View Single Post
Old 9th May 2021, 11:37 am   #4
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,805
Default Re: SSB adapter, converter to suit Collins R390A receiver.

These things usually take an IF signal from late in the final IF. Onlt then does the signal get exported to the adaptor and meet a proper SSB-bandwidth filter. The Base receiver is set up with its AM filter operating.

Thus the frequency space of the unwnted sideband goes right through the base receiver and can use-up its dynamic range and dominate AGC action if it contains any signals larger than is in the sideband that gets chosen later in the adaptor.

Consequently even a very good AM set with an SSB adaptor is easily out-performed by a receiver with an SSB filter positioned early in its gain profile.

As a result, the professional users with the money to pay for an R390 in the first place, did not buy many SSB adaptors, they shifted over to receivers designed for SSB from the outset. That's why SSB adaptors are fairly hard to find. Military comms went more for RTTY than for SSB in the period. R390s and RA17s did have filters for this service and the late IF outputs suited it.

They do work, but in difficult circumstances they can be found somewhat disappointing.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now