Icom AH-4 Manual
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Icom AH-4 Manual

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Inside the Icom AH-4 Tuner
This paper describes the Icom AH-4 wide range antenna tuner. It attempts to compensate for a rather
sparse instruction manual by providing information on how to interface the AH-4 with any HF radio. In
addition, it also provides recommendations regarding antennas for fixed locations. An overview and
description is presented as well. Those who are interested in antenna tuners (the AH-4 in particular)
and those who just plain like to look into the guts of hardware and see how things work will want to
read on.
Chris, K9EQ
AH-4 Operation
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K9EQ
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Summary of Contents for Icom AH-4

  • Page 1 Inside the Icom AH-4 Tuner This paper describes the Icom AH-4 wide range antenna tuner. It attempts to compensate for a rather sparse instruction manual by providing information on how to interface the AH-4 with any HF radio. In addition, it also provides recommendations regarding antennas for fixed locations. An overview and description is presented as well.
  • Page 2 1. Overview The AH-4 is a wide-range antenna tuner capable of matching a 50 ohm feed line to an antenna feed impedance in the range of 10 to 5,000 ohms. The tuner is designed to operate with up to 120 watts of power.
  • Page 3 2. AH-4 Design FIGURE 1: BLOCK DIAGRAM OF THE AH-4 AH-4 Operation K9EQ Page...
  • Page 4 RF out port and the ground connected to, well, ground. I much prefer feeding either a loop, with the AH-4 right at the feed point, or a flat top via ladder line. In both these cases the AH-4 works extremely well.
  • Page 5 FIGURE 3: A VIEW OF THE INSIDE OF THE AH-4 AH-4 Operation K9EQ Page...
  • Page 6 3. The KEY signal causes the radio to transmit a carrier at about 10 watts of output power. 4. The AH-4 verifies that the power is between 5 and 15 watts. If not, the AH-4 aborts the tuning operation.
  • Page 7 FIGURE 5: FAILED TUNING RESPONSE The command to reset the tuner causes it to pass-thru (tuning network out of circuit). FIGURE 6: TUNER RESET 
 AH-4 Operation K9EQ Page...
  • Page 8 Similarly, the AH-4 pulls the KEY line to 5 volts through a 22 K ohm resistor/diode combination. The radio also pulls this line to 13.8 volts through a resistor. The AH-4 pulls this line to ground to assert the signal (indicate tuning status to the radio.) 6.

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