RF Modulators and Bad Audio

[Penthode]

I have noticed a number of TV Channel 3/ Channel 4 modulators (particularly the ones built into the recent coupon DTV set top boxes) produce moderate to poor sound quality FM sound. The modulation level is low and the aural RF I have measured low on a spectrum analyser on some boxes.

To overcome the problem, I have resorted to putting an old (and known good) modulator from an old VHS machine in a separate box which I power from a "Wall Wart". I have also acquired a "professional" unit made by Blonder Tongue on the bay which works well.

The boxes with poor RF modulated audio include Zenith, RCA and Magnavox. The baseband audio fed to my outboard modulators work much better.

Have anyone else out there noticed the indifferent RF modulated audio from the DTV boxes?