A method of assigning carrier levels in an SCPC system with mixed earth stationG/Tsis developed which optimizes system performance for uniformly spaced and randomly assigned carrier frequencies. The optimum transponder backoff is shown to be identical to that for a system of uniform carriers in which the (common) earth station(G/T)^{-1}is a weighted average of the different(G/T)^{-1}values in the mixed system. With the transponder backoff determined, the carrier level to be transmitted to each station type is simply expressed in terms of the stationG/T. Since the carrier frequencies are randomly assigned, the technique described is ideally suited to the design of a demand-assignment system. Alternatively, the same performance can be realized through a pseudorandom choice of frequencies in a system of fixed frequency assignments. In the particular case of two station types with an equal number of large and small carriers, a system employing a random assignment of carrier frequencies is compared with one in which the large and small carriers alternate in frequency. It is shown that, if equal carrier-to-noise ratios are required for the two carrier sizes, the two systems are capable of identical performance. However, the system of alternating carriers requires a lower EIRP per carrier from the smallerG/Tstations.

The tau-dither loop is often selected in place of a delay-locked loop (DLL) because of the DLL's sensitivity to arm gain imbalance. This letter presents an implementation of a DLL for which arm gain imbalances do not cause static loop offsets.

TheKuband subsystem for the NASA Space Shuttle Orbiter operates either as a radar system during rendezvous with other space vehicles or as a two-way communications system with the ground through the Tracking and Data Relay Satellite System (TDRSS). In its radar function the equipment searches for, acquires, tracks, and provides the spatial data needed to make a quick and efficient rendezvous. In its communications function it searches for, acquires, and tracks the TDRS to provide high quality two-way communications from the Orbiter to the ground station via the TDRS System. The communications and radar systems are integrated since components such as the transmitter, receiver, antenna, and servos can perform well in either role. This paper describes the equipment as used in both roles but focuses on communications capabilities.

A recent paper has been published giving the true lock and false lock behavior of conventional Costas loops. The results are in the form of an integral which has been evaluated in closed form for the case of anRCarm filter. This paper derives closed form results for the case of an arbitraryn-pole filter whose poles are all of multiplicity one. Results are plotted for Butterworth filters of several orders.

Carrier-to-intermodulation (C/IM) power ratios are derived for two types of single-channel-per-carrier (SCPC) systems in terms of the single-carrier transfer characteristic of the satellite TWT. The first system is based on a set of equal-amplitude, uniformly spaced carriers and is appropriate whenever complete earth-station interconnectivity is required in a bandwidth-limited environment. The second system is designed to handle traffic flow between a large number of small stations and one or more large stations. It utilizes a frequency plan of alternating large and small carriers. The C/IM ratios for the twolevel system are expressed in terms of the C/IM ratio for a single-level system operating at the same TWT backoff. Application of the results to a power limited system of either type is also indicated.