WIRELESS

Nelson Evening Mail, Volume LXVI, 19 August 1933, Page 4

WIRELESS

tests on tall building HEIGHT IS NOT EVERYTHING interesting results Radio fans all over the world have, no doubt, looked at photographs of the Empire State Building in New York City and have wondered as to what results would he obtained with a radio receiver atop that edifice. Many arc the efforts expended to obtain a few extra feet height on aerial masts for broadcast receivers what results might be expected from an aerial 1280 feet high? Radio technicians in New York became interested in this question and arrangements were made through the president of the Empire State Corporation for a series of tests to. he made atop the tower of the building. In order fully to appreciate the tests, an understanding of the phi sical characteristics of the building is necessary. The Empire State is the tallest buildiii" in the world, its tower rising to a height of 1280 ft above street level. The building itself covers an entire block on fifth Avenue, in the heart of the city. The elevation of the SGtli floor is 1000 ft. From this height a tower rises to an additional height of 280 ft. 'This tower is, in reality, a huge steel cylinder, pierced by an elevator shaft through which visitors are taken to the 103rd floor. This floor, on the very top of the building, consists of a glassenclosed gallery completely encircled by an outdoor promenade. (It is to this promenade that gang planks will be lowered if, the building is c\oi used as a dirigible mooring mast). Mounted on the roof of the tower are wind-pressure instruments which are connected to registering dials in various parts of the building. A registering wind-direction indicator is also mounted on the 15ft pole atop tlie

tower. . ’ The first consideration in the actual preparation for the radio reception tests was the location of an aciial. Because of the fact that the steel-pipe mast on top of the tower was extremely inaccessible, it was decided to string a wire from the 103rd floor to the building top proper at the SGtli floor level. This provided for an aerial nearly 280 ft in length, so it was decided to break this span in the centre with an insulator, thus providing two entirely separate aerials, the upper of wlncli might be used for tests at the 103 i cl floor level and the lower for any tests which were considered necessary at the SGtli floor level. Inasmuch as it was desired to conduct tests on both long and short wavelengths and a duplicate receiver was not desirable, the Scott All-wave Superheterodyne was selected for the experiment. In addition, the lcccuei had been used in several other transmission tests during the months picceding; consequently its performance was a known factor. In order to be prepared for. whatever conditions might arise during the period of the tests, it was decided to construct '.a headphone adaptor box, with which it would he possible to cut out the loud-speaker and place headphones in the circuit. On the afternoon of the tests, a considerable crowd gathered on the SGtli floor of the building, drawn by the fact that transatlantic wireless reception was under way. Within a very short time after the tests had begun, the SGtli floor was crowded with interested people, whose presence made the actual manipulation of the receiver very difficult. It was at that time that the wisdom of preparing for headphone reception was fully realised. During the day, a great many broadcast stations in New York City, and within a radius of 250 miles of the city, were tuned in. There was no noticeable improvement in reception on account of the very great height, although there was a considerable decrease in “man-made” static which is prevalent about the city (on account of tho great number of electric motors and °other electrical devices which cause disturbances of the ether).

COMPLETE ISOLATION The complete isolation of the location from surrounding buildings was no doubt responsible for this. During the evening hours, broadcast reception was considerably improved, stations as far away as 1000 miles being logged without difficulty. These results were somewhat surprising, as well as disappointing, for it had been anticipated that the great height would result in greatly increased range to pick up. (These results were compared with results obtained with the same receiver during tests conducted previously on or near the ground). However, quality was such that several of the executives of the building operating company expressed the intention of installing receivers in the tower to pick up programmes for distribution to points throughout the building. Reception of European transmitters was also disappointing, there being no improvement in volume level, over reception from locations within 50 or 100 ft of the ground. For a given volume-control setting a slightly lower extraneous noise level was noted, which increased the understandibility of the signals somewhat. There was no increase in signal strength. After several days of tests from this 80th floor station, the receiver was taken to the 103rd floor and set . up. Tests were conducted from this height for a period of two weeks, both day and night. Still there was no increase in signal strength, although a slightly improved extraneous noise level was noted.

All of the' regularly received European short-wave stations were tunedin, but with no better reception than is usually obtained from stations all over the city and near the ground. The best foreign reception was obtained from the short-wave station in Rome, Italy. Chelmsford, in England, however, was a close second. The steel of the building and a

waterpipe were connected together ar

used as an earth for the receiver, so in effect the earth and aerial leads constituted a one-turn earthed loop aerial, of 9ft diameter. This loop was entirely enclosed within the steel shell of tile tower, but nevertheless signals were being received.

When the aerial load was insulated at the point where it entered the doorway, signal strength again went to its previous day’s level. This may be considered an excellent commentary upon the sensitivity of the receiver used in the tests.

, One of the greatest sources of trouble during the tests was the interference contributed by two television transmitting stations located not far from the Empire State Building. One of these stations was not more than 2000 ft in a straight line from the receiving station (lest reception).

USE OF A WAVETRAP This station was not only heard over a wide band near its own broadcast frequency, hut at innumerable points throughout the entire broadcast spectrum. In order to make certain that this was not due to some inherent defect in the receiver itself, a wavetrap was connected to the receiver, and tuned to the fundamental of tho television transmitter.

The harmonic signals still continued to come in, proving that the phenomena was due in no wise to receiver characteristics. (Fundamental wavelength signals were entirely eliminated in the wavetrap). Another television transmitter some blocks up Fifth Avenue caused similar trouble, although in no sense as pronounced.

Some experiments conducted were intended to investigate the effect of steel building “shadows” upon broadcast reception; these showed that there was no appreciable effect on tliis score. When the tests were originally begun, tile aerial was placed on the west side of the tower. When signal strength was determined as being poor, it was thought that perhaps the steel tower might he shielding the waves as they came from European stations, consequently the aerial was removed and placed on the east side of the building. DIRECT WAVES This would, theoretically, expose the aerial to the direct waves from the east and, had there been any “shadow effect,” should have resulted in a material improvement in European reception and a consequent decrease in reception from the western part of tho United States. There was no noticeable difference in reception after tho aerial had been moved, which led to the conclusion that there was no shadow cast by the steel tower of the building which would affect radio waves. The experiment led definitely to the conclusion that the relatively high capacity between the aerial and the tower was responsible for tlic poor reception —-in other words, it might bo stated that the effective height of tho aerial was not its height abovo the ground, but its height (or distance) from the steel tower of the building.

This average distance (from aerial to tower) was approximately 14ft, which under this premise would result in equal results to an aerial strung between two poles and 15ft above the ground. Tliis conclusion, however, did not fully explaiil the low signal strength, for the same receiver, when used in Connecticut (several hundred miles from New York City), during the summer months, brought in all European stations with sufficient volume that tlic signals could he heard 200 ft from the receiver. These tests indicate that reception is not improved by great height, at least in so far as steel buildings are concerned. Seddon Shield Broadcast On Saturday last the local station, 2ZR, Nelson, made an excellent relay of the Seddon Shield match from Greymouth. The broadcast- went over exceedingly well and afforded much pleasure to hundreds of Nelsonians interested in their representative team’s challenge against West Coast. Apart from the technical side of the broadcast tho running description of the game by Mr W. Reed, ex-Nelson representative, was of a high class. It was a great game and the announcer made the most of it. The station and Mr Reed are to he congratulated on the service provided. From a financial point of view the broadcast was a fairly expensive one and though 2ZR received the benefit of the gate takings at the Park, they would by no means cover the cost. However in its efforts to serve Nelson

listeners the 2ZR Club, whose funds are by no means in a healthy state, undertook the relay hoping that it would receive recognition in a manner which would enable it to continue the very fine service it is rendering to the radio listeners of this district.