Short Range Devices (SRDs) in 433-434 are bad news. The United Kingdom opened up 433/434 to SRDs in the 1990's. Automobile remote control key fobs used it - very short range, very low power stuff but the killer was the receivers.
The Key Fob receivers had wide-open front-ends and collapsed in the presence of nearby RF. The result was that some UK Amateur 70cm repeaters were forced to shutdown to protect the unlicensed SRD's. The UK regulator Ofcom made it mandatory that applications for UK 70cm (430-440MHz) repeater licenses had to prove that they wouldn't cause "interference" to these unlicensed devices, eg wouldn't block wide-open RF front-ends! Following on from Automobile key fobs came a host of other low power SRD applications that were keen to use 433/434MHz. These have caused interference over a wide area, see Thames estuary SRD Interference on 433.500MHz http://www.g4uvj.btinternet.co.uk/isleofgrain.html SRD in 433/434MHz also impacts the Amateur Satellite Service. Manufacturers of 10 milliwatt walkie-talkies for 433/434 have cleverly run some leads through the battery compartment. If the user cuts these leads their 10mw 433/434MHz walkie talkie or base station gets converted into a 4 watt output transceiver that operates from 433.075 right up to 435.525MHz - well into our satellite allocation, see http://www.southgatearc.org/news/august2009/intek_drs5070_pmr446_radio.htm YouTube - Intek MT 5050 Export http://www.youtube.com/watch?v=Sgk5NDRP5sQ Industry needs a Globally allocated license exempt UHF allocation between 400 and 2400MHz - there isn't one !! - Global UHF license exempt spectrum is fragmented - Industry is currently trying to get 433-435MHz allocated as Global Unlicensed Spectrum so equipment can be sold anywhere. Belatedly Europe is attempting to allocate 915-921MHz (in-between European cell-phone frequencies) to SRD's. If 915-921MHz doesn't become the Global UHF SRD band then Amateurs will lose 433-435MHz for ever. Other URL's that may be of interest: Australia - SRD Interference causes Repeater to move http://www.southgatearc.org/news/jun2005/repeater_move.htm New Zealand 3.6 and 433 MHz SRDs http://www.southgatearc.org/news/august2010/nz_revised_gurl.htm Short range devices in the 433 MHz band http://www.southgatearc.org/news/august2008/short_range_devices_in_433mhz_band.htm 73 Trevor M5AKA _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
