56 



TRANSMISSION EXPERIMENTS IN ENGLAND 



Iii,uh enough to be measurud) usually agree toleraljly 

 well with the expected values. For the Irish Sea paths, 

 as well as in otiier measurements, the maximum level 

 rarely goes ahove that calculated for flat-earth condi- 

 tions; this level is practically the same as that for 

 free space conditions for all the Irish Sea centimeter 

 links except for paths BF on S band (only) where 

 there is a difference of about 10 db. If complete guid- 

 ing were a common phenomenon over paths of the 

 lengths actually used, it would appear that levels above 

 free spiace should occur much oftener and more con- 

 tinuously than is observed. It appears to be a useful 

 working assumption that the level obtained under 

 favorable conditions over nouoptical paths is nearly 

 that calculated for rays with the same curvature as 

 the earth. 



3. The fact that the Irish Sea results show that (for 

 centimeter waves) the advantage lies only rarely wdth 

 the smaller heights and shorter wavelengths suggests 

 that the importance of complete guiding as a criterion 

 for siting stations may have been overemphasized. 



4. The good correlation obtained in a number of 

 cases between land-sea temperature difference and 

 signal level suggests that the importance of tempera- 

 ture may be greater than is indicated by existing 

 theory. 



5. It appears very difficult to account for the max- 

 imum levels reached on the basis of existing theory. 



6. The interference patterns of the type discussed 

 above in Section 5.1. .3 still await an adequate explana- 

 tion. 



5 2 PROPAGATION WORK IN PROGRESS 

 AT THE NATIONAL PHYSICAL 

 LABORATORY^- 



This rep)ort gives a summary of the present position 

 (ISTovember Wii) of various investigations being con- 

 ducted under the auspices of the Ultra Short Wave 

 Propagation Panel of the R.D.F. Applications Com- 

 mittee of the Advisory Council on Scientific Eesearch 

 and Technical Development, Ministry of Supply. The 

 items to which the Eadio Division of the National 

 Physical Laboratory is contributing may be listed 

 as follows : 



1. Analysis and study of centimeter and meter 

 wave propagation over sea ( 3-6-9 ) experiments. 



2. Study of properties of water vapor, water, and 

 ice, and the absorption and scattering by these and 

 other substances in the atmosphere. 



''By W. Ross, British Central Scientific Office. 



3. ^Measurement of rcilection coellicient of land at 

 centimeter wavelengths. 



4. Study of centimeter wave proiiagafion o\er land 

 (Whitwell Hatch to Wembley). 



The following sections indicate the progress that 

 has been made to date on items 1 and 4. For items 3 

 and 3, see Sections 10.5 and 9.3. 



^•^^ Analysis and Study of Centimeter 

 and Meter Wave Propagation over Sea 

 (Irish Sea Experiment) 



This project utilizes the results of radio transmis- 

 sions being conducted between two sending stations 

 in South Wales and receiving stations in North Wales 

 and Scotland, jointly by the Admiralty, ilinistry of 

 Supply and Air Ministry. 



The contribution of the National Physical Labo- 

 ratory to the installations being used for this investiga- 

 tion has been chiefly connected with the monitoring 

 equipment used at both sending and receiving stations 

 to insure that the radiation from the former and the 

 sensitivity of the latter are maintained constant, so 

 that any variations on the field strength records arc 

 known to be due to transmission effects in the atmos- 

 phere. The instruments required for the S hand are in 

 an advanced state of production, while for the X band 

 the necessary field strength meter for the transmitters 

 has been developed, Init some development work is 

 still required on the standard radiator for the receiver 

 calibration. In accordance with a recent agreement as 

 to the limitation of the scope of the investigation, all 

 work on instruments for other wavelength bands has 

 been put in abeyance. 



"•^•^ Study of Centimeter Wave 



Propagation over Land (Whitwell 

 Hatch to Wembley) 



A transmitter operating on a wavelength iu the S 

 band has been installed at the Admiralty Signal Es- 

 tal)lishment, Whitwell Hatch, and a continuous record- 

 ing is being made of the field intensity of the radiation 

 received at the Eesearch Laboratories of the General 

 Electric Company, Wembley, over a land path of 38 

 miles. Except for some houses and trees within about 

 5 miles of the receiver, the path is a clear optical one ; 

 originally the transmitter was also partially obscured 

 by some trees, removal of the tops of which produced 

 a rise in received field of 10 db. Field strength re- 

 cording has been in progress over this link since 



