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The radiometer is connected to a feed which illuminates a 10 foot diameter dish with f/D ratio of 0.4. The feed is made by adding a l/4 probe to the C-band (4.2 GHz) feed. The outer diameter of the C-band (4.2 GHz) feed. The outer diameter of the C-band feed is about 8" which supports a TE11 circular waveguide mode with a/l » 0.5 which is close to optimum for a f/D » 0.4 [see Methods of Experiment Physics, Astrophysics edited by Marton, vol. 12B page 32.] The aperture efficiency should be close to 60% (or 50% when the feed and feed support blockage is taken into account.) so that
-TA = (FAη/2k) × 10-2026
where A = area of the reflector
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The radiometer power is measured by using the pulsin routine (see stamp 1 manual) to count the stamp clock cycles in a pulse from the AD654 voltage to frequency converter. To enhance the accuracy we count up to 10000 10 microsecond cycles. During this time we may have several AD654 positive pulses so we return the total count w1 and the number of pulses counted w2. The host PC then calculates the power
Power = scalef*(w2/w1)
so that, for example, a 0.5 volt out of the OP-27 which produces a pulse length of 12 ms so that
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