opposed to the dual symbol type intelligence of 
QFM. (A dual symbol system is one where the 
binary intelligence is contained in a pulse on 
either of two channels, such as FSK teletype. ) 
Table I shows the modulation modes of 
the Air Force AN/URC-23 equipment. 
TABLE I 
AN/URC-23 Modulation Modes 
Number of 
QFM/QPM 
Channels 
Data Rates 
(bits/ second) 
Modulation 
The above table illustrates several of the 
modulation schemes possible with QFM and OPM 
but does not include any of the redundant modes of 
operation. (A redundant system is one where the 
same binary bit of intelligence is representedon 
two or more channels, thus giving repetition. ) To 
illustrate the modulation technique in more detail, 
a dual channel system with a redundancy factor of 
four will be described. 
Figure 4 shows a typical transmitter 
output as viewed at the antenna. The signal con- 
sists of a series of cosine-squared shaped pulses 
but not all at the same radio frequency and each 
group of four representing one binary digit. The 
separate received waveforms are shown witha 
small amount of multipath which exists inthe 
receiver system through detection and integration, 
but has no effect onthe converted digital output. 
This form of redundancy serves to improve 
reliability in the presence of interference. 
There are many possible configurations 
of QFM and QPM. Categorically, a particular 
system cannot be recommended for oceanographic 
use until such parametersas data rate, reliability, 
bandwidth allocation, and geographical locations 
are determined. In addition, several other 
problems enter into the system. If continuous 
24-hour data are required and interim storage at 
the source is impossible, operating frequency 
becomes a problem. Usually, the optimum fre- 
quency for daytime use will not even be usable at 
nighttime and vice versa, therefore, multiple fre- 
quencies will be required for continuous duty. 
Power, of course, will be anever-ceasing problem 
for anunmanned buoy but will not be treated here. 
63 
The final problem, but not inthe technical 
area, is one of getting a frequency allocation in 
the HF band. A recent letter from the FCC to the 
author indicates that there are presentlyno alloca- 
tions for oceanographic data use, noris the Com- 
missionanticipating the allocation of any for such 
work. This will not interfere with data collection 
by Government organizations because their cur- 
rent allocations may be used as they see fit in 
most cases; but the private institution will suffer 
unless their sponsoring agency grants an alloca- 
tion. However, experimental licenses and alloca- 
tions may be obtained and, although good only for 
a limited period of time, may be adequate to com- 
plete a specific program. 
FUTURE TECHNIQUES 
It has been suggested that in the future 
data may be collected in remote locations and 
telemetered to shore via a satellite system. 
This is probably very practical and feasible, but 
is still many years in the future considering the 
other more pressing requirements of communica- 
tion satellites. 
A possible new field of communications 
exists where the earth strata found just under the 
deep ocean floor may propagate transmitted energy 
toa receiver site. If so, oceanographic equipment 
may be placed on or near the ocean floor, thus 
eliminating the needfor surface equipment, except 
for a subsurface buoy for maintenance purposes. 
This would eliminate the surface equipment which 
is always subject to pilferage and ship damage. 
Investigation of these techniques is now in 
progress. 
REFERENCES 
1) Nichols and Ranch, Radio Telemetry, 2nd 
edition. 
2) J. D. Lambert, "High Frequency Multipath 
Analysis bythe Short Pulse—Long Pulse Method," 
IRE Convention Record, Part 1, pp 294 to 299, 
1957 Wescon. 
3) J. H. Chisholm, et al, ''Investigation of 
Angular Scattering and Multipath Properties of 
Tropospheric Propagation of Short Radio Waves 
Beyond the Horizon,'! Proc. IRE, Vol. 43, 
pp l3l7 toi 1335; Octoberwlg5o% 
"New System Defeats 
May 
4) George A. Scheer, 
Multipath Effect, '' Electronic Industries, 
1960. 
5) J. M. Snodgrass, ''Problems of the Oceanog- 
rapher in the Space Age,'' Proc. of the 
National Telemeterin Conference, p 12-9, 
1961. 
