appreciate a schematic if at all possible.
— Nathanial C. Blacker
AIf you have a roof mounted
community antenna, then the
reception is probably as good
as you can get. If you are
using a rabbit ears type of antenna, then
you need a better antenna. In order for
an RF amp to do any good, it must have
a lower noise figure than the TV RF amp.
For a better antenna, consider the
Terk TV55. It is a helical antenna with
an amp and covers VHF/UHF. I don’t
have any experience with it, but reviews
are good. The cost is about $100 and
you can order from: Crutchfield,
P.O. Box 9032, Charlottesville, VA
22906-9032. The antenna is less than
four feet long and about three inches in
diameter, so it should fit in your space.
The RF amp schematic that you
requested is shown in Figure 2. It is not
real wide band — it only covers the VHF
band — but the gain is nearly 20 dB (see
Figure 3). The transistor, 2SC3356/
NE85633, is an SOT-23 surface mount
and the resistors should be surface
mount as well for best performance.
The input impedance of the amplifier is
probably not 75 ohms, so the cable
from the antenna to the amp should be
short to avoid reflection problems.
PARTS LIST
PART DESCRIPTION
• S1-S5 SPDT Mini Toggle
• R1, R5 4 x 2. 21 MEG +160K
• R2, R4 4 x 22 MEG + 2 MEG POT
• RG1 500 OHM, 0.1%
• RG2 10 OHM, 1%
• RG3 10. 2 OHM, 1%
• IC1 INA128P
• C1, C2 10 μF, 16V, 10%
• C3, C4 0.1 μF, 50V, X7R
MOUSER PART NUMBER
108-1AS1T1171-EVX
71-CCF55-2.21M, 71-CCF55-162K
291-22M-RC, 81-PV37W205C01B00
71-PTF56500R00BYBF
271-10-RC
271-10.2-RC
595-INA128P
581-TAP106K016SRW
80-C320C104K5R
spectrum is wider than the old analog
signal so there would be some
degradation if the unmodified RF
sections of the radio were used. The
detector would have to be redesigned
and all the processing after the
detector would have to be designed.
Presently, reception of HD radio is
free but it is possible that in the future,
you will be able to purchase specific
channels (rock and roll, oldies, classical,
etc.). European countries have adopted
a different standard, so your USA radio
won’t work over there and vice versa.
prefer the output to light one of four
LEDs, or perhaps trigger a variety of
voice alerts. How would I construct a
circuit to convert a sequential series of
pulses to switch four separate outputs?
— Rob Gordon
AA shift register seems the
logical device for this
application. The relay
becomes the clock; the
■ FIGURE 2
HD RADIO
QThe question I have is about
the HD radio broadcasts. Is
there a way to modify a
regular FM radio to receive
these HD stations?
CONVERT SEQUENTIAL
PULSES TO FOUR
OUTPUTS
QI have a stand-alone wireless
motion detection unit that reports alerts from four detectors. The system sounds one
to four beeps to distinguish between the
detectors, and also conveniently closes
a relay in sync with the beeps. I would
— Bryan Fischer
AThe short answer is no. Broadcast stations now have the
ability to send all analog, hybrid digital (including analog),
extended hybrid digital with analog, or
all digital (no analog). There are presently no receivers available for all digital FM
and no all digital stations, as far as I know.
The digital signal can be subdivided into
multiple channels, each carrying a
different signal. The digital signal is
lower power than the analog and if the
digital signal is too weak, the receiver is
designed to switch to the analog signal.
The extended hybrid digital
■ FIGURE 3
February 2008 23