62 October 2017
READER - TO - READER TECHFORUM
Circular Polarizating Antennas
I’m an avid VHF/UHF listener,
and have always used a vertical
non-directional antenna for receiving
signals. However, after buying a
circular polarizing filter for my
Nikon, I realized that RF can be
circularly polarized as well. How can
I tell whether a signal is vertically or
circularly polarized, without investing
in a circular antenna? Do you know
of any resources for how to construct
circular polarized antennas?
#10171 Ed Moreno
My roommate keeps a piece of
masking tape over the lens of the
camera on his laptop. I think he’s
paranoid; he says he’s being safe. I’d
love opinions about which one of us
#10172 Neil Nelson
Temperature Rise Of A Heatsink In
An Amateur Radio Transceiver
I recently did a “tear-down” of
a Baofeng BL- 8 battery eliminator
(for use with a UV82 dual-band
tranceiver; see www.hamguyparts.
com, articles). The tear-down revealed
that the eight volt battery eliminator
actually used 2X L7808CV TO-220
voltage regulators connected pin for
pin in parallel, which is somewhat
Both regularors were mounted to
a common small ( 20 x 34 x 1.8 mm)
aluminum heatsink and all enclosed
within the plastic housing which was
sized to resemble the battery it was
In the ideal case, each regulator
would carry 1/2 the total maximum
current taken by the transceiver,
which is approx. 0.775 amps. Each
regulator produces a nominal 8.0
volt DC output and has to dissipate
approx 4. 6 watts of heat. The thermal
resistance of the TO220 package is
5°C per watt, junction to case (or
They are mounted dry, which
adds another 1°C per watt for
mounting the base to the heatsink.
Q1: What is the temperature rise in
the aluminum plate?
Q2: Since there is no direct path to
air, what further temperature rise may
take place inside the plastic housing?
#10173 Don Dorward
Should I Switch?
I’m torn between using 3. 3
and 5.0 volt components on my
microcontroller projects. Many
people seem to be moving to 3.3V,
but components don’t seem to be as
readily available as 5.0V components.
What are the advantages and
disadvantages of each?
#10174 Tony Sigler
New Brunswick, NJ
[#6173 - June 2017]
Sequential Turn Signals
The simple way to do an
automobile three-light sequential turn
signal is to let the blinker turn on bulb
#1 and then the circuit will do #2 and
then #3; not a problem.
The problem is the brake lights
that use the same filament in the
bulbs. Hit the brakes so left and right
will sequence once then stay lit, unless
you hit the brake again.
Same with turning. One side
sequences and if you hit the brake,
the other side will sequence once and
then stay lit while the turning direction
is still sequencing. However, if you hit
the brake, both sides will sequence
once and then stay lit.
Proper function can be
accomplished because aftermarket
kits are available that do it correctly.
Unfortunately, they are very expensive.
No matter what I think of, I
cannot come up with any logic circuit
that would prevent the brake indicator
from sequencing once, i.e., blinker
ON-OFF 12V, brake ON 12V; brakes
only, ON 12V both sides.
Any simple ideas? Hope I do not
need to program an IC. Guess I can
always learn at 72 years old. Started
reading N&V when it first began. Love
#1 I found a $20 flasher module
via a Web search for “turn signal light
sequencer.” The device will flash as
many as four lights. You’ll need one
module for the left-side lights and
another for the right-side lamps.
Creating your own controller
with simple logic circuits would get
complicated because only one signal
turns a brake or turn light on or off.
Thus, your circuit must distinguish
between a constantly-on signal for
braking and pulses for turning. You
could use a small PIC microcontroller,
but you don’t want to learn how to
program, which I understand.
If you change your mind and
want to start simply, look at the
Parallax Propeller FLiP Module (or the
Propeller QuickStart board) and use
the free BlocklyProp programming
tool. It doesn’t get any easier — you
simply choose graphical “blocks”
and stack them one on the other.
Concentrate on the problem and
let BlocklyProp create the code to
program the chip.
#2 You might not want to hear
this, but the easiest, most expedient
way to do this is with one of the
cheap Arduino boards available from
eBay. There are a myriad of power