Tuesday, 1 October 2013

Loopy Earth? Ghosts in the machine?


This carrier balance thing, its driving me mad. Even more so, after this mornings experiments. Nothing I do reduces the carrier level. A mock up mixer didnt show the problem either.

But, a change of probe due to a slightly iffy BNC connector resulted in this interesting spectrum

 Its not the display itself thats interesting here, but look where the probe is! The circuit is over two feet from the analyser, and the probe is not connected at all!

The only things connected to the circuit are the PSU, the Bird dummy load,a nd the AF lead from the Marconi 2955. Wrapping the power leads around a ferrite rod made no difference. Turning the AF generator output on and off made no difference (except to the sidebands), but turning the Marconi itself off, or disconnecting the AF lead, did! The carrier vanished!

It looks like ive hit a serious case of the Gremlins!

Next step then eliminate the 2955 - so I need now either a battery powered AF generator, or to mock up a tone circuit

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