----- Original Message -----
From: "Will Matney"
Sent: Tuesday, August 08, 2006 8:19 PM
Subject: Re: [Amps] grid resonance
<Also, concerning the so-called comparison by Coilcraft, I
didn't want to sound biased so I did some research to prove
my point.
Will,
It appears you are missing the entire point of the coilcraft
article. That article's primary focus is the test equipment
MUST read the component accurately at the operating
frequency. This is because as frequency is varied the
characteristics of the component also vary.
Missing this very important point often throws people for a
loop. Many people assume a 200pF capacitor is 200pF on every
frequency and a 10uH inductor used on 20 MHz can be measured
at 1hHz or 100kHz accurately. The component really has to be
measured at the operating frequency. That was CoilCrafts
main point!!
As for the equipment you listed:
<<
HP 4191A
4-1/2 digist
1 MHz to 1 GHz
Requires special test fixtures per HP spec sheet
3 ppm accuracy
"'evaluation' of LCR components".
Same functions as the HP 4192A except higher test
frequency.>>
That's not entirely correct. The 4191A does not require
users to calculate anything. It reads inductance and
capacitance value directly along with Q and a dozen other
parameters.
http://www.testequipmentdepot.com/usedequipment/hewlettpackard/impedanceanalyzers/4191a.htm
<<
Boonton 62AD Inductance Meter (3-1/2 digit)
Two wire measurements
1 MHz oscillator.
0.001 to 2000 uH measurement by manual.
Scale is 2 to 2000 uH.
0.5% accuracy
Model 62AD measures equivelant series inductance. Q's given
are the result of series resistance. If loss appears in
parallel with the test speciman, the 62AD will read the
equivelant series inductance, IE; a 10 uH with a Q of 1,
owing to parallel loss will measure 5 uH which is the
equivelant series inductance.>>
Look at::
http://www.testmartdirect.com/sp.cfm/LCRIMP/BON/62AD.html
It has a maximum frequency of 1MHz, an accuracy of 1.5%
It reads only **equivalent inductance**. It has very
limited utility unless you want to measure the equivalent
value of an inductor at low frequencies. You won't know how
much Q is affecting the inductance because it does not break
the complex impedance out. It's better than reading an
inductor on your multimeter, but certainly not good for HF
or VHF inductance or complex impedance at any frequency.
That was CoilCraft's reason for not using that particular
device.
All of the equipment you listed is almost useless for
reliable HF or VHF impedance measurements. That's what
CoilCraft was trying to get across.
1.) The test gear has to be accurate
2.) It has to measure at the operating frequency of the
component
3.) It has to normalize out stray impedances
It's very important for everyone to understand the basic
three things above That was CoilCrafts point.
If there was a way to know what was going on without buying
a network analyzer and an impedance test set, I'd have spent
the money on something else!
73 Tom
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