[bars] odd/rare/unresponsive callsigns on FTP

[Tim K1DC]

The protocol has to balance the size of the payload (bits sent) with the 
bandwidth required to send it.  The hash size they have chosen works the 
vast majority of the time.

One operating tip to reduce the chances of it happening to you is to 
/not /include any unnecessary suffixes to your call. For example, don't 
add '/QRP' to your call when operating FT8. You can put it into your TX6 
message instead. (e.g. 'CQ QRP K1DC FN42')

T.

On 03/06/2024 10:00, KC1SOZ wrote:
> 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
>     --
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.w1hh.org/pipermail/bars_w1hh.org/attachments/20240306/4439cdd2/attachment.htm>