Acom ACOM1010 User Manual

Contents

Acom ACOM1010 User Manual Manual pdf 12 page image

4-5. TuningTuning is possible only in the OPER mode.OPER mode.OPERa) Preliminary information.Tuning the amplifier involves a procedure of matching the impedance of the antenna and transmissionline to the amplifier tube’s characteristic load resistance. This will ensure maximum plate efficiency andRF gain at nominal output power, with minimal distortion and spurious output. Note that REFLECTEDPOWER readings depend on the antenna and transmission line impedances only, and not on amplifierPOWER readings depend on the antenna and transmission line impedances only, and not on amplifierPOWERtuning. If the load impedance is not a nominally resistive 50-Ohms, the REFLECTED POWER reading willREFLECTED POWER reading willREFLECTED POWERalways show a reading, no matter what the tuning settings. Proper tuning is always necessary, however,and will allow you to operate at a high power level, without distortion or any danger to the amplifier.Note also that the real OUTPUT POWER presented to the load (the antenna and transmission line)OUTPUT POWER presented to the load (the antenna and transmission line)OUTPUT POWERis equal to the difference between the FORWARD and REFLECTED power readings. For instance,with a 2.5:1 VSWR, readings of 800 W and 150 W FORWARD POWER andFORWARD POWER andFORWARD POWER REFLECTED POWERrespectively, the real OUTPUT POWER is 650 W. At very high VSWR levels, such as when no antennaOUTPUT POWER is 650 W. At very high VSWR levels, such as when no antennaOUTPUT POWERis connected or a badly mismatched antenna is used, the FORWARD and REFLECTED readings willbe almost equal, while the real OUTPUT POWER (the difference between them) will be nearly zero.OUTPUT POWER (the difference between them) will be nearly zero.OUTPUT POWERThe amplifier can operate safely as long as the REFLECTED POWER is LESS THAN 250 W. MatchingREFLECTED POWER is LESS THAN 250 W. MatchingREFLECTED POWERis assured for loads presenting a VSWR of up to 3:1. Nevertheless, for some loads and bands, matching ispossible at even higher VSWR levels, but the drive power must be reduced to prevent the REFLECTEDPOWER from exceeding 250W. Failure to comply with these guidelines will cause the protection circuitsPOWER from exceeding 250W. Failure to comply with these guidelines will cause the protection circuitsPOWERto trip. For example, if the antenna VSWR were 5:1, the maximum attainable forward power wouldbe 540 W, 240 W of reflected power and real output to the antenna and transmission line of only 300W. In the event your antenna cannot be adjusted to produce a lower VSWR, an external antenna tunermay be deployed.CAUTIONAt elevated VSWR levels, high voltages and high currents are distributed along thecoaxial cable to the antenna, risking internal arcing and heat generation, and likelydamage to the cable and any antenna switches that may be used. It is recommendedthat VSWR levels of more than 3:1 not be permitted with coaxial cable above 14MHz.It is advisable to adjust amplifier tuning when antennas have been changed, snow has fallen, new objectsare in the near field of the antenna, etc. Such changes may affect antenna impedance.NOTEIf you use more than one antenna on a band, the proper antenna must be selectedprior to performing the tuning procedure outlined below.CAUTIONTo avoid damage not covered under warranty, do not switch the BAND switch knobwhile transmitting. As discussed above, hot switching will damage the amplifier’sband switch!CAUTIONAlso, never apply drive longer than one minute continuously without pausing for atleast one minute to allow the tube to cool.