"Owen Duffy" wrote
Yes, but the trap (which is a parallel tuned circuit) doesn't need
to
be resonant in one of the operating bands, and there are reasons for
choosing resonance other than at an operating frequency. For
example,
you can design a 40/80 trapped antenna that uses a trap resonant
around 6MHz.

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Use program NOTATRAP. The parallel tuned circuit is not a trap at
either of the operating frequencies. Its resonant frequency lies in
between the two operating frequencies. The two operating frequencies
do not necessarily have to be harmonically related.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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