Abstract: A simulcast system for broadcasting the same signal for a number of spaced-apart broadcast sites is disclosed. The system (20) of this invention includes a hub (28) adapted to receive the signal to be simulcast and a number of stations (30) that actually broadcast the signal. The hub places the digital signal packets referred to as PDBs (36). As part of the signal packetization process, the hub evaluates the rate at which the signals should be broadcast and assigns a start time at which the signals should be broadcast; this information is attached to the PDBs. After a PDB is created it is forwarded to the stations over a link channel. Each station includes a station controller (32) and a station transmitter (34). The station controller, upon receiving a PDB, forwards the signal therein to the transmitter at the start time indicated and at the appropriate broadcast rate.

Abstract: A modem for use in a simulcast paging system includes a modulator (26) and a demodulator (30), both of which produce very low jitter, enabling the modem to be used at data rates well in excess of 1,200 baud. Both the modulator and the demodulator are implemented in software using a digital signal processor (DSP) (66). The modulator initially samples a non-return-to-zero (NRZ) input at a sample rate of 19.2 KHz, interpolates transitions between logic levels, and produces a frequency shift keyed (FSK) modulated signal at a center frequency different than that used for transmitting the modulated signal. Using an interpolation timer that responds to changes in logic level on the input, the modulator changes the frequency of the FSK modulated signal at the appropriate time with much greater accuracy than would be possible without interpolation. The FSK modulated signal is filtered to substantially attenuate frequencies outside a 3 KHz bandwidth, producing a filtered signal.

Abstract: A sealed, seamless box (10) that forms an RF-wave- or gas-tight enclosure is disclosed. The box of this invention includes a box body (12) formed of a single metal sheet (23) with a base panel (16) and upwardly extending side panels (18). The side panels are provided with tabs (20) that are thinner than the basic metal sheet. The tabs are seated in complementary cutouts (22) formed in the adjacent side panels. The cutouts have a depth equal to the tabs so that the side panels have a substantially uniform thickness equal to the thickness of the basic metal sheet. The tabs are secured in place by pins (30) formed integrally with the tabs that extend into openings (32) formed in the portions of the adjacent side panels that define the cutouts.

Abstract: A temperature-compensated tuning screw (22) for use with a cavity filter (20) is provided. The tuning screw (22) has an elongate body (36) with a longitudinal bore (38). A compensating member (40) is positioned at least partially within the bore (38). At least one compensation bimetallic washer (44) deflects with decreasing temperature and causes the compensating member (40) to protrude further from the body (36). The compensation bimetallic washers (44) become flatter with increasing temperature and a coil spring (42) causes the compensating member (40) to be partially retracted into the bore (38). The movement of the compensating member (40) causes an overall length, L, of the tuning screw (22) to change. The tuning screw (22) can be screwed into a hole (32) in a cavity filter (20) so that the tuning screw (22) penetrates the cavity filter (20) a distance, P. A temperature-induced change in L, .DELTA.L, causes a change in P, .DELTA.P. The change in penetration, .DELTA.

Abstract: A coupler mount assembly 14 includes an open-side box to which may be secured a housing 10 of an item of electronics or other equipment. A first jaw member including upper and lower, parallel hooks 54A, 54B and a second jaw member including upper and lower, parallel hooks 58A, 58B are supported by the open-sided box for relative translative movement. To install the coupler mount assembly on the coupler 12 of a railway vehicle, the hooks of the first jaw member are inserted through respective relief holes 84A, 84B in coupler side wall 12A and the hooks of the second jaw member are inserted through respective relief holes 86A, 86B in the coupler side wall. The first and second jaw members are then drawn toward each other by rotation of a rod (through a handle 66) passing through and effectively bearing on the first jaw member and threadedly received in the second jaw member, until the hooks thereof clamp an intermediate portion of the coupler side wall between the relief hole pairs.

Abstract: Demodulation of an ac signal that has been modulated by discrete changes in its amplitude, frequency or phase, is effected by first feeding the modulated ac signal through an amplitude limiter and hence through a bandpass filter tuned to a preselected frequency of the ac signal. The resulting bandpass-filtered ac signal defines a variable amplitude envelope which varies in response to amplitude, frequency or phase modulations of the input ac signal. Amplitude variations of the envelope of the bandpass-filtered ac signal are detected by a switching circuit whose operation has been termed "self-synchronous," because it is synchronized to the frequency of the ac signal prior to the passage of the ac signal through the bandpass filter. More particularly, the switching circuit is opened and closed in response to the ac signal appearing at the input to the bandpass filter, to cause alternate, like-polarity half cycles of the bandpass-filtered ac signal to be selectively conducted to a low-pass filter.