| Odbiór szumu Jowisza na 77 GHz |
| W ostatnim EME newsletter 432 MHz and above (K2UYH) , RW3PF donosi o swoich doświadczeniach z pomiarem szumu Jowisza na 77.5 GHz na jego systemie EME. Wartośc tego szumu to 0.0035 dB. Jak można do tej wartości dojść do tej wartości tłumaczy CT1DMK na Moon, w odpoweiedzi na pytanie JH1KRC. Poniżej wklejam treść informacji RW3PF oraz treści maili CT1DMK i JH1KRC. Fascynujące, co mogą radioamatorzy ! 73's de Staszek SP6GWB p.s niestety, miałem problem z wklejeniem wykresu. ----------------------------------------------------------------------------------------------- TECHNICAL: JUPITER NOISE ON 77 GHz -- RW3BP notes that evaluating RX system quality (G/T ratio, etc.) can be a major problem on 77 GHz. On the lower bands it is possible to check Sun or Moon noise, but on 77 GHz the angular size of Sun and Moon is too big in comparison to antenna beam widths. So we can check system noise temperature (T), but cannot check antenna gain (G) and related G/T. My idea was to use Jupiter as a noise source. Unfortunately this is not easy test. With my system, Jupiter noise was only about 0.0035 dB! I used the wide band radiometer module by CT1DMK but even with a 40 MHz BW, it was impossible simply to point antenna by maximum of noise in real time. 77 GHz Jupiter noise measured by RW3BP ------------------------------------------------------------------------------------------ Hello Sergei, Al, Peter and all: In the TECHNICAL article of 432 & Avobe News of Feb./March issue, Sergei RW3BP writes his Jupiter noise measurement for 7 7GHz receiving evaluation. It looks so fascinating to me and I have written an article on it in my EME column for JA CQ magazine, April 2014 issue.... In his system Sergei detected Jupiter noise of only about 0.0035 dB(!) measured with CT1DMK noise meter in 40 MHz bandwidth in 400 MHz IF. Sergei concludes his receiving system shows his 2.4m offset antanna has a -3 dB beamwidth 0.11x0.12 deg. He continues it was impossible simply to point antenna by maximum of noise in real time. I think it must be an amazing results, but one question comes up to me. How can he measure -3 dB beamwidth using 0.0035 dB Jupiter noise? He says he cannot point his antena in real time. I guess it takes more time to measure it accurately. So I hope Al would compile the next 432 and Above News dealing with more Juuntil noise measurement until April 1, or so.... Mike JH1KRC ------------------------------------------------------------------ Mike, > How can he measure -3 dB beamwidth using 0.0035 dB > Jupiter noise? The radiometer measures the total power so the total power ratio is pointing to Jupiter versus pointing away from Jupiter. Lets use temperature instead of Power, which in reality is equivalent but more convenient while addressing these matters. Tsa is system temperature including atmosphere, Tja is the Jupiter temperature as seen by the antenna Y = ( Tsa + Tja ) / Tsa or Y = 1 + Tja/Tsa = 1.000806 = 0.0035dB when jupiter is 3dB down, seen at the -3dB antenna point Y = 1 + (Tja/2 ) / Tsa = 1.000403 = 0.00175dB So the antenna 3dB happens at 0.00175dB point each side of the peak. 73's Luis Cupido ct1dmk |