READER FEEDBACK Continued from page 6
HAPPY WITH HISTORY
I had been a subscriber for a few
years, and my wife let my subscription
expire. So, I went on your website and
re-subscribed. I have since received my
third issue and this month I am especially proud of your great publication
for remembering the history of “The
Triode”and “The Great Pioneers” in our
field. I have been in electronics most all
my life, and at 64 I was beginning to
think no one was interested in its history anymore. I am very happy to see that
you aren’t letting that important history
go down the tubes. Thanks again and
keep up the great work you are doing.
Rene Stover CET
POSITIVE OR NEGATIVE?
Regarding the November 06 article
on the triode, page 69: Regenerative
amplifiers are positive feedback devices,
not negative feedback as stated.The
focus on positive feedback, or regeneration, allowed the skilled operator to get
the most out of the low-gain devices of
the day, but had the over-whelming handicap of instability. The stability problem
was helped a lot with the advent of the
super-regen circuit sometime later.
The really great advances arose
after the focus shifted to negative feedback, which improved stability at the
expense of gain. The claimed invention
of the negative feedback amplifier by
Black (patented 1937) at Bell Labs is by
some accounts suspect. However,
whether Black really invented it or simply was the first to realize its benefits,
the Bell folks lost no time in applying it
to all manner of things. Except for the
essential function performed by oscillators, electronics has mostly depended
upon negative feedback devices since.
FYI ON KITSRUS
In Chuck Hellebuyck’s article on
“USB PIC Programmers” in the October
Nuts & Volts issue, he mentions those from
kitsrus. I have been using two of these.
One has a USB powered programmer
(the K128) that, contrary to statements in
the article, includes a ZIF- 40 socket, as
well as an ICSP. These programmers only
program Flash PICs. The supplied software
is excellent and, together with
the firmware, automatically sets up the
proper programming pins for the many
supported PICs in the 40-pin ZIF.
The only drawback is that the
firmware has not been updated for over
two years and so does not include
support for PICs like the 18F2550 (a
favorite of mine). It does support PICs
such as the 16F88 (another favorite).
This may stem from the death last year
of Peter Crowcroft, principal at kitsrus.
AC POWER ON THE
The Nixie clock on your cover
(Nuts & Volts Vol. 27 No. 10) got my
attention so I bought a copy, my first.
I’ve now read the issue from cover to
cover, and enjoyed much of the content, so please keep up the good work!
The Power Line Frequency Monitor project by Bob Armstrong was of
interest as we tend to take the AC
utility service for granted in this country, and how and why it is regulated was
not clearly described in the article’s text.
Utility companies regulate the AC
power line frequency so that in a given
24 hour period, electric clocks remain
accurate in the long term to within a few
hundred parts per million. This is done
by comparing a clock driven by the AC
utility power against a similar one driven
by a standard of known accuracy (
traceable to an atomic clock standard), as it is
known that the 60 Hz AC power line will
complete 5,184,000 cycles in 24 hours.
Typically, the daytime load on the utility
slows the generators, or operators allow
the voltage to drift downwards to reduce
demand and avoid outages. This also
slows down our clocks. During the night,
the load is much lighter and operators
allow the generators to speed up (
higher line frequency) to sync clocks that use
the power line frequency for timing. There
are short term errors, typically less than
0.5 Hz, which the N&V project displays.
What would have been a nice
feature on the project is an error display,
as we already know the expected
frequency is 60 Hz (or 50 Hz in some
countries), and a fixed display of 60 Hz
most of the time is redundant. How
about a plus or minus percentage
change or PPM (parts per million) display? Also, how about a daily readout
of the previous day’s maximum deviation and the time during the day that hit
the highest and lowest frequency? While
we’re monitoring the AC line, how about
a voltmeter function to record and
display the instantaneous voltage, and
its min and max? I think a multiple (or
scrolling) display of several metrics would
have greatly enhanced this project.
Continued from page 57
NEW MCM CABLE SITE
MCM Cables has launched a new
website at www.mcmcables.com.
The MCM Cables.com website provides
a total cable solution, offering a large variety and competitive pricing on cables
for home theater, computer, networking,
professional audio, and security applications. Features of the website include:
An enhanced search engine to
make finding products easy; Detailed
descriptions for thousands of products; Large product photos to see
product details; Connector diagrams
to make finding the correct cable foolproof; and Enhanced category browse
for easy website navigation.
Available cables include HDMI,
DVI, Component, and S-Video for
home theater; USB, Firewire, Cat5
and Cat6 for computer or networking;
BNC and coax for security; XLR and
snake cables for professional audio, as
well as many others. Bulk cable is also
available on the site.
Whether installing a new home
theater system, whole-house audio system, security system, setting up a wireless network, or merely connecting
cable to a TV, www.mcmcables.com
has many options. NV