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Hi,

thanks.

The TEK box looks as if it is made of sheet metal.

 

It just looks like it, but no I think about. I think it's a µ-metal plate that is annealed at 1100 ° C for 5 hours. This stabilizes the plate's permeability.

I posted the link from the company Vakuumschmelze, there it is described in the pdf how the shielding plates are finished (Chapter 5).

PB-PHT-001 e neu (vacuumschmelze.com)

Or its another material, I don't know; next week I'll ask Tekbox.

It is made entirely of double sided copper clad board.  The two copper layers are joined by "vias" (holes withe wire soldered in) at regular intervals.

It's OK up to 1GHz, .

Aha, ok thanks.

What I think is, hm..., the septum is a PCB with striplines and resistors (zoom the picture, I thinks you can see this).

Here is a fine description (it is in English):

Tekbox TBTC3 TEM Zelle, für EMC Pre-Compliance Testing, 103,8x50x30,5 cm - Rekirsch Elektronik - Ihr Partner für Messtechnik, Telekommunikation und Touchscreens

From this link:

"A TEM cell is a stripline device for radiated emissions and immunity testing of electronic devices. It is not a replacement, but due to its size and cost it is a convenient alternative to measurements in an anechoic chamber.

A TEM cell consists of a septum, the conductive strip in the centre section and walls which are connected to ground. The geometry is designed to present a 50Ω stripline. The device under test (DUT) is placed in between the bottom wall and the septum.

The TBTC1/2/3 are so called “open TEM cells”, which got no side walls for convenient placement of the DUT. It may pick up RF background noise, which however can be taken into account by doing a measurement of the cell output signal before powering on the DUT.

Tekbox open TEM cells got a better frequency response compared to standard TEM cells of similar size. TEM cells suffer from higher order wave modes which limit the usable bandwidth. A unique design feature of the Tekbox TEM cells implements resistance perpendicular to the desired propagation direction of the wave. Consequently higher order wave modes and resonances are supressed."

You don't need an enclosing box, except maybe to reduce emissions that may upset your neighbours.

Yes, I think so too.

Now my fingers are tingling and I'm excited to build the TEM cell myself.

You did a great job. The measured values on the FPC1500 look good.

Gerald

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fixed

Thanks.

Very odd - I could see it OK.

This has happened to me recently with some other peoples psts where I can't see all the images.

I've added it again.

MK

Michael, I can see all images, except the first one. It gives this error in my log:

The TEK box looks as if it is made of sheet metal.

Our DIY design is completely described in the paper I linked to.

It is made entirely of double sided copper clad board.  The two copper layers are joined by "vias" (holes withe wire soldered in) at regular intervals.

It's OK up to 1GHz, .

You don't need an enclosing box, except maybe to reduce emissions that may upset your neighbours.

MK

Hi Michael,

Thanks very much.

Oh yes - I downloaded yesterday this PDF file from this link .

I also found that DIY Tem cell:

Mode Suppressed TEM Cell Design For High Frequency IC Measurements (clemson.edu)

This have resistors and it is built with striplines.

- Unfortunately I can't see your first picture.

The septum are these striplines or are they a double-sided laminate board only at certain points with via's?

An important point is, that the shielding case of the TEM cell is build with a ferromagnetic metal like µ-Metal or other.

69 to 82% Nickel-Iron Alloys | VAC (vacuumschmelze.com)

And this is really expensive.

So what is interesting for me - the septum how is it in details.

It seems it is a plate (PCB or what ever) in the dimension of the TEM cell. And on them runs the transmitted wave to the terminator.

But the Tekbox TEM cell shows parts on it.

TekBox TBTC2 - Open TEM Cell for EMC Pre-Compliance Testing, 100mm Septum – emcsupplies.com

And what I found out - there are resistors about so 40 Ohm (see the link above "Mode suppressed TEM cell design") on that, and that is made with striplines.

The Tekbox type does not show this details.

Figure 4 from Mode Suppressed TEM Cell Design For High Frequency IC Measurements | Semantic Scholar

Best Regards

Gerald

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Hello Gerald,

Our TEM cell was based on this paper:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjkidXXgeXyAhUXhlwKHe_OBgcQFnoECBMQAQ&url=http%…

I've posted a link rather than the .pdf for fear of copyright problems.

I've played with it alittle this morning but no publishable data yet. I'll have to stop and do real work .

From the pics below you will see that it's not very symetrical (I didn't make it !!), it works much better if the short end is driven and the long end is terminated (SWR below 3 up to 1GHz)

Last pic re-inserted because some members can't see it.

Sorry about the grim pics of FPC screen.

MK

Hi Michael michaelkellett ,

Thanks for posting your TEM cell. It's very interesting.

How looks on the other side of the septum in details?

What are this holes? Are they vias, (and) or resistors?

Best regards

Gerald

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Hi all.

I wanted to mention that I sent an email to R&S asking them what model (I presume the FPC1500) and what options are they going to provide in the spec. analyzer that's part of this special project. Since it's a holiday weekend over here in the U.S., I would expect an answer next week.

Randall

Hi Michael,

The TEM cell looks fantastic! Really great seeing this, to get an idea how it could be physically constructed.

The amplifier module looks well made too, for the range they specify.

I was looking at diecast boxes but assembly of SMA connectors at each end complicates those. I guess extruded seems to be the way to go.. and shielding strips can always be added if need be.