Transcript SlowCW Telemetry 500mW G4JNT/P 70.031 Started on 24192.905

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The GB3SC# Microwave Beacons
What we have (now)
Frequency
Callsign
Output EIRP
2320.905MHz
GB3SCS
3 Watts
3400.905MHz
GB3SCF
6 Watts
5760.905MHz
GB3SCC
10 Watts
10368.905MHz
GB3SCX
18 Watts
GPS Locked, RTTY Data
24048.905 MHz
GB3SCK
5 watts
Started on 24192.905
47088.905 MHz
G8BKE/P
200mW
Directional, Turned on when
needed
70.031
G4JNT/P
500mW
SlowCW Telemetry
<= 100mW
802.11b WLAN Link
2.4 GHz
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Notes
GPS Locked, RTTY Data
South Coast Beacon
Complex
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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…………..
G0API
GB3SCX
Bell Hill
Loc IO80UU59
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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 –
Good take off in most
directions
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

Temperature Plots
Mast Renovation
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Needed a lot of work
Four sets of Guys and
stakes
New Haul and luffing
ropes.
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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
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

Cable hoops prevent
swinging
 Cables can’t be
bound together or
harness could never
be moved !
 Duct at lower end
into hut

DON’T
DO
THIS
AT
HOME !
The Head assembly
Need to survive high
winds
 Mounted on scaffold
across tower faces

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…….
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`
Tests and Measurements

Alford slots weren’t doing their job properly
Field distribution along the slot was wrong
 Needed small diameter
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One coax was much lossier than expected

Fault in coax connector - ¼ wavelength
suckout at 12GHz (for 24GHz, GB3SCK)
Power Supplies
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Mains cable 1km long, 1.5mm2 armoured
 23 ohms loop resistance
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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
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Mains Failure
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Extended mains or PSU failure could flatten
battery – one 24Ah battery lost already
Two levels of protection added
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Software puts beacons to standby immediately if
mains goes off or DC drops below charge voltage
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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, crossstrapped, allows for failure of sensing unit / main
PSU.
Earthing / Protection
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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
Remote Control
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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 5digit 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
Telemetry
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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
47GHz turned on
(We know what
you’re doing, Chris
and John !)
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!

Equipment rack
Beacon Head
Units
Inside the Beacon Hut
GB3SCS
GB3SCF
GPS Locked 10MHz
Reference
GB3SCC
GB3SCX
UHF Command and
Telemetry Module
Power
Monitor
Mains
Supply
GB3SCK
Switching Relays
UHF
Antenna
12V 30A PSU
Mast
25A-Hour Pb/H+
Battery
GB3SCF with frequency locked
source
+12V
DDK004 Source Module
324MHz
108MHz
MHz
X3
Crystal
Oscillator
Multiplier
1.3GHz
648MHz
X2
X2
2.6GHz
X2
Bandpass
filter
Head Unit
LDF 450 Feed to
Masthead
Slotted
Waveguide
Antenna
X4
Block Diagram of
GB3SCX (the original
version before
frequency locking)
10.368GHz
Power
Amplifier
70MHz Dipole
Cable Duct
into cabin
47GHz