Hi Kurt,
I've worked with these for ~30 years (now semi-retired). As you note,
the design is simple. However, the impedance curve required is hard to
achieve* if you only build according to the schematic. Older LISNs in
particular tend to have resonances due to inductor turn-to-turn capacitance.
Since lab assessors these days don't credit anyone with the ability to
check things for themselves (or can't tell if it's right when they see
it done), it has become common to just get the paperwork from an outside
CAL lab, and rarely does a test lab make its own equipment any more.
This keeps the cost up.
I have one 625 ?H LISN and four 5 ?H LISNs, and gave away a 50 ?H one to
the League lab years ago; it had been among the items sold as scrap from
our EMI lab at Tandy when they sold off the computer business and
shipped 2/3 of the equipment to AST research. The ARRL lab is still
using it, too, darn it! I could use it now.
*See for example www.elmac.co.uk/pdfs/ff26_report.pdf
Cortland
KA5S
On 2/29/2012 1533, KD7JYK DM09 wrote:
> I picked up a LISN, Line Impedance Stabilization Network box from a fellow
> many years ago. This box allows me to apply power to a device under test
> and monitor any noise the device produces on the power line on a spectrum
> analyser. They are used for electromagnetic compliance testing.
>
> Now for the fun part!
>
> These boxes are very simple in design and you can connect the output to your
> receiver.
>
> You can plug any device operating on household power to the box, connect it
> directly to your radio and all you'll hear in your receiver is the garbage
> your item produces over the power lines and possibly radiates into the
> neighbourhood. Want to hear what a lightbulb produces, plug on in, fire up
> your receiver. How about a power supply for your computer? Plug it in,
> spin the dial. Doorbell transformer with an odd smell? Plug it in, fire up
> your receiver, listen to the hash and arcing... How about the noise another
> receiver produces to the first?
>
> It's great for learning what everything you own, and only what that device,
> generates.
>
> Basic info:
>
> http://en.wikipedia.org/wiki/Line_Impedance_Stabilization_Network
>
> A search on Google brings up some designs for those that want to roll their
> own, there's a few on ebay, but they must be full of cocaine or gold bricks,
> the cheapest is about twenty times what I paid for a used one from a govt'
> contractor used to seeing big $ signs.
>
> Kurt
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