VK2RH ham radio

Category: DATV

  • Portsdown 4 build – powering ahead

    Every day I seem to relearn the wisdom of the old saying – “if it ain’t broke, don’t fix it!’ – and how it truly applies to reassembling equipment.

    Here are the immediate tasks I’m addressing as components arrive:

    • Ask myself how I managed to install the touchscreen upside down!?! Or to put it another way – turn the whole front panel upside down and put controls upside down on the wrong side of the display?!? Luckily it’s a simple fix (Menu 3 > System Config > Invert Touchscreen)
    • Reconnect Raspberry Pi and the touchscreen and the fans on the Pi to confirm all working as before disassembly for drilling work on front & rear panels. All good!
    Success! – Portsdown updated software and sent a testcard across the world via the internet. Now for the RF.
    • Plan how to implement 5V distribution wiring for all devices needing it – all (including of course the Raspberry Pi, to be fed from the XL4016 DC-DC power supply module (purchased from Mini Kits in Adelaide) set to deliver 5V from 13.8V via the Anderson Powerpoles on the rear panel. These include:
      • power for LCD touchscreen (via Raspberry Pi GPIO?)
      • Ras Pi fans (via the Raspberry Pi GPIO?)
        These two items simply require some way of extending the connections to the relevant pins on the GPIO PCB. (I’ll make “bespoke” dupont style leads with slightly heavier wire with appropriate connectors.)
      • a voltmeter display to confirm and monitor the voltage setting of the XL4016 PSU module – to deliver the appropriate voltage to the Raspberry Pi (5.1 or 5.2V). I’ll probably attach this near the PSU module as I’m not sure this small display warrants a presence on the front panel but we shall see… (This will depend upon how much the output varies depending upon the different 12V supplies that might be used.)
      • small 5V fans for Pluto & LimeSDR Mini enclosures? I’ve seen recommendations to do this on the BATC forum, and presumably if you’re blowing cooling air into a small enclosure, there needs to be a way for the warmed up air to escape?
      • two perhaps larger 50mm fans on the side walls of the main Portsdown enclosure??? Perhaps I need first to devise some way to monitor temperatures within the enclosure as the project progresses. This will have some bearing on the way I orientate the PSU module and its heatsinks.
    • Plan how to connect all the USB connected devices
      • PSU module to directly power the Raspberry Pi via J8 on GPIO, and two USB hubs, one powered directly from the PSU module 5.1V out, the other via one of the Pi’s USB sockets.
      • Raspberry Pi to power directly via GPIO: the LCD touchscreen display, the 2 x Pi fans and then via one of its own USB3 ports > the Adalm Pluto
      • C920 webcam – via the USB2 socket on the rear panel connected to the USB hub
      • Audio dongle – via microphone and headphone sockets on front panel to dongle on to USB hub
      • Video dongle – via three RCA sockets on rear panel through to Video Capture dongle connected to a USB hub
      • LimeSDR Mini – via direct connection to a USB hub
      • Langstone “mouse’ tuning encoder etc – via a connection to a USB hub
      • RTL-SDR dongle – via SMA or BNC connector on rear panel on to dongle and then to a USB hub
    • Now that there’s a switch and an LED on the front panel, install the shutdown circuitry as outlined on the schematic for the orginal GPIO break out PCB and omitted from the later one.

  • Portsdown 4 build

    After quite a lot of time thinking through what my plans might be for the specific bands and modes with the Portsdown 4 I’ve spent a few hours over a couple of days drilling and nibbling holes in the panels. When I first built it a couple of years ago I only managed to make the cutout for the 7” touchscreen and install a sheet of aluminium in the closure to act as a chassis to mount the Raspberry Pi.

    I am now – almost – able to connect it up and put the lid on it. I’m also finally installing the shutdown components for the Pi. I still have to work out how to mount one of the DSI to HDMI PC boards on the chassis and against the panel to enable a PiCam to be connetced via a regualr HDMI cable. This will probably involve a piece of aluminium to hold the tiny PCB and HDMI socket against the rear panel.

    The beauty of it all is that once the process has some momentum, things can move quickly.

    marked up and drilled and nibbled rear panel of my Portsdown 4 build demonstrating how urgently I need to invest in a drill press!
    The marked up and drilled and nibbled rear panel of my Portsdown 4 build demonstrating how urgently I need to invest in a drill press!

    I’m glad I was able to spend some time planning both the front and rear panels’ layouts. But I’m sure there’ll be many re-thinks and more probably, mistakes along the way, in spite of all the planning and thinking!

  • DATV and bands in VK

    Traditionally ATV and its associated analog 7 MHz bandwidth has been restricted to UHF and microwave bands, and bandplans have reflected that. With the global emergence of DATV and RBTV (reduced bandwidth TV) experimentation is now taking place on lower bands, down as far as 10m.

    During a recent radio club meeting where there was general discussion about the new fee-less class licence system just introduced in VK (it began on 19 February 2024), I was looking at the pages on the ACMA website (the regulator in VK) and followed links to the legislation (Radiocommunications (Amateur Stations) Class Licence 2023), a relatively succinct 34 pages complement to the 483pp of Radiocommunications Act 1992.

    Alongside conditions about qualifications, licences, callsigns and electromagnetic energy exposure, there is a schedule detailing “Permitted frequencies and limits on operation” organised in terms of licence type – Foundation, Standard or Advanced.

    The main national organisation of Australian radio amateurs, the Wireless Institute of Australia last updated its detailed 32 page bandplan in September 2020.

    In contrast the recent handful of pages listing permitted frequencies and limitations indicates a light touch administration that may well enable innovation on the bands especially above 28 MHz and future proof the management of these bands. (But of course legislation and band plans are different documents with different purposes.)

    Above 52 MHz there are no bandwidth limitations on amateur transmissions.

    The limitation imposed on transmissions on 10 m is

    If a person operates an amateur station with an emission mode that has a necessary bandwidth exceeding 16 kHz, the maximum power spectral density from the station must not be greater than 1 watt per 100 kHz 
    from Tables B & C, Schedule 2
    Radiocommunications (Amateur Stations) Class Licence 2023 

    And the limitation on the 50-52 MHz segment of 6 m is

    A person must not operate an amateur station with an emission mode that has a necessary bandwidth exceeding 100 kHz 
    from Tables B & C, Schedule 2
    Radiocommunications (Amateur Stations) Class Licence 2023

    It will be interesting to see how different groups of amateur users negotiate a coordinated way to use the bands, and still maintain freedom for technical innovation for such modes as RBTV and DATV and whatever else might emerge in the future.

    I imagine anyone building a Portsdown DATV setup in Australia like I am right now, should consider bands beyond 70 cm & 23 cm. Exciting times.

  • Portsdown 4 project back on track

    I’ve been building bits and pieces of what will become a digital amateur TV capability for just on five years! I lost my momentum after building a number of components and it’s only in the last few weeks I’ve found a renewed enthusiasm to get on with it!

    One of the main prods has come from watching the weekly DATV net on VK3RTV. Anyone anywhere can watch this either live via this BATC streamer link or via Ian VK3QL’s YouTube channel. The net attracts an energetic and skilled group who easily sustain a fast paced 60 minute video conversation. It’s very smoothly presented with lots of visual variety and useful information and very few technical hiccups. The Melbourne DATV amateurs seem to have a very professional sense of time and audience interest and keep the show moving.

    My other inspiration is the weekly BATC Oscar 100 net scheduled for 8pm Thursday which is either 6am or 5am(!) on Friday morning here in eastern Australia. I’m trying to work out how I might record it off the streamer while I sleep. This international net happens over the brilliant geostationary satellite QO-100 whose footprint unfortunately doesn’t include Australia, but it does appear to have boosted interest and activity in satellite communications and DATV in Europe. If I set the alarm I can watch this BATC net via the BATC streamer .

    a block diagram to help think through the interconnections between the different components makig up the Portsdown 4 DATV transceiver.

    This is the first result of my planning the build of my Portsdown 4. I’m sure it will change over the next few weeks. It’s also to help me work out which controls and connectors might go where on the front and back of the enclosure. I actually find this thinking very enjoyable.

  • British Amateur TV Club

    This is the day I joined the BATC which must surely be one of the best value amateur radio groups in the world. They produce a professional colourful quarterly journal CQ-TV with top quality practical technical articles and manage a growing global community of amateur TV enthusiasts. The BATC has become a focus for effort to take advantage of emerging technologies to generate quality digital TV signals at affordable costs and to explore the practical limits to reduced bandwidth to deliver still usable DATV signals, even over HF!

    CQ-TV Winter 2018

    Full information about the BATC can be found at https://batc.org.uk/

    The BATC hosts a detailed frequently updated members’ wiki with full information about DATV formats, hardware, software etc. It’s at https://wiki.batc.org.uk/BATC_Wiki.

    There is also a busy forum site at https://forum.batc.org.uk/ for help, information and the interchange of ideas.

    Like all great amateur radio clubs they source and supply components and essentials for their DATV projects. I have started building the Portsdown DATV Transmitter and the MiniTiouner Receiver.

    Hams living in the UK, Europe and Africa are also able to take advantage of the DATV facilities of the QO100 satellite. But even from distant Australia, we can at least watch the BATC QO100 DATV net live every Thursday night at 8pm UK time (generally 6am Friday in Eastern Australia) at https://batc.org.uk/live/oscar100net which is full of focused technical discussion about DATV with occasional diversions to railways and antique carriage clocks!

    By the way, all back numbers of CQ-TV over two years old are free to view and download from https://batc.org.uk/cq-tv/cq-tv-archive/.