gb3edn edinburgh 23 cm beacon update · googlemap. coverage • originally licensed for 2 x corner...
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![Page 1: GB3EDN Edinburgh 23 cm Beacon Update · Googlemap. Coverage • Originally licensed for 2 x Corner reflector • NE and NW • Good coverage of Central belt and north • Clear path](https://reader033.vdocument.in/reader033/viewer/2022050208/5f5b6412cfa97d33e91dce53/html5/thumbnails/1.jpg)
GB3EDN Edinburgh 23 cm Beacon Update
Brian Flynn
GM8BJF
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GB3 EDN Specifications
• Output frequency 1296.990 MHz• Output power ~5 watts• Keying F1A • Callsign only once per minute
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GB3EDN Location
• University of Edinburgh• Kings Buildings Campus• Antenna on top of the Faraday Building• (four storey block)• IO85JW91
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GB3EDN History
• Original hardware• Installed in 1977• Licence received and turned on in 1978• Run continuously with 2 short outages
since then• Hardware very reliable• Simple!• ~32 years in virtually continuous operation!
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Googlemap
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Coverage
• Originally licensed for 2 x Corner reflector• NE and NW• Good coverage of Central belt and north• Clear path to north sea
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Beaconspot.eu spots since 2008
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GB3ANG Spots
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GM6BIG spots
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GB3CSB Spots
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Existing hardware
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Existing TTL Keyer
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Corner Reflectors: 1978 -1986
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Existing Hardware
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Antenna 2010
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Antenna just after installation
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Close-up of antenna
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Another view
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General View
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Motivation for new Design
• Improved frequency accuracy• Improved stability• Reduced power consumption• Existing hardware draws ~5 amps at 12 V
and uses a linear power supply regulator• Improved keying and QRA locator added
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New design – Initial thoughts
• Want to generate signal from accurate standard
• Generally 5.0, 10.0, 12.4 or 15.0MHz• Not harmonically related to 1296.990 MHz• Ideally want to phase lock VHF xtal to
standard
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DDS techniques
• In the last 15 years DDS ICs have become available from a few manufacturers notably Analog devices
• Normally used to generate arbitrary frequencies from a VHF clock typically 100 MHz
• Output frequency set by a 32 bit tuning word• Output frequency step = 100MHz /2^32=23mHz!
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DDS continued
• DDS allows the generation of virtually any frequency from a frequency standard
• The big drawback is that the outputs are relatively noisy with both spurs and phase noise
• Use of DDS to replace a crystal oscillator not the way to go.
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Reverse DDS (RDDS)
• An alternative is to use the DDS chip as the divider in a conventional PLL
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Advantages of RDDS
• Can use high reference frequency • Phase noise and spur performance is
good• Narrow PLL bandwidth keeps output clean• FSK can be implemented easily by
changing tuning word• UK Microwave group produce a PCB to
implement circuitry!
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Complete Block Diagram
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UK Microwave RDDS PCB(Top)
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UK Microwave RDDS PCB (Bottom)
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G4DDK2001 PCB (Top)
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G4DDK2001 PCB (Bottom)
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G4DDK2001 Circuit
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Hardware