Hi Sunny,
AC 21.4 (2) para 7.2 makes a generic statement regarding the fact that no components of an aircraft issued with an experimental CofA are required to be certificated. This blanket statement would include radios, instruments etc.
Although not certificated/TSO'd, these components would still require calibration iaw acceptable practices.
As for requiring "approved" radios, transponders etc. for flight in CTA, we'd better ask the SAAA Techman. I recall seeing this question raised in an Airsport magazine quite a long time ago but cannot recall the references provided in the response.