You would need the 'P' variant.
Don't get the TTL serial and RS232 levels mixed up, the former will be 0v-5v (or 3.3v) but the latter can be +24v to -24v (normally +/- 12v) for the signals. Depending on the serial input of the transponder that could cause permanent damage. Double check everything before plugging in.
If your transponder is expecting 4800 (or can bet set to 4800) then also check if it is the normal 8 bits, No parity, 0 Stop bits (8,N,0) too. If they match then in theory it should work at the physical layer.
I guess it boils down to how comfortable you are using a unit based on a chipset no longer in production, so of potential dubious origin, to feed your transponder?