On Thu, 2 Jan 1997 16:37:55 -0500 W8JITom@aol.com writes:
>Hi Carl,
>Tuners are the most unclearly rated products on the amateur market
today,
and will remain so until everyone demands a change in
>the meaningless transmitter input power rating system.
>
>My secondary point is the roller for the 989 has been greatly improved,
and
>has higher Q than the Cardwell roller AND no series resonances at the
>upper end of HF.
Hi again Tom, here we go with phase 2. My original reply was in response
to 4X1AD's MFJ query which was on many reflectors, not just 160M. It was
not I that decided to broadcast a reply to this reflector. Indeed; my
response was to your, IMHO, very biased post.
If I am incorrect on your MFJ employment status, I am sorry.The true
picture is between you and the IRS and Martin F. Jue. Perhaps you can
then enlighten us as to why any serious technical/engineering problems
phoned into Ameritron/MFJ are always referred to you. The Mississippi
staff can barely answer the telephone, much less give serious technical
help. I am also just going by your own statements here, on various
subjects over the months, as to your past/present involvement with
Heath; Dentron; Ameritron; MFJ; etc.
I will not belabor the Reflector on your various T Match assertions,
they have been well documented and are essentially correct.
However, I do believe that your former involvement with Heath, Dentron,
etc. had possibly a bit to do with the current misconception of power
ratings. Since that is where it seemed to have mushroomed from in the
70's. "Innocent" engineering statements transformed to advertising
hype, etc. Continued by MFJ today. At least Dentron didnt try and
copyright every word or phrase.
>2.) A change from # 12 to # 10 wire in an inductor results in a minor
almost
>undetectable) change in Q. Especially when the inductor is less than
optimum
>in L/D ratio and all other physical design attributes.
>In an optimized air core inductor, maximum Q generally occurs with wire
>between number eight and number 14 AWG. Make the wire too big and Q
drops,
>make the wire too small and Q drops. Q is more radically affected by
the
>turns spacing, L/D ratio, insulation in the areas of concentrated
electric fields, and spacing to other metalic objects (in particular to
end plates) than by wire size.
At no point did I discuss or even mention Q. The MFJ Delrin core was a
total disaster, period... Flame City, etc. . At 1.8MHz I doubt if the Q
difference between a well processed ceramic core, or an air wound one of
otherwise equal parameters, would make much, if any, difference. I would
certainly welcome you sending me a "new" MFJ coil to evaluate on some
nice HP test equipment. BTW, is MFJ going to issue a recall to all the
customers stuck with the old garbage??
By increasing the size of the wire and contact roller area from #12 to
#10 the benefit is in current capacity. A major concern of low impedence
160M antenna users. Not Q, Not voltage, just pure RF power.
Cardwell/Multronics has over 60 years experience in understanding the
relationship between size, diameter, etc in coil design. They are the
premier supplier to the commercial world at up to 50KW+ and I dont think
that they need a primer in basic coil theory.
>
>3.) Silver plating does almost nothing to change loss in a copper HF
>inductor, except as it reduces contact loss due to oxidation.
Correct except that a silver plated roller riding on a silver plated coil
will have less long term problems compared to dissimilar or inferior
metals. The contact resistance, and therefore heating, arcing, pitting,
will be at a minimum.
There would be almost no measurable change in HF Q because the skin
>depth is
>much deeper than the practical plating depth.
This is not even a discussion issue.
>4.) A tuner can only be optimized only for one impedance range and
frequency
>range. There is a certain optimum value of components and load impedance
that
>allows maximum power handling and efficiency. What works best for a low
Z 160
>load will be unworkable at a high Z load, especially on higher bands.
What
>works best on high bands and/or with high Z loads won't work well in the
opposite
>conditions.
>All tuners are compromises, there is no magic solution. It certainly
isn't as
>simple as changing two wire guages or silver plating, especially since
form
>factor affects Q much more than wire size and silver plating offers
almost no
>improvement at all over a clean copper or tinned copper surface at HF.
My only disagreement here is with the final sentence. Since this whole
thread was centered on the MFJ-989 roller inductor tuner, there is a BIG
difference between "clean copper", etc. Bare or tinned copper would have
a verrrrrrrrry short life on a roller inductor. Do you really think that
Cardwell and others (including OEP) would have spent even a penny on
silver plating if it was not important?
Again, I must congradulate Tom for an excellent response and a superbly
crafted dance around the real issue....MFJ Junk. I wish him a great
year and his unknown employer a profitless '97.
73..........Carl KM1H
>I had to use a four inch diameter AIR INSULATED # 8 roller coil and a
>pair of
>1600 pF variable capacitors to handle 1500 watts normal CW use with a
>25 ohm
>-25 j load to 100 ohm +j10 in my antenna system. These components
>won't allow
>matching above 15 MHz or at impedances above a few thousand ohms, and
>would
>cost someone $1000 in production units.
>
>73, Tom
>
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