* Continuum instability ("ripple") can occur with all receivers, making pointing and focusing difficult.

 * In general some receivers are better than others in this respect as summarized here:

  * A100 generally OK for pointing. (2003-11-12) 

  * B100 OK, is best for pointing. '''B100 is the standard reference for the heterodyne pointing model'''

  * /!\ C150 often bad for pointing, ripple. (2002-07-16) 

  * D150 generally good performance for pointing.(2002-07-16) 

  * /!\ A230 often unstable, bad for pointing and flux monitoring. (2003-11-12) 

  * B230 OK 

  * /!\ C270 can be unstable and difficult for pointing. (2007-04-30) 

  * /!\ D270 can be unstable and difficult for pointing. (2002-07-16)