COMMUNICATIONS DEVICES, THEORY RATE HIGH AT SHOW

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03330A004100100001-0
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 1
• Document Creation Date: December 22, 2016
• Document Release Date: February 15, 2012
• Sequence Number: 1
• Publication Date: August 1, 1959
• Content Type: OPEN SOURCE

Declassified and Approved For Release 2012/02/15: CIA-RDP78-03330A004100100001-0
I
General News
Communications Devices,
Theory Rate High at Show
By WALTER JOHNSON
SAN FRANCISCO. - Numerous
exhibits of the latest in communi-
cations equipment attracted notice-
able attention from the large crowd
and several technical papers were
read outlining fresh and interesting
ideas in communications technique.
Some or those described as the
most fascinating dealt with
meteor-burst transmission meth-
ods, with speakers declaring that
tests support the belief that this
type of propagation will reliably
meet certain medium-range. air-
ground needs for data transmis-
sion, as well as for other forms of
communications.
Bruce M. Sifford, Stanford Re-
search Institute, Menlo Park,
Cal., in a paper describing the
optimum transmission rate for
low-power meteor-burst commu-
nications systems, stated a reli-
able low-power VHF system has
been developed which will operate
up to 1,300 miles.
Meteor. - burst systems transmit
Intermittently by reflecting signals
from ionized trails left by disinte-
grating meteors. They are consid-
ered particularly useful for mobile
operations.
Synchronous Detection.
Mr. Sifford said tests indicate
that the amplitude and. phase of
received signals can be relatively
C A.-11 ~
r'41459
stable during a burst so that syn-
chronous detection can be used.
For a low-power transmitter, he
said, an optimum bandwidth could
be around 500 cps.
He presented considerable data
gathered on a Bozeman (Mont.)-
Palo Alto (Cal.) link.
Mr. Sifford pointed out that
higher frequency systems do not
have as much capacity as lower
frequency systems, but they are
less susceptible to severe ionospheric
disturbances which plague the low-
er frequencies.
As an example of capacity, he
said that with'a bandwith of 2.3 kc
(representing a "bit" transmission
rate of 1,150 bits per second), an
average information rate of nine
bits per second is possible. This
means a- 25 word message, at six
letters per word and five bits per
letter, would take some 1% minutes
to transmit. (The optimum duty
cycle of such a,system at this fre-
quency would be only about 1.3 per
cent).
He emphasized that these results
were based on a limited amount of
data taken on a particular path
during early morning hours of op=
eration. A system designed for
other times and paths, he noted,
would require additional propaga-
tion measurements. Wide varia-
tions from this avarge can also be
expected for short operating times,
he stated.
. Bandwidth Dependence.
Mr. Sifford concluded that the
best bandwidth is dependent upon
other system parameters, such as
transmitter power, antenna gain
and threshhold level.
Since npost useful meteor trails
are apt to be off the direct path
between transmitter and receiver,
he pointed out it is not likely that
narrow-beam antennas would sig-
nificantly increase the capacity of
such a system.
On Tuesday, Donald R. Church,
Acoustica Associates, Inc., Mineola,
N. Y., described a new type under-
water, low-frequency sound source
analogous to highly directional
end-fire antenna arrays.
The sound source is a long, thin
rod which radiates sound energy
into water. A 10 kc per second
model, 13:feet long, showed a di-
rectivity index of over 20 db, he
stated, w'th an. efficiency of over
60 per cent and a power handling
capacity Af over 2 kw.
In a paper written on electro-
magnetic effects associated with
hypersonic reentry vehicles, R. F.
Whitmer, Microwave Physics Lab-
oratory, Sylvania Electric Products,
Inc., Mountain View, Cal., put a
lot of emphasis on the effect of the
ionized shock layer around the ve-
hicle on propagation characteris-
tics.
He summarized factors affecting
electromagnetic wave transmission
and reception in connection with
remote controlled guidance, tele-
metry, voice communications and
radar tracking of a reentry vehicle.
G. Swarup and K. S. Yang, of
Stanford University Radio Propa-
gation Laboratory, Stanford, Cal.,
discussed some of the interfero-
meter phasing problems encoun-
tered at microwave frequencies.
K. E. Perry, Massachusetts Insti-
tute of Technology (Lincoln Lab-
oratory), Lexington, Mass., said a
device is being designed to encode
a digital message into a redundant
form for transmission over a phone
line or similar channel.
Declassified and Approved For Release 2012/02/15: CIA-RDP78-03330A004100100001-0