Questions and Answers

Radio Record, Volume II, Issue 24, 28 December 1928, Unnumbered Page

Questions and Answers

a é ANSWERS IN BRIEF, "A.E.B." (Wellington) asks the kind of valves to use with a resistance coupled amplifier. This question would either involve a long table of selections from all the makes of valves on the market, or recommendation of a particular make which we could not in fairness-do. Consult a reliable dealer. Effective Height of Aerial. "T AM keenly interested in the notes appearing in the ‘Radio Record,’ and I shall be much obliged if you will be so kind as to answer the following questions :- "1, In the issue of December 14, and in the article ‘Choice of Aerial,’ it is stated: ‘the effective height of an aerial is its distance from the nearest earthed object." My aerial does not pass over the house, but it runs alongside and. not far distant from the house, although above it. According to the above, the effective height of my aerial is its distance from the house. Is this so?" It must be remembered that though ‘the aerial passes near the house it may not be in very close proximity to an earthed object. It may run near the wall, in which case, poor results should only be expected during wet weather. If on the other. hand it passes very close to the roof, which is

connected to the earth by‘a downpipe, then the effective height. is the distance from the roof.’ That is not to say an aerial as high above the ground as the. aerial is from the roof would be equally effective. There are more factors to be considered. "2. Then again, the lead-in is near to the house. Does this affect the height of the aerial? Or, is this only so when the wire is not insulated?" This only affects the height when not insulated. All leads in should pe insulated. "3. ‘A.S.T.’, Wellington, says his set works just as well without an earth. I have a factory five-valve set, anid, after reading the above, I tried my set without the earth, and on returning I could bring in 2YA just as good ‘as ever. Also, on disconnecting the aerial and connecting the earth wire to the aerial terminal, I can tune.in 2YA Aj. There are no breaks in the earth wire as far as I can see. My earth consists of two kerosene tins of sea-water sunk two or three feet in the ground and the lead is not more than 6 feet. Have I good earth’ :- 2YA comes in at sufficient strength to work some sets without aerial... or

earth, so that it is hardly a fair test. Try disconnecting these on a weaker station. The earth is quite good. ) . "4, Owing to alterations to my house I may have to shift my aerial. Will an aerial, L type, running west, 75 feet long, lead-in 18in., be effective? You will notice that one aerial mast will be attached to the verandah so that the aerial will again be near an earthed object, and the lead-in will run down close to the side of the house, Of course, I shall have insulated wire for the lead-in right from the connection with the aerial wire. An 18 foot mast is provided for on the veranda end, a 36 footer at the other" -this should be effective under the circumstances, but there are one or two points to watch. The actual aerial should not be commenced near the. veranda mast. Allow, say, 12 feet, from the verandah. This would offset the proximity of the. earthed roof, See that the lead-in is heavy stranded cable, and well insulated. Keep this clear of the walls by insulators. "5. The lead-in will have to run ‘along the veranda 18 feet to the leadin tube. Will this be safe? TI will

put the lightning arrester on the aerinl mast or post of the veranda."-The best q place for the arrester is on the ver7 anda post, if possible, in a sheltered ‘spot. This would be quite safe. See 7 ire Underwriters’ regulations in last week’s issue, page 29. "6. Which will. be the better, to have the lead-in on the outside or on the inside of the veranda? I shall. obtain some small insulators to attach the lead-in to, and so keep the wire off the wood."-The insulation would be better protected if the lead-in were placed in the inside of the verandah. "7, Will there be any leakage on ac"count of the lead-in being so close to the wood?’-Not if the precautions ; mentioned above are taken. "8. I will also have to run the earthwire across the veranda. Will insulated wire running along the floor be sufficient? To run the wire along the roof would make it too long." Providing the wire is equally as j heavy as the lead-in it should be very s effective. There would be no point in ‘running it round the roof and there -is.no need to use insulated wire exs cept where it is-in close proximity to a the lead-in. ;

Ducon Aerial Plug. "COULD you give me any information regarding the ‘Ducon’ aerial ' plug, for use with crystal sets."- | ALP.B.. (Wellington). : » "Dueon"’ is the trade name. for a product that is to be used -to enable ‘ signals. to be collected from the electric ‘ mains. In essence the plug consists of . & suitable support inta which there ‘are- two or more. fixed: condensers. When.the plug is ‘fitted into the light * socket these condensers are in contact , With the two wires. of the: mains. Ter.Minals are attached to each of the . Sets of condensers, from which leads can be taken to the set. One of. the contacts, will connect with the positive . Which passes through. the wall switch, _ While the negative. is grounded at the. _Switch-board. Obviously, it will be necessary. to plug into the positive lead

sé that if will be necessary-to try"each of the two terminals to find the better. The atachment is’ quite-safe in applicaion, the high yoltage being stopped by the condensers owing to the fewer cycles per second (50 as com.pared with, say, 1,000,000, in the case of an ordinary broadcast station.) This attachment is less suitable than a good outside aerial, and should be resorted to only where such an ‘aerial is not available. Low Filament Valves. | "VALVE" (Havelock North) writes: | I have a wireless set using 6-volt valves requiring a heavy filament current. I have been advised by one person to use low-filament 6-volt valves and thus save my A battery current. Another person tells me that my A battery current will be less, but the B current will be more, and also that they cannot be used unless the circuit is altered. Can you inform meF a 6-volt low-filament consumption valve can be used in the same circuit as a higher amperage valve without further alterations to set? Yes, providing the valve bases are the same. ’ S compared with the higher amper-. age valves do the low consumption use more or less B battery current? This is difficult to answer, as there seems to be a great diversity of opinion. There is no reason why they should, as the filaments of the low-consump-tion valves are constructed of thorium and tungsten, which accounts for the smaller amperage used. There is no relation between. this and the plate consumption. | : O the low-filament valves give poorer tone quality than higher? No.

The Baffle Board. "[S three-ply venesta suitable material to make the bafile with, and would the same material be suitable to make the whole cabinet?’ inquires "G.L.," Otago. No, the baffle board should be of heavier material-sav_ one-inch timbér. It is preferable,- too, to make the cabinet of heavy material, though not necessarily as heavy as the baffle. JOULD a bafile board 4ft. x 4ft. give better results than one much smaller? : . Yes, the size should not be less than 2ft. Gin. x 1ft. 10in.; if quality is desired. N the event of making a large baffle board, has the wnit to be pleced in centre of same?’ It is advisable. ‘ Yes.

(SOULD the baffle and cabinet be made high and oblong without detriment to tone and volume? Yes, providing it is not made too narrow-less than ift. 10in. (CAN the Mullard P.M. 22-power valve which is similar to the new Philips Penthode five-element valve be procured in New Zealand? Yes, It is stocked by all reliable dealers. Mean Time, "W HAT is the meaning of ‘G.M.T.’?" "GMT." signifies "Greenwich mean time," or the time. adopted as a standard by countries near the meridian Qdeg.-that is, the British Isles, Places

east or west from the "0" meridian are ahead or behind, according to their position. Four minutes are allowed every degree, so that New Zealand, on the degree 1724 KE., is llhr. 80min. ahead of English time. " HAT does 18.00 .nd 20.00 G.M,T, signify?" 7 In scientific caleulations the confusing a.m. and p.m. are abolished and ‘the hours numbered from 0 to 24, everything after 12 being p.m. Thus 18.00 G.M.T. is really 6 p.m. English time or 5.30 a.m. New Zealand time,