude Modulation on HF is that the mode can offer a warm, inviting sound for the style of operating found in this part of the hobby.  Operators frequently make extended transmissions while discussing a technical pursuit, or during nostalgic storytelling much in the manner of "old style" broadcast radio.  Conversations take place both one-on-one and in group "roundtables," where there is a taking-of-turns among several operators, including a more formal gathering taking place on a regular schedule. 

The carrier of a double-sideband AM signal provides important information to help operators carry the conversation.  The carrier acts as punctuation, essentially, its presence letting other operators know the person has not finished their thought, and allowing a more comprehensive pace with less risk others might inadvertently start transmitting before an operator has turned it over. 

But there is also the more familiar style of operating found on other voice modes: a rapid, give-and-take that more closely resembles people together and having a conversation. In this type of QSO, it's expected that when you finish a sentence and drop your carrier, anyone else in the roundtable should pick it up. However, it should be noted that VOX is rarely used on AM. Operators on both new and old gear manually throw between transmit and receive. This practice dates to now vintage equipment, with high powered components, relays and careful sequencing that took time to complete.

RECEIVING AM STATIONS VIA THE INTERNET 

In recent years, internet-based receiver nodes located around the world have added a dimension to shortwave reception very suitable to picking up Amateur AM stations around the United States.  This affords the hobbyist a way of hearing for themselves AM activity in selected parts of the country that might not be audible at home. 

Three of the most substantial internet based receiving platforms offer generally free use of their software-defined radios (SDRs). Some have timers so that the nodes can be shared more widely. Most have a user inteface that allows a range of adjustment for best reception.  

http://rx.linkfanel.net/ 

http://websdr.org/ 

https://www.globaltuners.com/receiver/list.php 

Reception among these nodes of U.S. based Amateurs on AM is often better than you can achieve at home.  Volunteers put up these nodes at locations as exotic as a former high seas telegraph site, or as prime as a low-noise tract of farmland with room for plenty of "aerial."  It's worth your time to learn the user-interface at each of these sites, and take a listen to AM activity in selected areas. 

When conditions are exceptionally good, most of these nodes offer a recording function such as the one made of AMers at a early morning gathering on 3885Kc (at this link:) 

AM OPERATING EVENTS

AM RALLY

THE AM operating event of the year, open to all who wish to make AM contacts. For more information than you want to know, please click here: www.amrally.com

Hint: The video is a must see!

ANOTHER FINE VIDEO:

2020 AM Rally, W1AW operation at ARRL Laboratory, using the Gates BC1T transmitter and FlexRadio Systems FLEX5000C (receiver only).  Ladies night!  (NEW!)

n1BCG Operating Events

n1BCG 2016:  Story of the special event operation in Greenwich, CT, honoring a milestone in radio technology, crossing the Atlantic using short wave, achieved first by Radio Amateurs in 1921.

n1BCG 2019:  Operation at W1AW for the 98th Anniversay.

n1BCG 2020: Operation is planned for the 99th Anniversary, but CT Laws regarding COVID-19 may impact the operation. 

Celebrating 98 years of short wave radio. Stand by for the really, really reeeeealy big event in 2021 !!!

AM MODULATION MONITOR: A MUST

The ARRL Laboratory recommends using a modulation monitor to maintain high level, but undistorted transmit modulation in the AM mode. An excellent example of a modern modulation monitor is made my Radio Engineering Associates

Here's a Demonstration Of a Modern AM Modulation Monitor, made by Radio Engineering Associates

 

Gates BC1T at the ARRL Lab

Download

Tim Smith converted a Gates BC-1T AM Broadcasts Transmitter to 160 and 75 meters. The Transmitter is owned by the Vintage Radio and Communications Museum of CT and was acquired from the Nation Capital Museum of Radio and Television. Restoration to 1340 kHz was done by VRCMCT's Dan Thomas, NC1J. Renowned AM enthusiast, Tim Smith, WA1HLR had the task of converting the Gates for Amateur use. Watch him do this here! If you like large tubes, big components and dangerous lethal voltages, you'll enjoy this video.

Articles, Forums and More

AM FONE; A forum site dedicated to Amplitude Modulation.

AM FORUM on QRZ:  See what the AM Community is talking about.  Also a good place to discuss problems with vintage equipment, finding parts and meeting others with the same technical interests.

AM & FM Tutorial    Understand how Amplitude and Frequency Modulation works.  Most popular video explanation on Youtube. (NEW)

AM & FM Tutorial   1964 Army Training 16 mm Film. The presentation is vintage, but informative. (NEW)

AM Tutorial & AM Low Power Transmitter Circuit   Excellent explantation of a basic low power AM transmitter  (NEW)

QST Product Review of the K7DYY Super Senior 80 and 40 Meter AM Transmitter, Class D Modulation.

Classic Rigs and Amplitude Modulation: Friendly, Nostalgic Ham Radio Partners
QST February 1993, pp. 43
An introduction to current day AM activities within Amateur Radio.

Some Principles of Radiotelephony:
QST 1954

The basics of AM in four easy parts.

·A Course in Radio Fundamentals, Part 6 -- Modulation
QST November, 1942, p. 53
Another good AM primer.

Introducing: The AM Radio Network
QST December 1995, pp. 46
More on current day AM operation.

Hams Redeem Old Transmitter at Fountain of Youth Members Only
QST November 2003, pp. 56
The story of a rescue and Restoration of a Collins 300G Broadcast Transmitter
 

Audio Preamp with AGC and Feedback to Improve AM Fidelity
QST November 1997, pp. 36
A sweet little mic preamp that also helps control modulation levels.

Constant-Carrier AM for the Drake Twins (Hints and Kinks)
QST November 1994, pp. 85
Make these venerable radios sound much better.
 

Technical Topics - Some Facts on Modulation 
QST March 1951, pp. 49-51, 116.
An excellent explanation of how AM works. A good read for beginners and old-timers alike.

Technical Topics - Linear Amplifiers for AM  Members Only
QST Feb 1956, pp. 39-41
There's more than one way to generate AM. Get the scoop on using a linear.
 

Radiotelephone Transmission Members Only
ARRL Handbook, 1929, pp. 98-107
See how AM was done in the early days.
 

Lop Sided Speech and Modulation Members Only
QST February, 1940, p.14
Get the straight dope on speech asymmetry and its application to AM.

Three Control Six-Band 813 Transmitter

o    QST, Jan 1954, pp. 11-16, 112, 114, 116
o    QST, Jun 1954, pp. 37-39, 118  
o    QST October 1956, pp. 33-38
o    ARRL Handbook 1957, pp.192-197 

This transmitter was all the rage in its day and would be the envy of many AMers today.

The Ultra Modulation System Using Higher Audio Power Without Splatter
QST, October 1956, pp. 27-29
Shows how to increase modulation peaks for more effectiveness.

An AM/CW Exciter for 144 Mc.  Members Only
QST September 1965, pp. 39
Try some local contacts without the repeater.
 

Synchronous Detection of AM Signals
QEX September 1992, pp. 9
Feedback:
 

Nov. 1992 p. 21
Dec. 1992 p. 15

A great primer on sync detection and the advantages of using it for AM signals.

A Simple Synchronous-AM Demodulator and Complete Schematics for the DDC-Based Receiver
QEX September 1997, pp. 3
 

A Synchronous Detector for AM Transmissions
QST July 1993, pp. 28
Build a sync detector for yourself.
 

Synchronous AM Detectors Members Only
QST September 1992, pp. 65 


Web Links

 ·         The AM Window
This web site, previously featured in the Surfing' column, contains extensive coverage of AM topics, including information on construction and modifications, AM operating events and social gatherings, AM Nets worldwide, audio and visual coverage of AM stations and operators, and much more.

 ·         AM Fone.net
A vast storehouse of AM information and regional coverage of AM operators and activity. This site also feature a bulletin board for quick and easy access to AMers around the globe and their radio knowledge.

 ·         The Official Class E Transmitter Web Site
The goal of this site is to present a working, practical tutorial on class E transmitters (a complete explanation of class E is included), and to provide sufficient information to allow someone with reasonable radio experience, technical skills and knowledge to construct a working class E transmitter or design a transmitter using similar RF and modulation methods.


         

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AM Activity On the Dial

Send us Your Photos!

Would you like to see your AM station on our web site? Send your photo as a JPEG file to me and if it's of good quality, I'll post it!

Send to Bob Allison, WB1GCM ARRL Test Engineer at:

ballison@arrl.org

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