ARACNEWS - ARAC - Andover Radio Amateur Club · THE MARCONI LODESTONE RECEIVER The Block diagram...

ARAC

SPRING BOOT SALE

ARACNEWS

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

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

mailto:[email protected]




AracNews

A GREEN COMPUTER

Volume 3 Issue 2

ing Corps radio and the com-

puter would really look the part

next to the Clansman radios. It

was then loaded with the Cadet

coding program, logging, and

“Hamcom”. Many may remem-

ber this one that, with a simple

hardware interface, would do

RATT, CW, FEC, & ARQ. It

now could be put to good use

on the Sea Cadet FEC broad-

cast and, later the ARQ mail-

box.

Later it developed a fault, was

put under the bench where it

remained as one of those “one

day” jobs. More modern com-

puters with Fldigi software su-

About ten years ago a friend of

mine bought this Siemens*

computer at a junk sale. It

worked but, with it’s custom

software, appeared to be a spe-

cialised military data terminal.

He then asked me to see if it

could be put to any good use.

I’m not an expert in computers

however I knew a man who

was.

After a lot of investigation it

was decided to format the 500

MB hard drive, install DOS 6

and Windows 3.1. Unfortu-

nately this probably removed

the program for the modem and

X25 drivers.

The owner, like me, was heav-

ily involved with the Air Train-

perseded it. A few more years

passed and, as the result of a

clear out, I inherited it with a

suspect power supply fault.

After undoing 16 screws I was

able to slide it out of the case. It

had been built very much with

tempest and EMC considera-

tions in mind. Both rubber and

braid gaskets were on all re-

movable panels and the LCD

display was separated from the

CPU part. The last did present a

problem, as the ribbon leads to

the bulkhead IDC connectors

were very short. Having been

told the PSU was dead I took

one look at the complex

switched mode board that ap-

peared to be a multi layer with

a ground plane on the back. I

bypassed the front panel on-off

switch and applied power.

None was getting to the unit.

With no suitable extenders to

connect all to the front unit it

was decided to put re-assemble

it and put it by for later investi-

gation.

It proved impossible to recon-

nect the short 4 ribbons and 1

molex connector to the bulk-

head so off came the front dis-

play panel, unscrew and re-

move the bulkhead connector,

and through the small hole re-

cover the ribbons and reconnect

on both sides. With all re-

assembled power was applied

but still dead. On operating the

On-Off-Trip switch on the rear

panel (something I had tried

before) then it came to life –

but only with the switch held in

the reset position. Holding the

switch over and with one finger

typing all seemed to be OK.

There was then a load “click”

from the trip switch and since it

has been working fine.

For those who were not able to

see it at a recent ARAC meet-

ing some details-

CPU 80486, Co-processor 80387,

500MB HDD, & 1.4 MB 3.5 in

floppy.

640K base & 31,774 extended

memory.

*Labelled Siemens/ SAIC Elec-

tronics Systems, a division of Sci-

ence Applications International

Corp.

Richard. M1CFW

A Green Computer (Continued)

AracNews Volume 3 Issue 2

The Gate Patrol Hard at Work!!

Mud mud glorious mud

The Boot Sale entrance was changed

Some More

BOOT SALE PICTURES


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.


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.


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.


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).


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.


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


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

11.41 7.150 GB1BWM Bursledon Windmill / Southampton

12:31 7.136 GBØHSM High Salvington Windmill / Worthing

12:44 7.140 GBØJAJ Jack & Jill Windmills / Clayton, West Sussex

12:50 7.143 GB2DWM Duloe Windmill / St. Neots, Cambridge

12:55 7.143 G2HR Not a Mill Station, Silverthorne Radio Club

13:18 7.140 GB3LMW Llyanrafon Water Mill / Cwmbran, Wales

14:21 7.113 GB2MBB Mill of Bellabeg / Aberdeenshire

15.05.2016

11:36 7.151 GB2QM Quendale Mill / Shetland

13:17 7.109 GB6MW Meopham Windmill / Kent

13:44 7.173 GB5HW Heage Windmill / Spondon, Derby

14:00 7.140 GB5GSM Gunton Saw Mill / Hanworth Fen, Norfolk

16:00 7.176 GBØSM Skidby Mill / East Yorkshire

14.05.2016 Crux Easton Wind Engine - Amateur Radio Station Log GBØCEE.


The Andover

Radio

Amateur

Club is

affiliated to

the Radio

Society of

Great Britain

ICOM 703 FOR SALE

ICOM IC703 all mode hf/50mhz 10 watt transceiver

auto/manual tuner - complete with mic, 2 DC power leads,

manual and box - very good condition, no marks etc - £375 ono

See Cliff at the club for demo or phone 01264 359219 or email

[email protected]


ARACNEWS - ARAC - Andover Radio Amateur Club · THE MARCONI LODESTONE RECEIVER The Block diagram...

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Transcript of ARACNEWS - ARAC - Andover Radio Amateur Club · THE MARCONI LODESTONE RECEIVER The Block diagram...