ARAC SPRING BOOT SALE A RAC N EWS May 2016 NEWBURY RADIO RALLY Newbury Showground Next to M4 J13 19th JUNE (Fathers Day) Admission £2.50 Boot Pitches £12.50 Details:- [email protected]Date for your Diary Arac Spring Boot Sale Page 1 WANTED - ARTICLES Page 1 A Green Computer Page 2 More Boot Sale Pictures Page 3 MF Direction Finding at Sea Page 4-9 Mills on Air Day Page 10-11 For Sale Page 11 New Volume 3 Issue 2 IN THIS ISSUE The EDITORS DESK Please send all your News, Reports and Articles to [email protected]Microsoft Word is the preferred format if possible Thanks - Tony GØOMD The Arac spring boot sale was this year booked for Sunday 17th April. The weather was kind but a bit on the chilly side first off - (that was an under statement I hear you early starters say). Soon the sellers were starting to set up and they were closely fol- lowed by the bargain hunters. Everyone seemed to be enjoying themselves, even Martin, on the right, seems to be enjoying himself preparing food for the masses! The Magazine of the Andover Radio Amateur Club Martin MØMWS Don’t just say “I couldn’t possibly write an article for the Newsletter”, without even trying – Dust off your keyboard and put a few thoughts together – send it to [email protected]Microsoft word is the ideal format What could be simpler – don’t just leave it to the others, have a go yourself! WANTED Articles for AracNews
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ARACNEWS - ARAC - Andover Radio Amateur Club · THE MARCONI LODESTONE RECEIVER The Block diagram (1) above shows it was a single conversion super heterodyne receiver. Frequency range
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
I know that some of the members of ARAC are active in VHF and HF DF so I thought there might be interest in the Medium wave
DF equipment that I used at sea in the 1960’s.
When I was a Merchant Navy Radio Officer in the days before GPS, the ships I sailed on had very little in the way of electronic aids to
navigation. There were hyperbolic radio systems in operation at the time such as Loran and the Decca Navigator chains, but these
were not used by the shipping company that I worked for.
When out of sight of land and beyond radar range, navigation was performed by dead reckoning or by the use of a sextant for Sun
and Star sightings. When navigating in bad weather when sextant position fixes were impossible the ship borne Radio DF equipment
would be used to determine its position, subject to radio beacons being within range.
An Internet search on DF equipment of the time will yield a tremendous amount of information on the theory and practice of the dif-
ferent types of systems and equipments that were then in service. However I only sailed with the Marconi Lodestone DF receiver and
the Bellini Tosi loop system for which the Marconi Marine Company held the patents so it is those I will describe. My explanation of
the theory of how that system worked is descriptive. In this article, hope to explain how the DF system worked, the factors that af-
fected its accuracy and how it was used.
From 1934 it was legally compulsory for ships over 1600 tonnes to carry DF equipment because DF was considered essential to
Safety of Life at Sea. It was the only electronic navigational aid of the time so mandated.
To illustrate its importance, Radio Surveyors inspected the date of the last calibration that had been carried out and the results. They
would also inspect the details of any maintenance work that had been undertaken on the DF equipment to establish the impact (if
any) on its accuracy.
Irregularities or non compliance with any of the regulatory requirements relating to the DF could result in the ship being refused per-
mission to sail until the deficiency was corrected.
It was usual practice at the time for the DF receiver in the ships that I sailed on to be located in the radio room and operated by the
Radio Officer.
The principal components of the system were: The Bellini Tosi Loops.
The Marconi Lodestone receiver incorporating
The radio Goniometer.
THE BELLINI TOSI LOOPS
The Bellini Tosi loop system was invented in the early 1900’s by the two Italians after which the antenna was named. Dr Bellini was
a scientist and Captain Tosi was a Naval Captain. The installed loops of 1960 were mounted on the centreline of the ship and were
(as far as was practical ) clear of obstructions and ship’s superstructure. The smaller (inner) of the two loops was placed along the
Fore/Aft line of the ship. The Internet picture above shows one installation.
MF RADIO DIRECTION FINDING AT SEA IN THE 1960’s
by John Leary G4YSB
This second picture shows the Bellini Tosi loop system stripped of its protective paintwork. The outer brass (non ferrous) tubes were
prevented from acting as electromagnetic screens by having their conductivity broken by insulators at their base. The loop wires
themselves were contained within the tubes. The length of the loop wires were a fraction of the wavelength of the received signals
and were never tuned to resonance. The vertical rod, (not fitted to all loops) acted as the sense antenna. When the sense rod was
not fitted, a separate short wire antenna would be used instead. The sense antenna was tuned.
THE RADIO GONIOMETER
The photograph above was generously given to me by Richard Powell / M1CFW and is an aeronautical Goniometer. To be honest, I
have never seen a maritime unit! I imagine the two are very similar.
AracNews Page 5 Volume 3 Issue 2
THE MARCONI LODESTONE RECEIVER
The Block diagram (1) above shows it was a single conversion super heterodyne receiver. Frequency range 250 – 550 kHz. You will
note that the receiver had no loudspeaker. All monitoring of the audio output was undertaken through the use of headphones.
All of the signal phase measurements, signal combining and sense/search coil selection took place before the Radio Frequency Am-
plifier of the Lodestone receiver.
A picture of the Marconi Lodestone DF receiver. The size (ignoring the sloping front) was approximately 18” cubed. Picture obtained
from the Internet.
HOW IT WORKED
Firstly, the basic loop theory bit.
Consider a single loop that is capable of being rotated through 360 degrees relative to a fixed point transmitting source that pro-
duces a vertically polarised wave. The radiated electromagnetic wave induces voltages Ea and Eb in the vertical sides (a) and (b) of
the loop. Any phase difference between the two voltages causes a resultant loop voltage Er. For this simple analysis we will assume
that there are no radiated signals inducing voltages in the top or bottom section of the loop. As the loop is rotated through 360 de-
grees relative to the direction of the transmitted signal, there are two positions of maximum and two positions of minimum output.
Plotting the resultant Er gives us the familiar figure of eight polar diagram.
AracNews Page 6 Volume 3 Issue 2
Now the actual bit.
In the Bellini Tosi loop system, the Fore/ Aft and Port/Starboard loop windings were connected to their corresponding field windings
on the radio Goniometer that was located within the Lodestone receiver. These two sets of windings were wound on its insulated for-
mer at 90 degrees to each other. These two sets of windings created an electromagnetic field within the Goniometer that was identi-
cal to that impacting on the loops. Inside the Goniometer were two sets of coils wound at 90 degrees to each other and mounted on
a rotatable, common shaft. One coil was known as the search coil and the other the sense coil. These search/sense coils were con-
nected to the slip rings shown in the Goniometer photograph above.
For bearing taking, the minimum level (nulls) from the search coil was chosen because they were more clearly defined than the maxi-
mum (at the top of the figure of eight). However there is clearly an ambiguity with a figure of eight polar plot with two nulls, particu-
larly if you do not know where you are in relation to the beacon signal, because there are two possible directions from which the sig-
nal can come.
Sensing
The two null ambiguity referred to above was eliminated through a process called “sensing”. If we combine the radio beacon signal
from the Goniometer search coil with the voltage induced in a vertical (sense) antenna; which is Omni directional, the resultant is the
heart shaped or cardioid polar plot shown below. The signal from the vertical sense antenna was adjusted by a front panel Zero
sharpening control for the sharpest null. The wire sense antenna was short at around 10-15 feet.
The eagle eyed reader will have noticed that in the cardioid polar plot above, that the null produced by combining the search coil and
(Omni directional) sense antenna signals has been shifted by 90 degrees. This error was corrected by bringing into service the sense
coil during sensing which the reader will remember was mounted at right angles (90 degrees) to the search coil.
The rotatable shaft that connected to the Goniometer’s search/sense coils was itself connected to a pointer on the Lodestone’s
front panel that rotated around a graduated scale starting from 0 degrees (ships head) 90 degrees (Starboard beam) 180 degrees
(astern) and 270 degrees (Port beam).
The polar diagram switch on the Lodestone’s front panel had four positions selecting one of four polar plots, namely:
Stand BI (Omni directional),
DF (Figure of Eight),
Sense check 1 (Cardioid),
Sense Check 2 (Cardioid but operating a second graduated 0 to 360 degree scale that was 180 degrees different from
that in Sense check 1.
Moving between Sense check 1 and 2 would quickly determine which had the lowest signal and therefore the true bearing of the
beacon.
AracNews Page 7 Volume 3 Issue 2
ERRORS
The two main categories of error that impacted on bearing accuracy were site errors and propagation errors.
Site Errors
The ships metallic hull and superstructure acted as receiving and re-transmitting antennas when subjected to transmitted electro-
magnetic radiation. These re-radiated signals of the wanted DF transmissions combined with the wanted signals at the loops to
cause an error to the measured bearing. The primary error was the quadrantal error where the mass of metalwork along the Fore and
Aft line of the ship lead to errors that peaked at 45, 135, 225 and 315 degrees ( four quadrants hence the name). The effect of this
quadrantal error was to move the actual bearing more towards the centreline of the ship.
The second error was known as semicircular error. This was caused by the ships superstructure in the viscinity of the loops. The ef-
fect of this error which peaked at 90 and 270 degrees tended to move the wanted bearing thwartships (ie at right angles to the cen-
treline of the ship).
In practice these errors combined to produce a complex error profile, the nature of which had to be established through a process
called calibration (see below).
Mounted within the Lodestone receiver cabinet was a correction panel that was adjusted to reduce the scale of the quadrantal error
at the time of calibration. This correction circuitry was generally but not always connected across the Fore/Aft loop wiring.
Propagation Errors
The DF system described could be affected by propagational errors that fell into three distinct categories, namely coastal refraction,
coastal reflection and night effect.
A radio wave transmitted from a shore based station could be bent (refracted) when it left the coast and passed over the sea due to
the different dielectric constants of the two mediums. One way to overcome this error was to mount the beacon transmitter on the
sea (light houses or light ships) or as near to the coast as possible.
Reflection could be caused by beacon radio waves hitting shore based objects and being propagated in a different direction. The
problem on board ship was that you might be unaware that it was happening. One method of detecting whether it was happening
was to swing the search coil in the Goniometer to see whether there were other close- in nulls.
As the name suggests, night effect occurred during night time when surface waves are influenced by signals produced by the same
transmitter that are reflected by the ionosphere. The presence of night effect could be determined to some extent by the presence of
fading of the beacon’s signal.
CALIBRATION
When the DF was calibrated it was practice to use a radio beacon that was within sight of the ship e.g. a Lightship. Physical distance
was usually about a mile. Calibration was carried out by taking simultaneous visual and radio bearings as the ship was swung slowly
through 360 degrees at least twice. Visual and radio bearing had to be taken every 5 degrees. A gong button on the DF receiver
would ring a bell on the bridge to inform the navigator when to take a visual compass bearing.
The results of the visual and radio bearings would be plotted on chart paper to produce a calibration curve and from this, data would
be extracted to create a table of bearing corrections. After the calibration curves had been plotted it was usual to adjust the quad-
rantal error correction panel to minimise the effects of this error. However on one ship that I sailed on, where the original DF receiver
was replaced due to age, both the old receiver and the new one required the correction circuitry to be connected across the
Port/Starboard loop wiring because the semi circular error on that vessel was by far the predominant error.
Prior to calibration all of the ships antennas (with two exceptions) would be isolated. The first exception was a single wire antenna
connected to the ship’s Auto Alarm. The second exception was the DF’s sense antenna. Any broadcast receiver antennas in the vicin-
ity of the loops would have to be lowered and stowed away neatly. The ships antenna setup prior to calibration would all have to be
recorded in the ship’s wireless log.
Check bearings would be taken throughout a voyage when the ship was within sight of a radio beacon. These would be taken along
one side of the vessel or the other as the ship was underway. As mentioned previously the calibration and check bearing date re-
cords and results were very important to Marine Radio Surveyors.
On the ships I sailed on, all DF bearings were relative to the ships head. Later versions of the Lodestone receiver could be fitted with
a gyro repeater so that both true and relative bearings could be displayed simultaneously but this was never a feature of any of the
DF receivers that I used.
HOW IT WAS USED
The details of radio beacons were published in documents produced by the International Telecommunication Union (ITU) that were
carried on all ships (2). The 1966 details of the Lundy Island North Light House are shown below. (Purely chosen as an example).
AracNews Page 8 Volume 3 Issue 2
The map above shows the position of the radio beacons mentioned in the Table (marked by the push pins).
A ship travelling from the South Atlantic to say Liverpool or the Port of Bristol could take bearings on Tuscar Rock, South Bishop and
North Lundy beacons. The triangular intersection of the three bearings (when corrected from the information on the calibration
chart), would create what was known as a cocked hat when drawn on the navigator’s paper chart. The ship’s position would lay
within the area intersected by the three bearings. The smaller the cocked hat the more accurate the results.
A ship in distress would as part of its Auto Alarm distress signal, produce a continuously modulated carrier on 500 kHz (the Interna-
tional Distress frequency) that would be used by rescue ships to take bearings on its position.
On one ship I sailed on, I was required to take bearings over a period of about 8 hours on an aeronautical beacon located at the air-
port immediately behind the port of Jeddah in Saudi Arabia. This was to enable the ship to navigate the treacherous approach to the
Port at night (most unusual for Jeddah), in order to meet a time critical arrival schedule.
In more recent times I have seen Bellini Tosi loops on ships, particularly Foreign warships but I have no idea whether they are still
used and if they are to what purpose.
The MF Marconi DF system and the radio beacons described (certainly around the UK) together with the Radio Officers that used
them, have now all passed into history having been made totally redundant by advances in technology and the extensive civilian use
of GPS location information.
References. (1) Marine Radio Manual. Danielson & Mayoh .
(2) ITU. List of Radio Determination and Special Service Stations March 1966.
AracNews Page 9 Volume 3 Issue 2
John G4YSB
The weekend 14th/ 15th
May 2016 saw members of the Andover Radio Amateur Club taking part with the special event callsign GB0CEE for the second year at this location in northwest Hampshire.
Cliff G0WKK, Mal G8FHI, and Ivan 2E0DUM manned the station over the weekend in the comfort of a caravan. The equipment used was a Kenwood TS 570, and a Yaesu FT450d with a choice of 3 anten-nas, a half wave end fed wire on 40m, a halfsize G5RV, and a club project 7m fishing pole vertical.
Unfortunately the HF band conditions have been poor
MILLS ON AIR DAY by Mal G8FHI
CRUX EASTON WIND ENGINE GBØCEE
AracNews Page 10 Volume 3 Issue 2
lately and this trend con-tinued over the weekend making it very difficult to work within the UK and into near Europe where the Mills were located. We only managed to work 16 other Mills and most of these after mid-day on both days when 40m sud-denly opened up for no more than a couple of hours and faded away again. We did hear Mills on other bands but could-n’t raise them.
Crux Easton is a small hamlet in North West Hamp-shire and the Wind Engine is located next to the well house that it served to lift water for the farm, run a barn thresher,
and grind corn, the 350 ft well predates the Wind Engine by about 100 years. The Wind Engine was built in 1891/92 by the engineer John Wallis Titt ( Warminster) and was restored in 2002. More information can be found on the Hampshire Mills website.
We are invited to take part next year from Crux Easton Wind Engine, we hope conditions are much better.
73s the GB0CEE team.
CRUX EASTON WIND ENGINE
GBØCEE
Photo by Cliff GØWKK
Time UTC Frequency Station Worked Mill name / location
09:36 7.158 ON2CYV/P Windmill / Belgium
09:50 7.177 GB1WW Wilton Mill / Wiltshire
10:04 7.121 PI4WFL/MILL De Herder / Medemblik North Holland
10:28 7.107 GB2GW Gleaston Water Mill / Ulverston
11:15 7.084 PI4DHG De Vlieger Windmill / Netherlands