David,

You are close but RC5 is biphase or Manchester encoding. But to back up, Barry Gordon wrote a piece on decoding Pronto hex [Link: remotecentral.com]

The first 0000 means learned, 0070 is when converted to decimal N, an indicator of IR carrier frequency according to this formula F(in KHz)=1000/(N*.241246) and the next to two byte words (when converted to decimal) are, in order, the number of One time burst pairs and number of Repeat pairs.

Thereafter each 2-byte word is alternating on and off times in order, expressed in wavelength of the IR carrier frequency. So 20 hex means 32*N*.241246 in microseconds. The last word longer because it is the is the gap between frames.

Most IR signals use pulse width modulation (PWM) and the most common, the NEC family of protocols use Zero =(+550uSec On and -550uSec off) and One =(+550 uSec On and -1650 uSec off). RC5 however uses Zero = (+880 uSec -880USec) and One = (-880 uSec +880 uSec) ; i.e., the pulse inverts from one to the other.

Barry's article pretty much explains PWM but here is a further explanation of bi-phase and RC5 encoding [Link: hifi-remote.com]

-Jon