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Trap question

Jan 10th 2018, 11:25

jtabatch

Joined: May 27th 2017, 18:34
Total Topics: 0
Total Posts: 0
do the trap windings , besides resonating at a particular frequency, also add length to the antenna outside the resonant frequency , and if so how much ?

Thanks

Justin KB2ZVD
Jan 12th 2018, 09:54

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

No, that is an incorrect way of looking at it.

http://hamwaves.com/antennas/inductance.html
Assume a 5 turn 37mm diameter coil made out of 2mm diameter wire.

With a length of 74mm the inductance is 0.56 uH. With a length of 37mm the inductance is 0.70 uH One would expect the change of inductance to change the effective shortening effect on the antenna. You can see this by making a Variable Frequency Oscillator using an air wound coil as one of the frequency elements and squeezing the turns together.

www.eznec.com
The demo program may be adequate for designing what you want.

https://www.smeter.net/antennas/tuned-trap-antenna.php

Zack Lau W1VT
ARRL Senior Lab Engineer

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