[RTTY] USB to serial converters, again

[Doug Faunt N6TQS +1-510-655-8604]

Hi all,
I have a slightly different problem:  I need to provide enough voltage
at the RS232 port to drive a rig level converter for my ICOM radios.

I have one marked "Tripplite" which works well with a K1NU converter,
but it's only one port, and I've run out of USB ports.
I have a Byterunner two-port USB-RS232 converter which doesn't work
with the K1NU unit, nor my homemade unit (both of these work well with
my laptops).

So, has anyone some information about this aspect of USB-serial
converters?

73, doug