Chris Beck wrote:
> The weird part is the 5 watt radio caused more issues than
> the big rig. I could wipe out every TV in our house with
it.
>
Chris, ain't that fun. My 2.3W-carrier VHF handheld, at 20
feet from small (cheap) TVs, will briefly make the screen
black and kill audio. But just inches anywhere from a new,
big Sony flat-screen digital -- absolutely nothing. It may
be as much circuit design as shielding of the "victim"
device, as interference I guess is intolerable for the big
bucks you have to pay!
> 2) Make sure you are using good coax for the antenna
> lead (double shielded if necessary - foil and braid)
I would consider "bettering" the coax a last resort. If I
take said handheld and xmit in the vicinity of a RG-58 patch
cable (unterminated) at the input of my 200mHz oscilloscope,
coax about antenna length, I might see like only 10mV a few
feet from this cable.
Since receive is the reciprocal of xmit in these matters,
the corollary is shielding the input wires to the victim
device, single or multi-conductor as convenient. The shield
would not be a ground path, just grounded at the instrument
end, I would say.
> 3) Get a ferrite bead assortment (Amidon is one brand).
Ferrite beads or small toriod donuts have a frequency spec
and may be less than what we need if small. A larger donut
allows spiral winding (twice at least) around the core.
If instead of RG-58 in above test, I then use plain, solid
wire. Again about 1/4-wavelength. Scope sensitivity will
have to be readjusted...a lot! If I lengthen the wire to
random length (nonresonant), way down. If I then take a 1"
ferrite cylinder with even 3/8" ID, pass the wire through it
and near the BNC input, scope trace is way down. Make one
spiral turn around the ferrite, way down again. So,
ideally, the wire should be spiral-wound around a donut a
couple times. For instrumentation as the victim device, I'd
try input wires first, like sensor wires. Ten of millivolts
on the 14V or ground wire shouldn't matter much.
Google: ferrite core suppressor, for ideas, sources, and
white papers on the science. Rather than undo wiring, I'd
first try the plastic encased clamp-on suppressors. One may
be able to liberate one off a consumer device wall charger,
and affix it around the wire bundle to the instrument. To
see if we're going in the right direction.
Reg,
Fred F.
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