http://www.scrbg.org/

The GB3SC# Microwave BeaconsThe GB3SC# Microwave BeaconsWhat we have (now)What we have (now)

FrequencyFrequency CallsignCallsign Output EIRPOutput EIRP NotesNotes

2320.905MHz2320.905MHz GB3SCSGB3SCS 3 Watts3 Watts

3400.905MHz3400.905MHz GB3SCFGB3SCF 6 Watts6 Watts GPS Locked, RTTY DataGPS Locked, RTTY Data

5760.905MHz5760.905MHz GB3SCCGB3SCC 10 Watts10 Watts

10368.905MHz10368.905MHz GB3SCXGB3SCX 18 Watts18 Watts GPS Locked, RTTY DataGPS Locked, RTTY Data

24048.905 MHz24048.905 MHz GB3SCKGB3SCK 5 watts5 watts Started on 24192.905Started on 24192.905

47088.905 MHz47088.905 MHz G8BKE/PG8BKE/P 200mW200mW Directional, Turned on when Directional, Turned on when neededneeded

70.03170.031 G4JNT/PG4JNT/P 500mW500mW SlowCW TelemetrySlowCW Telemetry

2.4 GHz2.4 GHz ------ <= 100mW<= 100mW 802.11b WLAN Link802.11b WLAN Link

Had been operational on Had been operational on the Purbecksthe Purbecks

Good site for GB3SCX Good site for GB3SCX and we just about had and we just about had 3.4GHz running QRP3.4GHz running QRP

Starting to install others.Starting to install others. Kicked off site by mobile Kicked off site by mobile

phone operatorsphone operators So, we needed a new So, we needed a new

site…………..site…………..

GB3SCXG0API

South Coast Beacon Complex

Bell HillBell Hill

Used for contesting by Used for contesting by FRARS for yearsFRARS for years

Unused Versatower Unused Versatower and cabin – it had and cabin – it had mains powermains power

Rusty fittings, but all in Rusty fittings, but all in a useable conditiona useable condition

So we took over the So we took over the site in 2001 – site in 2001 –

Loc IO80UU59

Good take off in most directions

Hut PreparationHut PreparationHad been an animal Had been an animal

sheltershelterNeed to prevent Need to prevent

condensation condensation Limit temperature Limit temperature

extremesextremesWalls and door covered Walls and door covered

in polystyrenein polystyreneAll holes and gaps All holes and gaps

blockedblocked

Temperature Plots

Mast RenovationMast Renovation Needed a lot of work Needed a lot of work Four sets of Guys and Four sets of Guys and

stakesstakes New Haul and luffing New Haul and luffing

ropes.ropes. Old haul rope broke Old haul rope broke

when winching downwhen winching down New one had to be New one had to be

installed installed in-situin-situ Everthing stripped Everthing stripped

down and soaked in down and soaked in dieseldiesel

Anti-rust paintAnti-rust paint

Old PMR Antenna jammed in winch mechanism

Cable SupportCable Support

Five 12 metre runs of Five 12 metre runs of LDF4-50 plus LDF4-50 plus lightning + spare.lightning + spare.

Too heavy to self Too heavy to self hang from tophang from top

Mid point cable Mid point cable support – ‘revolver support – ‘revolver breech’ supported breech’ supported from pulleyfrom pulley

Cable hoops prevent Cable hoops prevent swingingswinging

Cables can’t be Cables can’t be bound together or bound together or harness could never harness could never be moved !be moved !

Duct at lower end Duct at lower end into hutinto hut

DON’T DO

THIS AT

HOME !

The Head assemblyThe Head assemblyNeed to survive high Need to survive high

windswindsMounted on scaffold Mounted on scaffold

across tower facesacross tower faces

Antenna Range TestsAntenna Range Tests

All antennas mounted close togetherAll antennas mounted close together Tests needed to see if there were Tests needed to see if there were

interactions / gaps in coverageinteractions / gaps in coverage Antenna test range from G0API driveway to Antenna test range from G0API driveway to

a neighbour across the road – just in far field a neighbour across the road – just in far field but with no Fresnel zonesbut with no Fresnel zones

Showed we had a workable systemShowed we had a workable system But…….But…….

`̀

Tests and MeasurementsTests and Measurements

Alford slots weren’t doing their job properlyAlford slots weren’t doing their job properlyField distribution along the slot was wrongField distribution along the slot was wrongNeeded small diameterNeeded small diameter

One coax was much lossier than expectedOne coax was much lossier than expectedFault in coax connector - Fault in coax connector - ¼¼ wavelength wavelength

suckout at 12GHz (for 24GHz, GB3SCK)suckout at 12GHz (for 24GHz, GB3SCK)

Power SuppliesPower Supplies

Mains cable 1km long, 1.5mmMains cable 1km long, 1.5mm2 2 armoured armoured 23 ohms loop resistance23 ohms loop resistance 750 Watts absolute maximum (2.5kW Kettle = Zo)750 Watts absolute maximum (2.5kW Kettle = Zo)

260 W for beacons and PC = 190 to 210V 260 W for beacons and PC = 190 to 210V input. Switch Mode PSU essentialinput. Switch Mode PSU essential

All beacons run from 12V battery floated All beacons run from 12V battery floated across PSU - 10 Amps totalacross PSU - 10 Amps total

PC has its own UPSPC has its own UPS

Mains FailureMains Failure Extended mains or PSU failure could flatten Extended mains or PSU failure could flatten

battery – one 24Ah battery lost alreadybattery – one 24Ah battery lost already Two levels of protection addedTwo levels of protection added

Software puts beacons to standby immediately if Software puts beacons to standby immediately if mains goes off or DC drops below charge voltage mains goes off or DC drops below charge voltage

3A to keep oscillators, ovens and TLM active, 8 to 10 hours3A to keep oscillators, ovens and TLM active, 8 to 10 hours

Then a hardware shut-off if DC drops below 10VThen a hardware shut-off if DC drops below 10V

Small auxilliary PSU for TCmd/TLM, cross-Small auxilliary PSU for TCmd/TLM, cross-strapped, allows for failure of sensing unit / main strapped, allows for failure of sensing unit / main PSU.PSU.

Earthing / ProtectionEarthing / Protection Problems with lightning on an exposed hilltopProblems with lightning on an exposed hilltop Tower metalwork has poor bonding – dedicated Tower metalwork has poor bonding – dedicated

conductor up mast for high E-fieldsconductor up mast for high E-fields Nearby ground strikes are the biggest problemNearby ground strikes are the biggest problem All metalwork in hut, rack mount, firmly bonded All metalwork in hut, rack mount, firmly bonded

to feeders, mains cable sheath and extensive to feeders, mains cable sheath and extensive array of ground radials / rods in 10m circle array of ground radials / rods in 10m circle around the cabinaround the cabin

Everything jumps togetherEverything jumps together Varistors were fitted on the mains input after a Varistors were fitted on the mains input after a

nearby strike took out the PSU last Junenearby strike took out the PSU last June

Remote ControlRemote Control Distant site – no quick access for the nominated keepers Distant site – no quick access for the nominated keepers

(30 – 80km trip) – one local op. G7RMG(30 – 80km trip) – one local op. G7RMG Radio controlled link, Radio controlled link, Bi-directional, 70cm FM, allows verification of Bi-directional, 70cm FM, allows verification of

commands. T7F transceiver modulecommands. T7F transceiver module PIC Based controller with own battery back up. DTMF PIC Based controller with own battery back up. DTMF

tones for control from handie-talkie using rolling set of 5-tones for control from handie-talkie using rolling set of 5-digit access codes for security. digit access codes for security.

Three PIN tables for different usersThree PIN tables for different users Position in code table accessible on commandPosition in code table accessible on command Status of each circuit on/off state can be requestedStatus of each circuit on/off state can be requested

Switches 8 circuits on/off via relays with isolated contactsSwitches 8 circuits on/off via relays with isolated contacts

TelemetryTelemetry Dedicated PIC based TLM monitor with A/D convertersDedicated PIC based TLM monitor with A/D converters Mains Voltage / Current, DC Volts, Temperatures, Status Mains Voltage / Current, DC Volts, Temperatures, Status

SwitchesSwitches Originally just sent CW when demanded on UHF link.Originally just sent CW when demanded on UHF link. Later, 70MHz low power Tx (G4JNT/P) sending basic Later, 70MHz low power Tx (G4JNT/P) sending basic

parameters as CW / SlowCWparameters as CW / SlowCW PC logging data via RS232 link from monitorPC logging data via RS232 link from monitor 18km WLAN link and webserver18km WLAN link and webserver Possibility for alarms sent to users by text message / Possibility for alarms sent to users by text message /

Email.Email. Video linkVideo link

47GHz turned on (We know what

you’re doing, Chris and John !)

Frequency LockingFrequency Locking

‘‘Simple GPSDO’ on site, supplying 10MHz Simple GPSDO’ on site, supplying 10MHz with typical 10with typical 10-9-9 accuracy accuracy

GB3SCF and GB3SCX locked to this GB3SCF and GB3SCX locked to this using DDS solution – others to followusing DDS solution – others to follow

10368.905010368.90500068 MHz (32 bit DDS)68 MHz (32 bit DDS)3400.904993400.904999999985 MHz (48 bit DDS)99985 MHz (48 bit DDS)But only to GPSDO accuracy!But only to GPSDO accuracy!

Equipment rackEquipment rack

UHF Antenna

Mast

25A-Hour Pb/H+ Battery

Mains Supply

Power Monitor

Beacon Head Units

GB3SCS

GB3SCF

GB3SCC

GB3SCX

GB3SCK

12V 30A PSU

Switching Relays

UHF Command and Telemetry Module

Inside the Beacon Hut

GPS Locked 10MHz Reference

GB3SCF with frequency locked source

Head Unit

Block Diagram of GB3SCX (the original

version before frequency locking)

LDF 450 Feed to Masthead

Crystal Oscillator Multiplier

Bandpass filter

324MHz 648MHz 1.3GHz 2.6GHz108MHzMHz

X3 X2 X2 X2

DDK004 Source Module+12V

X4

Power Amplifier

10.368GHz

Slotted Waveguide Antenna

Cable Duct into cabin

47GHz

70MHz Dipole