October 1958 Popular Electronics
[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Popular
Electronics was published from October 1954 through April 1985. All copyrights are hereby acknowledged. See all articles from
like the title: "Put PEP in Your Antenna Tuner." For those not familiar
with transmitter lingo, PEP is Peak Envelope Power, but f course
the word "pep," as in energy, is a clever double entendre. If you
aren't averse to building a tube circuit and have a 6AG5 in your
parts box, then here's a simple antenna tuner circuit.
all articles from
Put PEP in Your Antenna Tuner
By Joseph W. Doherty, K2SOO The coupler you built
last November grows up with just a few extra parts
you built the pi-section receiver antenna coupler described in November
POP'tronics ("Soup Up Your DX with an Antenna Tuner"), here is a
worthwhile addition you can make at slight expense and in little
If you have not yet built the coupler, you can put
together the complete unit in one evening. It is sure to pay extra
dividends in improved reception. As a matter of fact, this unit,
which started out as a simple antenna tuner and grew into a preselector
and signal booster, can make your old receiver practically jump
right off the table.
HOW IT WORKS
The pi-network coupler
is the tuned grid circuit of the 6AG5 tube. An untuned plate
circuit is used to prevent oscillation. The output is resistancecapacity-coupled
and fed directly to the receiver input terminals where it may
be peaked by the receiver input circuits, depending on design.
Choke RFC1 maintains a high impedance to ground in the
grid circuit of the amplifier, and provides a grid return circuit.
Capacitor C8 provides an r.f, grounding path from the negative
side of the power supply. PARTS LIST
CI-360-μμfd. variable capacitor
C3-100-μμfd. disc ceramic capacitor
C4, C5, C8-0.001-μμfd. disc ceramic capacitor
disc ceramic capacitor
C7a/C7b-50-30 μfd., 150-volt electrolytic
L1-3" x 1" coil (B & W Miniductor #3015-48
turns, tapped as shown in schematic)
R2-12,000-ohm, 1/2-watt resistor
R4-100-ohm, 1-watt resistor
R6-2700-ohm, 1-watt resistor
resistance line cord (JFD #2190)
RFC1-2.5-mh. r.f. choke
S1-2-p., 5-pos. shorting switch (Centralab #1404)
SR1-Silicon diode Type 1N1084 (Sarkes Tarzian
It combines the impedance-matching properties of the pi-network
coupler with a signal booster amplifier. The power supply is self-contained
but, if desired, an external supply can be used. No expensive components
are required and the layout is extremely simple.
. This signal booster will provide
amazing improvement even in a well-matched antenna system. There
is a band selector switch position which allows you to bypass the
coupler without having to disconnect the antenna and reconnect it
to the receiver.
The power supply is of the a.c./d.c. type.
However, neither leg of the line is connected to the chassis, thus
eliminating the shock hazard associated with power supplies of this
type. The rectifier is a silicon diode #1N1084 which comes complete
with mounting hardware and 10-ohm resistor in the Sarkes Tarzian
Replacement Kit #M150. Any other type rectifier with a 20-ma. or
higher rating may properly be substituted.
To conserve space,
a resistance-type line cord was used. Take care not to coil or bunch
this cord, since it must be allowed to give off heat. Also, do not
attempt to shorten it. The built-in resistor is 390 ohms "long."
. The original design
was modified to accommodate the r.f. amplifier with minimum expense
and fewest circuit changes. Follow this procedure.
remove the original Bypass jumper from S1a, S1b. Disconnect the
lead to the junction of L1 and C2. Then disconnect the antenna input
lead from S1a.
Connect the antenna input lead to the wiper
contact of S1b. Connect a lead from the 80-meter position on S1b
to the S1a 80-meter position and S1a wiper. Now connect the Bypass
lead from S1b to the ungrounded output terminal and, finally, connect
the grid lead from C3 to the junction of L1 and C2.
there is considerable gain in the amplifier, it is recommended that
the input and output leads be kept well separated or oscillation
may result. As an example of the gain obtainable, one station heard
in the bypass position was read on the receiver S-meter at "S6."
The preselector raised this same signal to 40 db over "S9," thus
pulling it well out of the noise.
The coupler should be
grounded to a cold water pipe or similar good ground. If the receiver
used is of the a.c./d.c. variety, connect the coupler output terminals
to the receiver antenna terminals only. Tuning the
. Tuning is not difficult if you remember that
C1 is the loading capacitor and C2 is the frequencydetermining
capacitor. There is some interaction between the two but, to keep
it simple, adjust both alternately for the loudest signal. It is
best to start out with C1 at maximum capacitance, tuning C2 until
the signal is loudest. Keep in mind that the bandswitch must be
in the proper position.
the capacitance of C1 gradually until the signal starts to fade.
Readjust C2 for the loudest signal. If the signal has increased,
decrease C1 still further and repeat the process until the greatest
signal strength is achieved.
In most cases, a point will
be reached where advancing C1 will cut the signal strength in spite
of adjusting C2. This point is just beyond optimum coupling, which
means that the antenna is overcoupled. At this point, rotate C1
in the other direction slowly while adjusting C2 through resonance
until the optimum adjustment is found.
NOTE: While we normally bar a.c./d.c. chassis
projects because of the possibility of shock hazard, in this case
- since the antenna preamp was built up from an earlier project
on the same chassis - using a transformer would have been difficult
due to lack of space. While all B -- points are raised above chassis
ground, there is still some possibility of leakage. Therefore, we
advise using an isolation transformer with this project. The Editors
The B -return shown on the schematic must be kept above chassis
ground; this can be done by using a tie strip as return point. Note
that R7 is the line cord dropping resistor. SR1 and R5 are included
in the replacement kit as indicated in the text. Photo on opposite
page shows completed under-chassis wiring. Photo at top left shows
top of tuner, while photo above indicates proper method of connecting
tuner to receiver's antenna input.