[bars] odd/rare/unresponsive callsigns on FTP

[KC1SOZ]

The problem may be the use of the wrong hashing algorithm. They are
generating max of 22 bit hashes. Too me, that is ancient history. I only
use sha256 to generate hashes.

On Wed, Mar 6, 2024, 9:48 AM Tim K1DC <k1dc.radio at gmail.com> wrote:

> In the last few weeks while operating FT8 I've seen calls from Nigeria
> (ATNO for me), North Korea (ATNO for most everyone) and Antarctica that
> were suspiciously loud and completely unresponsive to my calls.  A quick
> check of QRZ.com indicated that there was no info on these calls.  I was
> experiencing an FT8 'hash collision'.
>
> The short version of the story is that the FT8 protocol uses a shortcut (a
> hash code) to send some callsigns.  In some rare-ish cases it is possible
> for multiple call signs to have the same hash code value.  For example
> (this is a made up example), 'PY2PEACE' could share the same hash code as
> 'P5AXXX'.  So while PY2PEACE is active on FT8 it may appear in your decode
> list as P5AXXX.  You start frantically calling P5AXXX with no response.
> There is a much longer, and detailed description of the issue here:
> https://bit.ly/49AnNOC
>
> So if you happen to run across a P5 on 10m FT8 and it is not under the
> Mother-of-all-pileups you can simply restart your FT8 software and it will
> rebuild the hash code table.  This will work a lot of the time, but not
> always.  So do a little research on that too-good-to-be-true call before
> you tape down your 'Enable TX' button.
>
> 73,
> Tim - K1DC
> --
>
> Courageously sent from a non-Apple device that *includes* a headphone
> jack.
> ------------------------------
> <https://k1dc.com/img/k1dc-qsl-card-front.png> Tim Carter - K1DC (was
> KC1RET)
> +1.978.710.0133 <1.978.710.0133>
> k1dc.radio at gmail.com
> https://k1dc.com
>
> "Computers are incredibly fast, accurate and stupid; humans are incredibly
> slow, inaccurate and brilliant; together they are powerful beyond
> imagination." -- *Albert Einstein*
>
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