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Electronic Circuits for the Hobbyist, by VA3AVR
Electronic Circuits for the Hobbyist, by VA3AVR
Circuits for the Hobbyist
by VA3AVR
Tony's Message Forum Ask your questions here. Someone may answer them.
2SC2570 Pin-
Heat Sensor -- OFF-LINE (performance problems)
Motor Accu Lader (Dutch language)
Radio Shack Special - Transmitters by Patrick Cambre
Pro
10-27-2004
Spelling, 8-05-
"Green" means on-line, "Red" means off-line
Bookmark this valuable page with 'Ctrl-D' .
Just in case you're gonna ask: All drawings are created with Paint Shop Pro
Circuits Archive - Older circuits. Most are working, some are not. Could be still useful.
Tony's Data Sheets - Data Sheet for common Semiconductors
Data Sheets Archive - Link to tons of data sheets.
Radio Shack Partnumbers - Most common order numbers for my circuits
Resistor Value Calculator - By Danny Goodman, AE9F
Tandy Corporation - European/Australian counterpart of Radio Shack
TUP/TUN/DUS/DUG European transistor replacement system
PN100/200 - Data Sheets for the PN100 and PN200
LF13741 - Monolitic JFET Input OpAmp Data Sheet
Toroids, RF/EMI Cores - Variety of commonly used toroids, colors, etc.
Guelph Amateur Radio Club - GARC--Official Homepage
Jonathan's Electronics Message Forum - More help if you need it!
Other Interesting Links - Links to other interesting and informative Electronics Websites.
November 1,
2004
DISCLAIMER: I take no responsibility whatsoever for the use and/or implementation thereof, or the misuse
leading to damage to equipment, property, or life, caused by the above circuits. Check with local, provincial and
federal laws before operating some of these devices. You may also check your life insurance and/or the fact if they
cover death by electrocution if you intend to play with Micro-wave ovens and other possible lethal HV devices.
Safety is a primary concern when working with high power circuits or con/inverters. Play it safe!
Copyright © 1995, Tony van Roon (VA3AVR). ALL RIGHTS RESERVED.
Last Updated December 17, 2004
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Alternating ON-OFF Switch
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Page Copyright © 1995 -- Tony van Roon
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AM-FM-SW Active Antenna
Active Antenna for AM/FM/SW:
This simple little circuit can be used for AM, FM, and Shortwave(SW).
On the shortwave band this active antenna is comparable to a 20 to 30
foot wire antenna. It is further more designed to be used on receivers
that use untuned wire antennas, such as inexpensive units and car radios.
L1 can be selected for the application. A 470µH coil works on lower
frequencies and lie in AM, for shortwave try a 20µH coil. This unit can
be powered by a 9 volt alkaline battery. If a power supply is used,
bypass the power supply with a 0.04µF capacitor to prevent noise
pickup. The antenna used on this circuit is a standard 18-inch
telescoping type, but a thick piece of copper, bus-bar, or piano wire will
also work fine.
The heart of this circuit is Q1, a JFET-N-Channel,
UHF/VHF amplifier in a TO-92 case.
It can be replaced with an NTE451.
Output is taken from jack J1 and run to the input on the receiver.
Source: "Popular Electronics" magazine, July 1989 issue.
Copyright © Gernsback Publications, Inc. 1989. (Gernsback no longer in business).
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Copyright © 2003 - Tony van Roon
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Active Antenna AA-7 HF/VHF/UHF, 3-3000MHz, Antenna booster
Active Antenna AA-7 HF/VHF/UHF, 3 to 3000 MHz
By Fred Blechman
"Lift those hard-to-hear signals out of the mud with this handy receiver accessory."
If you have a shortwave or high-frequency receiver or scanner that
is struggling to capture signals with a short, whip antenna, and
you'd like the kind of performance that a 60-foot longwire antenna
can provide but lack the space to put one up, consider building the
AA-7 HF/VHF/UHF Active Antenna described in this article. The
AA-7 is a relatively simple antenna that is designed to amplify
signals from 3 to 3000 MegaHertz, including three recognized
ranges: 3-30Mhz high-frequency (HF) signals; 3-300Mhz very-
high frequency (VHF) signals; 300-3000MHz ultra-high (UHF)
frequency signals. Those bands are typically occupied by
shortwave, ham, government, and commercial radio signals.
Active Antennas:
In its simplest form, an active antenna uses a small whip antenna that feeds incoming RF to a preamplifier, whose output is then connected
to the antenna input of a receiver. Unless specifically designed otherwise, all active antennas are intended for receive-only operation, and
thus should not be used with transceivers; transmitting into an active antenna will probably destroy its active components. A well designed
broadband active antenna consider field strength of the desired signal (measured in microvolts per meter of antenna length), atmospheric and
other noise, diameter of the antenna, radiation resistance, and antenna reactance at various frequencies, plus the efficiency and noise figure
of the amplifier circuit itself.
Circuit Description:
Fig. 1 shows the schematic diagram of the AA-7, which contains only two active elements; Q1 (an MFE201 N-Channel dual-gate MOSFET)
and Q2 (a 2SC2570 NPN VHF silicon transistor). Those transistors provide the basis of two independent, switchable RF pre-amplifiers. Two
double-pole double-throw (DPDT) switches play a major role in this operation of the AA-7. Switch S1 is used to select one of the two
preamplifier circuits (either HF or VHF/UHF). Switch 2 is used to turn off the power to the circuit, while coupling the incoming RF directly
to the input of the receiver. That gives the receiver non-amplified access to the auxiliary antenna jack, at J1, as well as the on-board
telescoping whip antenna. With switch S2 in its power-on position, the input and ouput jacks are disconnected and B1 (a 9 volt battery) is
connected to the circuit. With switch S1 in the position shown in the schematic, incoming RF is directed to the HF preamp circuit built
around Q1 (an MFE201 N-Channel dual-gate MOSFET). The HF preamp operates with an exceptionally low noise level, and is ideal for
copying weak CW and singe-side band signals. When S1 is switched to the other position, the captured signal is coupled to the VHF/UHF
preamp built around Q2 (a 2SC2570 NPN VHF silicon transistor), which has exellent VHF through microwave characteristics. With the on-
board whip antenna adjustable to resonance through much of the VHF-UHF region (length in feet = 234 divide by the frequency in Mhz),
the VHF/UHF mode is ideal for indoor and portable use with VHF scanners and other receivers. Either mode can be used when tuning 3-30
Mhz HF signals. The VHF/UHF preamp offers higher gain than the HF preamp, but also has a higher noise level. You can easily choose
either amplifier for copying any signal; of interest--just try both positions. The RF gain control (R5) can be used to trim the ouput of either
amplifier.
Caution: The AA-7 is not intended for transmitting operation (be it Ham, Maritime, or CB); if it is used with a transceiver of any kind,
make sure it is not possible to transmit by accidentally pressing a mike buton of DW keyer. Transmitting RF into the AA-7 is likely to ruin
one of both of the transistors in the circuit.
Construction:
The AA-7, which can be built from scratch or purchased in kit form from the supplier listed in the Parts List, was assembled on a printed
circuit board, measuring 4 by 4-11/16 inches. A template for the pcb board is shown in fig. 2. You can either etch your own board from that
template, or purchase the circuit board or the complete kit of parts (which includes the pcb and all parts, but not the enclosure). The kit
comes with a 16-page kit instruction manual that gives step-by-step assembly instructions and contains additional information not covered in
this article. Kit assembly time, working slowly and carefully, should take less than an hour. Most of the parts specidied in the Parts list are
standard components and can be procured through conventional hobby electronics suppliers. However, some parts--J1, J2, S1, S2, and R5--
have particular physical mounting dimensions; the Printed Circuit Board is designed to accept these particular parts. In addition, Q1 and Q2
can be hard to find; however, it is possible to make substitutions provided that you can find a supplier. Suitable replacements for Q1 and Q2
are given in the Parts List.
The telescoping whip antenna screw-mounts to the board; the screw provides contact between the printed circuit board traces and the
antenna. To save time and trouble locating and ordering hard-to-find parts, a Special Parts Kit is also offered by the supplier listed in the
Parts List.
A parts placement (layout) diagram for the AA-7's printed circuit board is shown in figure 3. When assembling the circuit, be especially
careful that transistors Q1 and Q2, and the electrolytic capacitor C4, are oriented as shown.
Although not shown in the schematic (Fig. 1) or the layout (Fig. 3) diagrams, an optional led power indicator can be added to the circuit.
Adding a power indicator to the circuit allows you to tell at a glance if the circuit is on; leaving the circuit on, even though the AA-7 draws
only about 0.7 mA, will eventually discharge the battery. Of coutse, adding an led will increase the current drain to by about 7 mA, but the
red glow makes it obvious when the unit is on.
If you decide to include the indicator in your project, power for the indicator can be easily taken from the switched 9-volt DC terminal of S2
(center terminal, right side, looking at the top of S2). Simply connect the positive voltage to the anode (longer wire) of the led and connect
her cathode lead through a current limiting resistor of about 1000 ohm to a ground point on the printed circuit board, or as the author did
fromt the frame of R5. Mount the led at any convenient point near the switch.
Although not supplied with the kit, a custom plastic enclosure (with front and back panels) or a regular 'hobby' case of some sorts, and
knobs for the switches and gain control is offered in the Parts list. The enclosure comes pre-drilled and silk-screened with the appropriate
legends for all the circuit controls and connecteors, but is not equipped with holes for the whip antenna or the led (if you include one)>
Test and Use:
Prepare a coaxial cable to connect the RF output of the AA-7 to
the antenna input of your receiver or scanner. One end of the
interconnecting cable must be terminated with an RCA phono
plug; the other end connector depends on the target receiver or
scanner. With some receivers, the only practical connection is to
clip the output of the AA-7 to the receiver's antenna, although that
connection won't be as effective as conventional (ground-return
type) coupling.
To increase signal strenght, especially for the lower frequencies,
you can connect a simple supplementary portable antenna of any design (a dipole, random-lenght wire with Earth ground, a bigger vertical
whip of some kind, etc.) to the circuit. Just use a small-diameter coaxial cable terminated in an RCA plug for mating with J1.
No alignments are required. If you're using the whip antenna, simply connect the output of the AA-7 to your receiver, with the unit turned
off (that's the bypass position) and the RF gain control (R5) turned fully counter-clock wise. Turn on the receiver and tune-in a weak station.
Switch S2 on, and adjust the gain control clockwise to increase the output signal. Toggle S1 back and forth to see which setting gives you
the best results. Don't be surprised if the gain control overloads the receiver; if so, back it off.
Troubleshooting:
The fact that there are two independent preamplifiers in the AA-7 makes faults easeir to diagnose than with many other devices. If a problem
occurs, only at one setting of S1, concentrate on that part of the circuit. If the problem is common to both settings, the components and the
connections common to both preamps should be checked. Maker sure the jumper wires are in place.
There are other characteristics or phenomena associated with preamplifiers and active antennas that does not mean that your circuit is
malfunctioning. For example, if you have strong AC hum in the HF setting, the antenna is too close to an AC cord or powerline. HF signals
may be clearer at the VHF/UHF setting than ast the HF setting. Why? Although either preamp may be used for HF, the signal strength will
be greater with the VHF/UHF preamp. However, the HF signal-to-noise ration is better with the dual-gate-MOSFET-based preamp. Try both
and use the best for your particular receiver conditions.
Some portable receivers not enclosed in metal cases may break into oscillation when connected to any RF preamplifier. Try reducing the AA-
7's gain and make sure that good grounds are provided with the interconnecting coax cables. A preamplifier will intensify any problems due
to poor receiver design: overloading, images, or any other problems with selectivity and image rejection.
Parts List and other components:
Semiconductors:
Q1 = MFE201, SK3991, or NTE454. N-Channel, dual-gate MOSFET (see text)
Q2 = 2SC2498, 2SC2570, 2N5179, SK9139, or NTE10. NPN VHF/UHF silicon transistor (see text)
Note: If you use the NTE107 as a replacement, make sure to insert it correctly
into the pcb. The orientation is different than as shown on the parts layout
diagram. (e-c-b seen frontview for NTE107). See this Data Sheet
Resistors:
All Resistors are 5%, 1/4-watt
R1 = 1 Mega Ohm
R2 = 220K
R3,R6 = 100K
R4 = 100 ohm
R5 = 10K potentiometer, (pc mount)
Capacitors:
C1,C2,C5,C6 = 0.01µF, ceramic disc
C3 = 100pF ceramic disc
C4 = 4.7 to 10µF, 16WVDC, radial lead electrolytic
Additional Parts & Materials:
B1 = 9-volt alkaline battery
S1,S2 = DPDT PC mount pushbutton switch
J1,J2 = PC mount RCA jack
ANT1 = Telescoping whip antenna (screw mount)
MISC = PCB materials, enclosure, enclosure, battery holder and connector,
wire, solder, etc.
KIT = NO kit is available at this time. I may supply kits on demand.
Fig. 1. "The AA-7 Active Antenna contains only two active elements: Q1 and Q2 (a 2SC2570 NPN VHF silicon transistor), which provide
the basis of two independent, switchable RF preamplifiers."
Fig. 2. "The AA-7 was assembled on a printed-circuit-board (PCB), measuring about 4 by 4-11/16 inches. A template for the printed-circuit-
board is shown here. Note that it may not be to scale.
Parts assembly diagram (layout) is shown in Fig. 3 to make soldering the unit together a breeze!"
Fig. 4. shows the finished assembly without the enclosure. Make
sure the antenna-hole in the enclosure is in-line with one on the
pcb. On mine I used a stud with thread on both sides to enable me
to use different length antenna's; all I have to do is unscrew and
screw another antenna back in without taking the AA-7 apart. I
used a 9-volt battery tray which allows me to replace the battery
without opening up the case, but the regular battery clip and
battery works fine. As you can see from the pictures, this is a nice
one-evening project.
I fully support this
project. since my unit
has been in operation
for quite a few years
now and still running
on the same battery.
Power consumption if
minimum. Most parts
can be obtained via
your local electronics store. I will answer all questions but via "Tony's Message Forum" only.
This Forum can be accessed via the main page, gadgets, or circuits page.
Copyright and Credits:
Source: "Electronics Hobbyist Handbook", Spring 1994. Copyright © Fred Blechman and
Gernsback Publications, Inc. 1994. Publised with permission from Gernsback. (Gernsback
Publishing no longer excists).
Document updates & modifications, all diagrams, PCB/Layout drawn by Tony van Roon.
Re-posting or taking graphics in any way or form of this project is expressily prohibited by international copyright laws.
Back to Circuits page
Page Copyright © 1995 - Tony van Roon
Project Copyright © 1994, by Fred Blechman
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Active FM-Amplifier
Active FM-Amplifier:
With only a small handfull of parts you can built this trusty FM Amplifier. It works with only 1 UHF/VHF type transistor,
MFE201. This amplifier will pull in all distant FM stations clearly. The circuit is configured as a common-emitter tuned
RF pre-amplifier wired around VHF/UHF transistor MFE201. There are a couple other models that probably would work
too, like the NTE107, 2SC2570, etc. but I have not tried it.
Adjust capacitor trimmers C1 and C2 for maximum gain. Input coil L1 consists of 4 turns of 20SWG enamelled copper
wire over a 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only
three turns. Pin configuration is shown in the diagram.
Source: "Popular Electronics" magazine, Copyright © Gernsback Publications, Inc. 1996. (Gernsback is no longer in
business).
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