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Friday, May 23, 2014

Amplitude Modulation - How it was done before Single Side Band

Before Single Side Band amateur radio operators used amplitude modulation (AM) to send their messages to other stations.

For many on HF the AM button radio was something that you pushed to tune your antenna to your rig before calling CQ on upper or lower side bands.  Next time you tune up, stay in the AM mode for a bit and listen in for some AM traffic.  You are bound to be surprised with the quality of the transmissions heard.



Many AM'ers use vintage tube, retired military and hybrid radios to participate in AM nets throughout the world.  Some hams even built their own radios from radio gear used in old commercial AM stations.

Some photos of AM stations found around the Net:

Andy Howard, WA4KCY at the Gates BC-250GY operating position.
Photo byJoe Veras and CQ Magazine

Jeff May, W0XV, built this excellent 813 amplifier to use with his Harvey Wells station

Jeff May, W0XV, is the proud owner of this great looking BC-610 Station





Here is a list of frequencies used for AM communications:
All Frequencies in MHz
160 Meters: 1.885, 1.900, 1.945, 1.985 (USA)
                     1.850 (W. Europe)
                     1.933 &1.963 (in the UK)
                     1.843 (Australia)
80 Meters:  3.530, 3650 (South America)
                    New3615, 3625 (in the UK)
                    3705 (W. Europe)
                    3.690 (AM Calling Frequency, Australia)
75 Meters: 3.825, 3.870 (West Coast), 3.880, 3.885 (USA)
40 Meters:  7.070 (Southern Europe)
                    7.120, 7.300 (South America)
                    7.175, 7.290, 7.295 (USA)
                    7.143 (UK)
                    7.146 (AM Calling Frequency, Australia)
20 Meters: 14.286
17 Meters: 18.150
15 Meters: 21.285, 21.425
10 Meters: 29.000-29.200
6 Meters: 50.4 (generally), 50.250 Northern CO
2 Meters: 144.4 (Northwest)
                 144.425 (Massachusetts)
                 144.28 (NYC-Long Island)
                 144.45 (California)
                 144.265 (Los Angeles, CA)

 * Source - http://www.amwindow.org/



Sample of an AM Ham Net found on YouTube:





Where and when AM'ers meet
A schedule of AM Nets was found posted at:
http://www.amwindow.org/nets/netday.htm


Find out more
I found a great article on AM in the archives of the ARRL:
http://www.arrl.org/files/file/Technology/tis/info/pdf/9302043.pdf

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