It would be interesting to see what a 1kHz instrument would read with that
same core.
A 2 mix is a poor performer at 50kHz and you might be reading true
inductance.
Also at 30 mHz it only takes a few turns in the typical input network. At 6M
the 6 mix is the core of choice.
Carl
KM1H
----- Original Message -----
From: "Larry Benko" <xxw0qe@comcast.net>
To: <amps@contesting.com>
Sent: Tuesday, March 30, 2010 1:30 PM
Subject: Re: [Amps] LCR meter
> Here are some real numbers I just measured on a network analyzer
> calibrated at the plane of the core being measured.
>
> Core = T94-2 powdered iron u=10, 22 turns #18 occupying about 80% of core
>
> Msmt. freq. L(measured)
>
> 50KHz 3.06uH
> 100KHz 3.86uH
> 200KHz 4.53uH
> 500KHz 4.51uH
> 1MHz 4.50uH
> 5MHz 4.50uH
> 10MHz 4.58uH
> 20MHz 4.89uH
> 30MHz 5.52uH
> 40MHz 6.80uH
> 68.1MHz parallel resonant freq.
>
> As can be seen frequencies above 10MHz show the beginning effects of the
> parallel resonance and low measurement frequencies underestimate the
> inductance by a significant amount. Also mounting the inductor in a
> metal box will reduce the inductance. I suspect if the measurement freq.
> was 1KHz the values would be even lower. I always measure near the
> frequency I intend to use the inductor at and if possible with the
> inductor mounted in the enclosure. Then calibrating to the inductor
> plane gives the "real" inductance and filters and matching networks come
> out as predicted.
>
> 73,
> Larry, W0QE
>
>
>
>
> Vic K2VCO wrote:
>> On 3/30/2010 4:47 AM, Jack/W6NF wrote:
>>
>>> I have used an HP LCR meter at work but never paid any attention to the
>>> frequency at which the measurement is made. I wonder what discrepancies
>>> in
>>> measurement values of L and C could be encountered if one measured at
>>> various RF frequencies, and why they might occur. I have seen such
>>> discrepancies, using a popular antenna analyzer, even though I was
>>> careful
>>> not to introduce sources of error, like lead lengths.
>>>
>>
>> If the coil has a ferrite or iron core of any kind, the inductance varies
>> a lot with
>> frequency. Inductors with cores must be measured near the operating
>> frequency. And in
>> general, as you raise the frequency the various stray capacitances and
>> inductances in the
>> device under test become more significant.
>>
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