This message concerns an antenna used for EMC measurements but I am
sure you will be able to reply.

We are setting up an EMC testing laboratory, one of the (very
impressive!) antennas that will be used is a "Stacked
Logarithmic-Periodic Test-Antenna", the details of which are in
http://www.schwarzbeck.de/k9128e.pdf.

The antenna has been assembled, but the elements were not placed as in
the photo (see pdf). Let me try to explain:

The elements were not placed diagonally opposite, as I imagine is
required. (If the uppermost longest element is on the right, the next
lower longest element should be on the left, as far as I can
understand.)

I imagine that this will affect the directional 'balance' of the
antenna, although I have no prior knowledge of EMC testing, just a
basic understanding of antenna theory.

+
|
| +
| |
| | + Top "layer" of antenna shown.
| | | next "layer" should be mirror image...
| | | + (or should it?)
| | | |
.+-----+-----+-----+----.
'---+-----+-----+-----+-'
| | | +
| | |
| | +
| |
| +
|
+

created by Andy´s ASCII-Circuit v1.23.080803 Beta www.tech-chat.de

On 20 Aug 2003 05:27:15 -0700, (Abdullah Eyles)
wrote:

The antenna has been assembled, but the elements were not placed as in
the photo (see pdf). Let me try to explain:

The short answer: start over and do it right.

The elements were not placed diagonally opposite, as I imagine is
required. (If the uppermost longest element is on the right, the next
lower longest element should be on the left, as far as I can
understand.)

Description is vague at best. You are starting off with a presumption
that may be faulty as you infer.


I imagine that this will affect the directional 'balance' of the
antenna, although I have no prior knowledge of EMC testing, just a
basic understanding of antenna theory.

Guessing aside, and taking a clue from this "diagonally" expression, I
would offer that you look at the antenna from above as you attempted
in your picture and see if it looks like:


+
|
| +
| |
| | +
| | |
| | | +
| | | |
.---+-----+-----+-----+----. two rails, one hidden by top
| | | |
| | | +
| | |
| | +
| |
| +
|
+

And confirm that each element, in order on one side, alternates
between the two rails that hold them. This is equivalent to:

+ element 4-B
|
| + element 3-A
| |
| | + element 2-B
| | |
| | | + element 1-A
| | | |
.---O-----+-----O-----+----. rail A
.---O-----+-----O-----+----. rail B
| | | |
| | | + element 1-B
| | |
| | + element 2-A
| |
| + element 3-B
|
+ element 4-A

Where the connections of elements denoted by "O" pass to the OTHER
rail. Both sides (common elements of any dipole pair) swap at each
step down the progression.

73's
Richard Clark, KB7QHC

Richard:

Don't you consider it a little frightening that this is a guy setting up a
lab to do EMC measurements, probably for EU certification, and asks a
question like this?

--
Crazy George
Remove NO and SPAM from return address

On Wed, 20 Aug 2003 22:46:21 -0500, "Crazy George"
wrote:

Richard:

Don't you consider it a little frightening that this is a guy setting up a
lab to do EMC measurements, probably for EU certification, and asks a
question like this?

Hi George,

Dunno, a lot of the recent postings seem just as off kilter. Maybe
it's the proximity of Mars.

73's
Richard Clark, KB7QHC

The short answer: start over and do it right.
Yes! I agree!

Guessing aside, and taking a clue from this "diagonally" expression, I
would offer that you look at the antenna from above as you attempted
in your picture and see if it looks like:


+
|
| +
| |
| | +
| | |
| | | +
| | | |
.---+-----+-----+-----+----. two rails, one hidden by top
| | | |
| | | +
| | |
| | +
| |
| +
|
+

And confirm that each element, in order on one side, alternates
between the two rails that hold them.

This is what I think, but how can I explain to our managers, who got
the lab set up by a contractor, that they (the 'experts') assembled
the antenna wrongly? what are the possible effects on the measurements
to be made?

As you may have seen in the pdf, the antenna consists of four beams,
in two pairs, meeting at the front (feed point?)

All the longest dipoles are on the right-hand side!

On 21 Aug 2003 00:37:42 -0700, (Abdullah Eyles)
wrote:


This is what I think, but how can I explain to our managers, who got
the lab set up by a contractor, that they (the 'experts') assembled
the antenna wrongly? what are the possible effects on the measurements
to be made?


Hi Abdullah,

Ask them for a refund, and drop them from your vendors list.

What effect did it have? Sorry to say this, but it sounds like you
are going to spend far more money doing it yourself than if you had
simply farmed out the job to a real lab that was registered with the
FCC.

73's
Richard Clark, KB7QHC

Abdullah Eyles wrote:
"What would the effect of this mistake be?"

Detrimental. There is no way the antenna can perform as expected if the
elements are different and misplaced. So, you should demand as-built be
as-designed. Then, if it doesn`t perform, take it up with the supplier
and designer.

Best regards, Richard Harrison, KB5WZI

Many thanks to all who contributed to this thread, I visited the Lab
again today and realised that they have corrected the mistake!

I don't know if it's because of my insistence, or that they just
couldn't get it to work properly, but to see a result is pleasing!

More power to your (collective) elbow!