October 1959 Popular Electronics
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
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you know what a Fahnestock clip is? Chances are you would know one
if you saw one, but you never knew what it was called. This article,
requested by RF Cafe visitor Jan C., references a Fahnestock clip
in the parts list for constructing an easily tunable long-wire antenna.
The simple circuit uses just a handful of components for matching
the high impedance antenna to a relatively low impedance coaxial
cable feeder. A flashlight bulb and a few turns of wire act as an
RF sniffer to tune for best match. A high quality ground is essential
to the setup's operation so the author describes using copper sulphate
crystals or rock salt to treat the ground rod vicinity for better
conduction. It's a short article so go ahead and read it - if for
no other reason than to see what a Fahnestock clip is.
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The Novice 90 Antenna
Simple tuner makes long-wire antenna effective on 40 and 80 meters
By Jay Stanley
Simple tuner makes long-wire antenna effective on 40 and 80
the antenna tuner for the shortest possible ground wire while
maintaining accessibility for tuning. A remote waterproofed
tuner installation is possible but this would make tuning more
difficult. PARTS LIST
C1-350·µµf. (or larger) midget TRF single-gang variable
J1-RCA type phono jack (or suitable coaxial cable
L1-Six turns of B&W 2"-diameter Type 3900
Many a Novice ham has difficulty in "getting out" - and nine times
out of ten the trouble lies in failure to put power into the antenna.
Fifteen watts of power actually in the antenna will put out a reliable
signal on the Novice bands.
Transferring power from transmitter
to antenna can be tricky business, and this is particularly true
when you try to feed most ordinary long-wire antennas with the typical
pi network stage of a transmitter. In many cases, the antenna represents
a high-impedance load - and feeding it from the low-impedance output
of the transmitter makes for a big waste of precious power.
This problem is neatly sidestepped with the "Novice 90" antenna,
which is designed to be end-fed with a low-impedance line. Thus,
the antenna is very simple to erect and, even more important, you
can adjust resonant length right in the operating room. The adjustment
is easily made using a 10-cent flashlight bulb which shows you the
point of maximum antenna current.
This current is the power
being soaked up by the antenna. Construction
The "heart" of the antenna is a simple tuner, consisting of a TRF-type
single-gang tuning capacitor (C1) and coil L1. These parts are mounted
on a convenient board as shown in the diagram. Stand-off insulators
support the coil and the antenna terminal.
C1 and the Fahnestock clip for the ground connection are mounted
directly on the board. The RCA phono input jack J1 (a regular coax
connector could be used instead) is mounted on a small metal angle
bracket screwed to the board. Jack J1 connects to the coaxial cable
jumper which runs to your transmitter output terminal.
coil for the antenna tuner consists of six turns of No. 14 wire
approximately 2" in diameter. Turns are spaced approximately 1/8"
apart. Wind the coil yourself or cut some turns from a piece of
B & W 2"-diameter No. 14 wire coil stock (Type 3900).
The antenna itself is a 90' "L"-shaped length of wire. How much
is horizontal and how much is vertical is not particularly important:
for example, 30' up to 60' out is ideal. However, other combinations,
such as 40' up and 50' out, will work as well.
results, keep the ground lead under 10' in length, the shorter the
better. If it must be longer, subtract the length of the ground
lead over 10' from the antenna length in feet. For example, if the
ground lead is 14', make the antenna 86' instead of 90'.
You can build an efficient ground as shown in the diagram. Use
a standard TV ground rod (the longer the better) and then improve
the conducting characteristics by chemically treating the ground
nearby. Copper sulphate crystals are excellent, as is rock salt.
Ordinary table salt will work well also, but of course is more expensive.
Dump in the chemicals, soak down the area with a garden hose, and
you will have a ground far more efficient than the usual water pipe
ground. The latter should be used only as a last resort and cannot
be expected to work as well.
In a typical station layout,
the antenna tuner should be mounted alongside a window sill. The
ground should be just outside the window, close to the house. The
antenna tuner can be connected to the transmitter by any convenient
length of 50- or 52-ohm (approximately) coaxial cable.
attach a two-turn loop of wire to a No. 44 dial light bulb or a
bulb from a two-cell flashlight. The loop and the bulb provide an
indicator for antenna current. Then, connect the coaxial cable from
the transmitter to the antenna tuner. Set the capacitor on the antenna
tuner approximately one-half "open."
Next, set your transmitter
for 80 meters, and tune it following the manufacturer's instructions.
Load up the transmitter final by adjusting the antenna loading and
plate tuning capacitors in the transmitter. Now, couple the pickup
loop and bulb (as shown in the photograph) to the antenna coil,
and adjust antenna tuning capacitor C1 for maximum brightness. When
you find this point, you have the antenna at resonance and it is
taking maximum power.
On 40 meters the adjustment is quite
similar, although the resonance point is usually very broad, as
shown by the tuning loop indicator. On this band, set the antenna
tuner capacitor to as high a capacity as possible (plates almost
closed) where the tuning indicator is at maximum brilliance.
The last step is to adjust the transmitter tuning for proper
load as indicated by the milliammeter in the final of the transmitter.
Don't make any big changes in the antenna resonance adjustment already
achieved, but check for maximum brilliance of the bulb.