The book from which this chapter is excerpted was sold by British Marconi's publishing arm, The Wireless Press, and covers standard Marconi shipboard equipment, including spark transmitters, plus magnetic and crystal receivers.
The Maintenance of Wireless Telegraph Apparatus, Percy W. Harris, 1917, pages 1-9:
CHAPTER I
GENERAL INFORMATION
THE WIRELESS CABIN
BEFORE considering in detail the apparatus used in a wireless telegraph station, it will be well to give some thought to a few matters relating to the room or rooms in which the apparatus is arranged. On land stations accommodation is generally spacious, but on board ship, where every inch of deck space is of value, more restricted quarters are the rule, particularly on old vessels where the wireless cabin is not a part of the original design. Because of this restriction of space it is absolutely essential to keep everything in a tidy and orderly condition, otherwise inefficient working will result.
The operating cabin is provided with drawers, and frequently with cupboards, to contain books, papers and spare parts. Those drawers which are adjacent to, or immediately beneath the operating table should be allotted to telegram forms, pencils, and the stationery most frequently required. Stores of forms and documents rarely needed should be made to occupy the less accessible compartments. It is also well to give up a drawer to the tools and spare parts most likely to be of service in cases of emergency, and in the same place should be stored cotton waste, oily rags and the rough cloths used for cleaning. Other tools and spares should be locked in the tool-box and not distributed through the various drawers and cupboards.
Having disposed of the stationery, books, spare parts, tools, cleaning materials, etc., in the most convenient places, the operator should see that he has a good supply of sharpened pencils and pens to hand. Nothing is more irritating than to find, when the point of a pencil suddenly breaks, that there are no sharpened pencils in reserve. If the rule is made never to allow a pencil to go unsharpened for longer than it takes to complete the work on hand, there never need be any trouble in this connection. Similar care should be given to pen nibs and ink, no corroded pens being allowed to accumulate.
Among the spare parts which it is necessary to have in an immediately accessible position are the spare telephones, spare primary and secondary for magnetic detector, spare iron band, spare crystals (if a crystal receiver is carried), extra key and coil contacts, and fuses. It is also advisable to keep a clean duster solely for the purpose of dusting the receiving instruments and the operating table. This duster should never be used for wiping anything oily or greasy, otherwise it will become useless for the purpose for which it is intended.
On board ship it is necessary to make a periodic and thorough examination of the cabin roof, walls and floors to see whether the structure continues waterproof and weather-tight. We have known cases where operators have neglected to examine the silence chamber for several days on end, with the result that a leaky roof, by going undiscovered, has been the cause of considerable damage to the apparatus. Other cases have come to our notice where a port hole immediately above the receiving table has been left improperly secured and on a wave dashing over the cabin the receiving instruments have been drenched with salt water.
The point of junction between the walls of the cabin and the deck will sometimes be found to be leaky, particularly after a long spell of dry, hot weather. All leaks should immediately be reported to the Chief Officer, in order that the necessary steps may be taken to repair them.
TAKING OVER AN INSTALLATION
Considerable time and trouble will be saved if the following method is adopted when examining an installation to see that it is in proper working order.
1½-Kw. Set.--Start the inspection at the mains, and carefully examine the main switch to see that the fuses are in position, that all connections are tight, and that the switch blades make proper contact with the jaws. Next, with the main switch "off," examine the starter and field regulator for tight connections and proper contact of the starter handle brush with the studs. Then see that the brushes on the commutator and slip rings of the converter are making contact, and are not bearing too firmly upon the metal, noticing at the same time that all the converter connections are properly made and tight. The guard lamp board should then be examined and then the A.C. Switchboard. Here the fuses, switch contacts, voltmeter, and ammeter connections, and all terminals should be looked over, after which one can proceed to the manipulating key. This should be examined for play of contacts, their smoothness and clean condition, and the proper adjustment of the telephone short-circuiting device. If the terminals are tight and everything else satisfactory, the magnetic key should then be looked over and, if necessary, adjusted according to the instruction given under the heading of "Magnetic Key."
The position of the connections of the low frequency iron core inductance should be checked up with the station chart, after which the transformer connections should be examined for tightness, cleanliness and correct joining up. On coming to the high tension side of the apparatus care must be taken to see that all leads are sufficiently clear of one another to prevent cross sparking.
Checking up connections with the station chart and seeing that all terminals are properly screwed up, we pass to the sliding inductance which must be accurately set according to the diagram, and the condenser, the straps of which must be in proper position. From the condenser we proceed to the rotary discharger, where it should be ascertained that the aluminium teeth are not irregularly worn and that the proper clearance exists between these and the stationary electrodes. If a fixed discharger is fitted, the gap should be measured to see that it is correct. The jigger should then be examined and the distance from the top of the instrument to the secondary box measured and checked with the station diagram. On the aerial side, the flexible connections must be in the proper position on the jigger secondary and aerial tuning inductance according to the Engineer's Chart, as also the connection between the Bradfield insulator and the aerial tuning inductance. On the earth side of the jigger the connections to the earth arrester must be examined and an inspection made of the earth arrester gap, to see that proper clearance exists between the upper and lower plates, and that the mica ring is in situ. From the bottom plate of the arrester gap a lead passes to the earth bolt, which, of course, must be perfectly tight and free from corrosion. There should be no corrosion on the Bradfield insulator connections, either inside or out of the cabin, and the aerial connections must be neatly and properly made. If the aerial down lead is disconnected, it should be passed through the hole in the iron shackle, drawn out in a loop, given a turn round the shackle, and the two ends carefully connected to the terminals of the centre rod. Whilst on the roof the opportunity should be taken to see that the Bradfield gland is properly screwed down, so as to avoid any leakage of water into the cabin.
If it is possible to examine the aerial and all insulators this should be done, not forgetting to make a careful inspection of the spreaders to see that there are no cracks in the wood which may cause a breakage when the aerial is hauled tight. Methods of treating aerial insulators are described in the chapter devoted to aerials.
After an inspection of the transmitting apparatus has been made on the lines suggested above, the main switch should be put in, and if conditions permit, the set started up. If the set then fails to work, which is very improbable, the tracing faults will be greatly simplified, seeing that in practically all cases where installations have failed to work, the fault has been found to exist at one of the points referred to above. All fault tracing should be carried out systematically, and if any particular instrument is suspected, the section of this book devoted to the particular instrument should be carefully perused as a guide to what faults may occur.
On the receiving side the lead from the earth arrester gap to the tuner, all tuner terminals, switch contacts, etc., and the detector connections must be given attention. A frequent source of trouble on the receiving side may be traced to bad adjustment of the short circuiting contacts on the manipulating key, as, of course, if these contacts are together when the lever is up, the whole of the receiver is put out of commission. Where valve receivers are used, it must be seen that the voltage of the accumulator battery is properly maintained, and in the case of crystal detectors the voltage of the dry cells must be similarly watched. It should be remembered that very small currents pass through the receiving instruments, and therefore the slightest film of dust or dirt on a terminal or connection may either cut out signals entirely or seriously reduce them. We would take this opportunity of reminding readers of the extreme importance of cleanliness in wireless instruments.
As in the case of the transmitting instruments if any faults are thought to exist in particular pieces of apparatus the sections of the book devoted to them should be carefully perused and a search made for the faults on the lines indicated.
Inspections of the ½-kw., ¼-kw., and other installations should be carried out on exactly the lines indicated for the 1 ½-kw. set, a start being made at the mains, and the inspection carried through the various circuits in their proper sequence.
Before going over the emergency apparatus the sections on accumulators and the 10" coil should be studied, or if a ¼-kw. emergency set is fitted, this should be gone over from start to finish in the manner indicated for the 1 ½-kw. set.
SOLDERING
When it is found necessary to solder, the soldering lamp supplied with the set should be charged with methylated spirit by means of the measure supplied. Not more than one measureful should be put into the lamp, and if the job is only small, a smaller amount of spirit should be used.
When the lamp has been filled and the cap screwed securely in place, a small quantity of spirit should be poured into the measure and ignited with a match. The measure with the burning spirit should then be placed underneath the lamp and left there until the lamp begins to roar. Once properly ignited, the lamp will continue to burn by itself until all the spirit is used up, the flame providing the necessary heat for vapourising the spirit.
Before commencing to solder, the two articles to be soldered must be thoroughly cleaned and sandpapered, and should then be rubbed with soldering paste. Too much paste must not be used, a thin film being quite sufficient.
Where possible the articles must next be heated with the soldering lamp and the solder applied. The paste should be kept at hand and a little more applied if the solder does not take. A small piece of wood such as a match should be used to apply the paste, as it often causes an unpleasant soreness when it comes in contact with the skin.
Both articles must be heated if good contact is to take place. When a soldering bolt is used, it should first be thoroughly heated, and the copper bit then dipped in the paste and given a coat of solder. The method of soldering the connections of the magnetic detector primary and secondary, will be found described on page 66.
PREPARING AN INSTALLATION FOR LYING-UP
It frequently happens that an operator arrives in port on a ship which will be out of commission for a period of several months. In such cases he is instructed to prepare the installation for lying up. He should proceed as follows:--
See that all fuses are removed from the main switch and switchboards, and carefully locked away. All switch contacts must be left open, the pressure removed from the brushes on the converter or motor generator, and the brushes lifted. All brasswork must be covered with a thin coating of non-corrosive vaseline and the flexible connections, such as those between the Bradfield insulator and the aerial tuning inductance and between this latter and the jigger, removed and packed away. In the case of a prolonged lay-up the aerial should be lowered and rolled up, the whole Bradfield insulator taken out and the roof plugged. When using vaseline it must not be allowed to touch the ebonite of the receiving instruments. The receivers themselves should be carefully covered over with cloths or dust sheets. See that the telephones have been disconnected and locked away, the key and coil contacts unscrewed and stored in a small box properly labelled, and the switchboard lamps and guard lamps removed and carefully packed.
For instructions as to the treatment of accumulators in such circumstances, see the section "Accumulators."
All drawers and cupboards must be locked, the keys being tied together, labelled, placed in a sealed envelope, and left in the cabin. The key of the cabin should be handed to the Chief Officer.
Before leaving the cabin the operator should leave a note in the inspection book stating just what has been done to the installation, for the benefit of the succeeding operator.