As far as I can tell, the dedicated PSK transceiver kit projects like
the Small Wonder Labs offerings are dead.
Not "technically" true. The DL-QRP Club Shop still offers
the "Digifun" dedicated QRP PSK-31 transceiver kit.http://www.qrpproject.de/UK/digifun.htm
(only one of the three PC boards in the kit is shown on
that page, FYI)BUT.....
it is now extremely expensive (209.50 Euros, approx $217 USD, plus shipping) is an extremely difficult build and alignment,
mostly due to a VERY poorly written manual,
(translated from German)
inexistent company support, and usually arrives missing
many, many parts. Stay VERY FAR AWAY!
The Small Wonder Labs PSK rigs are no longer being offered
but you can still find them for sale from time to time. As
mentioned, they are excellent
little transceivers. I have
the PSK-20, 40, and Warbler (80m simpler version).
I had one of the rare PSK-10's but sold it. (Still kicking myself)I would stick with one of the 20m versions.
Remember that the older ones required a Serial Port
to key them. The later ones had VOX and a little more
power output. (But I think the higher parts count
earliest versions with the Serial Port have better receivers).
I have had phenomenal QSO's with my PSK-20 with
stations all over the world with very simple and modest antennas.
It's an insanely good
Anyway, there are PSK apps for Pads and Smart Phones even,
so you don't need to spend a fortune for a NUE PSK Modem.
(Though that they now support RTTY and CW is pretty darn cool!)http://www.nue-psk.com/
Back when those Nue PSK Modems were newer, simpler, and
cheaper, and still available as a kit, I saw one built into an
enclosure with a Warbler and it was a really spiffy setup!
I also have the Hendrix BITX20A and even after warm up I
don't think it's quite stable enough for PSK. Maybe for very short
QSO's, but you don't want to end up chasing each other up
and down the band. I'm sure that the DDS VFO Mod
would solve that problem.
Good luck in your quest, whatever you decide on!
73 & God Bless, Ken AD6KA