[TowerTalk] MFJ259B

[Rod Elliott]

I agree with Jim re the older MFJ259. I've had mine about 5 years. I use it 
daily for tuning a transmatch on an antenna fed with ladder line. It has 
seen lots of action including several Field Day operations. It's SWR and 
frequency calibration have remained perfect, although over the years the R 
reading has slipped from 50 to 40 ohms at SWR=1:1. But I don't care... the 
R value is not needed for practical antenna tuning.

Re calibration standards, I believe an easier way is to solder two 100-ohm 
1/4 or 1/10 watt resistors in parallel into a PL-259. With the smaller 
resistors you can achieve zero lead length between the pin and the solder 
holes in the shell, thus minimizing inductance. This way you get a compact, 
stable reference calibrated to 50 ohms plus or minus whatever the tolerance 
of the resistors (usually 1% these days). They show negligable reactance to 
well above 100 MHz. And, of course, they mount conveniently right on the 
MFJ259.

I've made these in 0-ohm, 50-ohm, 25-ohm, 100-ohm sizes. The 0-ohm is made 
with a very short piece of 12-AWG copper wire instead of resistors. Using 
the 25 and 100-ohm sizes should give a SWR reading of 2:1, so along with 
the 50-ohm unit, you get a good idea of the linearity of SWR readings below 
that point.

These standards tell me that my MFJ259 has stayed in excellent SWR 
calibration over the years, regardless of the aberrations of he R reading.

73
Rod Elliott VE3UW / VE3IRF


At 06:29 08/30/03 -0700, you wrote:
>I have the older version (without the R and X display.. just frequency and
>the two analog meters) and I've found it's actually quite rugged (i.e.
>bouncing around in a milk crate in the back of the car). It's not a
>metrology grade piece of lab gear so don't expect gnat's eyelash precision.
>The battery holder does come loose and rattle (clunk) around a bit.  The
>frequency accuracy over temperature isn't all that wonderful, but seems to
>be fairly consistent at the same temperature (so, if it's been sitting in
>the sun in a hot car for 5 hours, watch out).  You can always check it by
>zero beating against WWV.
>
>You might open it up and see what might change if it's banged around?  On
>mine, there aren't any components that would be obviously bent or moved by
>shock loads or vibration.  Perhaps a few trim pots, but they're blobbed with
>lacquer.
>
>You could also make yourself a few calibration standards that you could
>periodically check.  A piece of coax with an open and/or short at the other
>end makes a dandy reference, and if you treat the coax nicely, it would
>serve quite well.  Doesn't even have to be a particularly high quality coax,
>just stable.  A piece of RG58 or RG59, loosely coiled (so the dielectric
>doesn't cold flow) should work.
>
>Jim, W6RMK
>----- Original Message -----
>From: "Peter Sundberg" <sm2cew at telia.com>
>To: <towertalk at contesting.com>
>Sent: Saturday, August 30, 2003 5:53 AM
>Subject: [TowerTalk] MFJ259B
>
>
> > A friend of mine told me that the MFJ259B can easily go out of calibration
> > if it is banged around or not handled carefully. Anyone with experience of
> > this, and what type of error is likely to occur under such conditions ?
> >
> > Just bought an MFJ259B new, and since I heard this I am handling it like a
> > newborn baby... :-))
> >
> > 73/Peter SM2CEW
> > www.qsl.net/sm2cew
> >
> >
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
> >
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>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless 
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
>any questions and ask for Sherman, W2FLA.
>
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