Getting the Ionosphere on the air in WWII.

[Geoffrey Sinclair]

An excerpt from a report, probably written in 1945.

THE OFFICIAL HISTORY OF THE R.A.A.F.
DIRECTORATE OF TELECOMMUNICATIONS AND RADAR
BY W/CDR, G. F. GATES

IONOSPHERIC ORGANISATION.

Radio communication, over all but relatively short distances, is effect by
reflection of the waves by the ionosphere, or ionised layers in the upper
atmosphere.

Radio waves penetrate, or are reflected by the different layers of the
ionosphere according to their frequency, and the layers themselves vary in
height with season, climate changes, and the sunspot cycle, so that the
height of the relevant reflecting layer, combined with the angle of
radiation, determines the angle of reflection and consequently the length of
"hop" for any given transmitting frequency at a particular time. Further,
from a study of ionospheric conditions, it is possible to submit either the
optimum frequency or the maximum usable frequency for any given distance and
time.

The R.A.A.F., at an early stage in the war, sought to promote extensive
ionospheric studies, not only within the Service, but throughout Australia,
and finally on the international plane. This policy was based on a
statement made by the International Consultative Committee for Radio
Communications (C.C.I.R.) in a report prepared by the Committee on Radio
Wave Propagation in London on the 25th November, 1937. In this report, it
ware made clear that then wore only two methods open for the specification
of long distance transmissions-

(i) Derivation of accurate, but at that time, limited results based on
normal incidence/equivalent height frequency curves of the ionosphere.
(ii) Use of extensive practical knowledge of the transmission of radio waves
over the earth's surface for the construction of more comprehensive but less
accurate charts of the ionosphere.

The R.A.A.F. chose the scientific path and having noted the statement that
normal incidence as a survey of the results then available were inadequate
ionosphere all over the earth and, having regard also to the Committee's
conclusion that extensions of such measurements and prompt publication would
be highly desirable, decided to take steps to foster such measurements and
the speedy exchange of information which, it foresaw, was clearly necessary
if its aim of maintaining communication 24 hours a day, 365 days of the year
was to be realised. Had it not been for this action, it seems clear that the
work of many physicists would have been shelved until after the war, and a
valuable weapon thus lost.

In 1940, the Watheroo Magnetic Observatory of the Carnegie Institute was
approached for assistance in the preparation of short-term predictions of
maximum usable frequencies and reports of ionospheric disturbances. The
Watheroo Magnetic Observatory co-operated fully in this matter. Shortly
afterwards, a request was made to the Mount Stromlo Observatory, Canberra,
for the supply of a daily report of ionospheric conditions. That service
was commenced within a short time.

The records obtained at Canberra had been analysed by the Radio Research
Board in Sydney for some years past, and the question of monthly predictions
of maximum usable frequencies was taken up with the Board. It was agreed
that the supply of additional ionospheric data was desirable, and curves
prepared by the Sydney Laboratory have been published regularly since that
time. At this stage, curves of maximum usable frequency were available only
for the latitudes of 40°N and 30°S, and these had to suffice for all
communications both in the Commonwealth and abroad.

It was laid down early in 1941 that R.A.A.F. Signals Officers were
responsible for selecting correct frequencies for operations from those
allotted, and that they must, at all times be familiar with the maximum skip
distances expected on any given frequencies so as to obviate operational
communication failures. However, it was soon found that conditions in
tropical regions were not being satisfactorily predicted, and the need for
additional data was indicated.

The Carnegie Institution of Washington agreed to send by cable monthly
summaries of ionospheric data for Huancayo, Peru, at 12°S, and the Radio
Research Board offered to calculate maximum usable frequencies from this
data. Similarly, with the co-operation of the New Zealand Radio Research
Board, use has been made of data obtained at Christchurch, New Zealand, at
latitude 43°S.

By July, 1942, graphs of predicted maximum usable and optimum working
frequencies were available for four latitudes: for Huancayo, Peru, latitude
12°02.7' South; Watheroo, latitude 30°19.1' South; Canberra, latitude,
35°19' South and Christchurch, New Zealand, latitude 43°35' South. The
initial distribution of these graphs was 47 copies, of which 30 were
distributed to R.A.A.F. units, the remainder being sent to other Services
and overseas authorities. Watheroo Observatory supplied one set of
predictions whilst the Radio Research (Sydney Section) supplied the
remainder.

In September, 1942, graphs for each 10° of latitude for both Northern and
Southern latitudes, from 40° North to 50° South, for October, were prepared
by Radio Research Board and issued by the R.A.A.F. Only Southern hemisphere
graphs from the Equator to 40° South were issued to operational units, but
complete sets were issued to Government organisations, scientific and
certain other bodies where full use of the graphs could be made.

This comprehensive service was made possibly only as a result of
co-ordination of effort by the various centres of the Carnegie Institution,
Washington; the Radio Research Boards, Sydney and New Zealand; the National
Physical Laboratory and the Central Ionospheric Bureau, London, and the
National Bureau of Standards, Washington. In this connection, the aim of the
R.A.A.F. was to bring home to all concerned the need indicated above for
speedy interchange of data and to demonstrate its operational importance by
supplying, as far as lay within its power, the administrative machinery
incidental to organisation on the international plane. Research physicists
in this area of operations were thereby to be relieved of all detail likely
to detract from the main purpose, that of providing up-to-date predictions
of ionospheric conditions based on the most recent results of research
throughout the world.

In the same month (September, 1942), the Department of Air convened an
inonospheric conference in Sydney under the chairmanship of Sir John Madsen,
as a result of which the Australian Radio Propagation Committee, consisting
of representatives of the Services and Scientific Centres, was formed as a
Committee of the Radio Research Board or the Council for Scientific and
Industrial Research. (File No. 12/501/132) At the first meeting of this
Committee, it was agreed that the R.A.A.F. should continue collection and
distribution of ionospheric data, and that, in order to facilitate the
handling of Service matters, the R.A.A.F representative should be Conjoint
Secretary of the Committee. The 23rd meeting of the Committee was held in
Melbourne on Tuesday, 20th March, 1945. Studies being undertaken by the
Committee include -

(i) Tropospheric Propagation.
(ii) Ionospheric studies.
(iii) Preliminary Loran-Ionosphere observations in the Darwin area.
(iv) Noise level investigations - North Western Area. (Australia)
(v) Co-ordination of operating data regarding radio circuit performances and
ionospheric data.
(vi) Development and production of Ionospheric recorders.

Because the monthly predictions only cater for transmission via the regular
layers for average conditions, the R.A.A.F, in collaboration with the
Watheroo Magnetic Observatory of the Carnegie Institution, inaugurated a
short-term forecasting service. This was later extended to include a weekly
signal predicting transmission conditions for the forthcoming week ending
2359 hours G.M.T. Friday. The R.A.A.F. based its assessments on magnetic
data from Watheroo and Toolangi and reports of sun- spot activity from
Commonwealth Solar Observatory, in additional to data available from
Washington. On the formation of the Australian Radio Propagation Committee,
the Commonwealth Solar Observatory became responsible for issuing forecasts
of conditions for the Southwest Pacific Area. (Reference File No. 201/86/7)
This forecast is issued each week to the R.A.A.F. for immediate distribution
to the higher commands in this area for notification of all units under
their control.

In December, 1943, the Australian Radio Propagation Committee decided to
issue monthly bulletins of Ionospheric data to all the armed forces in the
Southwest Pacific Area. It contained firstly, a Scientific Item telling
something of ionospheric phenomena, how they were observed, measured, and
upon which facts the monthly predictions and weekly forecasts are based;
secondly, an Operational Item telling how to use the data and its
application to communications in general; thirdly, an analysis of
ionospheric conditions and short-period forecasts for the previous month but
one. The aim was to increase all signals personnel's knowledge of the
ionosphere since a practical understanding of the behaviour of the
ionosphere with regard to radio waves would help to ensure the efficient
selection and use of frequencies for communication purposes. These
bulletins also provided a means of explaining to personnel in the field, the
data as prepared by the Australian Radio Propagation Committee either in the
form of graphs, contours or tables and the weekly and/or special forecast of
radio transmission conditions.

However, during November, 1944, it became evident that for the data to have
direct application to a particular service it was desirable that each
Service issue its own bulletin. Therefore, in December, 1944, the R.A.A.F.
issued its first Propagation Bulletin. The contents of the Bulletin now
include an introduction and operational item, analysis of the Stromlo
forecasts and complete sets of graphs of predicted maximum usable and
optimum working frequencies from 70°N to 50°S. The operational items to
April, 1945, have included three, items on "Loran and the Ionosphere" and
the first of the series of articles on selection and performance of aerials.
In addition to the monthly graphs, world contours and predicted maximum
usable frequencies for distances 0 to 2500 miles in 500 mile intervals are
also issued to certain units only since they are applicable only to
multi-hop transmissions. In addition, it became increasingly evident that
the link between the supply of Ionospheric data to units in the field, and
the full application of such data was not complete, inasmuch as, whilst it
was possible to predict suitable frequencies for various conditions of
communication, it was obvious that insufficient consideration had been given
to the selection of appropriate aerial systems. Efforts are now being made
to associate more closely, the supply of Ionospheric data with the
performance of the various types of radiating systems available in the
R.A.A.F.

The seven chief uses made by the R.A.A.F, of the monthly graphs are -

(i) Allocation of correct frequencies for operations.

(ii) Deciding most suitable frequencies and time of change of channels to
ensure reliable 24 hours communication on point-to-point circuits.

(iii) Laying down frequencies and hours of service for R.A.A.F. H/F C.R. D/F
Stations which are situated at various latitudes throughout the
Commonwealth. These time tables must be arranged in advance so as to avoid
giving bearings when the transmitter is in skip distance from the D/F
station.

(iv) Arranging intelligence interception watches to ensure that no time is
wasted in searching frequencies higher than the maximum usable for any
distance.

(v) Determining from skip distances given implicitly in the curves, the
minimum probable distance of enemy transmissions.

(vi) Evaluation of bearings taken on enemy transmissions

(vii) Within the LORAN organisation in N.W.A. (North Western Area)

In connection with above sections (i) to (iii), an officer with two years
experience in the use of ionospheric data, and in circuit analysis, is now
located in that section responsible for frequency allocation, and is
consulted in all matters pertaining thereto.

In 1942, it was decided that additional Ionospheric observing stations were
required to provide additional propagation data to the Armed Forces and
action was taken by the R.A.A.F. to procure three Ionospheric Recording
stations for implementing facilities in Southwest Pacific Area, vide Air
Board Agenda No 3842/42. Air Board Agenda 3842/42 proposed the purchase of
three ionospheric Recorders from C.S.I.R. and Air Board minute dated 10th
April, 1942, approved this proposal. This R.A.A.F. order for three was
portion of an order for six placed through the Ministry of Munitions on
C.S.I.R., of which two went to New Zealand and one to United States. (File
No 201/16/757 Enclosures 2A, 3A & 5A.)

The equipment is of the equivalent height/multifrequency variety, and covers
a frequency range from 1.0 to 13 Mc/s in 1 minute 55 seconds. It is an
automatic recorder, that is, it switches itself on and off at appropriate
times (every ten minutes), tunes its transmitter and receiver progressively
from 1.0 to 13.0 Mc/s. and makes a photographic record of the heights from
which any echoes within this frequency range are obtained. (Radiophysics
Publication PD25/2 - "Handbook for Ionospheric
Recorder, Type J28".)

During 1943 it became evident that it was necessary to set up a long term
plan to ensure the extension of communications as fighting areas move
northwards from Australian and therefore it was decided by the Australian
Radio Propagation Committee that Radiophysics Laboratory should build seven
additional Ionospheric recorders of modern design and wide range. Of these
seven, six go to pool, two for the R.A.A.F., two for the Army and two for
the Navy, and the seventh is for the Commonwealth Solar Observatory, Mt.
Stromlo. These recorders were to be built to the R.A.A.F. Specification
Y.111.

In June, 1943, the Radio Research Board recorder at Brisbane commenced
continuous operation and records are available from that date. The first
R.A.A.F. recording station at Higgins, North Queensland, commenced operation
late in November, 1944. Installations are under way at Momote (Admiralty
Is.) and Stuart Creek near Townsville. (Reference File No. 201/23/443.) A
further site is nearing completion at Hobart but the A.R.P.C. considers that
Northern sites hold priority in the distribution of equipment. It is
intended that one of the further seven recording sets being produced by
Radiophysics will be installed at Hobart. From analysis of the records from
Brisbane over the twelve months period and from early records from Higgins
it has become evident that the frequency range will need to be increased and
the new recorders are to be built to cover the range 1 to 16 Mc/s. instead
of 1 to 13 Me/s.

In September, 1943, Radiophysics approached the Department of Air for the
R.A.A.F to make available a suitable person to take over the information on
Ionospheric Recorders and to assist with the installations. W/O. G.S.
Johnston proceeded to Radiophysics and remained there for approximately nine
months assisting in the development, assembly, and testing of the various
units of the equipment. In October, 1944, after selecting a recorder site
at Momote, W/O, Johnston proceeded to Higgins, Cape York, and supervised the
installation and training of operators for the recorder there. Mr. A.J.
Higgs of R.P.L. who was responsible for the design of the equipment
proceeded to Higgins with R.A.A.F. approval for the calibration and final
test of the recorder.

In September, 1943, it was decided that the development of a direct reading
Ionospheric recorder was well within reach of practical achievement of the
Radiophysics Laboratory and that such an equipment would be an invaluable
adjunct to the Signals Organisation within the R.A.A.F. Approval of
expenditure amounting to £3,000 for this initial equipment was granted in
November, 1943. (File No. 134/2/36.)

In April, 1944, an International Radio Wave Propagation Conference was held
in Washington. This was proceeded by a preliminary Ionospheric conference
in London in March, 1944. The R.A.A.F. was represented at both of these
conferences, by Squadron Leader A.L. Hall. (Report - "The International
Radio Wave Propagation Conference, Washington, 1944" - by Squadron Leader
A.L. Hall.)

With the opening of new long-haul circuits covering distances up to 3,000
miles it has become evident that frequencies higher than those anticipated
can be used most efficiently. A considerable amount of study is being done
on this work and it appears that over an area of Eastern and North-Eastern
Australia reliable communication to say 80% of total time is being
maintained by transmission via the Abnormal "E" layers. In this connection
a preliminary report entitled "Occurence of Abnormal "E" Echoes at Cape
York" by D.O. Stewart, No R.R.B. R/16 is to hand. (File No. 201/86/1.) As a
result of these facts a proposal has been put forth that some type of mobile
recorder should be made available to the R.A.A.F. in order that a more
immediate complete picture of the Ionosphere over these areas can be
obtained without waiting for the initial installation of our Ionospheric
recorders in this area.

In accordance with the findings of the International Radio Wave Propagation
Conference, Washington, April, 1944, it was decided that certain officers
should be attached for a period up to ten days to the Sydney Laboratory or
the Radio Research board for a period of intensive study and reading to
enable them to have a more complete appreciation or the work being carried
out in the field of Wave Propagation.

Geoffrey Sinclair

[Jim Wilkins]

"Geoffrey Sinclair" <gsinc...@froggy.com.au> wrote in message
news:B--dnRu3I8xpBOnD...@westnet.com.au...

I received my radio training and ham license from a retired British
radar wizard who had done fundamental studies of the ionosphere.