The Washington times., 1925-10-23
Y A | j { IS
SEEN IN
DEVICE
Extremely Complicated Re-
ceiving Set Would Be De-
manded by This Invention
By ROBERT S. THoRNBURGH

By ROBERT s. THORNBURGH
A remarkable invention by John
Hays Hammond, jr., son of the
widely known capitalist-engineer,
by which it is possible to trans
NIT from a single machine eight
separate radio signals on the
same wave length, has been ex-
amined by Navy experts, and
while they believe cit has enor-
nous possibilities" it has been
found impracticable for service
use at present, it was learned
today.
Uses Single Carrier Waves
Officials who studied the Ham,
mond device expressed the opinion
that its operation on wave lengths
between 200 and 500, where most
broadcasting takes place, would
complicate rather than solve the
present congestion in radio COM
munication channels.
They pointed out, however, that
the Hammond invention operates on
very low wave lengths, or high
frequencies, now employed exclu-
siyely for special or experimental
purposes. It's possible application
20 the higher wave lengths was
studied since 1t Is the relief of over
crowding in this channel that is
necessary to meet the interference
problem.
Briefly, experts said, the Ham
mond machine makes possible the
broadcasting on q single wave
length of eight separate signals
through the use of distinct net
OF contemporaries"
Therefore, it would be theoretical
iy possible to combines eight sta
lions and transmit the various pro-
grams of each simultaneously from
q single machine, on a single wave
length, thus releasing seven other
channels for the use Of other sta
tions. II successful it would mean
that over $500 stations could oper-
ate where but 500 are now on the
air.
Experts explained that the device
operates with a single carrier
wave" but with eight sub-fre-
sQuencies, superimposed on the origi-
nal wave.
They declared that q receiving set
20 catch" broadcast programs from
the multiple-signal machine would
require not only one detector with
its tube, coil and set of dials for
the carrier wave, but a second de-
tector and accessories to get the
sub-frequency signal. This receiv-
ing set would be extremely compi-
rafad IN hIIiId and OnPrate.
None of the 100000 commercial
sets in operation in the United
States would be capable of receiv-
ing the multiple signals, but ex-
perts consider it possible that with
proper development Of receivers
and broadcasting stations, multiple
broadcasting may ultimately prove
e solution of interference.
The ordinary receiver tuning in
on q multiple signal station would
get a heterodyne squeal, similar to
that noticed when two or more sta
lions are operating on the same
wave length. The carrier wave
could be picked up but not the sub
frequencies.
A second objection found by ex-
perts was in the creation by the
multiple signal machine Of a greater
operating on a given wave creates
a first harmonic or ''undertone" at
half it's wave length.
IF eight signals are being trans
mitted on a 5O0-meter wave eight
harmonies are created at $50 meters,
causing just eight times the present
interference" an expert said.
Officials said that the Hammond
device is aimed at doing in the
air what has been accomplished on
telegraph and telephone cables,
where a number of different signals
are sent simultaneously on the same
wire. No harmonic difficulty is
found on wire transmission.
The suppression of harmonies is
one of the big problems Of radio
engineering which has not yet been
worked out successfully. Elimina-
ton Of these curious 'undertones"
will go a long way toward meeting
the interference problem, officials
said.