[R-390] Racal RA-17

[Robert Nickels]

On 7/31/2019 4:46 PM, wb3fau55 at neo.rr.com wrote:
> Some folks say these are even better than a good R-390A.

Of course "goodness" would need to be defined but the most significant 
advantage that the RA-17 has over an R-390 and most other receivers of 
the same vintage is the Wadley drift-cancellation loop.   This circuit 
eliminates drift without the complexity and other issues associated with 
a frequency synthesizer.   Unlike a PLL, the Wadley Loop does not 
attempt to stabilize the oscillator, instead it cancels the drift 
mathematically.  Dr. Trevor Wadley invented this elegant circuit in 
South Africa and attracted the attention of Racal in the mid-50s when 
the emergence of SSB was putting a premium on receiver stability, 
especially at the higher frequencies.   It came at an opportune time for 
Racal as negotiations to build the Collins 51J series had fallen 
through, and the Royal Navy was supportive.

The RA-17 beat all other receivers for stability but was a solid 
performer otherwise as well, and introduced other innovative design 
features including upconversion. which provided a very high degree of 
image rejection, and the tape-type dial scale.

The complete story of the RA-17 development is quite interesting and can 
be found here:

https://www.electronics-notes.com/articles/history/radio-receivers/racal-ra17-development-story.php

73, Bob W9RAN