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On their web site, SSTran states very clearly that the wire antenna delivered with the AMT5000 is intended to be used indoors – they recommend using a whip or pipe antenna outdoors (which is where the testing was conducted) and they even have references to the building of a base loaded antenna (the internal tuning circuitry can be bypassed to use such an antenna).
A base-loaded, constant-OD, linear conductor with a physical length of 3 meters needs the following inductance to resonate on 1640 kHz, the test frequency used in the Challenge:
OD, inches………AWG……Inductance, µH (approx)
Note that that radiation resistance for a given conductor length and frequency is independent of the OD of the conductor.
As no mention was made in the text of the Challenge report that the AMT5000 antenna system was not tuned to resonance when tested, we’ll have to conclude that it was tuned to resonance, regardless of the OD of the antenna wire that was supplied with the AMT5000.
LESS inductance is needed to resonate conductors having large(er) OD, so it is likely that the internal loading coil in AMT5000 would be able to resonate an external whip antenna, given enough taps on that coil.
Probably the fact that the AMT5000 internal coil can be bypassed for antenna systems using an external loading coil accomodates those who might use a loading coil having less r-f loss than the one in the AMT5000. Maybe PhilB could comment on that…?
For other conditions the same (physical geometry, resonance, power at the coil output, ground connection loss, etc), it would not affect the results of the Challenge whether the AMT5000 used a wire conductor of 14 AWG or even smaller or a 3-m whip as its antenna, as long as the wire was stretched out to be linear and in the vertical plane, and was not affected by nearby conductors.
1. The internal loading coil in the AMT5000 can be used to resonate an external 3-m whip, assuming tap resolution permits setting it to the needed inductance, and
2. The performance of the AMT5000 in the Challenge cannot necessarily be attributed to its use of a wire antenna rather than a whip.