AM Is Hardly “Ancient Modulation”!
Although at times it is jokingly referred to as “Ancient Modulation” by its detractors, AM is “Angel Music” to those who enjoy this special mode of modulation. AM refers to the method of modulating the RF carrier, in this case, Amplitude Modulation. Amplitude Modulation (AM) was the first voice mode used in amateur radio, and is now very much alive at it enters the 7th decade of its life. AM is a well-regarded specialty within the radio hobby, and its operation offers a warm, rich audio quality that provides for more personal interaction. AM is rich with tradition, and the time honored tradition of elmering and homebrewing equipment are no exception. AMers often build and maintain their own antennas and transmitters. The simplicity of AM circuit design encourages hands-on restoration, modification and homebrew construction to an extent no longer found among contemporary radios.
You may find AM culture is a bit different than what you are used to. Often QSOs tend to center around technical discussion, especially relating to tube type gear. Antennas are also a popular topic, and different styles and methods of feedline construction are often debated. Transmissions tend to be more extended, and VOX is rarely used. In fact, the pace of AM QSOs is often quite leisurely. AM slang is very descriptive, do not be surprised to hear some rather interesting terms, from some quite interesting people!
Technical items are not the only issues discussed however, and established nets deal with topics ranging from UFOs to historical events. Two of the more interesting nets, in this authors opinion, are the “Future Net” found on 3.875MC Sundays at 4:00 PM and the “Gray Hair Net” on 1.945MC Tuesdays at 8:00PM. Not to be missed is the “AM Swap Net” on 3.885MC Thursday at 7:00PM, where equipment and parts are exchanged in a “tongue in cheek” fashion. Locally look for the “Sunday Morning Brunch” net on 3.815MC around 9:00AM, the “160m Early Morning Net” on 1.885 which starts around 6:00AM and the “2m AM Net” on 144.450MC Sunday evenings at 8:00PM.
AM activity can be found on a variety of other frequencies both day and night. For daytime operation check around 7.290, 14.286 and 29.10 MC. Evening and early mornings 1.885, 1.888, 1.945, and 3.885 are your best bets. Most AM operators will gladly welcome newcomers to the mode, give it a try!
That’s it; you’re ready to get on the air on AM. If you are running a solid state rig, you will want to reduce the RF output to about ¼ of the maximum valve. For most of today’s rigs this equates to 25 watts carrier. You might also want to reduce the mic gain somewhat from what you are running with SSB. These settings may not be exactly right but this should get you close. Once you get on the air, ask for an audio report to determine to determine if you need to do any tweaking. If you access to an oscilloscope, by all means, use it to adjust your mic gain. Using a scope, you can determine your percentage of modulation and if you are “flat-topping”. Flat topping refers to the distortion that occurs when a transmitter is driven past its max power output. Distortion, and splatter onto adjacent frequencies occur during flat topping, something that you want to avoid.
If you run your transceiver into an amplifier, follow the same steps with the linear in line. One important thing to remember is that your amp will be running at about 20 -25% efficiency, and what does not go up the antenna as RF is given off as heat. So, you may want to get your calculator out and determine how many watts you can run without exceeding the plate dissipation rating of your linear. Remember that AM is a 100% duty cycle mode, as opposed to 30-50% for SSB. So the tubes and the power supply in your amp will be working much harder. You may not want try to squeeze every last watt out of your rig. The difference in received signal strength is just not worth it. Err on the side of safety.
The AM mode can be a tremendous bit of fun. Although it is most often associated with older, tube gear, modern day transceivers can produce some very good sounding AM when properly adjusted. Whether you were an active AMer in the past, or new to the AM mode, by all means get on the air and give us a call. Welcome aboard!