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How to Use an AM Transmitter on the HF Bands

During the late 1950s, SSB (Single Sideband) supplanted AM (Amplitude Modulation) as the predominant mode of voice communication on the HF (High Frequency) amateur radio bands. Although SSB uses both bandwidth and transmitter power more efficiently, it cannot compare in pure audio quality to an AM signal from one of the old vacuum-tube transmitters. For this and nostalgic reasons, pre-SSB AM transmitters are in high demand. Each of the original HF bands has a dedicated AM frequency, but 3,885 KHz on the 80 Meter band is the most active AM frequency by far. Antique AM transmitters are more difficult to operate than a modern SSB transceiver, but users consider that a part of their charm.

Things You'll Need

Transmitter operator's manual
Ground wire
Coaxial transmit-receive relay
Two coaxial jumpers
Microphone

Instructions

- 1
  Unplug the power cord of the transmitter. Connect a ground wire from the transmitter grounding lug to the station ground bus. Disconnect the antenna feedline from the receiver.
- 2
  Connect the antenna feedline to the transmit-receive relay. Connect one coaxial jumper to the "T" connector of the relay, and to the antenna connector on the transmitter. Connect the other jumper to the "R" connector of the relay, and the antenna connector on the station receiver.
- 3
  Connect the control line from the transmit-receive relay to the antenna relay connection on the transmitter.
- 4
  Plug in the transmitter. Set the transmitter bandswitch to 80 and the VFO to 3,885 KHz and switch on the power. While it is warming, switch on the receiver and tune to 3,885 KHz.
- 5
  Switch the receiver mode control to "CW." Turn the transmitter VFO control until you hear a high-pitched tone in the receiver, then continue to turn it so the tone lowers in frequency and finally disappears. Stop tuning at the exact moment the tone disappears. Reset the receiver mode to "AM."
- 6
  Load and tune the transmitter according to the directions in the manual. Briefly, set the "Load" and "Tune" controls at a mid-point and the "Drive" control to minimum. Set the meter to display output power. Switch on the "HV" and "Transmit" controls. Advance the "Drive" control until the meter just begins to deflect, then adjust the "Load" and "Tune" controls for maximum power. Advance the "Drive" control to just below the point where further increase no longer causes further meter deflection, then adjust the "Load and "Tune" controls for maximum power. Turn the "Transmit" control off.
- 7
  Connect the microphone. Set the meter control to indicate modulation. Switch on the "Transmit" control and set the transmitter audio control so the meter displays 100 percent modulation while you are speaking in a normal voice.
- 8
  Identify with your callsign and switch the "transmit" control off.

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