I have a Racal SA33 frequency converter, which uses RA 17 technology to 
subtract 1 to 29 MHz from the input frequency for feeding to a frequency 
counter.  It seems to have been designed in the era when most frequency 
counters did not go above 1 MHz.  It has been fitted with an internal 1 MHz 
reference.

It has not been used for more than 30 years, so it may be of more interest to a 
collector.  Nevertheless, if anyone is interested will they please let me know. 
 The equipment is at present at my house in Suffolk.

I have a couple of pages of circuitry.

73
John F5VLF