The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1925-10-02

Herald Tribune.
One stage of tuned radio-frequency
amplification. one stage of choke coil
coupled, regenerative radio-frequency
amplification. crystal detector and
two stages of transformer coupled
audio-fl'equency application are the
main elements that make up the pres
ent receiver.
When the diagram of the receiver,
which Is published herewith, was
shown to radio fan long since past
the novice stage he remarked that ev-
erything In the receiver was done
backward. Well, not everything is
done backward, for most of the circuit
is strictly orthodox, but there is one
thing which Is done In the reverse
order. and 1t Is this fact which makes
the receiver unique. This fact Is the
manner in which regeneration Is OBJ
tanned n he second tube As will be
this stage is placed in the plate circuit
of the tube, and tie ticker coil La
connected in series with the grid lead
OF the tube is placed in inductive re-
lation with the tuned coil L3 In this
manner a voltage is induced in the
coil Ia, and this is added to the input
voltage across the resistance R. If
this added voltage is sufficient regen-
Grafton will be obtained. provided, of
course, it is In the right phase.
Use of Crystal Detector.
The tuned coil LIB was placed in the
plate circuit for several reasons. In
the first place, it was desired to use 4
crystal for detecting the signals so
that advantage could be taken of the
greater quietness and economy of OPP
GRAFTON obtainable With this device. 1t
was also found that the signals could
be increased tremendously by connect
ing the crystal directly across the
plate coil and tuning 1t instead of con-
Meeting the crystal across tuned sec
ondary. No tube noises go into the
crystal because the audio frequency
difference of potential across L3 is en-
tirely negligible, and there Is no dam
ger of injuring the crystal by heavy
direct current, because the DC differ
ence of potential across L3 is even
less than the audio-frequency alter
mating current potential difference.
Hence neither tube noises nor direct
current of appreciable magnitude will
go into the crystal detector circuit.
The fact that the crystal detector cir
cult is connected to the positive side
of the plate battery does not mean
that the plate battery voltage is in the
crystal circuit.
Since the grid coil LA is not tuned
It requires closer coupling between
L3 and LA to obtain regeneration than
when the grid coil is tuned and when
the ticker is in the plate circuit. For
this reason it will be necessary to
use high inductance In LA in order
to obtain satisfactory regeneration. AS
it is desirable to have a compact coil
for ticker, Ia should preferably be
wound with fine wire. The writer used
100 turns of No. SO double cotton
covered wire wound on a diameter of
two inches.
Since the crystal circuit is connect
ed across the tuned circuit L3 CO and
takes considerable energy from it, the
latter is naturally very broad and non
selective. In order to increase the Sc
lectivity of the arrangement L3 should
be wound with fairly heavy wire, and
the low-loss method of constructing 1t
may be employed. Two or three taps
should also be provided on it so that
the crystal circuit may be connected
across only portion of L3 when
greater selectivity Is required.
Does Not increase seIectivity.
The regeneration does not increase
the selectivity to the same extent in
this case as it does in the ordinary
circuit. The reason for this is that
the grid coil is aperiodic and responds
equally TO currents of all frequencies
which are surging in L3 C3. That
is. the side bands are intensified by
regeneration almost to the same extent
as the carrier frequency. The set re-
produces faithfully. but, of course, the
quality is dependent on the perform
ance of the audio-frequency trans
formers. If the choice of these has
been lucky or well advised the set will,
make pleasant listening.
The antenna coil 10 and the first
tuning coil Ii may be the two wind
ings of an ordinary radio-frequency
tuning unit, which may be purchased
in any radio store. The coupling be-
tween the two windings should be