G4USP (MB7ILH) |
Page last updated: 02/10/2014 |
Analogue Gateway
The analogue gateway of MB7ILH is based around a Phillips FM1100 transceiver, a Raspberry Pi, and SVXlink software written by Tobias SM0SVX. On transmit the FM1100 transceiver output power is set to 0dBW (1 Watt) into a Groundplane antenna mounted 6m above ground level, whilst feedline and other losses equate to around 2.5dB bringing the transmit ERP to -2.5dBW (1/4Watt).
1) The FM1100 transceiver - configured as follows:
Basic control head.
Ptt LED / Busy LED / Pwr LED.
A single channel is configured, all other channels disabled.
Signalling disabled.
Rx CTCSS disabled - CTCSS decoding is done by SVXllink software.
Tx CTCSS enabled - CTCSS encode is not done by SVXlink software.
Rx squelch opens @ 9dB SINAD.
Tx power 1W.
Configuration is relatively strait forward all be it a little tedious with a PDP (Portable Data Programmer) / FDP (Factory Data Programmer) as apposed to the CDP (Computer Data Programmer). Alas CDP's are somewhat scarce, requiring a specific ISA card for an IBM XT compatible PC as well as software. The PDP will do the job but each channel has numerous settings associated with it.
It took me around an hour to reconfigure my FM1100, but I made a particular point of clearing and disabling all but the one channel, just to ensure that the transceiver could never be accidentally changed onto the wrong channel and hence frequency.
2) The control head - I have built a cut down version of the Basic Control Head, providing the following functionality:
A regulated 5v supply for external device.
A TTL compatible Busy output signal.
A TTL compatible Ptt input signal.
A 600 ohm line output ~ -10dBm.
A 600 ohm line input ~ -10dBm.
3) The Raspberry Pi - the RPi setup is headless, with SVXlink software package
4) The USB sound card - not a lot to say here, other than some are better than others
See also