1)Yeah, if you call 9.99 to 10.09 anything ! And then you DON'T even guess
how much stray inductance you added when you soldered it in with unknown
length pigtails!!
2) Rauch is right! That , when you hit series resonance, reactances add in
series opposing and cancel. that how you get a trap. The effect , though, is
pronounced only close to resonance.
3) when you compress a coil you increase the self inductance, but also the
self resonant frequency.
3) could you please explain to us munchkins what you mean by the last
statement?
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Jim Thomson
Sent: Thursday, April 01, 2010 1:15 PM
To: amps@contesting.com
Subject: [Amps] LCR meter
Date: Thu, 1 Apr 2010 09:32:42 +0300
From: "Alex Eban" <alexeban@gmail.com>
Subject: Re: [Amps] LCR meter.
The AADE instrument is more than adequate for all practical purposes. It's
nice to have variable frequency option, but in any case, at the higher
frequencies, the influence of unpredictable strays in the circuit becomes so
strong, that frequency dependent variables in the component cease to be
relevant. These unpredictables strays make any accuracy over a few percents
superfluous.
BTW, another very adequate instrument is the Autek RFxx series at half the
price of an MFJ, with variable frequency AND reactance sign.
Alex 4Z5KS
## bottom line is.. when a 10 uh coil measures anything other than 10 uh,
you will screw up your pi-net, LC networks etc, guaranteed.
## rauch claims the stray C [Xc] between turns of a coil will negate
from the coil itself [Xl]. If that's the case, then why is it, that when
I compress
the turns together on any tubing coil, the uh goes WAY up ?
## as a side note, that's what F-12 uses on their infamous tornado
drive, to get their 80m rotary dipole's and 80m yagi's, from ssb band..
to the cw band, and no rolling contacts, like in a roller inductor.
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).
## IF I use a MFJ-259 to tap a tank coil, at say 4 uh... and the same
tap shows as 6 uh on my 875B, now I have a discrepancy. The GM3SEK PI
spreadsheet
will depict values for C1, L, C2. IF the spread sheet wants 4 uh,
and XXX for
C1.... and YYY for C2..... and the mfj is used to tap the coil at 4uh....
then what happens is the C1 and C2 values [after tweaking for resonance on
the standard test jig] are way on
the LOW side. The coil is in reality 6 uh.. and not 4 uh !
## Now if the 875 is used to tap the coil to 4 uh, then both the C1 and
C2 caps [ both
jennings ceramic vac caps] come out dead on VS the Pi spread sheet.
The point here is,
sure, there might be variations in measuring uh on your favorite test gear,
but the giveaway is when the same coil is used in a tuned circuit, like a
PI net..... or in a LC network. IF I use the MFJ to tweak the tubing coil
in the LC network, used for 50 ohms in.. and 25 ohms out [ to handle
2 x 40m yagi's] the LC network is a mile off. [ caps used are paralleled
HT-50/58 doorknobs]...
and ditto with the 50 ohm in, 16.66 ohm out LC network, [used for 3
x 20m yagis].
## I can't rely, or use the MFJ to design any of these networks, it
doesn't work, plane and simple !
I also used the B+K 875 to wind the tubing coils used for making
hairpins for the 160 vertical,
80m rotary dipole, 40m yagi, and 20m yagi. When I require precisely, a
say .8 uh coil for a hairpin
tubing coil, I don't want a ,9uh.. or a .6 uh..... none of which will work
anyway. I use stokes book to get
the tubing coil winding [L to diam ratio I'm using] into the ballpark.
Then tweak with the 875.... then install it,
then flat swr right off the bat. Plan B is.. the coil is compressed
/expanded till flat swr results. Coil is then
measured on the 875... and it' measured value is dead on VS Bings RF
software network analyzer
spreadsheet I use to design LC networks. The hairpins also come out dead
on.
Nothing more frustrating than tearing your hair out with a mfj, that flat
out can't measure pf and uh.
I also bought the pair of mating 'grid dip coils' for the mfj-259b.
Totally useless as a grid dip meter.
I can't grid dip anything with them, even simple 10uh coil and parallel
cap on the bench.... and neither
can any of my associates. Even rauch sez they don't work.... so don't
waste your money.
The 259 is a glorified swr meter, that's handy on top of a tower.. and
that's about it.
Jim VE7RF
I only have the AADE meter here in are the Fo there is variable; as well as
the MFJ.
73/jeff/ac0c
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