Q&A
■ WITH RUSSELL KINCAID
In this column, I answer questions about all
aspects of electronics, including computer hardware,
software, circuits, electronic theory, troubleshooting,
and anything else of interest to the hobbyist. Feel
free to participate with your questions, comments,
or suggestions. Send all questions and comments to:
Q&A@nutsvolts.com
WHAT’S UP:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
Solar Controller ✓
● DSL Carrier Detector
Hobby Motor Speed Controller
✓
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COMB GENERATOR
REQUEST
QI found your article on comb filter design to be most interesting! I would like to inquire if you might
have a circuit for a comb generator?
I’d like it to have equal amplitude
marker signals spaced 100 KHz
apart, all the way up to 30 MHz. This
test generator has multiple uses for
calibrating receivers, scopes, etc. Any
chance that you might be able to
come up with a schematic?
— Harry Weber
AA comb generator is made by generating narrow pulses at the comb spacing frequency. The narrower
the pulse, the wider the range of the
comb, but the amplitude also reduces.
I arbitrarily set - 60 dB as the useable
limit which puts the comb range to
about 30 MHz. My circuit is in Figure
BANDPASS FILTER
REDESIGN
QRecently, I asked if the bandpass filter that was published in the December ’09 issue (page 25) could
be redesigned to 420.455 kHz. The
original filter was 200 kHz;
remember that I am working with
vacuum tubes.
— C. Kendrick Sellen
AThe original design was a top coupled type with 18 pF coupling capacitors. Doubling the frequency will
reduce the coupling capacitors but it
should still be buildable; see Figure
3. The inductors are 283.6 µH and
can be made by 40 turns on
RadioShack 273-104 RF choke core
using whatever wire you have handy
that fits.
SOLAR CONTROLLER
QI have only received a couple of issues of Nuts & Volts and enjoy your Q & A section. Therefore, I
thought you might be able to help
■ FIGURE 1
22
September 2011
■ FIGURE 2
