On May 9 2020 (PST) I had the pleasure of speaking at the MicroHams Digital Conference (MHDC) 2020. Due to COVID-19 presenters attended via Zoom, and the conference was live streamed over YouTube.
Thanks to hard work of the organisers, this worked really well!
Looking at the conference program, I noticed the standard of the presenters was very high. The organisers I worked with (Scott N7SS, and Grant KB7WSD) explained that a side effect of making the conference virtual was casting a much wider net on presenters – making the conference even better than IRL (In Real Life)! The YouTube streaming stats showed 300-500 people “attending” – also very high.
My door to door travel time to West Coast USA is about 20 hours. So a remote presentation makes life much easier for me. It takes me a week to prepare, means 1-2 weeks away from home, and a week to recover from the jetlag. As a single parent I need to find a carer for my 14 year old.
Vickie, KD7LAW, ran a break out room for after talk chat which worked well. It was nice to “meet” several people that I usually just have email contact with. All from the comfort of my home on a Sunday morning in Adelaide (Saturday afternoon PST).
The MHDC 2020 talks have been now been published on YouTube. Here is my talk, which is a good update (May 2020) of Codec 2 and FreeDV, including:
- The new FreeDV 2020 mode using the LPCNet neural net vocoder
- Embedded FreeDV 700D running on the SM1000
- FreeDV over the QO-100 geosynchronous satellite and KiwiSDRs
- Introducing some of the good people contributing to FreeDV
The conference has me interested in applying the open source modems we have developed for digital voice to Amateur Radio packet and HF data. So I’m reading up on Winlink, Pat, Direwolf and friends.
Thanks Scott, Grant, and Vickie and the MicroHams club!
I love the idea of applying the FreeDV modems to Winlink. It makes me anxious that VARA is becoming a favored mode even though it’s completely closed and only runs on Windows.
Hi David
I was wondering how much improvement over classic G3RUH would be possible in standard VHF channels with such kind of a modem. Do you reckon there would be a way improving speed with reasonable efforts, or maybe robustness only? Just being curious, knowing VHF is not your main interest and of course replacing older open standards is also not a sign of urgency at all.
Regards
Diego
Hi Diego – it’s an interesting question. Much of the Ham packet scene is using the1990’s “COTS radio with data port” model. This limits us to constant envelope waveforms and 25 kHz bandwidth, but lets us use off the shelf hardware at high power.
It is possible to do better than 9600 using this paradigm, e.g. VARA-FM, by sending more exotic waveforms over FM. However it is rather power inefficient.
Mark (VK5QI) and I, are interested in low power SDR based approaches, for example using a HackRF/LimeSDR/Pluto. Using QAM to keep the bandwidth within 25kHz I estimate we can get 100 kbit/s using just 10mW EIRP over a 100km line of site link.
We already send wideband RF (a few 100 kHz) 100 bits/s 2FSK over such links, for our balloon SSTV work. This is OK in Australia, where UHF spectrum in not busy.
– David
I was actually looking into lime sdr a while ago and really liked the idea of using something like it for experiments, but unfortunately I have not the skills to make anything useful out of it on my own (or more exactly am lacking the time to acquire them).
If I see what is possible with cots silicon in the 2.4GHz band.
I think such an approach free of any legacy handcuffs as you describe it would be great. Without a lot of optimisation we are already soeculating about a 10x + increase, leaping packet ahead of GSM in spectral efficiency and also bringing it into an area where it’s getting useful for “light multimedia” use…
I mean, don’t misunderstand me, it won’t replace 5G or fiber internet, but it would give a huge field for experiments for hams.
Do you reckon such a modem could besides the above mentioned SDRs also be realised with general purpose MCUs on a low IF?
Wow just now realised you were talking about balloon SSTV (not always easy reading properly on a phone screen), that sounds very interesting, hope you or VK5QI will find some time soon to write about it.
Hi Diego – yes the modems would probably run on a small machine like a Pi or maybe a uC. the modem CPU scales with symbol rate, which stays pretty low for QAM. The FEC CPU tends to go up with bit rate, so that might start to dominate.
We have written about the balloon SSTV system (Wenet) in several previous posts.
Cheers,
David
Thanks David
Have to dig into the archives then.
Very exciting times now that uCs are so capable.
Cheers
Just warming up this thread, as I came across those figures in a 5G NR publication:
PEAK SPECTRAL EFFICIENCY | 30 bps/Hz for downlink and 15 bps/Hz for uplink
For 25kHz thats 375kb/s uplink for NR, so your estimate of 100kb/s is really very close to what needed a huge development effort of an industry consortium…