D'OH...of course, I should have thought of that with the inductors.
However, I am seeing discrepancies on capacitors, as well. For example, a
good quality 5kv mica, rescued from a salvaged broadcast transmitter, has
measured 2200pf (it's rated value) at 500kHz, about 1900pf at 1MHz and 1700
pf at 1.8MHz. That certainly has me puzzled.
Let's see if there's a response that rates another D'OH :>)
On Tue, Mar 30, 2010 at 4:51 PM, Carl <km1h@jeremy.mv.com> wrote:
> 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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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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>
--
Jack, W6NF
Silver Springs, NV
DM09ji
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