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8066Re: [RADIOSHACKDX394] Re: Metal Covers

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  • R. Mark Barnett
    Jan 12, 2014
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      I have never used RF blocking paint in a radio, but I HAVE used it in an audio patchbay and inside an oak audio amplifier cabinet with good results. (located about 500yrds from a commercial radio transmitter/antenna) I believe it is sold in a spray too... somewhere.. http://www.lessemf.com/paint.html  I have seen this type of sheilding used on some plastic radio cases. I have always thought it would be good to put it on a plastic faceplate, but I'm too lazy... LOL The effort vs benefit isn't high enough for me, as I am not having any RFI problems. 
       
      Mark B. N8PGV
       
      Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.
      ~ Nikola Tesla


      From: Tom H <ve3meo@...>
      To: RADIOSHACKDX394@yahoogroups.com
      Sent: Saturday, January 11, 2014 1:56 PM
      Subject: [RADIOSHACKDX394] Re: Metal Covers

       
      Thanks for your comments, Tim.

      The challenge to achieving the most effective shielding of the 394 is to completely enclose it with electrostatic and ferro-magnetic material. The chassis or frame is good material but only 3-sided. The plastic lids can be replaced or supplemented by electro-magnetic material as has been done in a variety of ways. If well-connected to the frame, a 5-sided enclosure is the result.

      Unfortunately, that still leaves the front which is basically plastic and the logic pc board. The ground lands of the latter may provide some shielding but it is impossible to close the box with material between the front panel and the frame - too many things penetrate the plane. Likewise, holes for the loudspeaker, ventilation, power cord degrade the shields.

      The most effective shield would be an enclosure around the whole radio, power it from a battery within the enclosure and have an access door (a compromise) to reach the controls. The shielded coax from the antenna would pass through a coaxial feed through connector. Not very appealing operationally.

      Re your first comment, Alfred Santee is an alias for Ernie Rice which might be an alias for...

      Tom, ve3meo

      --- In RADIOSHACKDX394@yahoogroups.com, "T. Hills" <thills@...> wrote:
      >
      > Tom,
      >
      > That's "Alf"'s addy, not Ernie's ;)
      >
      > I had the same experience with the 160s and other receivers with
      > internal loopsticks, some worked better than others. The metal
      > chassis/box types like the 160 using the same sheet metal you mentioned
      > between the fiberboard back and case and moving/retuning the loopstick
      > worked rather well for local noise and strong local BC but not good
      > enough for DX work. I wound up using tuned inductors out of an old
      > Ray-Jefferson DF unit and now with the antenna inputs shorted it's very
      > quiet on HF though I still get some from the local MWBC stations.
      >
      > The same mod did not work well at all with Copper plated Steel flashing
      > on the plastic cased 440 I tried it on. The loopstick on the 440 isn't
      > tuned and disconnects but there was still very little noise reduction on
      > MW and HF.
      >
      > I suppose one could build a metal case for the 394. Shouldn't be that
      > hard if someone had a bending brake and drill press ;) One of these days
      > I'll get another 394 and maybe give it a try..
      >
      > Tim Hills
      > Sioux Falls, SD
      >



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