The Redifon R408 must have been an early example of a receiver using mostly silicon transistors. As far as I know, the Ge-to-Si move started in earnest around 1966-67.
The Wireless World write-up on the R408 said:
“The modes of operation include a.m., c.w., s.s.b. (pilot or suppressed carrier) and i.s.b. (switch selection of upper or lower sidebands).”
Whilst I initially interpreted that as having full ISB capability, upon reflection a better “translation” would be that its SSB capability allowed it to receiver either sideband of an ISB transmission, but not both simultaneously. One cannot be sure, but the way its SSB capability was described, it was able to make use of the pilot carrier when it was transmitted, rather than simply treating a pilot carrier transmission the same way as a suppressed carrier transmission.
Regarding the maritime mobile HF and MF R/T transition from AM to SSB, this was mentioned in an item in WW 1968 January, attached. But this would have referred to a mandatory change; presumably before then vessels were free to use SSB to the extent that shore stations could accommodate it.
Here is an ISB question though: when vessels used ISB for ancillary purposes, such as passenger telephone calls, did they use frequencies within the marine HF bands, or within the bands assigned for point-to-point communications? I suppose that may have depended upon the nature of the land-based station with which they connected. On the other hand, presumably transmission within the marine bands would have been limited to approved transmitter types, which could well have excluded the typical shipboard ISB equipment in the 1950s and 1960s.
Quote:
Originally Posted by Radio Wrangler
The marine main receiver qualification was a serious hurdle, but it was proof of some qualities. Some other receivers would have passed without modification, but the manufacturers were concentrating on other markets and did not see al the hoop-jumping as profitable. Some receivers simply were not good enough in one or more performance areas. The RA17 would have not met the filter template requirements and would have had trouble with the intermod tests.
|
I have the impression that front-end selectivity may have been an issue for marine receiver qualification, and perhaps that was why in part at least Marconi with its Apollo and Eddystone with its EC958 chose traditional topologies with narrow-band tracking RF filters and lowish 1st IFs even when practice at the time was moving towards upconversion. Even then, the marine version of the EC958, the EC958/5 (Marconi Nebula) required a bandpass tuned input down to 54 kHz in order to pass the qualification tests, whereas the standard version was bandpass above 1.6 MHz, but single-tuned below. The Redifon R550/551 was upconversion with sub-octave filters, but with a wideband RF agc system operating a diode attenuator ahead of the push-pull amplifier with CATV transistors.
Cheers,