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[Amps] Inductance Variations

To: amps@contesting.com
Subject: [Amps] Inductance Variations
From: Mike <k4gmh@arrl.net>
Date: Tue, 08 Feb 2005 00:00:53 -0500
List-post: <mailto:amps@contesting.com>
Hello,

Couple of questions regarding inductance - measurement and use.

Identifying the tap positions on an inductance w/ an Autek RF-1 for use in a Pi-L tank circuit and noticed a marked difference when the unused portion of the coil is shorted. Example, 12 turn coil has a total inductance of 15.0 uH (@ 4.8 MHz measurement frequency, w/ 517 Ohm impedance). Six turns inductance is 5.9 uH (@ 9.0 MHz w/ 392 Ohm impedance) w/o short on the unused portion of the coil; same six turns w/ the unused portion of the coil shorted is 4.32 uH (@ 9.0 MHz w/ 275 Ohm impedance). Which method, shorting or non-shorting, should be used for determining where the taps should be placed on the coil?

Next question is related in that tank circuits in most commercial amplifiers use a shorting switch to select the inductance values. Where as, the amp. circuit designs in ARRL Handbook, etc. use a non shorting switch. Which is the better (electrical) switch method - shorting or non-shorting?

        73,
        Mike, K4GMH


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