Try his Facebook link, Josef, if you have a Facebook account. There are about 1600 members in that group, someone should be able to provide some information.

It appears that the "highfields-arc.co.uk" domain has been allowed to expire.

Looked at the wayback machine, and found the following:

Review of the AT-5555: https://web.archive.org/web/20140919...ews/at5555.htm

Software and Data Files: https://web.archive.org/web/20140928...at5555dats.htm

Sidetone: https://web.archive.org/web/20130531...55sidetone.htm

Freq Mod: https://web.archive.org/web/20131229...555freqmod.htm

Not all of the links from these pages work, but hopefully you can get some useful information. It looks like our friend stopped updating the project because of other folks copying his work.

Good luck!
Luke