I have an external hard disc enclosure (attached to the tv) which when switched on causes so much noise on the HF bands it's hard to hear anything. Today I decided to kill or cure it. I had already cracked open the case (no such luxuries as screws) to see what (if any) filtering was already fitted, but there was absolutely nothing. I had a rummage in my bag of toroids recovered from an old pc power supply and found a likely candidate. Making a bit of room on the pcb involved removing the IEC power input socket and with a little trimming of the pins on the toroid base and removing the wiring from the pin contacts on one side, and drilling a couple of holes in a vacant area was able to get it fitted on the board. With a couple of 10n 1kv caps on the back of the pcb it was time to switch on whilst monitoring with a pick-up loop on the spectrum analyser, and with an HF receiver alongside, to find only a merest trace of any troublesome emissions. The case did need a little surgery to accommodate the height of the toroid but additional insulation was put in place to cover the top of the toroid. If I had a suitable plastic box I would have transferred it all to that, which I may do if it proves to operate ok.
It now has a fixed power lead and switch salvaged from something else, which is more convenient than having to switch off at the plug !.
There is useful information EMC on the RA website here (probably an obsolete page since they were taken over / renamed as OFCOM many years ago, but google found it !)
It now has a fixed power lead and switch salvaged from something else, which is more convenient than having to switch off at the plug !.
There is useful information EMC on the RA website here (probably an obsolete page since they were taken over / renamed as OFCOM many years ago, but google found it !)
A successful job completed.
N.B.
I must mention that I have 2 of these units, of different makes, and although the power supplies look very very similar in design and casing features, are very slightly different, the other causes no interference, and the mini plug which connects to the enclosure is wired differently so are
NOT INTERCHANGEABLE
N.B.
I must mention that I have 2 of these units, of different makes, and although the power supplies look very very similar in design and casing features, are very slightly different, the other causes no interference, and the mini plug which connects to the enclosure is wired differently so are
NOT INTERCHANGEABLE