Home › Forums › temp › SSTRAN Now Accepting Orders for the New AMT5000 High Efficiency AM Transmitter Kit › External Option
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All the interest in connecting the external loading coil antenna to the AMT5000 came as a big surprise to me. One prime objective in the design was to eliminate the need for the external loading coil. The option is there, but it isn’t covered in detail in the manual. The web page: http://www.sstran.com/pages/sstran_buildant.html is so far unchanged and it only describes tuning for peak as is done for the AMT3000.
To use the external base loaded antenna with the AMT5000, the jumpers related to tuning should be set as follows:
Jumper S2 bypasses the toroid. Jumpers S12 and S13 bypass the small inductors used for tuning below 1350 kHz. Jumper S1 should be open so the big trimmer capacitor C2 is not connected. C1 (6 pf) trimmer remains connected, but has no effect on tuning with the base loaded antenna.
The base loaded antenna capacitance is fine tuned by means of the length adjustment portion of the base loaded antenna.
To tune the base loaded antenna, adjust the tap point and the antenna length to get the highest peak as indicated by the voltage across the “RF INPUT CURRENT” test terminals. The equivalent to “adjusting C1 one full turn clockwise” is to lengthen the antenna slightly to add about .7 pf. Calculations show the required length increase adjustment is about 3 inches when using 1/2″ copper pipe.