Radio Module: Yes, it's a RFM98W on a UpuTronics shield. TX data straight
from the UART into DIO2, bypassing all the packet handling stuff. I have
been using LoRa modules for other balloon telemetry (command and control),
so I just modified some of the shields I already had to add the line
between the RPi's TXD and the RFM98W's DIO2 line.
I did actually start out using RFM22B modules, as I wasn't initially aware
the RFM98W's could do the direct-async thing. They have the same footprint
as the RFM98W modules, hence I still had them soldered down to a LoRa
shield. I think that's whats shown in one of the presentation photos.
I'm only using these kinds of modules because it was the easiest way to
transmit FSK at 115kbaud at short notice. If anyone has any better
alternatives I'm all ears! I suspect moving to something like 4FSK is going
to require me to offload packet buffering and modulation onto something
that actually does operate in realtime.
- Mark
On Mon, Mar 13, 2017 at 6:52 AM, David Rowe <[email protected]> wrote:
> Hi David,
>
> I'll let Mark VK5QI field these questions - as he developed all the
> aspects covered by your questions below.
>
> I should point out that Wenet is a joint effort of many people. While I
> did some modem and integration work, Mark developed the payload software
> and hardware, Bill VK5DSP designed the LDPC code, and Brady KC9TPA
> ported the FSK Modem to C. The Wenet payloads are launched and tracked
> as part of http///www.areg.org.au club High Altitude Balloon (HAB)
> activities.
>
> Cheers,
>
> David
>
> On 13/03/17 04:20, David Ranch wrote:
> >
> > Hello David,
> >
> > I did read your blog entry, the associated WeNet presentation, and the
> > Wenet github page. It all sounds fascinating but it was very high level
> > on the TX side (just highly brushed over). I'd love to see a higher
> > throughput solution out there and I have questions like:
> >
> > - Which FSK TX board were you using? It looks like it's based on a
> > RFM98W RoRA board which might be soldered onto another Rpi HATT board
> > (hard to tell from the 2016_11_wenet_presentation.pdf but maybe that's
> > the FSK modem sitting on top of another Hab Supplies board?
> > - This design seemed to be uni-directional but do you think it would
> > be hard to make bidirectional? The current design seems to take a
> > picture, apply FEC, etc. and then send in batch.
> > - Did you ever measure the current draw when transmitting?
> > - There is very little detail on the antenna you used. Did you just
> > use a dipole? Maybe more of a panel design?
> > - Thanks for all the work in publishing the details at
> > https://github.com/projecthorus/wenet
> >
> > --David
> > KI6ZHD
> >
> >
> > On 03/11/2017 11:53 PM, David Rowe wrote:
> >> 100's of kHz wide. For FSK you need about the symbol rate spacing
> >> between tones, so for 2FSK at 115 kbit/s, the tones are spaced at
> >> 115kHz-ish, plus a bit more, think we use 400 kHz separation in
> practice.
> >>
> >> Yes we only managed these fine results through very careful engineering,
> >> and deliberately avoiding the common trap or re-using legacy FM radio
> kit.
> >>
> >> Cheers,
> >>
> >> David
> >
> >
> >
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