RADIO AND RADAR TRANSMISSION MEASURKMKN IS 



in front of tlie iiole soon iifter it ^y;\s erertcil ami 

 caused sufficient dislurliance of the air in tlie lowest 

 levels tlwt such measurements were not feasible. The 

 psychrograph, anemometer, and wind direction in- 

 dicator at the top of the pole continued to be useful, 

 however, and pro\ided tlie continuous information 

 recorded by the station. 



A 50-ft boat, the Wanderer, was used for making 

 measurements in Massachusetts Bay. The psychro- 

 graph used for measurements from 2- to 48-ft eleva- 

 tion is attached to a cable running between a boom 

 extending outward from the side of the ship and an 

 extension to the top of the mast. A similar psychro- 

 graph was used for soundings to higlier levels, operat- 

 ing from the winch at the rear of the boat. Further 

 essential meteorological information was provided by 

 the boat in frequent measurcmeiits of surface water 

 temperatures in Massachusetts Bay. A direction-find- 

 ing loop was used to determine position at great dis- 

 tances off shore. 



12 RADIO AND RADAR TRANSMISSION 

 MEASUREMENTS'' 



The purpose of this paper is to describe the results 

 of a rough preliniiiiary analysis of the transmission 

 experiment. A thoi'ough analysis must await the com- 

 pletion of the meteorological study, since the trans- 

 mission depends dii'cctly upon the meteorological 

 conditions over the path of the radiation. The em- 

 phasis here will therefore be mainly on the strictly 

 radio data with only qualitative reference to the 

 meteorological information. 



^■^■^ One-Way Transmission 



The values of the transmitted jjowers, antenna 

 gains, and receiver characteristics were chosen so as 

 to make the standard signal level, as computed for tlie 

 receivers at the top of the tower, well above the mini- 

 mum detectable level and the minimum level at 

 which the automatic frequency control [AFC] and 

 AFC search are effective. Sufficient compression was 

 used to give a range of about 60 db for useful recep- 

 tion, which had been expected to be enough for the 

 variations due to atmospheric conditions. It turned 

 out, however, that additional range was needed, es- 

 pecially in the direction of greater signal strengths; 

 to accommodate additional received power, attenua- 



••By Pearl Rubenstein, Radiation Laboratory, MIT. 



tors were inserted in the lines. Thus the actual range 

 of values observed is at least 90 db at the microwave 

 frequencies and 40 db at 117 mc. 



Signal Types 



Figure 2 shows that the types of signal observed 

 at the microwave frequencies (S and X) are not 

 essentially different from those observed in previous 

 tests on a shorter path. The first type is high signal 

 on the average, w^ell above the standard level, with 

 roller fades which may go down to the minimum de- 

 tectable level and with periods of 2 minutes to an 

 hour or so. These periods are generally shorter at 

 any time on X than on S band. "When this type of 

 signal is present on S band it is almost invariably 

 present on X band also and on both paths. It always 

 occurs simultaneously on the high and low receivers 

 at any frequency. 



The second type is high and steady. Its level may 

 be anywhere from 5 to about 30 db above the stand- 

 ard, generally higher on X band than on S band. 

 Most of the time this type of signal occurred simul- 

 taneously on S and X, but there were some occasions 

 when the S-band signal was of the high and steady 

 type while the X-band signal became of the first 

 type, high with roller fades. 



The third kind of signal is about standard and 

 fairly steady. (This may be a limiting case of tlio 

 liigli and steady variety.) It does not necessarily 

 occur on both frequencies and on both high and low 

 receivers at the same time. 



The fourth type is standard on the average, with 

 scintillation of more than 10 db. The preliminary 

 analysis has not revealed the reasons, or any correla- 

 tions, for the difference between this and the preced- 

 ing type ; it is certainly nothing obvious, such as wind 

 speed, for example; and it may occur on either fre- 

 quency when the other is steady. 



The fifth type is the "blackout," below standaid 

 and variable. This signal type is strongly scintillat- 

 ing. It occurs simultaneously on both frequencies, 

 both paths, and on high and low receivers (except 

 possibly for low X, where the difficulty mentioned 

 above of determining an average value of something 

 very low on the scale is important). 



Figure 3 shows the signal types observed at 25G 

 cm. These are distinct from those observed at the 

 microwave frequencies not only in appearance but 

 also in times of occurrence. In general no relation has 

 been found to exist between the types at the two 



