AM or SSB are there ‘windows’?

Amplitude Modulation has been used for voice transmission between Radio Amateurs for more than a century. A new voice mode appeared in 1947, when Wes Schum, W9DYV introduced the first Amateur Radio SSB transmitter, the Central Electronics 10A. By the late 1950’s and early 1960’s, competition for dial space began to “heat up” between the ‘died in the wool’ AM operators and the new, hard to tune in, Single Sideband operators. Eventually, there was a sit-down, face to face meeting, between some “Big Gun” SSB operators and long time, AM operators. Together, both groups decided on a ‘Gentlemen’s Agreement’, for AM dial space. For example, on 75 meters, they choose 3.870MHz to 3.890MHz as the “AM Window”. On 40 meters, AM around 7.290MHz. 20 meters, 14.268MHz; etc. These “windows’ were promoted by the ARRL and strongly observed by AM operators for a couple of decades.

During the 1980’s and 1990’s AM operations had declined, and many newly licensed SSB operators came to be. Many of them didn’t know AM even existed on the Amateur bands, as the AM Window concept was no longer promoted well, or not acknowledged. However, AM has seen a recent resurgence of popularity, in part due to the introduction of Software Defined Radio Transceivers, such as FlexRadio Systems lineup, the ICOM IC7300, Yaesu FT101DX, Kenwood TS890, Apache Labs Anan 80000DLE, etc. New and old AM enthusiasts have homebrewed Class E modulated solid state AM transmitters. In 2018, QST tested and reviewed the K7DYY AM (only) solid state, Class D transmitter, a near legal limit, AM only transmitter, with built in power supply, that weighs only 8 pounds!

With increased activity, some cross mode interference is sometimes unavoidable. It is always best to remember, NO ONE owns a frequency, regardless of mode. It is good practice to always check the tuned frequency, to make sure it is not already in use, by one, or more stations. Some AM Operators are crystal controlled and cannot easily change frequency. 3.885 MHz for example, is a popular crystal frequency used within the US phone band. With almost all SSB transmitters being frequency agile, would you give the 3885 kHz crystal controlled AM station a little leeway and move a few kHz, if he was there, first?

With the increased number of AM stations, there are now are a few other spots on the dial that AM operation can be found. Both SSB and AM mode users can avoid misunderstanding, or disagreement, if each party observes the AMATEUR’s CODE:

    The Amateur is considerate, never knowingly operates in such a way to lessen the pleasure of others.
    He offers his loyalty and encouragement to fellow amateurs.
    Keeps his station efficient and well maintained. His operating practice is above reproach.
    Offers kind assistance, cooperation and consideration for the interest of others.
    Radio is his hobby. He never allows it to interfere with duties to his home or family.
    His station is always ready for service of his country.

Adapted from the original Amateur’s Code, written by Paul M. Segal in 1928.

In addition, please ask, “Is the frequency In Use?”

As always, with any mode, asking if the frequency is in use, first, will alleviate an initial misunderstanding. Please remember that the ham bands can change quickly, causing new interference. Acknowledge the changing band, and be friendly about it. I encourage everyone to join AMI: Learn, appreciate, and enjoy AM operation. Lets all be courteous to each other and share our frequencies.

Dr. Bob Heil, K9EID, is the founder of Heil Sound and host of's Ham Nation which streams live each Tuesday at 6:00pm PT (9:00pm ET) at Contact him at [email protected].

2 Responses to “AM or SSB are there ‘windows’?”

  • Frank K4FMH:

    Hi Bob,

    Thank you for this kind reminder. I vividly recall the 75 Meter AMers who introduced me to amateur radio as a child. I’ll do more AM this year!


    ICQ Podcast

  • Don N4KC:

    Good reminder! Same goes for SSTV, but those guys aggressively defend their spot on 20 meters. We have a regular half hour group that gets together on Tuesday mornings at 1330Z on 3875. Some use vintage gear. Others of us coax AM out of our more modern radios. Some of us are former broadcasters, too, and thus our nostalgic affection for AM. We do sometimes have SSB encroachment but I must say, for the most part, it appears most hams allow us to insert carrier to our hearts’ content! 73 de Don N4KC

Leave a Comment

Subscribe FREE to's
Amateur Radio Newsletter
News, Opinion, Giveaways & More!

Join over 7,000 subscribers!
We never share your e-mail address.

Also available via RSS feed, Twitter, and Facebook.

Subscribe FREE to's
Amateur Radio Newsletter

We never share your e-mail address.

Do you like to write?
Interesting project to share?
Helpful tips and ideas for other hams?

Submit an article and we will review it for publication on!

Have a ham radio product or service?
Consider advertising on our site.

Are you a reporter covering ham radio?
Find ham radio experts for your story.

How to Set Up a Ham Radio Blog
Get started in less than 15 minutes!

  • Matt W1MST, Managing Editor

Sign up for our free
Amateur Radio Newsletter

Enter your e-mail address: