[Moon] QRA64 false decodes

[charlie at sucklingfamily.free-online.co.uk]

Hi Peter

Yes, QRA64 is not completely immune from false decodes - we saw one or two
while doing the simulation work that went into the Dubus 3/17 article and
I have seen one or two while monitoring band noise for long periods.  Joe
can probably explain this better, but there is always a finite chance of
the decoder reaching a false solution when the signal to noise ratio is
low.

The developers put in a significant amount of work went to reduce false
decodes to a level where they very uncommon.

Also, and quite importantly on the rare occasions where you do see one, 
our experience is that they are clearly obvious as false, like in your
example where the callsign and locator make no sense.

Both on the air and in the simulations (which involved many thousands of
files) we have never seen a false decode that could have confused or
invalidated a QSO, such as printing a wrong callsign or incorrect report. 
Because of this (and its superior decoding of very weak signals) QRA64 has
an advantage over other 'slow' modes, when employing correlation decoding
to improve sensitivity.


73

Charlie





 > Hi Charlie,
>
> This was a QRA64 decode today of the DL0SHF 10 GHz EME beacon,
> apparently there are false decodes in QRA64 also under certain
> circumstances:
>
> 1144 -22  2.5 1144 :* CQ AR8NDK JB02
>
> Normally decodes look like this
>
> 0820 -11  2.5  639 :* CQ DL0SHF JO54
>
> I often monitor Per DK7LJ's superb 10G EME beacon for extended
> periods to get a feeling for the different limitations of my EME
> window with my small dish. Limitations are mainly based on blockage
> from different towers on my property. And I must admit that the false
> decode above was quite surprising and  highly unusual.
>
> 73
> Peter SM2CEW
>
>
>
> At 10:46 2017-10-10, G3WDG via Moon wrote:
>
> snip..
>
>>With QRA64 it is our 100% experience
>>that you can rely on a decode being correct.
>>
>>73
>>
>>Charlie
>
>
>