Wednesday, March 17, 2010

News from the RSGB Tutors letter

Connecting Transceivers in Vehicles
Change of Recommended Practice
Guidance for vehicle installation was originally contained in MPT1362 issued by the Radiocommunications Agency after consultation with industry. That role has now passed to the Federation of Communication Services and re-issued as the UK Code of Practice FCS1362.
There is a significant change in the guidance, section which will affect the Advanced examination and the Advanced course book.
The advice in MPT1362 and all copies of Advance! up to and including the 2009 reprint was to connect the transceiver directly to the vehicle battery with appropriate fuses in both the positive and negative leads. Often there is an incidental DC route from the vehicle chassis via the antenna mount, coaxial cable outer, rig and negative power lead to the battery terminal. Some vehicle load current will take that route and if the battery negative to chassis strap fails then all vehicle loads including starting current (100A plus) could. Clearly a fire risk especially for the super thin coax intended to fit round a door or boot seal.
New advice.
The new guidance is to connect the transceiver negative directly to the vehicle chassis and no fuse in the negative. (Assumes negative earth.) The positive lead should still be fused and connected to the battery or in accordance with the vehicle manufactures specific recommendation.
Remember that transceivers should be specified for vehicle use and the manufacturer’s guidance on RF power limits, antenna placement and DC supplies must be followed. Failure to do so might affect your insurance cover and questions on this point must be directed to your insurance provider.
Effect on Examinations
Vehicle installations are covered in the Advanced specification, syllabus item 9c1. It is proposed to edit relevant questions shortly. Candidates may be asked questions to the new guidance from 1 September 2010 onwards. The old practice of a fused negative to the battery will not be used as a distracter, but from 1 September an unfused negative to the battery will be a legitimate wrong answer since that has always been wrong.

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