TTers,
I am rebuilding a long neglected HyGain TH5DX. The (10/15/20) driven element
and the (10/15/20) director have been cleaned up, the nesting sections cleaned
and reassembled (according to the drawings) with NoAlOx. There is DC continuity
from one end to the other of these elements (trap coils intact).
The first attempt to check the driven element (on saw horses - yes too close to
the ground) showed resonances way below the bands.
BUT I thought to check the "resonances" of each of the 4 half elements by
configuring each as a ground mounted vertical.
There are about 24 random length radials. The results are puzzling.
Both Drivens min SWR (1.2 - 1.5) at 13.4, 19.8 and 24.6 MHz.
This set of values is quite similar to what I got with the driven pair
horizontal on the saw horses.
Both Directors min SWR (1.2 - 1.5) at 13.6, 20.0 and 25.3 MHz.
Not messing with the Reflector until I find an answer.
Question 1:Does the min SWR when configured as a triband Yagi depend on the
interaction of the driven and the parasitics? In other words, is it erroneous
to expect to see the individual elements show dipole like behavior (somewhere
near the proper band)?
Question 2: The overall behavior could be explained by the trap capacitors or
inductors changing value. But would they change in such a way that the pairs
would test the same?
TIA for any help.
Larry K3VX
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