[aprssig] New VARA-HF Softmodem A Spectacular Improvement For HF APRS

Stephen H Smith WA8LMF2 at aol.com
Fri Jan 13 14:21:20 EST 2023

On 1/12/2023 12:44 PM, Stephen H Smith via aprssig wrote:
>> On Thu, Jan 12, 2023, 5:15 PM Scott Howard <showard at nd.edu> wrote:
>>     On Wed, Jan 11, 2023 at 3:40 PM Stephen H Smith via aprssig
>>     <aprssig at lists.tapr.org> wrote:
>>     > YES!   Here is the preliminary write-up on the planned test in February.
>>     >
>>     >     <http://wa8lmf.net/APRS_VARA_MFSK/>
>>     Thanks, these are interesting results and I'm looking forward to
>>     hearing how they go!
>>     After VARA HF was released, fldigi added "OFDM" modes [1] which I
>>     believe are based on the same underlying idea as VARA. If it is
>>     possible, it could be interesting to see how the fldigi OFDM modes
>>     (e.g., OFDM500F) compare to VARA HF as well since fldigi is common and
>>     open-source.
> I hadn't even noticed that recent releases of FLdigi did this new mode 
> (OFDM).  I just tried switching my test setup written up in the link above to 
> OFDM500, and it seems to work just fine.  It's noticeably faster, taking 16 
> seconds including the RSID. MFSK16 took 27.5 seconds to send the same 
> compressed posit and comment.    But does OFDM tolerate weak noisy signals 
> with multipath as well???
> You now have me curious.  I'm going to have to gin up ANOTHER test run 
> running MFSK vs OFDM.  Setup would be similar to my described setup, but with 
> TWO copies of FLdigi running from separate folders instead of FLdigi vs VARA.

I've just done some table-top testing of OFDM and have now re-jiggered the test 
setup to do ALL THREE modes alternately in one outing.

On Feb 11, I will be beaconing alternately on VARA, MFSK-16 and OFDM-500.  The 
long-suffering Panasonic CF-51 Toughbook now has THREE separate copies of 
UIview, VARA and two copies of FLdigi working stably. It's currently beaconing 
ACOUSTICALLY (laptop speaker-to-laptop mic) to a second laptop three feet away 
on the table reliably for the last three hours.

I will do a test in my driveway next week when the weather is supposed to warm 
up again to the upper '40s C.

I have revised my write-up on the Feb 11 experiment to reflect the changes.


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