[TowerTalk] BOUNCE towertalk@contesting.com: Approval required: (fwd)

[Bill Fisher - W4AN]

Date: Tue, 17 Nov 1998 07:25:03 -0500
From: "w8ji.tom" <w8ji.tom@MCIONE.com>
Subject: Re: [TowerTalk] ANTENNA MATCHING
To: wa3gin@erols.com, towertalk@contesting.com
Reply-to: w8ji.tom@MCIONE.com
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Hi Dave,

> capacitance. My operating preference on 75m falls on just a few
> frequencies. With many very strong signals on the band I'd like to
> adjust the tuner for the highest possible "Q" hopefully adding some
> selectivity to my old transceiver (enhanced bandpass filtering).

The Q of the tuner will never get high enough to improve receiver
performance, unless the receiver has front-end overload problems from
signals several dozens of kHz away. 
 
> o  Is it correct to presume the transmitter side of the tuner does not
> play a major part in
>     adjusting the relative "Q" of the circuit?

Every reactive component in the system adds Q to the tuner. Most formulas
used in Amateur text (like the one for amplifiers where tank Q equals Rp
over Xc1) only count one component, and calculates Q lower than it really
is. That misleads people into thinking one component sets the Q of a
system. 
 
> o  Is it correct to presume settings of  minimum inductance while using
> the maximum
>     antenna matching capacitance will yield the highest "Q"?

Not in the common C-L-C T network. Minimum L is minimum Q. A conventional
pi is the opposite.

Tuner loss increases and power handling decreases with more L in a
conventional T network. If you want to arc or burn-up a common T network
tuner (and increase Q), reduce the C and increase the L.

73 Tom


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