[OZAPRS] HF APRS

Fri Dec 22 09:25:19 AEDT 2017

back from the mine...

Robert, it's suitable for all bands, but  more effective on some bands 
than others.

many want to use standard FM radios which I understand for 6/2/70.

although many have HF/6m SSB radios and therefore opens that up to 6m 
using a narrowband mode.

By preprocessing, a standard FM radio can generate PSK and FSK on the 
mic input  , in a form...

Certainly good performance can be obtained on the TX side, whereas the 
RX side is somewhat restricted by the limiter predetection bandwidth of 
16kHz.

there are a few low hanging fruit to extract perhaps another 6dB out of 
a standard FM radio in FM mode TX and RX without much difficulty

I might look at that early in the new year once we have this new HF mode 
going.

On 20/12/2017 12:01 PM, Robert wrote:
> So will this new idea be used on 6M as well.
>
> Robert
>
> -----Original Message-----
> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English VK1XX
> Sent: Monday, 18 December 2017 2:17 PM
> To: ozaprs at aprs.net.au
> Subject: Re: [OZAPRS] HF APRS
>
> Yep
>
> It's ready to go. But I have to get work done this week, got to go to sort a few things out at a few sites. I need to get some python code written before going to site tomorrow.
>
> Over the weekend I remembered how it all works (it's a modem I wrote 4 years ago) , and modified a few blocks to reduce the CPU usage for this narrow band application, and also I added a block to generate IQ baseband signals from real input (radio output) , so it can use a standard radio.
>
> Compilation targets are x86 and ARM+NEON... If compiling for ARM, it is HEAVILY NEON optimized as it had to run on a certain platform ... (oDroid) .
>
> It searches through a specified bandwidth, throwing as many cores at it as you tell it to, each core gets a chunk of spectrum to work on. Roughly 50mS per second processing time per 2kHz of searching BW  on a
> 3.5 GHz i4670k single thread. Will run on a Odroid C1, C2, XU4 etc.
> might run on later Pis, never used them...
>
> Sync can be acheived at about 9dB below what is required for a decode (~ 1dB SNR), the modem can decode multiple transissions simultaneously in the passband and used a 1/5 rate LDPC code. Modulation is D2BPSK (2nd order diff ).
>
> g
>
> On 18/12/2017 1:30 PM, Graeme wrote:
>> Glen English has stated that he is working on something new for HF
>> APRS that should be a lot better than what’s currently available.
>> Graeme 2HFG
>> *From:* Gerard Hill
>> *Sent:* Monday, December 18, 2017 11:25 AM
>> *To:* Australian APRS Users
>> *Subject:* Re: [OZAPRS] HF APRS
>> PAs - as in Power Amplifiers, Andrew.
>> In the past I've run an IGate using PSK63 and GFSK63 using software
>> called APRS Messenger
>> <http://www.crosscountrywireless.net/aprs_messenger.htm>.
>> These modes have great performance even without Forward Error Correction.
>> Availability for mobiles is limited although there is a standalone
>> modem for PSK63 available called FreeTrak63
>> <http://www.ringolake.com/pic_proj/FT63/ft63_page.html>.
>> Some info on these modes from WA8LMF here
>> <http://wa8lmf.net/APRS_PSK63/index.htm>.
>> Be interesting to know more about what Matthew is referring to.
>> Cheers,
>> Gerard - VK2IO
>> On 18 December 2017 at 11:01, <vk4tec at tech-software.net> wrote:
>>
>>      What is “Pas”
>>
>>      Whats coming ?
>>
>>      *From:*OZAPRS [mailto:ozaprs-bounces at aprs.net.au] *On Behalf Of
>>      *Matthew Cook
>>      *Sent:* Monday, 18 December 2017 9:22 AM
>>      *To:* Australian APRS Users <ozaprs at aprs.net.au>
>>      *Subject:* Re: [OZAPRS] HF APRS
>>
>>      I'd wait until early next year and see what's coming in terms of
>>      HF ARRS, plans are a foot.
>>
>>      73
>>
>>      Matthew
>>
>>      VK5ZM
>>
>>      On 18 December 2017 at 09:48, Robert <rbaker at bigpond.com> wrote:
>>
>>          Hi All.
>>
>>          Just a quick question on HF APRS.
>>
>>          I have seen people chatting about modified FSK modem used
>>          directly onto Pas. My question is do I use these modified
>>          modems when I directly use say IC-706 mk2, or will a TT4,
>>          Opentracker do the job.
>>
>>          Thanks in advance.
>>
>>          Cheers
>>
>>          Robert
>>
>>
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