MFJ and accuarcy should not be used in the same sentence.
Carl
KM1H
----- Original Message -----
From: "Ryan Foster" <foster.ryan@gmail.com>
To: <amps@contesting.com>
Sent: Wednesday, March 31, 2010 12:06 PM
Subject: Re: [Amps] LCR meter.
I don't remember the exact results, but my mfj-259 was well off from
my cheap chinese lcr meter, and that was always within 2% of a
borrowed good B&K.
I have never trusted the mfj analyzer to do anything more than get me
in the ballpark. After that test I sent it back to them to be
calibrated even though it was new and they sent it back saying it
calibrated. The part that really lets me down is that is doesn't even
compare with my el-cheapo Chinese meter that was something like $30...
I have yet to try to calibrate the 259 myself though, maybe I just
need to have someone I can trust to do it right calibrate it ;)
--Ryan w8cya
Don't mean to hi-jack, but does anyone remember the formula for filter
caps for power supply design?
On Wed, Mar 31, 2010 at 11:23 AM, Jeff Blaine AC0C
<keepwalking188@yahoo.com> wrote:
> Jim,
>
> My question is to the fundamental accuracy of the MFJ vs. the effects on
> calibration variation. Is the MFJ really this inaccurate, or is the
> accuracy in your case atypical. It would be interesting if someone else
> could do a controlled test with the MFJ vs. a lab type unit (well, a unit
> of
> known capability).
>
> I only have the AADE meter here in are the Fo there is variable; as well
> as
> the MFJ.
>
> 73/jeff/ac0c
>
> --------------------------------------------------
> From: "Jim Thomson" <Jim.thom@telus.net>
> Sent: Wednesday, March 31, 2010 6:06 AM
> To: <amps@contesting.com>
> Subject: [Amps] LCR meter.
>
>> 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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>
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--
"If someone has a gun and is trying to kill you, it would be
reasonable to shoot back with your own gun." -- The Dalai Lama, May
15, 2001
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