The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1928-09-03
new RADIO SET
Tunes Medium
WAVE LENGTHS
SeIectiyity Featured in Cir
cult Designed for One
Frequency.

A new system of broadcast recep-
ton known as the Equasonne Cir
cult, which differs radically from
existing type of circuits, has been
developed by the Sparks Withing-
ton Company of jackson, Mich, and
Lester Jones of New York City.
The selectivity of the new circuit
is constant throughout the broad
casting band, the tuning being just
as sharp at 1900 kilocycles as at
$50. Another unique feature is that
only one stage of audio frequency
ampliflcation is required, the out
put from the detector being sufi-
Gent to operate a tventy-flve-watt
power tube up to the full capacity
of the letter.
AS most radio listeners are aware,
the existing types of sets suffer
considerable variation in Selectiv-
ity, tuning very much broader at
short wave lengths than at long.
Consequently, it becomes almost
impossible to receive a distant sta
ton without considerable interior
ence and background of noise be-
low $50 meters.
Improve Selectivity
It is this state of affairs which
has caused the shorter wave lengths
to be regarded by broadcasting sta
tons as being decidedly less valu-
able. 1t is possible to improve the
selectivity Of the ordinary types of
receiving sets at short wave lengths,
but this results in such sharp tun-
ing on the long waves that the tone
quality is seriously impaired.
The new system does away with
these difficulties by the use of a
selector circuit, or band-pass filter,
connected directly to the aerial and
ground, which permits only one
broadcasting channel of ten kilo-
cycles to pass through. This selec-
tor circuit has no tubes associated
with it and is composed OF recur-
rent network of inductance5.
The band of frequencies tc be.
selected is varied by varying the
capacities of a group of condensers
in the selector circuit. The width
of the band which is allowed to
pass through the selector remains
practically constant from 1900 to
$50 kllocycles so that the selectivity
is just as good on long waves as on
short.
The band of frequencies passed
through the Selector is then anpli-
fed by a system of circuits of fixed
adjustment which automatically
tune themselves to the impressed
frequency Instead Of the customary
tuning condenser the capacity be-
tween the grid and filament of the
tube is used.
Capacity Not Constant.
It is we'll known that this ca
pacity is not constant, but changes
with the impressed frequency, the
amount depending on the nature
Of the impedance in the plate cir
Culb Oh JIlG bQUGs 11ltllCI bOlO1C Glllo
variation was regarded with annoy
ance, but in the Equasonne. Circuit
this change in capacity is purposely
exaggerated so that it changes with
the impressed frequency by just the
amount needed to keep the coil
connected across the tube tuned to
resonance at all times.
The relatively large gain Of the
amplifier impressed voltages on the
detector which are far in excess of
those ordinarily encountered SO that
plate rectif1cation is employed. This
method, while less sensitive than
grid rectihcation which requires a
grid leak and condenser, has the
advantage of being able to handle
very large voltages without over
loading.
The Ern-Roe Sporting Goods
Company will have on display a
complete line of the new Sparton
radios employing the Equasonne
circuit.