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http://www.scrbg.org/. The GB3SC# Microwave Beacons What we have (now). GB3SCX. G0API. South Coast Beacon Complex. Had been operational on the Purbecks Good site for GB3SCX and we just about had 3.4GHz running QRP Starting to install others. Kicked off site by mobile phone operators

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  1. http://www.scrbg.org/

  2. The GB3SC# Microwave BeaconsWhat we have (now)

  3. GB3SCX G0API South Coast Beacon Complex • Had been operational on the Purbecks • Good site for GB3SCX and we just about had 3.4GHz running QRP • Starting to install others. • Kicked off site by mobile phone operators • So, we needed a new site…………..

  4. Bell Hill Loc IO80UU59 • Used for contesting by FRARS for years • Unused Versatower and cabin – it had mains power • Rusty fittings, but all in a useable condition • So we took over the site in 2001 –

  5. Good take off in most directions

  6. Hut Preparation • Had been an animal shelter • Need to prevent condensation • Limit temperature extremes • Walls and door covered in polystyrene • All holes and gaps blocked

  7. Temperature Plots

  8. Mast Renovation • Needed a lot of work • Four sets of Guys and stakes • New Haul and luffing ropes. • Old haul rope broke when winching down • New one had to be installed in-situ • Everthing stripped down and soaked in diesel • Anti-rust paint Old PMR Antenna jammed in winch mechanism

  9. Cable Support • Five 12 metre runs of LDF4-50 plus lightning + spare. • Too heavy to self hang from top • Mid point cable support – ‘revolver breech’ supported from pulley

  10. Cable hoops prevent swinging Cables can’t be bound together or harness could never be moved ! Duct at lower end into hut

  11. DON’T DO THIS AT HOME !

  12. The Head assembly • Need to survive high winds • Mounted on scaffold across tower faces

  13. Antenna Range Tests • All antennas mounted close together • Tests needed to see if there were interactions / gaps in coverage • Antenna test range from G0API driveway to a neighbour across the road – just in far field but with no Fresnel zones • Showed we had a workable system • But…….

  14. `

  15. Tests and Measurements • Alford slots weren’t doing their job properly • Field distribution along the slot was wrong • Needed small diameter • One coax was much lossier than expected • Fault in coax connector - ¼ wavelength suckout at 12GHz (for 24GHz, GB3SCK)

  16. Power Supplies • Mains cable 1km long, 1.5mm2 armoured • 23 ohms loop resistance • 750 Watts absolute maximum (2.5kW Kettle = Zo) • 260 W for beacons and PC = 190 to 210V input. Switch Mode PSU essential • All beacons run from 12V battery floated across PSU - 10 Amps total • PC has its own UPS

  17. Mains Failure • Extended mains or PSU failure could flatten battery – one 24Ah battery lost already • Two levels of protection added • Software puts beacons to standby immediately if mains goes off or DC drops below charge voltage • 3A to keep oscillators, ovens and TLM active, 8 to 10 hours • Then a hardware shut-off if DC drops below 10V • Small auxilliary PSU for TCmd/TLM, cross-strapped, allows for failure of sensing unit / main PSU.

  18. Earthing / Protection • Problems with lightning on an exposed hilltop • Tower metalwork has poor bonding – dedicated conductor up mast for high E-fields • Nearby ground strikes are the biggest problem • All metalwork in hut, rack mount, firmly bonded to feeders, mains cable sheath and extensive array of ground radials / rods in 10m circle around the cabin • Everything jumps together • Varistors were fitted on the mains input after a nearby strike took out the PSU last June

  19. Remote Control • Distant site – no quick access for the nominated keepers (30 – 80km trip) – one local op. G7RMG • Radio controlled link, • Bi-directional, 70cm FM, allows verification of commands. T7F transceiver module • PIC Based controller with own battery back up. DTMF tones for control from handie-talkie using rolling set of 5-digit access codes for security. • Three PIN tables for different users • Position in code table accessible on command • Status of each circuit on/off state can be requested • Switches 8 circuits on/off via relays with isolated contacts

  20. Telemetry • Dedicated PIC based TLM monitor with A/D converters • Mains Voltage / Current, DC Volts, Temperatures, Status Switches • Originally just sent CW when demanded on UHF link. • Later, 70MHz low power Tx (G4JNT/P) sending basic parameters as CW / SlowCW • PC logging data via RS232 link from monitor • 18km WLAN link and webserver • Possibility for alarms sent to users by text message / Email. • Video link

  21. 47GHz turned on (We know what you’re doing, Chris and John !)

  22. Frequency Locking • ‘Simple GPSDO’ on site, supplying 10MHz with typical 10-9 accuracy • GB3SCF and GB3SCX locked to this using DDS solution – others to follow • 10368.9050068 MHz (32 bit DDS) • 3400.90499999985 MHz (48 bit DDS) • But only to GPSDO accuracy!

  23. Equipment rack

  24. GB3SCS GB3SCF GB3SCC GB3SCX GB3SCK Beacon Head Units Inside the Beacon Hut GPS Locked 10MHz Reference UHF Command and Telemetry Module Power Monitor UHF Antenna Switching Relays Mains Supply 12V 30A PSU Mast 25A-Hour Pb/H+ Battery

  25. GB3SCF with frequency locked source

  26. +12V 324MHz 1.3GHz 2.6GHz 108MHzMHz 648MHz X3 X2 X2 X2 Crystal Oscillator Bandpass filter Multiplier X4 10.368GHz Power Amplifier DDK004 Source Module Head Unit LDF 450 Feed to Masthead Slotted Waveguide Antenna Block Diagram of GB3SCX (the original version before frequency locking)

  27. 70MHz Dipole Cable Duct into cabin 47GHz

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