fundamental within the receiving front end. The frequency falls within the 4.5 to 5.0-GHz band of the parametric amplifiers, and even though rejected by the final IF stage, it could disrupt the automatic level control at the antennas. Problems of this type, which result from nonlinear effects of strong signals outside the receiving passband, depend on details of the current electronic design and can be reduced or probably eliminated at the cost of considerable design modification. A more fundamental problem is the reduction of the tuning range of the receiving system, since it will almost certainly not be possible to operate with a harmonic of 2.45 GHz within the passband. Each harmonic will be accompanied by a narrow-band enhancement of the transmitter noise, but no information is available on the magnitude to be expected. The second harmonic noise band has been included in Figure 1 at an arbitrary level of -40 dB relative to the 2.45-GHz noise, as a reminder that the effect must not be ignored. The noise enhancement at 4.9 GHz could severely restrict the performance in the 6-cm band. This band is the one with the best combination of antenna efficiency, system temperature, and present usable bandwidth, and is likely to be the band most often used for observations of very faint sources. The terrain shielding between the array and the rectennas must be sufficient to keep the level of the second harmonic of the power signal and the accompanying noise from the rectenna at a tolerable level. The response of the array to radiation from broad sources around the horizon is complicated to determine, but a total flux density level of 13 dB above the CCIR 224-4 level should not adversely affect the performance of the array. The tolerable interference levels are likely to be more precisely defined in the future by further studies of the response of the array to interfering signals, measurements of antenna side lobes, etc. For some observing frequencies the width of the zone in which operation is precluded may depend on presently unknown levels of transmitter-generated noise and harmonics, rather than the thermal radiation. The loss of a wide declination band centered on the satellites would be extremely serious when considered with regard to the specification and aims of the VIA. Simpler arrays with a single east-west line of antennas are capable of producing satisfactory maps at declinations from
RkJQdWJsaXNoZXIy MTU5NjU0Mg==