American Agriculturist, May 5 ,1923 
407 
How To Make A “Reflex” Radio Set 
A Set That Is Well Suited To The Fan Who Likes To Experiment 
W HEN an impulse from a radio 
broadcasting station lands at the 
receiving aerial, it sets up currents 
vibrating in it at a frequency far above 
that to which the human ear will re¬ 
spond. For instance, a wave length of 
300 meters means a frequency of one 
million per second, and since the upper 
limit of human audibility is about 15,- 
000 vibrations per second, such a fre¬ 
quency can not be heard at all. 
It is the function of the crystal de¬ 
tector or tube detector to so group the 
oscillations, that they ai'e reduced to a 
frequency within audibility, or where 
the incoming wave carries voice varia¬ 
tions as well, to bring these into the 
phones for understandable reproduction. 
Where the impulses are weak, and 
fail to affect the tube or crystal de¬ 
parts for Reflex Circuit 
Vario-coupler. 
23 plate variable condenser. 
Audio transformer. 
Radio ti’ansformer. 
Crystal detector. 
Tube socket. 
Amplifying tube. . 
“A” battery for tube. 
45 volt “B” battery. 
300 ohm potentiometer. 
Rheostat for tube (5 to 6 ohms for 
WD-11, UV 201, UV 201 A, 30 
ohms for UV 199). 
3-.001 fixed condensers. 
2-Switch knobs and points for 
coupler. 
tector, it is utterly impossible to add 
any form of audio frequency amplifier 
such as the “two stage” type recently 
described, in order to magnify the 
sounds. What, ^ len, can we utilize to 
increase the strength of the incoming 
radio frequency impulses so that they 
may affect our detector? 
There is a type of amplification 
known as “radio frequency amplifica¬ 
tion” which precedes the crystal or 
tube detector in order of sequency, and 
whose function it is to bring up the 
strength of very feeble impulses to a 
point where the detector is enabled to 
operate. The amplification takes place 
through one or more circuits and tubes 
which are not tuned sharply, but merely 
approximately, so that the circuit will 
respond over a fairly wide range of 
wave lengths without adjustment of the 
radio frequency amplifier itself. It is 
of course essential that the antenna and 
secondary circuits be tuned in the usual 
manner, by means of a vario-coupler, 
or honeycomb coils, or by any other 
means decided upon. 
It is an abrupt step for the radio fan 
who has become acquainted with tube 
detection and audio frequency ampli¬ 
fiers, to add two or three stages of 
radio frequency to his set. “R. F.”, as 
it is popularly termed, is a ticklish 
proposition to handle, and therefore it 
is advisable for anyone interested in 
learning about it to attempt some sure 
and certain variety of this interesting 
method of increasing the distance over 
which broadcasting may be received be¬ 
fore starting off wfith the regular “R. 
P.” hook-ups. 
Perhaps the easiest scheme is that 
presented in the Reflex circuit. Not 
only has this advantages as far as in¬ 
creased distance and greater strength 
of signals are concerned, but it is also 
economical since one tube may be em¬ 
ployed to do the work of two nearly as 
effectively. In the accompanying plan 
diagram is given the single tube reflex 
circuit as it is to-day adaptable for 
broadcast work. There is no question 
that it is superior in most respects to 
the average single to be regenerative 
receiver both for distance and for vol¬ 
ume. And not only that, but the in¬ 
sertion of the crystal as the detecting 
medium adds wonderfully to the tonal 
quality of the music and speech. 
It will be noted that the tuning 
of the antenna circuit is accomplished 
in the usual manner by the primary 
winding of the vario-coupler with its 
two sets of switch points. The second¬ 
ary winding is . tuned by a variable 
condenser of about> 23 plates (.0005 
mfds.). Through the fixed condenser 
By BRAINARD FOOTE 
in the grid circuit the “R. F.” impulses 
are impressed upon the grid of the tube 
and thence amplified at radio fre¬ 
quency. It is essential that the tube be 
of the amplifier type for such work, 
and the most suitable tubes at present 
available ai’e the UV 199, the UV 201 
and the UV 201 A. The WD-11 is 
fairly satisfactory but has more tend¬ 
ency than the others to do some of the 
detecting work. 
Now comes the “trick” of the reflex. 
From the plate, the amplified radio 
frequency impulses pass through the 
primary of the radio frequency trans¬ 
former. This little instrument is some¬ 
thing like a vario-coupler, consisting 
of two windings placed upon a very 
finely laminated core of iron. It is the 
function of the core to “broaden” the 
tuning of the transformer or coupling 
device so that it is not necessary to 
adjust the wave length of it between 
the limits used by broadcasting sta¬ 
tions. These are usually between 250 
and 550 meters. 
The by-pass condenser across the 
phones is needed to “pass by” the “R. 
F.” oscillations along through the “B” 
battery and filament. As in the case of 
a vario-coupler, the current in the 
primary of the “R. F.” transformer 
sets up a current in the secondary. 
Remember—this is still at radio fre¬ 
quency. Here is where the crystal 
comes into play. It is the detector, and 
it does its work very efficiently and 
clearly, too. 
By the time the current reaches the 
primary winding of the audio fre¬ 
quency transformer, with whose opera¬ 
tion most of us are familiar, the cur¬ 
rent has been “rectified” or brought 
within the range of human hearing. 
Again it is amplified, this fime at an 
audible frequency, and the impulses 
once more strike the grid. Now the 
tube operates as an audio amplifier, and 
the results are most pleasing. Loud, 
and clear, far exceeding those obtain¬ 
able with the ordinary one tube re¬ 
ceiver. 
How about the potentiometer? This 
is inserted for the purpose of applying 
a little voltage to the grid of the tube 
through the coupler winding. It is 
thus that the tube can be made to 
“oscillate” and produce almost as great 
an effect as that noted when a regener¬ 
ative receiver is brought nearly to the 
point of oscillation. Thus it can be 
truly said that the reflex circuit not 
only amplifies, doubly, and detects, but 
also permits regeneration. And all 
with one tube. 
One should be careful in purchasing 
apparatus for the circuit to select only 
the very best. A fairly good gauge of 
quality is the price, and the total cost 
of the outfit, not including phones, bat¬ 
teries and tubes, is approximately $15. 
Including everything required from 
aerial to ground, the cost runs up to 
about $35 or $40. 
In wiring the set, the parts should 
be placed in such a manner that con¬ 
nections are short. Parallel •v^'ii'ing 
should be avoided if possible and the 
plan layout followed as much as pos¬ 
sible. If it be found that the circuit 
functions fairly well with the cat 
whisker off the crystal, the leads from 
the secondary of the radio frequency 
transformer should be switched around 
to find the proper direction for current 
in that winding. The “A” battery is 
connected as indicated, and about 45 
volts of “B” battery used with the tube. 
It should be pointed out, in closing, 
that an additional stage of audio fre¬ 
quency amplification, with which the 
same tube, “A” and “B” batteries may 
be used, will give results sufficient for 
the operation of the loud speaker ordi¬ 
narily reserved for use with a three 
tube outfit. 
The Valley of the Giants 
{Continued from 'page 406) 
through the general office. “It is post¬ 
poned.” 
CHAPTER XXXIII 
T hat trying interview had wrenched 
Shirley’s soul to a degree that left 
her faint and weak. She at once set 
out on a long drive, in the hope that 
before she turned homeward again she 
might regain something of her custom¬ 
ary composure. 
Presently the paved street gave way 
to a dirt road and terminated abruptly 
at the boundaries of a field that sloped 
gently upward—a field studded with 
huge black stumps showing dismally 
through coronets of young redwoods. 
From the fringe of the thicket the 
terminus of an old skid-road showed 
and a signboard, freshly painted, 
pointed the way to the Valley of the 
Giants. 
Parking her car by the side of the 
road, she alighted and proceeded up 
the old skid, now newly planked. On 
over the gentle divide she went and 
down toward the amphitheatre where 
the primeval giants grew. And as she 
approached it, the sound that is silence 
in the redwoods—the thunderous dia¬ 
pason of the centuries—wove its spell 
upon her; quickly, imperceptibly there 
faded from her mind the memory of 
that grovelling Thing she had left be¬ 
hind in the mill-office, and in its place 
there came a subtle peace. 
A cluster of wild orchids pendent 
from the great fungus-covered roots of 
a giant challenged her attention. She 
gathered them. Farther on, in a spot 
where a shaft of sunlight fell, she 
plucked an armful of golden California 
poppies and flaming rhododendron, and 
with her delicate burden she came at 
length to the clearing where the halo 
of sunlight fell upon the grave of 
Bryce Cardigan’s mother. There were 
red roses on it, and these she rear¬ 
ranged to make room for her own 
offering. 
“Poor dear!” she murn'ured audibly. 
“God didn’t spare you for much happi¬ 
ness, did He?” 
{Continued next r’eek) 
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Here is the layout of the Reflex Set, which is well adapted 
for distance work. 
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