[G8BBZ]

Hi All,
With regard to the Redifon R550/551, the synthesizer phase noise issue was recognised in the design phase of this equipment in the late 60's, though I am not sure if the term "reciprocal mixing" was current at that time. The receivers used an analogue VFO for the last 100 kHz to ensure a clean LO signal to the 1st mixer. An ancillary unit - the ARU11 - was available which can be switched in replacement of the VFO to provide synthesized steps down to 100Hz, though this did affect the RF performance of the receiver if the 10's kHz, 1's kHz or 100's Hz steps were not set to zero. There is a note in the User manual recommending that these decades be set to zero unless really necessary, though the degree of impairment of the receiver performance was never specified.
The companion Transmit Drive - the GK203 - which is essentially an R550 in reverse, used a different 2nd loop synthesizer module which had steps down to 100Hz as free tuning transmit drives were not popular and presumably the phase noise issue was deemed less critical.
The 38MHz filter in the receiver 1st IF was certainly referred to as a "roofing filter" by the time the receiver went into production (1970), but I do not know where the term originated.
cheers
Peter G8BBZ