Date: Tue, 30 Mar 2010 19:21:27 -0700
From: "Jack/W6NF" <vhfplus@gmail.com>
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.
### I tried using the inductance measuring capability of the MFJ-259B.. with
dismal
results. A 10 uh commercially made roller inductor, wound with 1/4"
tubing... measures
exactly 10 uh on my B+K 875-B lcr meter. Same deal on my 50 uh roller. When
the mfj
was used, the same coil measures a LOT less than 10 uh.... as low as 5
uh.....depending on
what freq the mfj is on. Even with the mfj set to 1.8 mhz.... the same coil
is way < 10 uh !!!
## If I design a simple PI net for a tube amp using GM3SEK's software.. and
it spits out
various values for C1... L... C2.... and then build it, using the B+k
875B.... everything comes out
dead on. And that's using a resistor between anode and chassis, to
simulate plate load Z....
[and mfj on output of C2]. Tune and load tweaked till mfj reads 1:1 SWR.
## If instead, the MFJ 259 is used in it's inductance measuring mode, to tap
the coil for the various
bands... the inductance, comes out on the HIGH side vs the 875B. What
happens, is the C1 and C2
caps both have to be DECREASED in value to compensate for the too high uh used
on each band.
This of course, results in decreased loaded Q.
## The mfj inductance measurements are just the opposite of the results in
the above tabulated
chart, which used a network analyzer. The mfj-259 shows lower uh values.. as
freq goes UP.
## the B+k 875A/B uses 1 khz for the measuring freq. I measured some
other commercially made
coils with it.. and the 875 is dead on with the stamped value of the
commercial coil.
## OK, now maybe the commercially made coil maker used a similar lcr meter to
wind his coils with.
Now if the coils are actually out to lunch in value... and a 10 uh coil is
actually 6 uh on the mfj-259...
OR is actually way higher than 10 uh per the network analyzer above....
then the give away/ proof
would be that the tune + load caps would be WAY off value from the spread
sheet.
## well, the tune /load / coil measurements are dead on.. when the 875A/B
is used.. and compared
to the PI spread sheet. All other test gear throws the pi net way off.
## I checked a LOT of vac caps with the 875.. and also stuff like HEC
ht-50-58-59 TX doorknobs, cardwell
air variable tune and load caps, broadcast variables, HV lytics , etc. Even
tried plane jane coax , and measured
pf between center conductor and braid... and it's all dead on. If I want a
screw up.. either the mfj-259 or the network
analyzer used in the above example will do the job of messing things up.
## we also used the 875 to build all the various tuned inputs over the
years, both the type that have 5-9 x
individual tuned inputs.. and also the tapped coil + 2 x broadcast variable
types. The LC networks were also
built using the 875 [ used to stack either 2 x identical yagis.... or 3 x
identical yagis] Ie: 50 ohms in... and either
25 ohms out.. or 16.66 ohms out. We used Bing's Rf software to design the
various LC networks, and then used
the 875 to build em. They came out dead on the 1st time round.
##Until I find something that works better, which is unlikely, I'm going to
stick with what I know currently works.
This is for 160-6m stuff....... nothing higher than 6m.
later....... Jim VE7RF
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