TemCell Woes

In our company we make stuff that must meet EMC requirements. Usually the radiated emissions are the most challenging. We have these checked in accredited test houses, which are expensive.

So we try to pre-check the products to see if there is fair chance of success.

We have no OATS or anechoic room, so we make do with a logper antenna in an empty office room. The ambient radio smog is making this virtually impossible nowadays.

I recently bought a secondhand 3m TemCell, intending to use it the wrong way around (not immunity, but unwanted radiation).

After reading up on the matter I became convinced that it should be possible to get at least a fair -albeit uncalibrated- impression of the radiated spurious of the EUT.

Not so however. If a EUT with known radiation characteristics is placed in the TemCell, all I see is a Flat line on the spectrum analyzer. I might as well have connected a dummy load. Even with a preamp I see nothing.

Connecting the same spec on the same setting on the antenna, the screen lights up. And the EUT does radiate..

Question:

Anybody else out there doing what I do? Am I expecting something that is not there? Does a TemCell not work both ways (reciprocal)?

Or is the cell just broken...and do I need to tear it open for repairs?

Thanks in advance!

Best Regards, Rene

Reply to
Blarp
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According to this site

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Yes, you should be able to pick up any radiated emissions (RF) from a DUT. Did you try rotating the DUT? otherwise it sounds like bad connectors.

Cheers

Reply to
Martin Riddle

Any chance the previous owner left an isolator or attenuator screwed on the port you are expecting signal out of??

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Reply to
RFI-EMI-GUY

Also is the TEM Cell good for the frequency band you are concerned with? May be operating below cutoff..

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Reply to
RFI-EMI-GUY

Thanks for all answers so far...The Cell is rated up to 300 MHz, and the EUT I selected (because it was emasured in a testhouse before, and has known radiations) - happily radiates in the 100MHz .. 1 GHz range.

I would not be amazed by a dropoff above 300 MHz, but a flat line..

@ Martin: Yes, I did rotate the EUT any witch way.. Had representative wiring connected. In free air (using the logper antenna) it (the EUT) even "outradiates" the considerable local radio smog.

I think I indeed need to check the connectors and such.

Thanks! - Rene

Reply to
Blarp

A common problem fro N connectors is someone trying to attach a PL259 and splaying out the fingers on the center conductor.

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Reply to
RFI-EMI-GUY

Or using the wrong impedance 'N' connector.

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Reply to
Michael A. Terrell

...but it's a BNC...

After the Xmas holidays I will check if the septum has broken loose from the connector - should have done that in the first place I guess..

Reply to
Blarp

The poster I replied to mentioned the 'N' connector. There are also differences in 50 & 75 ohm BNC connectors.

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Reply to
Michael A. Terrell

... but, unlike N-type connectors, the mating diameter of the pin is the same for 50 ohm and 75 ohm BNCs (see

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and then the technical drawings provided by companies such as Amphenol).

If it's a conventional TEM cell with a connector at each end, a quick check would be to feed a signal generator to a power meter, directly and then through the cell. If it's a GTEM cell or some other type with a built-in termination, a network analyser should show what's happening.

Chris

Reply to
christofire

Older BNC connectors weren't compatible. I've replaced enough of the over the years.

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Reply to
Michael A. Terrell

-snip-

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'50? and

75? connectors are intermateable'

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'All versions are fully intermateable'

Evidently, they are now.

Chris

Reply to
christofire

So, all the older BNC connectors have disappeared from the face of the earth? How naive.

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Reply to
Michael A. Terrell

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