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[#11053 - November 2005]
I'm trying to improve WWVB
reception here in Southern New
Hampshire. The problem seems to
be that the internal antenna (tuned
ferrite rod) in the clock can't be
oriented properly where I want the
clock located. I'm thinking along the
lines of a larger, 0.5 X 7. 5 inches,
tuned ferrite rod feeding a FET op-amp, maybe an LF356. Drive a small
audio transformer with the op-amp
output to provide something like an
eight ohm output to feed a twisted
pair feedline. At the clock, use
another transformer and connect it
to an added winding on the original
clock antenna rod. This would allow
placing the antenna in correct orientation, as well as allow selection of
a better antenna location. With the
carrier at 60 kHz, it would seem that
audio components could be used.
I've checked the transformer — a
RadioShack 273-1380 (1K ohm to 8
ohm) — and it seems useful at 60
kHz. My question is, will something
like this work, or is there something
better? Thanks for any help or ideas.
Have you tried a few loose turns
of wire around the ferrite rod and
running the wires out at different
angles? This method might capture
and couple more field to your clock,
and it’s a lot simpler than a powered
amp. Also check out www.select
atenna.com for ready-made signal
boosters.
■Bob Lindstrom, Broomfield, CO
[#12052 - December 2005]
I have some 4559 aircraft landing lights, they are 28 volt 600 watt.
I was hoping to use them for some
concert lighting I do. But, I haven't
come up with a way to power them,
being that I need a 28 volt 21. 5 amp
power supply (I assume AC or DC
will work).
I tried an off-the-shelf standard
home dimmer, carefully setting it
(low) to 12V-15V, but it just blew
the bulb.
Sounds like you had a bad or old
bulb. Running the 28 volt light is no
different than running a 12 volt light
on the old six volt tractors and cars;
it should just be dimmer than at the
full voltage, kind of like when the
batteries are going dead in your
flashlight. However, normally airplane landing lights are only used for
a couple minutes during the landing.
The bulb you have is a 600,000
candle power and the rated average
life in the lab is only 25 hours. I think
you should probably look for a better
light. You also ask if AC or DC
matters, this is a DC only bulb.
■Dennis Matthews, Cameron, NC
[#11055 - November 2005]
I’m looking for a way to temporarily turn off an
aquarium water pump during the feeding of my fish.
I need a circuit where the AC water pump (rated at
120VAC@40W) can turn off for about 10 minutes, then
turn back on again automatically. Ideally, I’d like a
momentary switch that would turn the pump off for
about 10 minutes. I was thinking of using a relay with
NC contacts and perhaps a battery-powered 555 circuit,
but do not know how to design this.
#1 Here is a simple 555 timer circuit, that when you
push the button, it will energize a relay for about 10 minutes. The timing formula is T=1.1 x R1 x C1, so 600 seconds = 1.1 x 1000000 ohms x .000554 farads (554mfd).
The 555 chip that I was working with has a supply voltage range of 5V to 16V, so a 12V wall wart would power
it nicely. You will need a SPDT relay based on the voltage
you pick. I think the schematic provided says the rest.
■Brandon Spivey, Nashville, TN
#2 Ten minutes is a long, long time for a 555 timer, but
a CD4541 programmable timer can do it easily. The
schematic below shows how I think it would work but I
have not built it, so there is no guarantee.
■Russ Kincaid, Milford, NH
#3 To temporarily turn off an air pump or filter for
an aquarium, an On-Delay relay such as Dayton 6X601
(60-900sec delay) or a 5B396 (36-3600sec delay) can be
used. This is in an octal based package and so a base
(part number 5X852) is needed to mount and connect
the relay.
Place the pump and/or filter on the leads indicated
"LOAD," and place a double pole momentary contact
push button across the input (115V power source). When
the relay is first powered up, the time delay period
begins. When the time delay period is done, the relay
allows the load to be powered up. The load remains
January 2006 95
