GB3OO
GB3OO is a Digital Amateur Television (DATV) repeater serving the amateur radio community across Kent, Essex, and the near continent. It went fully on air on 12 June 2026, transmitting on 23cm with a 70cm input, and streams its output live to the internet via the BATC.
| Location | Upper Arpinge, near Folkestone, Kent, CT18 8AD |
|---|---|
| Locator | JO01NC |
| NoV Holder | Justin D. Cockett, G8YTZ |
| Website | gb3oo.co.uk |
Quick Reference
| Parameter | Value |
|---|---|
| 23cm Output | 1304 MHz, DVB-S2, 2 MSym/s, FEC 3/4, roll-off 0.35, 150W EIRP |
| 70cm Input | 437 MHz, DVB-S/S2, 333 kSym/s, automatic FEC |
| 2m Talkback Input | 144.750 MHz FM, vertical, CTCSS 103.5 Hz |
| Web Stream (out) | rtmp://rtmp.batc.org.uk/live/gb3oo
|
| Web Stream (in) | Registered users only — see gb3oo.co.uk "Streamer" page |
| Antenna height | 30 m (self-supporting lattice mast) |
| Tx antenna gain | 12 dBi (slotted waveguide, PE1RKI design) |
Site Overview
GB3OO sits at a rural hilltop location near Folkestone, chosen for its excellent coverage across the surrounding area. The installation is built around a self-supporting lattice mast: at the summit, the 23cm slotted-waveguide transmit antenna and the 70cm "Big Wheel" receive antenna are mounted together. A brick-built equipment building at the base of the tower houses the full repeater rack.
Coverage
GB3OO's 23cm output covers a large area of Kent, Essex, London, and across the Channel into northern France and Belgium — conditions permitting, and especially well during tropospheric ducting.
The 70cm receive input has a correspondingly wide catchment for stations wanting to transmit into the repeater, fed by an omnidirectional dual-stack WIMO "Big Wheel" antenna (5 dBi gain).
During good tropo conditions, continental stations from France, Belgium, and beyond are actively welcomed — the repeater's French-language announcement specifically invites this.
Transmit Chain
The transmit chain starts at the power amplifier, delivering 10W RF output at 23cm.
- Feeder run: 4m LDF5-50 7/8" Heliax tail → 30m LDF6-50 1-5/8" Heliax main run (the larger diameter minimises loss over the long vertical run) → 2m LDF5-50 tail to the antenna feed point
- Connectors: 7/16 DIN throughout (chosen over N-type for low loss and superior intermodulation performance at these power levels)
- Antenna: Slotted waveguide, designed and built by Bert Moderman (PE1RKI) — seven radiating slots per face on two faces, giving an omnidirectional azimuth pattern within ±1.3 dB and 12 dBi gain
- Result: 150W EIRP, meeting the licensed limit once feeder and coupler losses are accounted for
- Return loss at commissioning: 30.5 dB — an excellent match, important at 23cm since poor return loss on a long feeder causes standing-wave echoes that visibly degrade DVB-S2 signal quality (closing the constellation "eye," raising EVM, lowering MER)
70cm Receive Chain
The receive chain is built for strong out-of-band rejection given the site's exposure to cellular and other nearby services:
- Interdigital bandpass filter (Bert Moderman, PE1RKI) — first-stage protection against strong out-of-band signals
- Low-noise preamplifier (also PE1RKI) — 15 dB gain, 0.35 dB noise figure, setting the noise floor for the whole receive chain
- SAW filter — ~60 dB attenuation at 470 MHz, eliminating interference from terrestrial digital TV and UHF PMR
- BATC Minitiouner DVB-S/S2 tuner running the Ryde Receiver for demodulation
Since interdigital filters have responses at odd harmonics, the second filtering stage (the SAW filter) is essential to fully clean up the signal before demodulation.
Equipment Rack
The repeater is housed in a wall-mounted 19" × 450mm(d) × 18U rack with removable side panels and a lockable glass front door. Two continuously-running 240V axial fans provide cooling, with heavy electrical loads mounted toward the top to keep a cool zone at the bottom of the cabinet.
Rack layout (bottom to top):
| RU | Contents |
|---|---|
| 1 | Cable management brush strip |
| 2 | Raspberry Pi shelf — media player, stream receiver, 70cm receiver |
| 3 | Network equipment — UniFi UCG firewall, 7-port PoE switch |
| 4 | Windows 11 PC — Bitfocus Companion software, VLC for audio announcements |
| 5 | Mains distribution 2 (low-power devices) |
| 6 | Pull-out drawer — Blackmagic ATEM Mini Pro video switcher, 2m receiver, 1TB SSD local storage |
| 7–8 | Receiver shelf — BATC Minitiouner |
| 9–10 | HF modulator, H.264 encoder, Modbus TCP/RTU telemetry |
| 11–12 | Ventilation panel |
| 13–15 | Power amplifier |
| 16 | Cable management brush strip |
| 17 | Air-tight blanking panel |
| 18 | Mains distribution 1 (PA, exciter, case fans) |
Exciter Shelf
The modulator is an SR-Systems "Minimod" HF modulator paired with an SR-Systems H.264 encoder, managed via a VT-100 emulation RS-232 interface accessed over Telnet through an in-built terminal server on a fixed IP.
The exciter shelf also carries the transmitter telemetry, via Modbus TCP/RTU:
- Temperature sensors (PTC): exciter air outlet, PA air outlet, PA heatsink
- Digital relay outputs: exciter load/PA co-ax relay, ATEM power on/off (cold reset only)
- Analogue input: PA forward power
- Digital output: PA power switching (local relays in the PA shelf)
Power & Infrastructure
- UPS: APC tower UPS, fed from a blue 16A "Commando" connector that also serves as the safety isolator. Emergency isolation is via removing the two 13A plug tops from the orange distribution board at the rear of the UPS.
- Metering: A Modbus-compatible meter in the mains distribution board (located above the repeater) tracks electricity consumption.
- UPS battery life: expected to need replacement around 5 years from commissioning (May 2026), usage-dependent.
Licensing & Insurance
- Ofcom: Licensed via Notice of Variation dated 30 September 2025, renewal due 29 September 2028. NoV holder: Justin D. Cockett (G8YTZ).
- Software: All repeater system software is open-source or perpetually licensed. The PiDeck media player is licensed from Guy, M0GUY, and requires a continual internet connection to remain licensed. Commercial components (UniFi, Blackmagic ATEM, Windows 11) are licensed per manufacturer T&Cs.
- Insurance: Covered under the RSGB's Repeater & Beacon insurance scheme, renewed annually each May by G8YTZ.
Control & Streaming Infrastructure
The site runs a Bitfocus Companion v4 control portal, giving webhook-triggered automatic input switching, an ATEM video switcher, and full session recording ("Time Machine") of repeater activity — all accessible to registered users via the website's Repeater Control Portal.
ATEM Streaming Watchdog
The ATEM Mini Pro video switcher has a known Blackmagic firmware bug: after a power cycle, its streaming configuration (RTMP URL, key, bitrates) can come back corrupted, silently taking the stream offline. A custom Python watchdog runs continuously on the site PC, detecting this condition and automatically restoring the correct configuration — no site visit required. Full technical detail, installation procedure, and troubleshooting are covered in the separate ATEM Watchdog manual.
Receiving GB3OO
GB3OO can be received cheaply — often with equipment already owned. Full detail is on the website's "Streamer" and reception guide pages; in summary:
What you need:
- A small 23cm Yagi antenna (wideband version recommended; e.g. Antenna Amplifiers' 23cm5ra or 23cm13dxr) plus feeder
- A standard HD satellite receiver — many modern TVs (LG, Samsung, Sony tested) have a suitable built-in tuner
- A small in-line amplifier to compensate for 23cm cable losses
Receiver settings:
| Setting | Value |
|---|---|
| LNB Local Oscillator | 9750 MHz |
| Symbol Rate | 2000 kSym/s (2 MSym/s) |
| Polarisation | Either — controls amplifier supply voltage, not signal |
| 22kHz Tone | OFF |
| LNB Power | ON |
| DiSEqC | OFF |
Then run a blind scan — if signal is good, the receiver will find and add GB3OO automatically.
Check the coverage map first; anyone in the "green" area with a clear line of sight toward Folkestone should have an easy time of it. Justin, G8YTZ, is happy to help assess individual locations (contact via QRZ).
If an antenna isn't practical, streaming into the repeater from a phone or via OBS is also supported — see the "Streamer Key and Instructions" page on the website.
Test Card
The GB3OO test card was developed with the assistance of Claude AI, generated as an SVG graphic and tailored specifically for DATV use rather than adapted from a generic broadcast template.
The card includes several purpose-built technical reference elements, mirrored on both the left and right sides for easy assessment regardless of framing:
- Frequency gratings at three resolutions — fine vertical line gratings sized for 1920×1080p (2.00px line width), 1280×720p (3.00px), and 1024×576p (3.75px), allowing viewers to judge effective resolution and detect aliasing or softness at FHD, HD, and SD respectively, whichever the receiving chain is actually delivering.
- EBU colour bars — the standard broadcast colour reference, useful for checking colour balance and saturation through the transmit and receive chain.
- Monochrome (greyscale) staircase — an 8-step greyscale ramp for checking tonal linearity and spotting clipping or crushing at the black or white end of the range.
The central animated graphic and "GB3OO" wordmark give the card a distinct identity, while the surrounding technical elements keep it functional as a genuine alignment and diagnostic tool rather than purely decorative.
History / Timeline
| Date | Milestone |
|---|---|
| 16 Sep 2025 | Website goes live; frequencies agreed |
| 8 Oct 2025 | Rack build underway — controller and receivers installed |
| 9 Oct 2025 | ATEM switcher and network equipment delivered and configured; ad-hoc streaming tests begin |
| 15 May 2026 | Antenna installation complete |
| 21–22 May 2026 | Equipment installed on site at Folkestone; output streaming live; 70cm receiver operational |
| 12 Jun 2026 | GB3OO officially on the air — 1304 MHz, 2 MSym/s, FEC 3/4 |
| 14 Jun 2026 | 70cm receiver lock-detection improved (5-second confirm timer to eliminate false/short locks) |
Membership & Community
Registration on gb3oo.co.uk is free and unlocks:
- Session Recordings ("Time Machine") — rewind and catch up on missed activity
- Repeater Control Portal — a live dashboard for repeater control
- Slack Notifications — alerts when the repeater comes into use
Anyone registered on the GB3JV website as of 31 December 2025 has had their login carried across automatically; anyone else needs to register separately.
Links
- Website: gb3oo.co.uk
- Coverage maps: gb3oo.co.uk/predicted-coverage-map
- Streamer / reception instructions: gb3oo.co.uk/receiving-the-gb3jv-network-stream
- Logbook: gb3oo.co.uk/logbook
- BATC: batc.org.uk
- Direct web stream:
rtmp://rtmp.batc.org.uk/live/gb3oo
This page draws on the GB3OO website, the GB3OO technical manual, and site documentation. Some sections (network/remote access IP plan, full control portal configuration, detailed component part numbers) are held in the restricted technical manual and are only summarised here — let Justin, G8YTZ know if you'd like any of those expanded.