[RTTY] RTTY numbers printed as letters

[RLVZ at aol.com]

Hi Guys,

Would anyone have a conversion list for determining what number was sent 
when "PRQ" and "PTT" was received instead of the serial number?

I worked one "F5" station this weekend that was S-9 +10dB and even after 
numerous repeats, all I ever got was PRQ PRQ PRQ PRQ PRQ.

If there is such a conversion list... I'd sure like to have one.  

Also, are there any MMTTY receive settings that can be changed on my end to 
reduce this problem?

I still have a ton to learn about RTTY- thanks for your patience!

73,
Dick- K9OM