80-Bus News


January–February 1984, Volume 3, Issue 1

Page 6 of 55

Dealing with RFI

I am glad to see that the problem of RFI is being considered seriously (80-BUS News Vol.2, Iss-5) and delighted to learn that we may get an issue devoted to Amateur Radio. For a starter, may I suggest the following additional hints on the problem of RFI.

  1. A metal case to enclose your computer is vital. Mine came from a Radio Rally, custom-made out of l6swg steel except for a 1/8th aluminium front panel for #15. This vast box measures 19x14.5x9 inches and leaves a lot of room for all the expansion boards.
  2. Multi-core screened cable for keyboard, printer and etc, may be obtained from Maplins whose catalogue may be read (and purchased) at W.H.Smiths. Screened cable is a must for stopping RF radiating from lovely aerials dangling from your computer.
  3. Ferrite rings (try Ambit International) are effective. All leads (power, cassete, tv/monitor) emerging from your case to be wound a few times around the rings, as near as the case as practicable.
  4. A mains filter (Ambit). This is effecitve both ways. It stops RF-escaping into the mains where the house wiring acts as a massive aerial and prevents the mains crud getting at your computer.
  5. Desperate measure. In Wireless World, September 1983, G3NRW recommends a 150 pF capacitor between the +12 V rail and ground.
  6. Another desperate measure. Try earthing all your bits (computer proper, tv/monitor, cassette, etc) at only one point.

RFI appears worst for amateurs at 70 MHz. I achieved a measure of success for that band with some of the above, plus critical computer/​radio spacing and complete success by executing HALT! ON 144 MHz, I have a few S1 whistles, but presently the lid is off the box and a Hobbit mechanism dangling on an unscreened lead.

By the way, has anyone made Hisoft Pascal talk to the Hobbit?

Yours, G. Orford, Bristol.

A Lunatic Writes

Dear Dirtbags,

Oldsters, who are, like, total vacuum-heads and do not understand the problems of a young person of today, often get the wrong idea about Waldo ‘D.R.’ Dobbs, who is like me, man. They think that I have no romance in my soul, which is, like, this incredibly strange thing that I have inside my body. To them I say: “You are totally incorrect, man”. It is, like, the total lack of 80-BUS NEWS that causes these sauzzball manifestations, man! Why, when I see these utterly horrible PLASTIC BOXES, I am, like, totally overcome with emotion. There are these worthless diseased MOLLUSCS all over the magazine stands in W.H. Nasties, reading about these disturbingly repulsive micros, man.

Degenerate reptile, man, I ask you to stop this senseless deprivation of REAL COMPUTERS that you are, like, doing to me, man.

Monstrously, hazardously, like, yours, man.

Waldo ‘D.R.’ Dobbs [No address given.]

Page 6 of 55