Marv,
Why sure I am. I just wish I knew where the old one went. I still think
it grew legs one day I had several visiting my workshop. After that, I
couldn't locate it after I went looking. That happened about a year ago
and just so happened you had a copy! =)
I'll say this, the old books had a lot more worth while information than
anything now new in print! About like that amp book just published by
the ARRL. It was touted by ads to be a great piece of work, until one on
here ordered it, and seen it was junk.
Will Matney
PS; I can vouch for Marvs stuff. It was shipped lightning fast, in good
shape, and packed good. I'll sure do business with him again!
Radio WC6W wrote:
Sooooo, using that book I sent you, I see! :-)
On Mon, 27 Sep 2004 13:20:28 -0400 craxd <craxd1@ezwv.com> writes:
I went back and decided to post some texts quoted out of the Radio
Engineers Handbook. I read on and also found a section termed, "Load
Resistors for Absorbing Radio-frequency Power". I'll start first
with
the uses text for the wound resistors then on to the load portion.
"The mica-card, reversed-loop, and figure-eight types of resistors
can
be made to have very low phase angles and are the types used in
radio-frequency attenuators. The mica-card, fish-line, and
woven-tape
types of construction are commonly used in decade resistance boxes
designed to have a low phase angle at radio frequencies,
particularly
for the high-resistance units. The Ayrton-Perry winding is also
suitable
for use at radio frequencies, particularly for resistances up to
several
thousand ohms. The simple bifilar winding is suitable at radio
frequencies only for resistances so low that capacity effects are of
no
importance. The slotted type of construction is used in very high
resistance units where only moderately low phase angle is essential,
as
in the case of voltmeter multipliers".
"Load Resistors for Absorbing Radio-frequency Power.-Resistors used
as
radio-frequency loads, i.e., as dummy antennas, present a
particularly
difficult problem, since here one desires a nonreactive unit capable
of
dissipating appreciable wattage. When the power is in the order of
fifty
watts or less, several satisfactory arrangements are available. One
consists of a bifilar resistance element supported on mica and
mounted
in a glass bulb filled with inert gas, preferably hydrogen". Sounds
like
a bomb to me..LOL (WM). "Another arrangement consists of a mica-card
type of unit mounted between two large aluminum castings that are
for
the purpose of conducting away the heat. Both these arrangements give
excellent phase-angle characteristics".
"When larger amounts of power are to be handled, various expedients
are
used. In most of these, the reactance is eliminated by tuning, and
the
dissipated power is evaluated by a calorimetric or photometric
method,
or by measuring the equivelant circuit resistance at the frequency
involved. Another possibility is to use a metalized type of resistor
immersed in cooling water (1). In this way, the rating can be
increased
to 50 to 80 times that for air, and is of the order of 100 watts per
square inch of surface. The power being dissipated can be determined
from the rate of flow and temperature rise of the cooling water. By
making the resistor the central conductor of a concentric line
shorted
at the receiving end, the reactance at the input terminals can, by
suitable design proportions, be made zero".
(1) See G.H. Brown and J. W. Conklin, Water-cooled Resistors for
Ultrahigh Frequencies, Electronics. Vol. 14, p. 24, April, 1941.
"The bifilar winding has negligible inductance, but the capacity is
relatively large, because the beginning and end of the resistance
are
close together. This capacity effect can be minimized to some extent
by
sub-dividing the total resistance into several bifilar sections, as
shown in Fig. 10h (Bifilar-series)".
Will Matney
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