[Amps] Inductance Variations

[Mike]

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