How about the converse, are there reasons not to put the ferrites on? Using
this example and assuming I had a balanced bicon so didn't need the
ferrites. If I put on a log periodic would I have to put ferrites on for
that?
If there is no drawback to the ferrites, then it seems that it would be
prudent to have them anyway? I'm afraid I have put them on simply because
...... Am I overlooking a tradeoff when using these, sensitivity etc.
Gary McInturff
-----Original Message-----
From: WOODS, RICHARD [SMTP:[email protected]]
Sent: Thursday, November 12, 1998 9:45 AM
To: [email protected]
Subject: RE: ANSI C63.4
Hans, you raised a very good point that needs to be discussed - the
need for
ferrites on the antenna cable. I have read articles indicating that
adding
the ferrites when taking NSA measurements was the only way they
could make
their site compliant. But I have also heard that the reason the
ferrites are
needed in those cases is that the antenna - most likely a bicon - is
poorly
balanced. I have also heard that a properly balanced bicon does not
need
ferrites. Comments anyone?
----------
From: [email protected] [SMTP:[email protected]]
Sent: Thursday, November 12, 1998 10:13 AM
To: [email protected];
[email protected]
Subject: Re: ANSI C63.4
A1. Since concrete is partly conductive and varies with
mositure
content and
ambient conditions, the reflected path with vary
substantially. The
solution
is to place a screen mesh over the top of the concrete.
A2. The specified size is that of the elipse which is 2d by
root3d.
A
practical size is 20m by 17m rectangle.
A3. running coax on the top surface most likely will not
affect the
measurements but for NSA measurements, to obtain maximum
repeatability ferrite
cores are placed every 1m on the mast cable. It would be
best to
feed the
cables diametrically opposed from each other so as to
minimize any
effects.
A4. Theoretically the conrete curbs, the hedges and metal
object can
cause
additional unwanted reflections. Those may or may not be a
problem.
Metal
objects will have the greatest effect since most of the wave
will be
reflected. Hedges will most likely act as absorbers at
certain
frequencies,
and the curb will cause reflections or absorbtion at certain
microwave
frequencies.
Hans Mellberg
EMC Consultant
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