Re: Output of uhf modulators
For high power, it was always separate sound/vision transmitters. The reason is inter-modulation distortion due to non-linearity in the output PA, whether it's a klystron, a valve (common at VHF) or semiconductor. For the same reason, at least in IF modulated transmitters (which became the norm), there was always the risk of sideband regeneration with the unwanted (and carefully filtered) lower sideband HF components re-appearing. The spectral purity of the VSB (Vestigial Side Band) transmission and its sound sub-carrier depended upon the absolute linearity of the PA.
At low powers, yes, you could combine the sound/vision and back-off on the output power to prevent all the LSB HF components coming back to haunt you, but at high power, you needed really good linearity correction and separate sound/vision chains to meet the specifications. Even then, high-power filters (cavity based) were often needed to meet specific local demands for band-plan conformance.
All gone now with digital, but the analogue wasn't half 'fun'!
Best regards,
Paul M
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