The answer is yes, depending on what mod technique you are trying to effect and
communication mode of interest. AM, FM, PSK, Tone Methods (like CTSS, FSK),
digitakl modes..... http://en.wikipedia.org/wiki/Amateur_radio#Modes_of_communication
AM is straightforward using a multiplying DAC (PSOC 1) or SW and a DAC
for PSOC 3 / 5. Or this approach http://www.psocdeveloper.com/forums/viewtopic.php?f=42&t=6868
There also is a mixer in PSOC 3 / 5 to do modulation.
And using a table and DMA to DAC one could real time modifiy table contents to modulate
Note PSOC 1 does not have DMA, only 3 / 5.
One last comment, a summary of approaches to modulate signals -
1) Via total analog techniques, for example using PSOC 3 / 5 OpAmps for
oscillator signal generation and for modulation of signal generated. Or
Or swcap in PSOC 1 http://www.psocdeveloper.com/uploads/tx_piapappnote/an2044.pdf
2) Partial analog and digital techniques, DACs, Counters, PWM to gen signals,
and DMA, software polling to effect modulation.
3) Verilog and/or UDBs to build a custom modulation engine, like a DDS approach.
PSOC 3 /5.