Setting up a solid state or hybrid rig for AM

So you've got a new rig right from the store, or perhaps you bought an early 80s model from a hamfest or friend. No matter what era yours is from, there are some key settings that need attention for you to sound your best when using the AM mode. Ideally, you have a manual (the manufacturers know best) or can download one from the net. If not, or you're curious about these settings in general, check this out...

 

ALC (Automatic Level Control)

A properly adjusted ALC (Automatic Level control) will limit distortion and interference during a transmission. In many modern radios the ALC can be very aggressive and tricky to set for use on AM. ALC is controlled using the mic gain adjustment on the rig. The best way to set the ALC or Mic Gain is to follow the manufacturer's recommendations in the manual. The most common procedure is to use the ALC display meter on the rig to properly adjust mic gain levels. In some cases these adjustments may have to be done while transmitting in SSB. To do so set the power out to 25% of the rig's rated output and adjust the mic gain according to the manufacturers instruction regarding ALC. Most likely the mic gain will have to be reduced when transmitting in AM.

You can also use an oscilloscope.

If those are not available, a PEP watt meter will give you a starting point. Connect your rig in the proper order to a peak reading watt meter and a dummy load. Turn the power output and the mic gain all the way down and select the AM mode. Then with no audio, set the AM carrier level, sometimes called a resting carrier or TX power output level, to 25% or less of the rigs rated output power. For example, a transmitter rated for 100 watt PEP on SSB would be set to 25 watts or less for an AM carrier power output level.

Next, speak into the microphone using a normal voice while adjusting the mic gain level up. Keep increasing the mic gain while observing the output reading on the meter. The mic gain is set properly when the watt meter stops increasing.

Note that this level may not be the perfect 100 % modulation level that AM operators want, but it is the audio level that your particular rig can produce without causing the ALC to activate.

Carrier LevelThe maximum setting for your carrier level is 1/4 (25%) or less of your rig's PEP capability when set to SSB. This is because the sideband energy in an AM signal modulated to 100% is four times that of the carrier, so reverse-calculating the carrier based on your peak sideband energy is important.

For example, your transmitter is rated at 100 Watts PEP on SSB. That means your carrier level should not exceed 25 Watts. In fact, setting it to 20 Watts provides some headroom without noticably affecting your signal strength and the clean audio will contribute a lot to your intelligibility.

Setting up a software based rig (Flex, Anan)

These rigs represent the latest in technology and can be kept up to date using software upgrades. Colorful displays showing every aspect of transmission and reception make software based amateur rigs particularly appealing as does having virtually complete control over both transmitted and received audio.

Comprehensive information is available from the W1AEX website:

Power SDR (Flex) tips: http://www.w1aex.com/psdrgain/psdrgain.html

Anan SDR (Apache Labs) tips: http://www.w1aex.com/anan/anan.html

Setting up a classic "Boat Anchor" or Homebrew rig for AM

If you own one of these then you're expected to know what you're doing. Oscilloscopes, trapezoidal patterns, carrier cut-off, linearity, frequency response, bandwidth limiting... all familiarIf you are not sure, why not ask one of your friendly local amateur radio club members.

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