[OZAPRS] HF APRS -2
Carlos Peco-Berrocal
carlos.peco at gmail.com
Tue Dec 19 10:27:54 AEDT 2017
Can you still use external sound cards with the Tinkerboard ?
What if you cook the internal one ?
cheers
Carlos
On Tuesday, December 19, 2017, Matthew Cook <vk5zm at bistre.net> wrote:
> Cool.. well that means I've got a suitable test bed ready and waiting.
> The receiver I've got lined up has a full rockwell collins 3kHz IF filter
(not 2k7 or 2k4 like most japanese radios) so that should work nicely.
> Time to start working out how to get the levels and drive right,
something for me to do over xmas.
> 73
> Matthew
> VK5ZM
> On 19 December 2017 at 09:24, Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:
>>
>> The original would run about 3kHz search window at full 'gain' on a C1
(quad A5).
>>
>> The XU4 would smoke it at 10kHz BW. The out of order reordering CPU
really smokes. but it also smokes the power supply.
>>
>> The C2 would run a 10kHz search window IRRC.
>>
>> I have some TV boxes with RK3288s and they also are excelllent processor.
>>
>> good on the internal sound card.
>>
>> code currently only uses the 2010 grade NEON, not the new v8 NEON
AArch-64 etc on the A53 etc .
>>
>>
>> g
>> On 19/12/2017 9:39 AM, Matthew Cook wrote:
>>>
>>> It will be interesting to see how this code goes on different platforms.
>>>
>>> I've been looking at the Odroids C2 (quad A53 @1.5GHz), C1+ (quad
A5 at 1.5GHz) & XU4 (quad A15 at 2.1GHz + quad A7 at 1.4GHz) there is no doubt the
XU4 has some serious grunt.
>>>
>>> However the ASUS Tinkerboards I've got at home have a RK3288 which is a
quad A17 running at 1.8GHz also featuring a Neon Co-pro! So on paper this
should give the C1+ and C2 Odroids a bloody nose in a MIPS fight or at
least a run for their money.
>>>
>>> What I really like about the Tinkerboards is they have an inbuilt sound
card (192kHz)/24bit) for both record (microphone) and playback (stereo out)
for the same money as an Odroid. So that would just leave me needing to
build a suitable PTT circuit with h/w timeout.
>>>
>>> It will be interesting to see just how hard I can push one of these
Tinkerboards, for ~A$85 delivered to VK they seem good value.
>>>
>>> The plot thickens.
>>>
>>> 73
>>>
>>> Matthew
>>> VK5ZM
>>>
>>> On 19 December 2017 at 06:42, Glen English VK1XX <
glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>> wrote:
>>>
>>> Good discussion
>>>
>>> yeah a small drop on PCB would be simple. I THINK that later Cx
>>> ODROIDS are header-compatible with the R-PI headers.
>>>
>>> after madly writing debugging python modules all day yesterday,
>>> and remembering how to write ODBC expressions heading out to do
>>> some mobile survey work and will get back on the case at xmas.
>>>
>>> SNR requirements are very low, so sound card quality is pretty
>>> unimportant except that the sample rate clock should be better
>>> than a free running LC...
>>>
>>> I will do a full writeup while familying with emily's family up
>>> north at xmas.
>>>
>>> The demodulator requirements are proportional to the recv
>>> bandwidth search window, the frequency step search, the sync
>>> threshold, and the LDPC FEC "gain control".
>>>
>>> The whole spectrum is step frequency searched with a matched
>>> filter-correlator for my sync word which provides the next stage
>>> time and frequency offset data. When a sync detection is
>>> triggered, the time and frequency offset of this "candidate" is
>>> pushed into a FIFO and is passed to stage 2, and that stage goes
>>> about extracting the samples from a deep buffer and attempting
>>> decoding. Stage 1 sync works on about 1 second of audio data,
>>> stage 2 works on about 10 seconds worth.
>>>
>>> Using an STM32F7 there would be enough memory to implement the
>>> demodulator with reduce peformance but stil very useable (say +3,
>>> +4 dB CNR).
>>>
>>> Pi Zeros probably on par with a STM32F7, the old ARM11
>>> architecture is pretty slow.
>>>
>>> Cache misses is what hurts the implementation. Care is taken not
>>> to abuse the cache, but the system operates by searching all over
>>> a large buffer so memory misses are part of the game.
>>>
>>> The existing implementation is 46.875 bps (48000/1024) however the
>>> bit rate can be change by simply changing a $define DIVIDER to
>>> anything you like. I was thinking 48000/512 was a good starting
point.
>>>
>>> This permits multiple use of a channel. a sideband channel can fit
>>> alot of 50Hz or 100 Hz wide signals, and the demod is designed to
>>> deal with it. I would say the end performance is something like
>>> PSK31 but with reduced SNR requirements. You can push it right
>>> down to 0dB SNR but the demodulator ends up spending a bunch of
>>> time in stage 2 attempting to demod candidates that are really
>>> noise ... CPU requirements increase.
>>>
>>>
>>> On 18/12/2017 10:04 PM, Matthew Cook wrote:
>>>
>>> That interface card is hideously expensive for what it is;
>>>
>>> Other options;
>>>
>>> * The wolfson sound card is less than a third that price
>>> including
>>> shipping from E14, however a syba USB sound card is less
>>> than $5
>>> from eBay.
>>> * PTT is just a transistor of an I/O pin, preferably with a
h/w
>>> monostable timer to prevent locking the transmitter on; I
>>> still
>>> don't trust Pi's with 100Wpep of HF present, box or no box.
>>>
>>> Personally I'll be trying a Tinkerboard first since it has
>>> onboard microphone and audio, more grunt that a Pi-3, wifi,
>>> BT, I/O and serial ports. In my case I can read the GPS from
>>> within the HF transceiver, which is already shared three times
>>> in the back of the car already.
>>>
>>> However will still experiment with STM32 option since this
>>> would make a very nicely integrated option in the new year.
>>>
>>> 73
>>>
>>> Matthew
>>> VK5ZM
>>>
>>>
>>>
>>> On 18 December 2017 at 20:57, Mark Jessop
>>> <lenniethelemming at gmail.com
>>> <mailto:lenniethelemming at gmail.com>
>>> <mailto:lenniethelemming at gmail.com
>>> <mailto:lenniethelemming at gmail.com>>> wrote:
>>>
>>> David Giddy has reminded me off-list of the existence of the
>>> UDRC-II: http://nwdigitalradio.com/product/udrc/
>>> <http://nwdigitalradio.com/product/udrc/>
>>> <http://nwdigitalradio.com/product/udrc/
>>> <http://nwdigitalradio.com/product/udrc/>>
>>>
>>> This is pretty much what I was looking for, with the
>>> exception of
>>> the onboard GPS. A little bit pricier than I was hoping
>>> for, but
>>> time vs money and all that...
>>> Would require a bit of coding to make whatever modem Glen
>>> writes
>>> key to the relevant GPIO pins, but hey - open source, and
>>> I'm more
>>> than happy to write and test code :-)
>>>
>>> 73
>>> Mark VK5QI
>>>
>>> On Mon, Dec 18, 2017 at 7:35 PM, Mark Jessop
>>> <lenniethelemming at gmail.com
>>> <mailto:lenniethelemming at gmail.com>
>>> <mailto:lenniethelemming at gmail.com
>>> <mailto:lenniethelemming at gmail.com>>>
>>> wrote:
>>>
>>> Given the cost of boards like the Raspberry Pi Zero,
>>> and other
>>> similar boards, I don't see it being targeted at
ARM-NEON
>>> being that big of a deal.
>>>
>>> I guess a good product to complement the modem would be
a
>>> 'shield' (or hat, or cape, or whatever the kids call
them
>>> nowadays), for a raspberry pi or similar, that includes:
>>> - An Audio codec chip (probably via I2S? Example DAC
board
>>> here, but no ADC:
>>>
https://core-electronics.com.au/pimoroni-phat-dac-for-raspberry-pi-zero.html
>>> <
https://core-electronics.com.au/pimoroni-phat-dac-for-raspberry-pi-zero.html
>
>>>
>>> <
https://core-electronics.com.au/pimoroni-phat-dac-for-raspberry-pi-zero.html
>>> <
https://core-electronics.com.au/pimoroni-phat-dac-for-raspberry-pi-zero.html
>>)
>>> - PTT interface (relay? FET?)
>>> - Maybe even a GPS unit? (Something like a uBlox MAX-8
>>> would
>>> go nicely)
>>>
>>> Of course you can do a lot of this with a USB sound
>>> card and
>>> some external circuitry, but I like the idea of a
>>> self-contained unit that you could mount in a small box.
>>>
>>> I might look into parts for such a board over the
>>> holidays, if
>>> I'm not too busy chasing balloons at Mt Gambier...
>>>
>>> 73
>>> Mark VK5QI
>>>
>>> On Mon, Dec 18, 2017 at 1:22 PM, Glen English VK1XX
>>> <glenlist at pacificmedia.com.au
>>> <mailto:glenlist at pacificmedia.com.au>
>>> <mailto:glenlist at pacificmedia.com.au
>>> <mailto:glenlist at pacificmedia.com.au>>> wrote:
>>>
>>> Matthew Cook asked me about the hardware and STM32 :
>>>
>>> STM32F7 MIGHT run the decoder, for narrow
>>> bandwidth search
>>> windows and slightly higher SNR requirements (+1
>>> dB say) .
>>> The search algorithm is intensive and the LDPC
>>> decoder is
>>> hard work, also. But there is a nice vernier
>>> control on
>>> the "how hard it tries" to control CPU usage.
>>>
>>> STM32-anything will definitely run the encoder
>>> (lots of
>>> LUTs in FLASH)
>>>
>>> (it already is implemented on STM32L151 back in
2014)
>>>
>>> talk soon when I am not so flat out
>>>
>>> cheers
>>>
>>>
>>>
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