This logic design is such that it should cover most current and future requirements of UK speech repeaters. Facilities incorporated in the logic include the usual selection of callsign, locator and location for ident, as well as tone burst detection, CTCSS encode and decode, DTMF decoding, and serial data using standard packet type audio tones. These latter two can be used for remote shutdown/start-up, or for 'on-air' modifications to operational characteristics.
Facilities also exist for a separate data/control channel, and extra control and audio inputs are included for future repeater linking. This linking facility exists in rudimentary form on the logic board, but does require external decoding circuitry for proper linking control. The current version of the embedded firmware does not yet support repeater linking, but a beta-test version is currently running the GB3TE and GB3CL repeaters as a co-sited linked pair.
Other features incorporated are implemented by the usual NE567 for tone burst detection, an FX805 for CTCSS, MV8870 for DTMF decoding and TCM3105 for serial data input and output.
Incoming audio from the receiver is amplified and then split to feed all the devices which require it. These are the NE567 tone burst detector, the MV8870 DTMF decoder and the TCM3105 data decoder. The received speech is fed via the FX805 CTCSS device, which detects and removes any incoming CTCSS tone, and then to the summing amplifier where all outgoing audio information is added together. This outgoing information consists of through audio, CTCSS transmit tone (generated by the FX805), CW ident and data tones. This combined audio is then peak clipped, to guard against over-deviation of the transmitted signal, and filtered by a 20 dB per decade low-pass filter. The output of this filter is fed to the repeater transmitter.
No de-emphasis or pre-emphasis is included in the logic. Any pre-emphasis in the repeater transmitter must be removed, to avoid attenuation of the outgoing CTCSS tone. Likewise the repeater receiver must also have its de-emphasis removed to match the transmitted audio response. The overall effect of not having any in-built audio tailoring, is that signals are transmitted as they are received, with the exception of the peak clipping and subsequent low pass filtering.
If required, the input to the MV8870 DTMF and the TCM3105 data decoders may be linked to a separate audio input for remote repeater control on a separate channel. Likewise, the TCM3105 data output may also be linked to a separate transmitter for the same reason and another audio tone feed is available to produce a 'pip' audio feedback on the normal channel.
All modifiable features are stored in the EEPROM, so are relatively easy to change. All features are accessible via a direct connection to the logic board itself (RS232), some may also be changed 'on-air' while the repeater is operational by using the datalink and a 'BayComm' modem. These latter changes are only simple ones, and do not affect the fundamental operation of the repeater. They are also protected by a password scheme which, although not unbreakable, is sufficiently difficult to break so as to deter the casual 'hacker'.
All modifiable features are controlled by a set of simple commands via the built-in RS232 serial port. A normal PC is suitable for this control, and a PC programme is freely available to implement all the configurable features (including automatic password generation).
Other UK repeaters using the logic include
6m - GB3EF, GB3HX
2m - GB3IG, GB3NA, GB3ZA, GB3BC, GB3CG, GB3WD, GB3WR, GB3DA, GB3EL, GB3TE
70cms - GB3HM, GB3WY, GB3LA, GB3HD, GB3DS, GB3MG, GB3HC, GB3CH, GB3VS, GB3UB, GB3WO, GB3OX, GB3DI, GB3CC, GB3BR, GB3LR, GB3ER, GB3CE, GB3CL, GB3IH, GB3DE
Note - not all these repeaters may be 'on-air' with the control logic. Some may be currently undergoing updates!
The required specification for 6m repeater operation is included in the internal control programme and the 6m repeaters GB3EF and GB3HX are currently using the G8CUL repeater logic.
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