(ii) The devices shall also function when the dashes are of not less than three or more than five seconds duration, and the spaces of not less than one-tenth or more than two seconds dura- tion. It was agreed also that some allowance should be made for approximations to the three and five seconds limits, as these are designed tolerances and something should be allowed for accidental departures from those in the actual instrument.
(iii) The design of apparatus should include
tell-
tales," for indicating failure of any portion of the apparatus, but it was thought that this point is one for decision by the Board of Trade. (iv) The devices shall be subjected to test by signals locally produced to ascertain whether they func- tion with the tolerances scheduled under (ii); 100 test calls within the tolerance limits indicated in
(ii) shall be made to determine this
(v) The devices shall be operated by a transmitter with a steady note of frequency not less than 100 per second, and shall be operative on a wave of 600 metres with conditions equivalent to ranges up to 80 miles with aerial equipment at the transmitting point giving a figure of 45 as the product of the maximum height of the antennæ in metres and intensity of current in amperes at the base of the antennæ.
(vi) All tests will be made with the receiver with which the devices will normally be associated, and approval of the devices will extend only to the use with the particular receiver combined with it when submitted.
(vii) The devices will be installed for 14 days in the neighbourhood of the Thames Estuary and the Straits of Dover, or other area where similar jamming conditions are experienced, and observa- tion made of the number, if any, of false calls recorded by the apparatus during that time. (viii) The devices will be installed in any position in Great Britain for a further test of 28 days' dura- tion, during which time they will be subjected to a minimum of 500 test calls under the conditions indicated in (v); during these tests adjustment of the apparatus shall be made only once every 12 hours and each call will consist of the calling signal being made for one minute.
9
(ix) During every third day of the trials under (vii), the device will be artificially subjected to vary- ing temperature conditions; for this test the devices will be enclosed in a chamber and the temperature of the interior of the chamber will be raised in one hour to 40° C., and maintained at that temperature for two hours and then allowed to cool naturally.
(x) For approval, the devices must satisfy the follow-
ing conditions:—
(a) They shall not fail in any particular
during the tests indicated under (iv).
(b) The number of effective calls as indicated under (viii) and (ix) to be not less than (*) of the total calls made.
(c) The number of false calls recorded under (vi), (vii) and (viii) shall not exceed (†).
* For decision by Board of Trade, a figure not less than 90 per cent, is feasible.
Not decided, but as false calls were considered negligible, it is recommended that only one or two false calls be allowed,