Evening star., 1925-08-25
RES|STENCES BIG
FACTOR IN RADIO
Elimination of Surplus Per-
mits Sharper Tuning and
Improves SeIectivity.

ReSiStdnceS are an inSeparable fac.
tor in all electrical circuits. 1t may
not be there in the form of a rheo-
stat, potentiometer or other piece of
resistance apparatus. but every part
of the circuit whether copper wire con
nections, condensers. coils or any other
unit has some resistance value. 1t may
be great or small, but it exists and is
a factor in the circuit. Copper wire
is a good conductor, meaning it's re-
sistance is low, while ii non-conductor
simply means something that has a
very high resistance.
Present day radio apparatus is so de-
signed as to reduce as far as practical
all resistance in the tune circuits.
Oscillation.
This elimination of surplus resist
lnce permits much sharper tuning and
therefore improves selectivity. But in
radio frequency circuits it multiplies
the tendency of tubes to go into oscil-
lation. producing the assortment of
squeals. howls, and whistle which not
only come out of the loud speaker, but
back up and go out in the air to play
havoc with the neighbors' reception.
The old and incorrect practice was
to add a potentiometer in the second
ary circuit of the radio frequency
stages. This was equivalent to re-
placing the resistance in the appara.
tus. 1t reduced the oscillation tend
ency, but it likewise killed the selec-
tivity that was desired and in addi-
ton materially reduced the volume.
Resistance should not be added where
1t becomes an integral part of the
radio frequency circuits.
The fundamental cause of oscillation
is due to great extent to the amount
of. voltage across the plate circuit. If
this voltage is controlled 50 that it can
be adjusted to a value just below the
point where oscillation starts then ra-
dio frequency amplification can be
used to full advantages. But this con-
troll must not be such as to add re-
sistance in the tuned circuits
Plate Voltage Control.
Oscillation can be effectively pre-.
vented if a variable resistance is con.
nected in series between the plate or
primary coils of the radio frequency
transformers and the B battery to pre-
vent oscillation by reducing the plate
voltage on the radio frequency tubes
Now by connecting a p MID con
denser between the B terminal of the
primary on the radio frequency trans.
formers and the filament terminal OF
the tubes, this artificial resistance can
be shunted out of the tuned circuit
This condenser closes the plate cir.
cult to the filament of the tube for
the radio frequency currents In
other words, on account of the con.
denSer these currents do not have 10
pass through thte resistance-hence
the resistance does not effect the
tuning and selectivity.
This variable resistance provides a
means of reducing the plate voltage
ana therefore controls oscillation,
This means of controlling oscillation
was first utilized commercially by +,
F. Andrews in the Deresnadyne re.
ceiVer. The use of this control for
radio receiving sets is covered bv
patent applications but its use by the
ran in building his sets or for remedy.
ing trouble in a set ne has made is
encouraged.
Mr.. Andrews has now developed the
use of this by-passed plate circuit re.
slstance as a volume control, as well
as an oscillation control This is
done bv using an extremely high vari.
able resistance having a maximum
value of several megohms. The cir.
cunt is just the same as for the con.
troll of oscillation. The first part of
the resistance can be used for osciIla.
ton control, and the high resistance
part for controlling volume. Volume
can thus be adjusted without the
slightest distortion, and with great
saving in B battery current.
This combination control is known
as the "Anostat," derived from ian.
ode" meaning positive or plate and
the word rheostat.