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K0CQ > TECH 02.07.07 03:06l 17 Lines 817 Bytes #999 (0) @ WW
BID : 37040_W0AK
Read: GUEST OE7FMI
Subj: Re: 6m VHF Filter Design
Path: DB0FHN<DB0MRW<DK0WUE<DB0RES<ON4HU<ON0BEL<N4ZKF<KQ0I<W0AK
Sent: 070701/2338Z @:W0AK.#CIA.IA.USA.NOAM #:37040 [Des Moines] $:37040_W0AK
From: K0CQ@W0AK.#CIA.IA.USA.NOAM
To : TECH@WW
What is happening is that the coils are going half wave resonant
at 280 MHz with the 6m tuning C doing a slight bit of series
tuning. The tab at the middle of the coil is at a high impedance
so it takes little capacitance to change the resonance at that
high frequency so the two don't match. There can be more such
resonances where the wire length of the coil reaches other odd
multiple and even multiple of a quarter wavelength. The odd
multiples will be loaded by the tuning capacitor, the even
multiples will mostly ignore the tuning capacitor. All coils do
this, mostly based on the length of the wire with that resonance
showing up whether the wire is straight or wound into a coil.
73, Jerry, K0CQ @ W0AK.#CIA.IA.USA
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