GB3JV Digital Amateur TV Repeater

GB3JV proudly uses SMARTY (A Which? magazine recommended mobile network provider) for the backup of our 5.8GHz Ubiquiti broadband link. SMARTY, owned by H3G, is unlike many MVNOs in that you get all the network services available on the parent network. SMARTY only offer a 30 day contract with unlimited calls & texts (EU roaming included) and superb 5G performance (439Mb/s as personally tested on a iPad M1 PRO here in Petts Wood). Get a £10 bonus and help GB3JV with this referral link: SMARTY Mobile

Thinking of moving to Octopus Energy? Use my referral link to get a £50 credit on your account: Octopus Energy £50 Referral Credit

Repeater background music licensed from and supplied by Artlist

Latest News Updates:

Click to stream GB3JV Live! (requires VLC to be installed)

  • 02/03/2024. Don’t forget to visit the National Radio Centre to see the new Interactive DATV display. Remember that if you’re an RSGB member you can get free entry to Bletchley Park by downloading a ticket from your RSGB web site portal.
  • 19/04/2023. From today the 70cm input will accept 333kS/s and 1MS/s (instead of 2MS/s). The reason for this change is an attempt to reduce the number of “false locks” caused by temporary traffic lights using 433.9MHz in the area local to the repeater.
  • 01/02/2023. A small graphics update: The digital on-screen graphics (ident logo) is now generally not displayed when a test card is being transmitted. It is always  displayed when in-vision content does not include the station ident or when the repeater is in use.
  • 21/11/2022. When you receive a SLACK notification that the repeater is in use, the message will also contain a link to the repeater’s stream output. For this to work you need to have the VLC App installed on your device. Many thanks to Roger, G8HKN for this suggestion.
  • 15/11/2022. A couple of small improvements went live today. The 10 minute lower third repeater ident has been replaced with a permanent DOG (digital on-screen graphic). Should the repeater be in active repeat mode it will also show the active input, or the most recent active input if Picture in Picture mode is active. Furthermore the repeater’s lower third graphics have been sharpened with a new font.
  • 14/11/2022. When the repeater is in idle (beacon) mode we’re screening various royalty-free videos that should be of interest to the amateur radio community. The videos also help test repeater’s ability to handle fast moving scenes and it’s enabled us to confirm the best results are achieved running the repeater with progressive scan at 25 frames/second. From time to time we might adjust codec settings to optimise the experience. Audio remains at 192kb/s AAC.
  • 10/11/2022. The web stream average date rate has been increased to 1.5Mb/s to reflect the improved internet capacity via the Ubiquiti 5.8GHz back-haul link. Audio data rate remains at 128kb/s AAC.
  • 01/09/2022. Justin, G8YTZ was delighted to give a presentation about GB3JV to the Crystal Palace Radio & Electronics Club. Gareth, G4XAT brought his portable station and demonstrated accessing GB3JV from the Churchyard. Justin hopes to see some CPR&EC members on the air soon!
  • 24/08/2022. Last evening we migrated the GB3JV internet connection to the new Ubiquiti 5.8GHz radio link equipment. This has improved the performance of the internet connection to the site, improved streaming performance and reduced operating expenditure.
  • 10/08/2022. Each night of this and next week at 19:00 and 21:00 we are replaying a presentation by Bert Hubert titled “How GPS Works”. If you’d like to join in with the GPS monitoring project and construct your own GPS monitor further information can be found Here
  • 04/08/2022. Yesterday evening we upgraded the 3.404GHz transmitter modulator to a new single-board design (HDMod) from SR-Systems. This modulator is the same type that’s used for the OSCAR-100 beacon and provides superior I-Q modulation performance, with direct conversion from the D-A converter. This coupled with the new up-converter from Kuhne Electronics fitted a few months ago means the GB3JV transmitter is producing an extremely high quality output. If you’re interested in the HDMod for your repeater please email the site admin and we will be pleased forward the contact  details.
  • 17/07/2022. Following successful beta testing, the new repeater feature “Session Recording” is now operational. As a registered user, when you log into the web site you’ll see a new top menu item “Session Recordings” The link on this page will take you to a Microsoft OneDrive page where the recordings can be played in a compatible browser or downloaded. Recordings are generally available within 4 hours of your repeater session.
  • 08/07/2022. We are planning an improvement in the internet connectivity to the GB3JV site; the project has met all its milestones at the design stage. The implementation is planned for August (dependency on OFCOM issuing the “Light License” for Band C. Currently the internet connection is provided by H3G and whilst this has performed well it cannot offer the bandwidth required for some of the new repeater features that are planned. To this end we’ve purchased a Ubiquiti 5.8GHz link equipment that will back to G8YTZ’s house. This will provide a reliable high-bandwidth (>100Mb/s) connection to the internet.
  • 05/06/2022. Here at GB3JV we think Morse Code is a teeny bit old fashioned, so we’ve decided to soup things up a bit: Today we went live with a new repeater feature; Audible Announcements! When you access the repeater you’ll get an input specific welcome from a friendly voice, and when you leave you’ll get a polite “goodbye” in addition, of course to the visual transitions that we’re getting famous for! At a later date we expect to expand this feature to other areas, so if you have an idea that you’d like to suggest the blog is to the right of this page!
  • 05/06/2022.
    • Initial results of the 70cm receiver upgrade have been very positive indeed, the receiver sensitivity has improved by at least 2dB.
    • The new cellular modem is also performing well and we’ve not seen a single stream drop since the upgrade.
    • Today we also performed a major upgrade to the user management software on this web site, please let us know if you experience any issues when logging on.
  • 24/05/2022. Today the GB3JV beta web stream input went live, if you’d like a stream key please register on this web site. Of course you have to be a licensed radio amateur of “Intermediate” or “Full” license grades as well as a member of the BATC. By registering you’ll also be invited to join the GB3JV SLACK channel and receive notifications of repeater activity.
  • 16/05/2022. Want a fantastic deal on a UK SIM-only card? Don’t forget you can help GB3JV and earn yourself a month free with SMARTY! 30 day contract by using the referral link below, great pricing and superb performance (as used by GB3JV for the network and streaming connectivity) and 5G is included (where available) and there’s 10% off every SIM in a group plan. Smarty is a Which? Best Buy provider to boot. GB3JV uses the “unlimited” plan, which is truly unlimited with no throttling or fair use policy.
  • 02/05/2022. From time-to-time I’m running some experiments to see how PiP might work, the idea is to allow (encourage) full-duplex QSOs via the repeater. Moving forward there are some sophisticated automation options, and/or manual user control of input switching from the GB3JV web site. (Yes, Justin is currently reading all about SMEE and Jenkins!). The idea is that if the repeater is already in use, a second user can join on another input. In its first implementation when you access the repeater a PiP box will appear in the top left corner showing the unused input; if a station then accesses that input they will take over the main screen and the original user will be relegated to the PiP window. When either user ceases transmission the repeater will revert to the media player, to restore video it will be necessary for the remaining station to momentarily drop transmission, or for a new user to access the (now available) input. We’ll have to see how it works out in practice, but at least it’ll be fun finding out! 🙂
  • 25/04/2022. Justin, G8YTZ is delighted to announce that the NoV (OFCOM License) was today renewed for a further 3 years. Many thanks to everyone at the ETCC and at OFCOM for their help
  • 18/04/2022. 
    • 23cm Input: The repeater’s 23cm input (1249MHz) supports 333kS/s and 2MS/s. from a west facing “WIMO” flat plate antenna
    • 70cm Input: The repeater’s 70cm input (437MHz) supports 333kS/s and 1MS/s. from an omnidirectional WIMO “Big Wheel” antenna with a gain of 5dBi 
    • 2m “talkback” Input: Accessed via the ATV calling channel 144.750MHz FM/Vertical, CTCSS 103.5Hz
    • Repeater Streamer: 1080p/25; URL for VLC and other H.264 media players is: rtmp://
  • If you have received the repeater, a reception report would be very welcome in the blog/comments section to the right. To increase the range still further I’ve switched the FEC to 1/2 so a received C/N of just 1dB should ensure a stable picture.

Tuning a domestic satellite receiver to receive GB3JV:

Firstly, you’ll need a “3.4GHz PLL” LNB or down-converter, designed for the “C Band”. A standard “Sky” LNB will not work. Unfortunately the Titanium C1W-PLL unit is no longer made and many of the alternatives have a built-in “4g or 5g” filter, so these will not work; you need one that covers the 3.4GHz band that features a PLL (Phased Locked Loop). We’ve seen quite a number of Norsat units on eBay that you can use with a horn antenna, but avoid the DRO versions. An off-the-shelf alternative down-converter is the Kuhne KU LNC 3239 C PRO, this is the very best solution, costs around €500, but can be pole mounted alongside a Wi-Max antenna such as the one linked below. You might require a pre-filter if you are close to a cellular mast. For filters I recommend contacting Bert Modderman . The down-converter is available from Kuhne Electronics

You can also obtain surplus Ionica receivers for around £40 on eBay, though you’ll have to add you own Local Oscillator, amplifier and split power supply unit. Ex Wi-Max flat plate antennas for the 3.4GHz band are very satisfactory for DATV reception. Prices are around £50 for what is a professional antenna that cost much more to manufacture. Here is the full parts list: 

With these components you’ll have a very robust and high performance Down-Converter with best of breed filtering built-in.

Many domestic TV receivers have an in-built satellite tuner. I’ve successfully tuned a Samsung 6000 series TV, my [pre-Android] Sony set, and a domestic set top box to receive GB3JV. I don’t however recommend any of the “FreeSat” boxes as the setup software seems to conspire against you entering direct frequencies into these products. The method used on the Samsung was to just leave it in the default “ASTRA” mode add the GB3JV frequency manually. To calculate the equivalent C-Band frequency you calculate like this:  9750 + 5150 – 3404MHz = 11496MHz. Enter this frequency into the receiver and then perform a “Channel Scan” so the receiver can detect the programme identifiers. You can also perform a “Blind Scan” if you are confident that you have a good signal being received by the LNB; perhaps you have already aligned the LNB with a Sat Meter like the “GT Media V8 Gold Satellite Finder Meter” that I purchased on Amazon. I’ll post a video in the next week showing how to set up a typical Samsung TV to receive Amateur repeaters on C-Band. Remember to turn off the 22kHz pilot tone (used for LO switching) and to set the Symbol rate to 2000kS/s on the receiver, everything else should be automatic.

It’s worth mentioning that if you have a fairly good line-of-sight from Petts Wood, unless you’re close to a cellular transmitter you’ll most likely only need the LNB with the supplied scaler and without a dish to receive the repeater. Remember that LNB’s are designed to receive tiny signals from satellites 50,000km away, they are very sensitive and really don’t struggle receiving a terrestrial signal just a few miles away. Today I stopped the car near Biggin Hill with my LNB and Satellite meter and received a solid signal with an 85% quality rating just standing in a car park, that’s about 5 miles away.

For a rough calculation, assuming that a typical satellite is 50,000km from us we can calculate the free space path loss to be about 207dB at 11.5GHz. Given the gain of a typical 60cm dish is about 37dB, then  207-37 = 180dB effective path loss to give a good signal and that’s at Symbol rate of 27,500kS/s! If we do the same calculation and assume no gain at the receive antenna (i.e. just the LNB) then the equivalent distance is 2,000km! Obviously this is only a comparison and for terrestrial situation we have obstructions, hills, houses and the curvature of the earth, but you can see that if you have a clear line-of-sight to the transmitter, gain of the receiving antenna is hardly going to be of much concern. For fringe areas I would recommend a Sky Mini-Dish (45cm) as a great compromise between gain and ease of alignment, but start with just the LNB mounted in a good unobstructed location and see how you get on. One thing I have noticed is that the Titanium LNB does not appear very weatherproof, so I would mount it in a plastic box or cover it in a black heat-shrink tubing. I purchased some for the Tx Antenna from Hilltop ProductsHeat Shrink Tubing HSP1″ which is UV resistant and does not inhibit RF transmission. 

Formula used to calculate free-space path loss (above)


The GB3JV Transmitter