Coil Q, with form/without
Subject: Coil Q, with form/without
Date: Wed, 12 Apr 1995 14:18:57 -0400 (EDT)
>Received: from ohstpw.mps.ohio-state.edu by ns-1.csn-dot-net with SMTP id AA29000 (5.65c/IDA-1.4.4 for <tesla-at-grendel.objinc.COM>); Wed, 12 Apr 1995 13:05:16 -0600
Here's some results reguarding Q factors of the formless coils I've made
4" dia 7" long tight wound with 25 gauge enamel magent wire
2 coats of celluose nitrate based laquer
Form: 4" PVC (not baked) approx 1/16" wall thickness
The Q was estimated by finding the center frequency fo, and the 2 half
power ( .707 amplitude) points, fo+df and fo-df. Then one gets Q=fo/(2df).
The coils were "base" driven with a signal generator and the loading of the
50ohm generator impedance was adjusted for by keeping its output voltage
fixed a some small value (1 volt). The ouput of the coil was monitored with
an o'scope probe without actually attaching the probe to the top of the
coil. The probe was mounted a few inches above the coil for very loose
capacitive coupling through the air. (I didn't want to load the coil with
the scope probe).
With PVC form:
2df = 3.6 kHz
Without PVC form:
2df=3.3 kHz Q= 240
%Difference = 9%
**********Suprisingly small difference!
Ferrite Chunk stuck in the middle of the coil (no PVC)
2df= 3.2 kHz Q= 237 lowered the frequency without
Small cup (styrofoam) of water placed in the center of the coil (no PVC):
2df= 3.5 kHz Q= 220
The next thing I'd like to do is get some different wire insulations to see
how big an effect they have on Q.