[bars] odd/rare/unresponsive callsigns on FTP

[KC1SOZ]

That only works for you but doesn't solve the problem of other people doing
it.

73,
KC1SOZ
Juan


On Wed, Mar 6, 2024 at 10:28 AM Tim K1DC <k1dc.radio at gmail.com> wrote:

> 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
>> --
>>
>
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