 GDO Some useful equations Ohms Law Ohms Law V = I * R R = V / I I = V /R V = Voltage (Volts) I = Current (Amps) R = Resistance (Ohms) So a current of 0.2 amps into a resisitance of 30 Ohms gives 0.2 * 30 = 6 6 Volts Wavelength Wavelength in metric 300 / ƒ (Mhz) = Wavelength in Meters 300 / 27.5Mhz = 10.9m Frequency Frequency in Mhz c / = freq in Mhz c = speed of light 3x108 / 10.9m = 27.52Mhz Halfwave cable lengths in meteric Halfwave cable 300 / ƒ / 2 * Vf ƒ = freq in Mhz Vf = velocity value of cable used So for RJ58 the Vf is 0.66 300 / 21.5Mhz / 2 * 0.66 = 4.604m BlackBody Spectrum Wiens Law max = 0.0029 / T = wavelength in meters T = temperature in Kelvin So a blackbody which peaks at a wavelength of 20cm would have a temperature of 0.0029 / 0.2 = 0.0145Kelvin Doppler shift Doppler shift 0 - 1 / 0 = v / c 0 = wavelength at which light is emitted (at rest) 1 = wavelength at which light is observed v = the relative velocity of the source and observer c = the speed of light So the wavelength at which the 21cm line would be observed if the source was moving away at 500 km per second is 0.21 * (5*105/ 3*108) + 0.21 = 0.21035 = 21.035cm