At 07:07 AM 3/9/2011, Trevor . wrote: >Short Range Devices (SRDs) in 433-434 are bad news.
Tell me about it! :/ >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. Australia also allowed SRDs in the mid-late 1990s. >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! This problem has been noted in certain locations, but they are not offered protection from this sort of interference here. >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 Ouch! Haven't seen those here. >Australia - SRD Interference causes Repeater to move >http://www.southgatearc.org/news/jun2005/repeater_move.htm There's many examples of repeaters having to move. The problem for us here was that there was no limit put on the duty cycle of the SRDs. The most troublesome devices down here have been industrial crane controllers, which have a 100% duty cycle. I for one had interference from these from an industrial area 1-2km from my repeater. The ACMA effectively legislated that these devices don't exist, when it comes to protection from interference. The walkie talkies disappeared off the market quickly here. I think the well established UHF CB service out competed them, offering more power (200 mW - 5W) legally, and more features for a similar price, as well as compatibility with a larger installed base. The other big problem here is cordless headphones, which tend to drift up and down the band, and even outside the SRD band. 73 de VK3JED / VK3IRL http://vkradio.com _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
